Special Conditions: Boeing Model 787-8 Airplane; Interaction of Systems And Structures, Electronic Flight Control System-Control Surface Awareness, High Intensity Radiated Fields (HIRF) Protection, Limit Engine Torque Loads for Sudden Engine Stoppage, and Design Roll Maneuver Requirement, 10941-10947 [E7-4306]
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Federal Register / Vol. 72, No. 47 / Monday, March 12, 2007 / Proposed Rules
of Federal Regulations to read as
follows:
PART 627—TITLE IV CONSERVATORS,
RECEIVERS, AND VOLUNTARY
LIQUIDATIONS
1. The authority citation for part 627
continues to read as follows:
Authority: Secs. 4.2, 5.9, 5.10, 5.17, 5.51,
5.58, 5.61 of the Farm Credit Act (12 U.S.C.
2183, 2243, 2244, 2252, 2277a, 2277a–7,
2277a–10).
Subpart B—Receivers and
Receiverships
2. Revise § 627.2750(h) to read as
follows:
§ 627.2750
Priority of claims—banks.
*
*
*
*
*
(h) All claims of holders of
consolidated and System-wide bonds
and all claims of the other Farm Credit
banks arising from their payments on
consolidated and System-wide bonds
pursuant to 12 U.S.C. 2155 or pursuant
to an agreement among the banks to
reallocate the payments, provided the
agreement is in writing and approved by
the Farm Credit Administration.
*
*
*
*
*
§ 627.2755
[Amended]
3. Amend § 627.2755(a) by removing
the words ‘‘described in § 627.2745’’ in
the last sentence.
Dated: March 7, 2007.
Roland E. Smith,
Secretary, Farm Credit Administration Board.
[FR Doc. E7–4427 Filed 3–9–07; 8:45 am]
BILLING CODE 6705–01–P
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. NM362 Special Conditions No.
25–06–15–SC]
Special Conditions: Boeing Model 787–
8 Airplane; Interaction of Systems And
Structures, Electronic Flight Control
System—Control Surface Awareness,
High Intensity Radiated Fields (HIRF)
Protection, Limit Engine Torque Loads
for Sudden Engine Stoppage, and
Design Roll Maneuver Requirement
Federal Aviation
Administration (FAA), DOT.
ACTION: Notice of proposed special
conditions.
jlentini on PROD1PC65 with PROPOSAL
AGENCY:
SUMMARY: This notice proposes special
conditions for the Boeing Model 787–8
airplane. This airplane will have novel
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or unusual design features when
compared to the state of technology
envisioned in the airworthiness
standards for transport category
airplanes. These design features include
electronic flight control systems and
high bypass engines. These special
conditions also pertain to the effects of
such novel or unusual design features,
such as effects on the structural
performance of the airplane. Finally,
these special conditions pertain to
effects of certain conditions on these
novel or unusual design features, such
as the effects of high intensity radiated
fields (HIRF). Additional special
conditions will be issued for other novel
or unusual design features of the Boeing
Model 787–8 airplanes.
DATES: Comments must be received on
or before April 26, 2007.
ADDRESSES: Comments on this proposal
may be mailed in duplicate to: Federal
Aviation Administration, Transport
Airplane Directorate, Attention: Rules
Docket (ANM–113), Docket No. NM362,
1601 Lind Avenue, SW., Renton,
Washington 98057–3356; or delivered in
duplicate to the Transport Airplane
Directorate at the above address. All
comments must be marked Docket No.
NM362. Comments may be inspected in
the Rules Docket weekdays, except
Federal holidays, between 7:30 a.m. and
4 p.m.
FOR FURTHER INFORMATION CONTACT:
Meghan Gordon, FAA, Standardization
Branch, ANM–113, Transport Airplane
Directorate, Aircraft Certification
Service, 1601 Lind Avenue, SW.,
Renton, Washington 98057–3356;
telephone (425) 227–2138; facsimile
(425) 227–1149.
SUPPLEMENTARY INFORMATION:
Comments Invited
The FAA invites interested persons to
participate in this rulemaking by
submitting written comments, data, or
views. The most helpful comments
reference a specific portion of the
special conditions, explain the reason
for any recommended change, and
include supporting data. We ask that
you send us two copies of written
comments.
We will file in the docket all
comments we receive as well as a report
summarizing each substantive public
contact with FAA personnel concerning
these proposed special conditions. The
docket is available for public inspection
before and after the comment closing
date. If you wish to review the docket
in person, go to the address in the
ADDRESSES section of this notice
between 7:30 a.m. and 4 p.m., Monday
through Friday, except Federal holidays.
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10941
We will consider all comments we
receive on or before the closing date for
comments. We will consider comments
filed late if it is possible to do so
without incurring expense or delay. We
may change the proposed special
conditions based on comments we
receive.
If you want the FAA to acknowledge
receipt of your comments on this
proposal, include with your comments
a pre-addressed, stamped postcard on
which the docket number appears. We
will stamp the date on the postcard and
mail it back to you.
Background
On March 28, 2003, Boeing applied
for an FAA type certificate for its new
Boeing Model 787–8 passenger airplane.
The Boeing Model 787–8 airplane will
be an all-new, two-engine jet transport
airplane with a two-aisle cabin. The
maximum takeoff weight will be
476,000 pounds, with a maximum
passenger count of 381 passengers.
Type Certification Basis
Under provisions of 14 CFR 21.17,
Boeing must show that Boeing Model
787–8 airplanes (hereafter referred to as
‘‘the 787’’) meet the applicable
provisions of 14 CFR part 25, as
amended by Amendments 25–1 through
25–117, except §§ 25.809(a) and 25.812,
which will remain at Amendment 25–
115. If the Administrator finds that the
applicable airworthiness regulations do
not contain adequate or appropriate
safety standards for the 787 because of
a novel or unusual design feature,
special conditions are prescribed under
provisions of 14 CFR 21.16.
In addition to the applicable
airworthiness regulations and special
conditions, the 787 must comply with
the fuel vent and exhaust emission
requirements of 14 CFR part 34 and the
noise certification requirements of part
36. In addition, the FAA must issue a
finding of regulatory adequacy pursuant
to section 611 of Public Law 92–574, the
‘‘Noise Control Act of 1972.’’
Special conditions, as defined in
§ 11.19, are issued in accordance with
§ 11.38 and become part of the type
certification basis in accordance with
§ 21.17(a)(2).
Special conditions are initially
applicable to the model for which they
are issued. Should the type certificate
for that model be amended later to
include any other model that
incorporates the same or similar novel
or unusual design feature, the special
conditions would also apply to the other
model under the provisions of § 21.101.
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Discussion of Novel or Unusual Design
Features
2. Electronic Flight Control System:
Control Surface Awareness
The 787 will incorporate a number of
novel or unusual design features.
Because of rapid improvements in
airplane technology, the applicable
airworthiness regulations do not contain
adequate or appropriate safety standards
for these design features. These
proposed special conditions for the 787
contain the additional safety standards
that the Administrator considers
necessary to establish a level of safety
equivalent to that established by the
existing airworthiness standards.
Most of these proposed special
conditions are identical or nearly
identical to those previously required
for type certification of the Model 777
series airplanes.
Most of these proposed special
conditions were derived initially from
standardized requirements developed
by the Aviation Rulemaking Advisory
Committee (ARAC), comprised of
representatives of the FAA, Europe’s
Joint Aviation Authorities (now
replaced by the European Aviation
Safety Agency), and industry. In the
case of some of these requirements, a
draft notice of proposed rulemaking has
been prepared but no final rule has yet
been promulgated.
Additional special conditions will be
issued for other novel or unusual design
features of the 787 in the near future.
With a response-command type of
flight control system and no direct
coupling from cockpit controller to
control surface, such as on the 787, the
pilot is not aware of the actual surface
deflection position during flight
maneuvers. These features are novel and
unusual when compared to the state of
technology envisioned in the
airworthiness standards for transport
category airplanes. These special
conditions are meant to contain the
additional safety standards that the
Administrator considers necessary to
establish a level of safety equivalent to
that established by the existing
airworthiness standards. Some unusual
flight conditions, arising from
atmospheric conditions or airplane or
engine failures or both, may result in
full or nearly full surface deflection.
Unless the flightcrew is made aware of
excessive deflection or impending
control surface deflection limiting,
piloted or auto-flight system control of
the airplane might be inadvertently
continued in a way that would cause
loss of control or other unsafe handling
or performance characteristics.
These proposed special conditions
require that suitable annunciation be
provided to the flightcrew when a flight
condition exists in which nearly full
control surface deflection occurs.
Suitability of such an annunciation
must take into account that some pilotdemanded maneuvers, such as a rapid
roll, are necessarily associated with
intended full or nearly full control
surface deflection. Simple alerting
systems which would function in both
intended or unexpected control-limiting
situations must be properly balanced
between providing needed crew
awareness and avoiding nuisance
warnings.
jlentini on PROD1PC65 with PROPOSAL
1. Interaction of Systems and Structures
The 787 is equipped with systems
that affect the airplane’s structural
performance, either directly or as a
result of failure or malfunction. That is,
the airplane’s systems affect how it
responds in maneuver and gust
conditions, and thereby affect its
structural capability. These systems may
also affect the aeroelastic stability of the
airplane. Such systems represent a
novel and unusual feature when
compared to the technology envisioned
in the current airworthiness standards.
A special condition is needed to require
consideration of the effects of systems
on the structural capability and
aeroelastic stability of the airplane, both
in the normal and in the failed state.
This special condition requires that
the airplane meet the structural
requirements of subparts C and D of 14
CFR part 25 when the airplane systems
are fully operative. The special
condition also requires that the airplane
meet these requirements considering
failure conditions. In some cases,
reduced margins are allowed for failure
conditions based on system reliability.
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3. High Intensity Radiated Fields (HIRF)
Protection
The 787 will use electrical and
electronic systems which perform
critical functions. These systems may be
vulnerable to high-intensity radiated
fields (HIRF) external to the airplane.
There is no specific regulation that
addresses requirements for protection of
electrical and electronic systems from
HIRF. Increased power levels from radio
frequency transmitters and use of
sensitive avionics /electronics and
electrical systems to command and
control the airplane have made it
necessary to provide adequate
protection.
To ensure that a level of safety is
achieved that is equivalent to that
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intended by the regulations
incorporated by reference, the proposed
special conditions are needed for the
787. These proposed special conditions
require that avionics/electronics and
electrical systems that perform critical
functions be designed and installed to
preclude component damage and
interruption of function because of
HIRF.
High-power radio frequency
transmitters for radio, radar, television,
and satellite communications can
adversely affect operations of airplane
electrical and electronic systems.
Therefore, immunity of critical
avionics/electronics and electrical
systems to HIRF must be established.
Based on surveys and analysis of
existing HIRF emitters, adequate
protection from HIRF exists if airplane
system immunity is demonstrated when
exposed to the HIRF environments in
either paragraph (a) OR (b) below:
(a) A minimum environment of 100
volts rms (root-mean-square) per meter
electric field strength from 10 KHz to 18
GHz.
(1) System elements and their
associated wiring harnesses must be
exposed to the environment without
benefit of airframe shielding.
(2) Demonstration of this level of
protection is established through system
tests and analysis.
(b) An environment external to the
airframe of the field strengths shown in
the table below for the frequency ranges
indicated. Immunity to both peak and
average field strength components from
the table must be demonstrated.
Frequency
Field strength
(volts per meter)
Peak
10 kHz–100 kHz .......
100 kHz–500 kHz .....
500 kHz–2 MHz ........
2 MHz–30 MHz .........
30 MHz–70 MHz .......
70 MHz–100 MHz .....
100 MHz–200 MHz ...
200 MHz–400 MHz ...
400 MHz–700 MHz ...
700 MHz–1 GHz .......
1 GHz–2 GHz ...........
2 GHz–4 GHz ...........
4 GHz–6 GHz ...........
6 GHz–8 GHz ...........
8 GHz–12 GHz .........
12 GHz–18 GHz .......
18 GHz–40 GHz .......
50
50
50
100
50
50
100
100
700
700
2000
3000
3000
1000
3000
2000
600
Average
50
50
50
100
50
50
100
100
50
100
200
200
200
200
300
200
200
Field strengths are expressed in terms of
peak root-mean-square (rms) values over the
complete modulation period.
The environment levels identified
above are the result of an FAA review
of existing studies on the subject of
HIRF and of the work of the
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Electromagnetic Effects Harmonization
Working Group of ARAC.
4. Limit Engine Torque Loads for
Sudden Engine Stoppage
The 787 will have high-bypass
engines with a chord-swept fan 112
inches in diameter. Engines of this size
were not envisioned when § 25.361,
pertaining to loads imposed by engine
seizure, was adopted in 1965. Worst
case engine seizure events become
increasingly more severe with
increasing engine size because of the
higher inertia of the rotating
components.
Section 25.361(b)(1) requires that for
turbine engine installations, the engine
mounts and the supporting structures
must be designed to withstand a ‘‘limit
engine torque load imposed by sudden
engine stoppage due to malfunction or
structural failure.’’ Limit loads are
expected to occur about once in the
lifetime of any airplane. Section 25.305
requires that supporting structures be
able to support limit loads without
detrimental permanent deformation,
meaning that supporting structures
should remain serviceable after a limit
load event.
Since adoption of § 25.361(b)(1), the
size, configuration, and failure modes of
jet engines have changed considerably.
Current engines are much larger and are
designed with large bypass fans. In the
event of a structural failure, these
engines are capable of producing much
higher transient loads on the engine
mounts and supporting structures.
As a result, modern high bypass
engines are subject to certain rare-butsevere engine seizure events. Service
history shows that such events occur far
less frequently than limit load events.
Although it is important for the airplane
to be able to support such rare loads
safely without failure, it is unrealistic to
expect that no permanent deformation
will occur.
Given this situation, ARAC has
proposed a design standard for today’s
large engines. For the commonlyoccurring deceleration events, the
proposed standard requires engine
mounts and structures to support
maximum torques without detrimental
permanent deformation. For the rarebut-severe engine seizure events such as
loss of any fan, compressor, or turbine
blade, the proposed standard requires
engine mounts and structures to support
maximum torques without failure, but
allows for some deformation in the
structure.
The FAA concludes that modern large
engines, including those on the 787, are
novel and unusual compared to those
envisioned when § 25.361(b)(1) was
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adopted and thus warrant a special
condition. The proposed special
condition contains design criteria
recommended by ARAC. The ARAC
proposal would revise the wording of
§ 25.361(b), including §§ 25.361(b)(1)
and (b)(2), removing language pertaining
to structural failures and moving it to a
separate requirement that discusses the
reduced factors of safety that apply to
these failures.
5. Design Roll Maneuver Requirement
The 787 is equipped with an
electronic flight control system that
provides control of the aircraft through
pilot inputs to the flight computer.
Current part 25 airworthiness
regulations account for ‘‘control laws,’’
for which aileron deflection is
proportional to control stick deflection.
They do not address any nonlinearities 1
or other effects on aileron actuation that
may be caused by electronic flight
controls. Therefore, the FAA considers
the flight control system to be a novel
and unusual feature compared to those
envisioned when current regulations
were adopted. Since this type of system
may affect flight loads, and therefore the
structural capability of the airplane,
special conditions are needed to address
these effects.
This proposed special condition
differs from current requirements in that
it requires that the roll maneuver result
from defined movements of the cockpit
roll control as opposed to defined
aileron deflections. Also, the proposed
special condition requires an additional
load condition at design maneuvering
speed (VA), in which the cockpit roll
control is returned to neutral following
the initial roll input.
This proposed special condition
differs from similar special conditions
applied to previous designs. This
special condition is limited to the roll
axis only, whereas previous special
conditions also included pitch and yaw
axes. A special condition is no longer
needed for the yaw axis because
§ 25.351 was revised at Amendment 25–
91 to take into account effects of an
electronic flight control system. No
special condition is needed for the pitch
axis because the applicant’s proposed
methodology for the pitch maneuver
takes into account effects of an
electronic flight control system.
Applicability
As discussed above, these proposed
special conditions are applicable to the
787. Should Boeing apply at a later date
for a change to the type certificate to
1 A nonlinearity is a situation where output does
not change in the same proportion as input.
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10943
include another model incorporating the
same novel or unusual design features,
these proposed special conditions
would apply to that model as well
under the provisions of § 21.101.
Conclusion
This action affects only certain novel
or unusual design features of the 787. It
is not a rule of general applicability, and
it affects only the applicant that applied
to the FAA for approval of these features
on the airplane.
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Reporting
and recordkeeping requirements.
The authority citation for these
Special Conditions is as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701,
44702, 44704.
The Proposed Special Conditions
Accordingly, the Administrator of the
Federal Aviation Administration (FAA)
proposes the following special
conditions as part of the type
certification basis for the Boeing Model
787–8 airplane.
1. Interaction of Systems and Structures
The Boeing Model 787–8 airplane is
equipped with systems which affect the
airplane’s structural performance either
directly or as a result of failure or
malfunction. The influence of these
systems and their failure conditions
must be taken into account when
showing compliance with requirements
of subparts C and D of part 25 of Title
14 of the Code of Federal Regulations.
The following criteria must be used for
showing compliance with this proposed
special condition for airplanes equipped
with flight control systems, autopilots,
stability augmentation systems, load
alleviation systems, flutter control
systems, fuel management systems, and
other systems that either directly or as
a result of failure or malfunction affect
structural performance. If this proposed
special condition is used for other
systems, it may be necessary to adapt
the criteria to the specific system.
(a) The criteria defined here address
only direct structural consequences of
system responses and performances.
They cannot be considered in isolation
but should be included in the overall
safety evaluation of the airplane. They
may in some instances duplicate
standards already established for this
evaluation. These criteria are only
applicable to structures whose failure
could prevent continued safe flight and
landing. Specific criteria defining
acceptable limits on handling
characteristics or stability requirements
when operating in the system degraded
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or inoperative mode are not provided in
this special condition.
(b) Depending on the specific
characteristics of the airplane,
additional studies may be required that
go beyond the criteria provided in this
special condition in order to
demonstrate capability of the airplane to
meet other realistic conditions such as
alternative gust conditions or
maneuvers for an airplane equipped
with a load alleviation system.
(c) The following definitions are
applicable to this special condition.
(1) Structural performance: Capability
of the airplane to meet the structural
requirements of part 25.
(2) Flight limitations: Limitations that
can be applied to the airplane flight
conditions following an in-flight failure
occurrence and that are included in the
flight manual (speed limitations or
avoidance of severe weather conditions,
for example).
(3) Operational limitations:
Limitations, including flight limitations,
that can be applied to the airplane
operating conditions before dispatch
(fuel, payload, and master minimum
equipment list limitations, for example).
(4) Probabilistic terms: Terms
(probable, improbable, extremely
improbable) used in this special
condition which are the same as those
probabilistic terms used in § 25.1309.
(5) Failure condition: Term that is the
same as that used in § 25.1309. The term
failure condition in this proposed
(ii) For residual strength
substantiation, the airplane must be able
to withstand two thirds of the ultimate
loads defined in subparagraph (f)(1)(i) of
these special conditions. For
pressurized cabins, these loads must be
combined with the normal operating
differential pressure.
(iii) Freedom from aeroelastic
instability must be shown up to the
speeds defined in § 25.629(b)(2). For
failure conditions that result in speeds
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(d) General. The following criteria
will be used in determining the
influence of a system and its failure
conditions on the airplane structure.
(e) System fully operative. With the
system fully operative, the following
apply:
(1) Limit loads must be derived in all
normal operating configurations of the
system from all the limit conditions
specified in subpart C of 14 CFR part 25
(or used in lieu of those specified in
subpart C), taking into account any
special behavior of such a system or
associated functions or any effect on the
structural performance of the airplane
that may occur up to the limit loads. In
particular, any significant degree of
nonlinearity in rate of displacement of
control surface or thresholds, or any
other system nonlinearities, must be
accounted for in a realistic or
conservative way when deriving limit
loads from limit conditions.
(2) The airplane must meet the
strength requirements of part 25 for
static strength and residual strength,
using the specified factors to derive
ultimate loads from the limit loads
defined above. The effect of
nonlinearities must be investigated
beyond limit conditions to ensure the
behavior of the system presents no
anomaly compared to the behavior
below limit conditions. However,
conditions beyond limit conditions
need not be considered if the applicant
demonstrates that the airplane has
design features that will not allow it to
exceed those limit conditions.
(3) The airplane must meet the
aeroelastic stability requirements of
§ 25.629.
(f) System in the failure condition. For
any system failure condition not shown
to be extremely improbable, the
following apply:
(1) Establishing loads at the time of
failure. Starting from 1-g level flight
conditions, a realistic scenario,
including pilot corrective actions, must
be established to determine loads
occurring at the time of failure and
immediately after failure.
(i) For static strength substantiation,
these loads, multiplied by an
appropriate factor of safety related to
probability of occurrence of the failure,
are ultimate loads to be considered for
design. The factor of safety (FS) is
defined in Figure 1.
beyond design cruise speed or design
cruise mach number (VC/MC), freedom
from aeroelastic instability must be
shown to increased speeds, so that the
margins intended by § 25.629(b)(2) are
maintained.
(iv) Failures of the system that result
in forced structural vibrations
(oscillatory failures) must not produce
loads that could result in detrimental
deformation of primary structure.
(2) Establishing loads in the system
failed state for the continuation of the
flight. For the continuation of flight of
the airplane in the system failed state
and considering any appropriate
reconfiguration and flight limitations,
the following apply:
(i) Loads derived from the following
conditions (or used in lieu of the
following conditions) at speeds up to
VC/MC, or the speed limitation
special condition, however, applies only
to system failure conditions that affect
structural performance of the airplane.
Examples are system failure conditions
that induce loads, change the response
of the airplane to inputs such as gusts
or pilot actions, or lower flutter margins.
Note: Although failure annunciation
system reliability must be included in
probability calculations for paragraph (f) of
the proposed special condition, there is no
specific reliability requirement for the
annunciation system required in paragraph
(g) of the proposed special condition.
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Federal Register / Vol. 72, No. 47 / Monday, March 12, 2007 / Proposed Rules
10945
(ii) For static strength substantiation,
each part of the structure must be able
to withstand the loads in paragraph
(f)(2)(i) of the special condition
multiplied by a factor of safety
depending on the probability of being in
this failure state. The factor of safety is
defined in Figure 2.
Qj = (Tj)(Pj)
Where:
Tj = Average time spent in failure condition
j (in hours)
Pj = Probability of occurrence of failure mode
j (per hour)
(iii) For residual strength
substantiation, the airplane must be able
to withstand two-thirds of the ultimate
loads defined in paragraph (f)(2)(ii) of
the special condition. For pressurized
cabins, these loads must be combined
with the normal operating differential
pressure.
(iv) If the loads induced by the failure
condition have a significant effect on
fatigue or damage tolerance then the
effects of these loads must be taken into
account.
(v) Freedom from aeroelastic
instability must be shown up to a speed
determined from Figure 3. Flutter
clearance speeds V′ and V″ may be
based on the speed limitation specified
for the remainder of the flight using the
margins defined by § 25.629(b).
Pj = Probability of occurrence of failure mode
j (per hour)
in Figure 3 above, for any probable
system failure condition combined with
any damage required or selected for
investigation by § 25.571(b).
(3) Consideration of certain failure
conditions may be required by other
sections of 14 CFR part 25 regardless of
calculated system reliability. Where
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Note: If Pj is greater than 10–3 per flight
hour then a 1.5 factor of safety must be
applied to all limit load conditions specified
in subpart C-Structure, of 14 CFR part 25.
V′ = Clearance speed as defined by
§ 25.629(b)(2).
V″ = Clearance speed as defined by
§ 25.629(b)(1).
Qj = (Tj)(Pj)
Where:
Tj = Average time spent in failure condition
j (in hours)
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Note: If Pj is greater than 10–3 per flight
hour, then the flutter clearance speed must
not be less than V″.
(vi) Freedom from aeroelastic
instability must also be shown up to V′
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(C) The limit rolling conditions
specified in § 25.349 and the limit
unsymmetrical conditions specified in
§ 25.367 and § 25.427(b) and (c).
(D) The limit yaw maneuvering
conditions specified in § 25.351.
(E) The limit ground loading
conditions specified in § 25.473 and
§ 25.491.
EP12MR07.001</GPH>
prescribed for the remainder of the
flight, must be determined:
(A) The limit symmetrical
maneuvering conditions specified in
§ 25.331 and § 25.345.
(B) The limit gust and turbulence
conditions specified in § 25.341 and
§ 25.345.
jlentini on PROD1PC65 with PROPOSAL
10946
Federal Register / Vol. 72, No. 47 / Monday, March 12, 2007 / Proposed Rules
analysis shows the probability of these
failure conditions to be less than 10–9,
criteria other than those specified in this
paragraph may be used for structural
substantiation to show continued safe
flight and landing.
(g) Failure indications. For system
failure detection and indication, the
following apply.
(1) The system must be checked for
failure conditions, not extremely
improbable, that degrade the structural
capability of the airplane below the
level required by part 25 or significantly
reduce the reliability of the remaining
system. As far as reasonably practicable,
the flightcrew must be made aware of
these failures before flight. Certain
elements of the control system, such as
mechanical and hydraulic components,
may use special periodic inspections,
and electronic components may use
daily checks, instead of detection and
indication systems to achieve the
objective of this requirement. Such
certification maintenance inspections or
daily checks must be limited to
components on which faults are not
readily detectable by normal detection
and indication systems and where
service history shows that inspections
will provide an adequate level of safety.
(2) The existence of any failure
condition, not extremely improbable,
during flight that could significantly
affect the structural capability of the
airplane and for which the associated
reduction in airworthiness can be
minimized by suitable flight limitations,
must be signaled to the flightcrew. For
example, failure conditions that result
in a factor of safety between the airplane
strength and the loads of subpart C
below 1.25, or flutter margins below V″,
must be signaled to the crew during
flight.
(h) Dispatch with known failure
conditions. If the airplane is to be
dispatched in a known system failure
condition that affects structural
performance, or affects the reliability of
the remaining system to maintain
structural performance, then the
provisions of this special condition
must be met, including the provisions of
paragraph (e) for the dispatched
condition, and paragraph (f) for
subsequent failures. Expected
operational limitations may be taken
into account in establishing Pj as the
probability of failure occurrence for
determining the safety margin in Figure
1. Flight limitations and expected
operational limitations may be taken
into account in establishing Qj as the
combined probability of being in the
dispatched failure condition and the
subsequent failure condition for the
safety margins in Figures 2 and 3. These
VerDate Aug<31>2005
16:38 Mar 09, 2007
Jkt 211001
limitations must be such that the
probability of being in this combined
failure state and then subsequently
encountering limit load conditions is
extremely improbable. No reduction in
these safety margins is allowed if the
subsequent system failure rate is greater
than 10–3 per hour.
2. Electronic Flight Control System:
Control Surface Awareness
In addition to compliance with
§§ 25.143, 25.671, and 25.672, the
following special condition applies:
(a) The system design must ensure
that the flightcrew is made suitably
aware whenever the primary control
means nears the limit of control
authority. This indication should direct
the pilot to take appropriate action to
avoid the unsafe condition in
accordance with appropriate airplane
flight manual (AFM) instructions.
Depending on the application, suitable
annunciations may include cockpit
control position, annunciator light, or
surface position indicators.
Furthermore, this requirement applies at
limits of control authority, not
necessarily at limits of any individual
surface travel.
(b) Suitability of such a display or
alerting must take into account that
some pilot-demanded maneuvers are
necessarily associated with intended
full performance, which may require
full surface deflection. Therefore,
simple alerting systems, which would
function in both intended or unexpected
control-limiting situations, must be
properly balanced between needed crew
awareness and nuisance factors. A
monitoring system which might
compare airplane motion, surface
deflection, and pilot demand could be
useful for eliminating nuisance alerting.
4. Limit Engine Torque Loads for
Sudden Engine Stoppage
In lieu of § 25.361(b) the following
special condition is proposed:
(a) For turbine engine installations,
the engine mounts, pylons, and adjacent
supporting airframe structure must be
designed to withstand 1g level flight
loads acting simultaneously with the
maximum limit torque loads imposed
by each of the following:
(1) Sudden engine deceleration due to
a malfunction which could result in a
temporary loss of power or thrust.
(2) The maximum acceleration of the
engine.
(b) For auxiliary power unit
installations, the power unit mounts
and adjacent supporting airframe
structure must be designed to withstand
1g level flight loads acting
simultaneously with the maximum limit
torque loads imposed by each of the
following:
(1) Sudden auxiliary power unit
deceleration due to malfunction or
structural failure.
(2) The maximum acceleration of the
power unit.
(c) For engine supporting structure, an
ultimate loading condition must be
considered that combines 1g flight loads
with the transient dynamic loads
resulting from each of the following:
(1) Loss of any fan, compressor, or
turbine blade.
(2) Where applicable to a specific
engine design, any other engine
structural failure that results in higher
loads.
(d) The ultimate loads developed from
the conditions specified in paragraphs
(c)(1) and (c)(2) are to be multiplied by
a factor of 1.0 when applied to engine
mounts and pylons and multiplied by a
factor of 1.25 when applied to adjacent
supporting airframe structure.
3. High Intensity Radiated Fields
(HIRF) Protection
5. Design Roll Maneuver Requirement
(a) Protection from Unwanted Effects
of High-intensity Radiated Fields. Each
electrical and electronic system which
performs critical functions must be
designed and installed to ensure that the
operation and operational capabilities of
these systems to perform critical
functions are not adversely affected
when the airplane is exposed to high
intensity radiated fields external to the
airplane.
(b) For the purposes of these Special
Conditions, the following definition
applies: Critical Functions: Functions
whose failure would contribute to or
cause a failure condition that would
prevent continued safe flight and
landing of the airplane.
In lieu of compliance to § 25.349(a),
the following special conditions are
proposed.
The following conditions, speeds, and
cockpit roll control motions (except as
the motions may be limited by pilot
effort) must be considered in
combination with an airplane load
factor of zero and of two-thirds of the
positive maneuvering factor used in
design. In determining the resulting
control surface deflections, the torsional
flexibility of the wing must be
considered in accordance with
§ 25.301(b):
(a) Conditions corresponding to
steady rolling velocities must be
investigated. In addition, conditions
corresponding to maximum angular
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Fmt 4702
Sfmt 4702
E:\FR\FM\12MRP1.SGM
12MRP1
Federal Register / Vol. 72, No. 47 / Monday, March 12, 2007 / Proposed Rules
acceleration must be investigated for
airplanes with engines or other weight
concentrations outboard of the fuselage.
For the angular acceleration conditions,
zero rolling velocity may be assumed in
the absence of a rational time history
investigation of the maneuver.
(b) At VA, sudden movement of the
cockpit roll control up to the limit is
assumed. The position of the cockpit
roll control must be maintained until a
steady roll rate is achieved and then
must be returned suddenly to the
neutral position.
(c) At VC, the cockpit roll control
must be moved suddenly and
maintained so as to achieve a roll rate
not less than that obtained in paragraph
(2).
(d) At VD, the cockpit roll control
must be moved suddenly and
maintained so as to achieve a roll rate
not less than one-third of that obtained
in paragraph (2).
Issued in Renton, Washington, on March 1,
2007.
Ali Bahrami,
Manager, Transport Airplane Directorate,
Aircraft Certification Service.
[FR Doc. E7–4306 Filed 3–9–07; 8:45 am]
BILLING CODE 4910–13–P
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA–2007–27508; Directorate
Identifier 2006–NM–252–AD]
RIN 2120–AA64
Airworthiness Directives; Empresa
Brasileira de Aeronautica S.A.
(EMBRAER) ERJ 170 Airplanes
Federal Aviation
Administration (FAA), Department of
Transportation (DOT).
ACTION: Notice of proposed rulemaking
(NPRM).
jlentini on PROD1PC65 with PROPOSAL
AGENCY:
SUMMARY: We propose to adopt a new
airworthiness directive (AD) for the
products listed above. This proposed
AD results from mandatory continuing
airworthiness information (MCAI)
issued by an aviation authority of
another country to identify and correct
an unsafe condition on an aviation
product. The MCAI describes the unsafe
condition as an obstruction at the cargo
compartment fire extinguisher system
drier metering unit (DME) inlet,
affecting the system effectiveness and,
consequently, making the fire
extinguishing capability at those
compartments inadequate should a fire
VerDate Aug<31>2005
16:38 Mar 09, 2007
Jkt 211001
erupt. The proposed AD would require
actions that are intended to address the
unsafe condition described in the MCAI.
DATES: We must receive comments on
this proposed AD by April 11, 2007.
ADDRESSES: You may send comments by
any of the following methods:
• DOT Docket Web Site: Go to
https://dms.dot.gov and follow the
instructions for sending your comments
electronically.
• Fax: (202) 493–2251.
• Mail: Docket Management Facility,
U.S. Department of Transportation, 400
Seventh Street, SW., Nassif Building,
Room PL–401, Washington, DC 20590–
0001.
• Hand Delivery: Room PL–401 on
the plaza level of the Nassif Building,
400 Seventh Street, SW., Washington,
DC, between 9 a.m. and 5 p.m., Monday
through Friday, except Federal holidays.
• Federal eRulemaking Portal: https://
www.regulations.gov. Follow the
instructions for submitting comments.
Examining the AD Docket
You may examine the AD docket on
the Internet at https://dms.dot.gov; or in
person at the Docket Management
Facility between 9 a.m. and 5 p.m.,
Monday through Friday, except Federal
holidays. The AD docket contains this
proposed AD, the regulatory evaluation,
any comments received, and other
information. The street address for the
Docket Office (telephone (800) 647–
5227) is in the ADDRESSES section.
Comments will be available in the AD
docket shortly after receipt.
FOR FURTHER INFORMATION CONTACT:
Todd Thompson, Aerospace Engineer,
International Branch, ANM–116, FAA,
Transport Airplane Directorate, 1601
Lind Avenue, SW., Renton, Washington
98057–3356; telephone (425) 227–1175;
fax (425) 227–1149.
SUPPLEMENTARY INFORMATION:
Streamlined Issuance of AD
The FAA is implementing a new
process for streamlining the issuance of
ADs related to MCAI. This streamlined
process will allow us to adopt MCAI
safety requirements in a more efficient
manner and will reduce safety risks to
the public. This process continues to
follow all FAA AD issuance processes to
meet legal, economic, Administrative
Procedure Act, and Federal Register
requirements. We also continue to meet
our technical decision-making
responsibilities to identify and correct
unsafe conditions on U.S.-certificated
products.
This proposed AD references the
MCAI and related service information
that we considered in forming the
PO 00000
Frm 00009
Fmt 4702
Sfmt 4702
10947
engineering basis to correct the unsafe
condition. The proposed AD contains
text copied from the MCAI and for this
reason might not follow our plain
language principles.
Comments Invited
We invite you to send any written
relevant data, views, or arguments about
this proposed AD. Send your comments
to an address listed under the
ADDRESSES section. Include ‘‘Docket No.
FAA–2007–27508; Directorate Identifier
2006–NM–252–AD’’ at the beginning of
your comments. We specifically invite
comments on the overall regulatory,
economic, environmental, and energy
aspects of this proposed AD. We will
consider all comments received by the
closing date and may amend this
proposed AD because of those
comments.
We will post all comments we
receive, without change, to https://
dms.dot.gov, including any personal
information you provide. We will also
post a report summarizing each
substantive verbal contact we receive
about this proposed AD.
Discussion
`
The Agencia Nacional de Aviacao
¸˜
Civil (ANAC), which is the aviation
authority for Brazil, has issued Brazilian
Airworthiness Directive 2006–01–03,
effective February 7, 2006 (referred to
after this as ‘‘the MCAI’’), to correct an
unsafe condition for the specified
products. The MCAI states that it has
been found the occurrence of one case
of obstruction at the cargo compartment
fire extinguisher system drier metering
unit (DMU) inlet, affecting the system
effectiveness and, consequently, making
the fire extinguishing capability at those
compartments inadequate should a fire
erupt. The MCAI requires installation of
a debris strainer at the DMU inlet. You
may obtain further information by
examining the MCAI in the AD docket.
Relevant Service Information
EMBRAER has issued Service Bulletin
170–26–0002, dated November 11, 2005.
The actions described in this service
information are intended to correct the
unsafe condition identified in the
MCAI.
FAA’s Determination and Requirements
of This Proposed AD
This product has been approved by
the aviation authority of another
country, and is approved for operation
in the United States. Pursuant to our
bilateral agreement with this State of
Design Authority, they have notified us
of the unsafe condition described in the
MCAI and service information
E:\FR\FM\12MRP1.SGM
12MRP1
]]>Agencies
[Federal Register Volume 72, Number 47 (Monday, March 12, 2007)]
[Proposed Rules]
[Pages 10941-10947]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E7-4306]
=======================================================================
-----------------------------------------------------------------------
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. NM362 Special Conditions No. 25-06-15-SC]
Special Conditions: Boeing Model 787-8 Airplane; Interaction of
Systems And Structures, Electronic Flight Control System--Control
Surface Awareness, High Intensity Radiated Fields (HIRF) Protection,
Limit Engine Torque Loads for Sudden Engine Stoppage, and Design Roll
Maneuver Requirement
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed special conditions.
-----------------------------------------------------------------------
SUMMARY: This notice proposes special conditions for the Boeing Model
787-8 airplane. This airplane will have novel or unusual design
features when compared to the state of technology envisioned in the
airworthiness standards for transport category airplanes. These design
features include electronic flight control systems and high bypass
engines. These special conditions also pertain to the effects of such
novel or unusual design features, such as effects on the structural
performance of the airplane. Finally, these special conditions pertain
to effects of certain conditions on these novel or unusual design
features, such as the effects of high intensity radiated fields (HIRF).
Additional special conditions will be issued for other novel or unusual
design features of the Boeing Model 787-8 airplanes.
DATES: Comments must be received on or before April 26, 2007.
ADDRESSES: Comments on this proposal may be mailed in duplicate to:
Federal Aviation Administration, Transport Airplane Directorate,
Attention: Rules Docket (ANM-113), Docket No. NM362, 1601 Lind Avenue,
SW., Renton, Washington 98057-3356; or delivered in duplicate to the
Transport Airplane Directorate at the above address. All comments must
be marked Docket No. NM362. Comments may be inspected in the Rules
Docket weekdays, except Federal holidays, between 7:30 a.m. and 4 p.m.
FOR FURTHER INFORMATION CONTACT: Meghan Gordon, FAA, Standardization
Branch, ANM-113, Transport Airplane Directorate, Aircraft Certification
Service, 1601 Lind Avenue, SW., Renton, Washington 98057-3356;
telephone (425) 227-2138; facsimile (425) 227-1149.
SUPPLEMENTARY INFORMATION:
Comments Invited
The FAA invites interested persons to participate in this
rulemaking by submitting written comments, data, or views. The most
helpful comments reference a specific portion of the special
conditions, explain the reason for any recommended change, and include
supporting data. We ask that you send us two copies of written
comments.
We will file in the docket all comments we receive as well as a
report summarizing each substantive public contact with FAA personnel
concerning these proposed special conditions. The docket is available
for public inspection before and after the comment closing date. If you
wish to review the docket in person, go to the address in the ADDRESSES
section of this notice between 7:30 a.m. and 4 p.m., Monday through
Friday, except Federal holidays.
We will consider all comments we receive on or before the closing
date for comments. We will consider comments filed late if it is
possible to do so without incurring expense or delay. We may change the
proposed special conditions based on comments we receive.
If you want the FAA to acknowledge receipt of your comments on this
proposal, include with your comments a pre-addressed, stamped postcard
on which the docket number appears. We will stamp the date on the
postcard and mail it back to you.
Background
On March 28, 2003, Boeing applied for an FAA type certificate for
its new Boeing Model 787-8 passenger airplane. The Boeing Model 787-8
airplane will be an all-new, two-engine jet transport airplane with a
two-aisle cabin. The maximum takeoff weight will be 476,000 pounds,
with a maximum passenger count of 381 passengers.
Type Certification Basis
Under provisions of 14 CFR 21.17, Boeing must show that Boeing
Model 787-8 airplanes (hereafter referred to as ``the 787'') meet the
applicable provisions of 14 CFR part 25, as amended by Amendments 25-1
through 25-117, except Sec. Sec. 25.809(a) and 25.812, which will
remain at Amendment 25-115. If the Administrator finds that the
applicable airworthiness regulations do not contain adequate or
appropriate safety standards for the 787 because of a novel or unusual
design feature, special conditions are prescribed under provisions of
14 CFR 21.16.
In addition to the applicable airworthiness regulations and special
conditions, the 787 must comply with the fuel vent and exhaust emission
requirements of 14 CFR part 34 and the noise certification requirements
of part 36. In addition, the FAA must issue a finding of regulatory
adequacy pursuant to section 611 of Public Law 92-574, the ``Noise
Control Act of 1972.''
Special conditions, as defined in Sec. 11.19, are issued in
accordance with Sec. 11.38 and become part of the type certification
basis in accordance with Sec. 21.17(a)(2).
Special conditions are initially applicable to the model for which
they are issued. Should the type certificate for that model be amended
later to include any other model that incorporates the same or similar
novel or unusual design feature, the special conditions would also
apply to the other model under the provisions of Sec. 21.101.
[[Page 10942]]
Discussion of Novel or Unusual Design Features
The 787 will incorporate a number of novel or unusual design
features. Because of rapid improvements in airplane technology, the
applicable airworthiness regulations do not contain adequate or
appropriate safety standards for these design features. These proposed
special conditions for the 787 contain the additional safety standards
that the Administrator considers necessary to establish a level of
safety equivalent to that established by the existing airworthiness
standards.
Most of these proposed special conditions are identical or nearly
identical to those previously required for type certification of the
Model 777 series airplanes.
Most of these proposed special conditions were derived initially
from standardized requirements developed by the Aviation Rulemaking
Advisory Committee (ARAC), comprised of representatives of the FAA,
Europe's Joint Aviation Authorities (now replaced by the European
Aviation Safety Agency), and industry. In the case of some of these
requirements, a draft notice of proposed rulemaking has been prepared
but no final rule has yet been promulgated.
Additional special conditions will be issued for other novel or
unusual design features of the 787 in the near future.
1. Interaction of Systems and Structures
The 787 is equipped with systems that affect the airplane's
structural performance, either directly or as a result of failure or
malfunction. That is, the airplane's systems affect how it responds in
maneuver and gust conditions, and thereby affect its structural
capability. These systems may also affect the aeroelastic stability of
the airplane. Such systems represent a novel and unusual feature when
compared to the technology envisioned in the current airworthiness
standards. A special condition is needed to require consideration of
the effects of systems on the structural capability and aeroelastic
stability of the airplane, both in the normal and in the failed state.
This special condition requires that the airplane meet the
structural requirements of subparts C and D of 14 CFR part 25 when the
airplane systems are fully operative. The special condition also
requires that the airplane meet these requirements considering failure
conditions. In some cases, reduced margins are allowed for failure
conditions based on system reliability.
2. Electronic Flight Control System: Control Surface Awareness
With a response-command type of flight control system and no direct
coupling from cockpit controller to control surface, such as on the
787, the pilot is not aware of the actual surface deflection position
during flight maneuvers. These features are novel and unusual when
compared to the state of technology envisioned in the airworthiness
standards for transport category airplanes. These special conditions
are meant to contain the additional safety standards that the
Administrator considers necessary to establish a level of safety
equivalent to that established by the existing airworthiness standards.
Some unusual flight conditions, arising from atmospheric conditions or
airplane or engine failures or both, may result in full or nearly full
surface deflection. Unless the flightcrew is made aware of excessive
deflection or impending control surface deflection limiting, piloted or
auto-flight system control of the airplane might be inadvertently
continued in a way that would cause loss of control or other unsafe
handling or performance characteristics.
These proposed special conditions require that suitable
annunciation be provided to the flightcrew when a flight condition
exists in which nearly full control surface deflection occurs.
Suitability of such an annunciation must take into account that some
pilot-demanded maneuvers, such as a rapid roll, are necessarily
associated with intended full or nearly full control surface
deflection. Simple alerting systems which would function in both
intended or unexpected control-limiting situations must be properly
balanced between providing needed crew awareness and avoiding nuisance
warnings.
3. High Intensity Radiated Fields (HIRF) Protection
The 787 will use electrical and electronic systems which perform
critical functions. These systems may be vulnerable to high-intensity
radiated fields (HIRF) external to the airplane. There is no specific
regulation that addresses requirements for protection of electrical and
electronic systems from HIRF. Increased power levels from radio
frequency transmitters and use of sensitive avionics /electronics and
electrical systems to command and control the airplane have made it
necessary to provide adequate protection.
To ensure that a level of safety is achieved that is equivalent to
that intended by the regulations incorporated by reference, the
proposed special conditions are needed for the 787. These proposed
special conditions require that avionics/electronics and electrical
systems that perform critical functions be designed and installed to
preclude component damage and interruption of function because of HIRF.
High-power radio frequency transmitters for radio, radar,
television, and satellite communications can adversely affect
operations of airplane electrical and electronic systems. Therefore,
immunity of critical avionics/electronics and electrical systems to
HIRF must be established. Based on surveys and analysis of existing
HIRF emitters, adequate protection from HIRF exists if airplane system
immunity is demonstrated when exposed to the HIRF environments in
either paragraph (a) OR (b) below:
(a) A minimum environment of 100 volts rms (root-mean-square) per
meter electric field strength from 10 KHz to 18 GHz.
(1) System elements and their associated wiring harnesses must be
exposed to the environment without benefit of airframe shielding.
(2) Demonstration of this level of protection is established
through system tests and analysis.
(b) An environment external to the airframe of the field strengths
shown in the table below for the frequency ranges indicated. Immunity
to both peak and average field strength components from the table must
be demonstrated.
------------------------------------------------------------------------
Field strength
(volts per meter)
Frequency ---------------------
Peak Average
------------------------------------------------------------------------
10 kHz-100 kHz.................................... 50 50
100 kHz-500 kHz................................... 50 50
500 kHz-2 MHz..................................... 50 50
2 MHz-30 MHz...................................... 100 100
30 MHz-70 MHz..................................... 50 50
70 MHz-100 MHz.................................... 50 50
100 MHz-200 MHz................................... 100 100
200 MHz-400 MHz................................... 100 100
400 MHz-700 MHz................................... 700 50
700 MHz-1 GHz..................................... 700 100
1 GHz-2 GHz....................................... 2000 200
2 GHz-4 GHz....................................... 3000 200
4 GHz-6 GHz....................................... 3000 200
6 GHz-8 GHz....................................... 1000 200
8 GHz-12 GHz...................................... 3000 300
12 GHz-18 GHz..................................... 2000 200
18 GHz-40 GHz..................................... 600 200
------------------------------------------------------------------------
Field strengths are expressed in terms of peak root-mean-square (rms)
values over the complete modulation period.
The environment levels identified above are the result of an FAA
review of existing studies on the subject of HIRF and of the work of
the
[[Page 10943]]
Electromagnetic Effects Harmonization Working Group of ARAC.
4. Limit Engine Torque Loads for Sudden Engine Stoppage
The 787 will have high-bypass engines with a chord-swept fan 112
inches in diameter. Engines of this size were not envisioned when Sec.
25.361, pertaining to loads imposed by engine seizure, was adopted in
1965. Worst case engine seizure events become increasingly more severe
with increasing engine size because of the higher inertia of the
rotating components.
Section 25.361(b)(1) requires that for turbine engine
installations, the engine mounts and the supporting structures must be
designed to withstand a ``limit engine torque load imposed by sudden
engine stoppage due to malfunction or structural failure.'' Limit loads
are expected to occur about once in the lifetime of any airplane.
Section 25.305 requires that supporting structures be able to support
limit loads without detrimental permanent deformation, meaning that
supporting structures should remain serviceable after a limit load
event.
Since adoption of Sec. 25.361(b)(1), the size, configuration, and
failure modes of jet engines have changed considerably. Current engines
are much larger and are designed with large bypass fans. In the event
of a structural failure, these engines are capable of producing much
higher transient loads on the engine mounts and supporting structures.
As a result, modern high bypass engines are subject to certain
rare-but-severe engine seizure events. Service history shows that such
events occur far less frequently than limit load events. Although it is
important for the airplane to be able to support such rare loads safely
without failure, it is unrealistic to expect that no permanent
deformation will occur.
Given this situation, ARAC has proposed a design standard for
today's large engines. For the commonly-occurring deceleration events,
the proposed standard requires engine mounts and structures to support
maximum torques without detrimental permanent deformation. For the
rare-but-severe engine seizure events such as loss of any fan,
compressor, or turbine blade, the proposed standard requires engine
mounts and structures to support maximum torques without failure, but
allows for some deformation in the structure.
The FAA concludes that modern large engines, including those on the
787, are novel and unusual compared to those envisioned when Sec.
25.361(b)(1) was adopted and thus warrant a special condition. The
proposed special condition contains design criteria recommended by
ARAC. The ARAC proposal would revise the wording of Sec. 25.361(b),
including Sec. Sec. 25.361(b)(1) and (b)(2), removing language
pertaining to structural failures and moving it to a separate
requirement that discusses the reduced factors of safety that apply to
these failures.
5. Design Roll Maneuver Requirement
The 787 is equipped with an electronic flight control system that
provides control of the aircraft through pilot inputs to the flight
computer. Current part 25 airworthiness regulations account for
``control laws,'' for which aileron deflection is proportional to
control stick deflection. They do not address any nonlinearities \1\ or
other effects on aileron actuation that may be caused by electronic
flight controls. Therefore, the FAA considers the flight control system
to be a novel and unusual feature compared to those envisioned when
current regulations were adopted. Since this type of system may affect
flight loads, and therefore the structural capability of the airplane,
special conditions are needed to address these effects.
---------------------------------------------------------------------------
\1\ A nonlinearity is a situation where output does not change
in the same proportion as input.
---------------------------------------------------------------------------
This proposed special condition differs from current requirements
in that it requires that the roll maneuver result from defined
movements of the cockpit roll control as opposed to defined aileron
deflections. Also, the proposed special condition requires an
additional load condition at design maneuvering speed (VA),
in which the cockpit roll control is returned to neutral following the
initial roll input.
This proposed special condition differs from similar special
conditions applied to previous designs. This special condition is
limited to the roll axis only, whereas previous special conditions also
included pitch and yaw axes. A special condition is no longer needed
for the yaw axis because Sec. 25.351 was revised at Amendment 25-91 to
take into account effects of an electronic flight control system. No
special condition is needed for the pitch axis because the applicant's
proposed methodology for the pitch maneuver takes into account effects
of an electronic flight control system.
Applicability
As discussed above, these proposed special conditions are
applicable to the 787. Should Boeing apply at a later date for a change
to the type certificate to include another model incorporating the same
novel or unusual design features, these proposed special conditions
would apply to that model as well under the provisions of Sec. 21.101.
Conclusion
This action affects only certain novel or unusual design features
of the 787. It is not a rule of general applicability, and it affects
only the applicant that applied to the FAA for approval of these
features on the airplane.
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Reporting and recordkeeping
requirements.
The authority citation for these Special Conditions is as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.
The Proposed Special Conditions
Accordingly, the Administrator of the Federal Aviation
Administration (FAA) proposes the following special conditions as part
of the type certification basis for the Boeing Model 787-8 airplane.
1. Interaction of Systems and Structures
The Boeing Model 787-8 airplane is equipped with systems which
affect the airplane's structural performance either directly or as a
result of failure or malfunction. The influence of these systems and
their failure conditions must be taken into account when showing
compliance with requirements of subparts C and D of part 25 of Title 14
of the Code of Federal Regulations. The following criteria must be used
for showing compliance with this proposed special condition for
airplanes equipped with flight control systems, autopilots, stability
augmentation systems, load alleviation systems, flutter control
systems, fuel management systems, and other systems that either
directly or as a result of failure or malfunction affect structural
performance. If this proposed special condition is used for other
systems, it may be necessary to adapt the criteria to the specific
system.
(a) The criteria defined here address only direct structural
consequences of system responses and performances. They cannot be
considered in isolation but should be included in the overall safety
evaluation of the airplane. They may in some instances duplicate
standards already established for this evaluation. These criteria are
only applicable to structures whose failure could prevent continued
safe flight and landing. Specific criteria defining acceptable limits
on handling characteristics or stability requirements when operating in
the system degraded
[[Page 10944]]
or inoperative mode are not provided in this special condition.
(b) Depending on the specific characteristics of the airplane,
additional studies may be required that go beyond the criteria provided
in this special condition in order to demonstrate capability of the
airplane to meet other realistic conditions such as alternative gust
conditions or maneuvers for an airplane equipped with a load
alleviation system.
(c) The following definitions are applicable to this special
condition.
(1) Structural performance: Capability of the airplane to meet the
structural requirements of part 25.
(2) Flight limitations: Limitations that can be applied to the
airplane flight conditions following an in-flight failure occurrence
and that are included in the flight manual (speed limitations or
avoidance of severe weather conditions, for example).
(3) Operational limitations: Limitations, including flight
limitations, that can be applied to the airplane operating conditions
before dispatch (fuel, payload, and master minimum equipment list
limitations, for example).
(4) Probabilistic terms: Terms (probable, improbable, extremely
improbable) used in this special condition which are the same as those
probabilistic terms used in Sec. 25.1309.
(5) Failure condition: Term that is the same as that used in Sec.
25.1309. The term failure condition in this proposed special condition,
however, applies only to system failure conditions that affect
structural performance of the airplane. Examples are system failure
conditions that induce loads, change the response of the airplane to
inputs such as gusts or pilot actions, or lower flutter margins.
Note: Although failure annunciation system reliability must be
included in probability calculations for paragraph (f) of the
proposed special condition, there is no specific reliability
requirement for the annunciation system required in paragraph (g) of
the proposed special condition.
(d) General. The following criteria will be used in determining the
influence of a system and its failure conditions on the airplane
structure.
(e) System fully operative. With the system fully operative, the
following apply:
(1) Limit loads must be derived in all normal operating
configurations of the system from all the limit conditions specified in
subpart C of 14 CFR part 25 (or used in lieu of those specified in
subpart C), taking into account any special behavior of such a system
or associated functions or any effect on the structural performance of
the airplane that may occur up to the limit loads. In particular, any
significant degree of nonlinearity in rate of displacement of control
surface or thresholds, or any other system nonlinearities, must be
accounted for in a realistic or conservative way when deriving limit
loads from limit conditions.
(2) The airplane must meet the strength requirements of part 25 for
static strength and residual strength, using the specified factors to
derive ultimate loads from the limit loads defined above. The effect of
nonlinearities must be investigated beyond limit conditions to ensure
the behavior of the system presents no anomaly compared to the behavior
below limit conditions. However, conditions beyond limit conditions
need not be considered if the applicant demonstrates that the airplane
has design features that will not allow it to exceed those limit
conditions.
(3) The airplane must meet the aeroelastic stability requirements
of Sec. 25.629.
(f) System in the failure condition. For any system failure
condition not shown to be extremely improbable, the following apply:
(1) Establishing loads at the time of failure. Starting from 1-g
level flight conditions, a realistic scenario, including pilot
corrective actions, must be established to determine loads occurring at
the time of failure and immediately after failure.
(i) For static strength substantiation, these loads, multiplied by
an appropriate factor of safety related to probability of occurrence of
the failure, are ultimate loads to be considered for design. The factor
of safety (FS) is defined in Figure 1.
[GRAPHIC] [TIFF OMITTED] TP12MR07.000
(ii) For residual strength substantiation, the airplane must be
able to withstand two thirds of the ultimate loads defined in
subparagraph (f)(1)(i) of these special conditions. For pressurized
cabins, these loads must be combined with the normal operating
differential pressure.
(iii) Freedom from aeroelastic instability must be shown up to the
speeds defined in Sec. 25.629(b)(2). For failure conditions that
result in speeds beyond design cruise speed or design cruise mach
number (VC/MC), freedom from aeroelastic
instability must be shown to increased speeds, so that the margins
intended by Sec. 25.629(b)(2) are maintained.
(iv) Failures of the system that result in forced structural
vibrations (oscillatory failures) must not produce loads that could
result in detrimental deformation of primary structure.
(2) Establishing loads in the system failed state for the
continuation of the flight. For the continuation of flight of the
airplane in the system failed state and considering any appropriate
reconfiguration and flight limitations, the following apply:
(i) Loads derived from the following conditions (or used in lieu of
the following conditions) at speeds up to VC/MC,
or the speed limitation
[[Page 10945]]
prescribed for the remainder of the flight, must be determined:
(A) The limit symmetrical maneuvering conditions specified in Sec.
25.331 and Sec. 25.345.
(B) The limit gust and turbulence conditions specified in Sec.
25.341 and Sec. 25.345.
(C) The limit rolling conditions specified in Sec. 25.349 and the
limit unsymmetrical conditions specified in Sec. 25.367 and Sec.
25.427(b) and (c).
(D) The limit yaw maneuvering conditions specified in Sec. 25.351.
(E) The limit ground loading conditions specified in Sec. 25.473
and Sec. 25.491.
(ii) For static strength substantiation, each part of the structure
must be able to withstand the loads in paragraph (f)(2)(i) of the
special condition multiplied by a factor of safety depending on the
probability of being in this failure state. The factor of safety is
defined in Figure 2.
[GRAPHIC] [TIFF OMITTED] TP12MR07.001
Qj = (Tj)(Pj)
Where:
Tj = Average time spent in failure condition j (in hours)
Pj = Probability of occurrence of failure mode j (per hour)
Note: If Pj is greater than 10-3 per flight hour then
a 1.5 factor of safety must be applied to all limit load conditions
specified in subpart C-Structure, of 14 CFR part 25.
(iii) For residual strength substantiation, the airplane must be
able to withstand two-thirds of the ultimate loads defined in paragraph
(f)(2)(ii) of the special condition. For pressurized cabins, these
loads must be combined with the normal operating differential pressure.
(iv) If the loads induced by the failure condition have a
significant effect on fatigue or damage tolerance then the effects of
these loads must be taken into account.
(v) Freedom from aeroelastic instability must be shown up to a
speed determined from Figure 3. Flutter clearance speeds V' and V'' may
be based on the speed limitation specified for the remainder of the
flight using the margins defined by Sec. 25.629(b).
[GRAPHIC] [TIFF OMITTED] TP12MR07.002
V' = Clearance speed as defined by Sec. 25.629(b)(2).
V'' = Clearance speed as defined by Sec. 25.629(b)(1).
Qj = (Tj)(Pj)
Where:
Tj = Average time spent in failure condition j (in hours)
Pj = Probability of occurrence of failure mode j (per hour)
Note: If Pj is greater than 10-3 per flight hour, then the
flutter clearance speed must not be less than V''.
(vi) Freedom from aeroelastic instability must also be shown up to
V' in Figure 3 above, for any probable system failure condition
combined with any damage required or selected for investigation by
Sec. 25.571(b).
(3) Consideration of certain failure conditions may be required by
other sections of 14 CFR part 25 regardless of calculated system
reliability. Where
[[Page 10946]]
analysis shows the probability of these failure conditions to be less
than 10-9, criteria other than those specified in this paragraph may be
used for structural substantiation to show continued safe flight and
landing.
(g) Failure indications. For system failure detection and
indication, the following apply.
(1) The system must be checked for failure conditions, not
extremely improbable, that degrade the structural capability of the
airplane below the level required by part 25 or significantly reduce
the reliability of the remaining system. As far as reasonably
practicable, the flightcrew must be made aware of these failures before
flight. Certain elements of the control system, such as mechanical and
hydraulic components, may use special periodic inspections, and
electronic components may use daily checks, instead of detection and
indication systems to achieve the objective of this requirement. Such
certification maintenance inspections or daily checks must be limited
to components on which faults are not readily detectable by normal
detection and indication systems and where service history shows that
inspections will provide an adequate level of safety.
(2) The existence of any failure condition, not extremely
improbable, during flight that could significantly affect the
structural capability of the airplane and for which the associated
reduction in airworthiness can be minimized by suitable flight
limitations, must be signaled to the flightcrew. For example, failure
conditions that result in a factor of safety between the airplane
strength and the loads of subpart C below 1.25, or flutter margins
below V'', must be signaled to the crew during flight.
(h) Dispatch with known failure conditions. If the airplane is to
be dispatched in a known system failure condition that affects
structural performance, or affects the reliability of the remaining
system to maintain structural performance, then the provisions of this
special condition must be met, including the provisions of paragraph
(e) for the dispatched condition, and paragraph (f) for subsequent
failures. Expected operational limitations may be taken into account in
establishing Pj as the probability of failure occurrence for
determining the safety margin in Figure 1. Flight limitations and
expected operational limitations may be taken into account in
establishing Qj as the combined probability of being in the dispatched
failure condition and the subsequent failure condition for the safety
margins in Figures 2 and 3. These limitations must be such that the
probability of being in this combined failure state and then
subsequently encountering limit load conditions is extremely
improbable. No reduction in these safety margins is allowed if the
subsequent system failure rate is greater than 10-3 per
hour.
2. Electronic Flight Control System: Control Surface Awareness
In addition to compliance with Sec. Sec. 25.143, 25.671, and
25.672, the following special condition applies:
(a) The system design must ensure that the flightcrew is made
suitably aware whenever the primary control means nears the limit of
control authority. This indication should direct the pilot to take
appropriate action to avoid the unsafe condition in accordance with
appropriate airplane flight manual (AFM) instructions. Depending on the
application, suitable annunciations may include cockpit control
position, annunciator light, or surface position indicators.
Furthermore, this requirement applies at limits of control authority,
not necessarily at limits of any individual surface travel.
(b) Suitability of such a display or alerting must take into
account that some pilot-demanded maneuvers are necessarily associated
with intended full performance, which may require full surface
deflection. Therefore, simple alerting systems, which would function in
both intended or unexpected control-limiting situations, must be
properly balanced between needed crew awareness and nuisance factors. A
monitoring system which might compare airplane motion, surface
deflection, and pilot demand could be useful for eliminating nuisance
alerting.
3. High Intensity Radiated Fields (HIRF) Protection
(a) Protection from Unwanted Effects of High-intensity Radiated
Fields. Each electrical and electronic system which performs critical
functions must be designed and installed to ensure that the operation
and operational capabilities of these systems to perform critical
functions are not adversely affected when the airplane is exposed to
high intensity radiated fields external to the airplane.
(b) For the purposes of these Special Conditions, the following
definition applies: Critical Functions: Functions whose failure would
contribute to or cause a failure condition that would prevent continued
safe flight and landing of the airplane.
4. Limit Engine Torque Loads for Sudden Engine Stoppage
In lieu of Sec. 25.361(b) the following special condition is
proposed:
(a) For turbine engine installations, the engine mounts, pylons,
and adjacent supporting airframe structure must be designed to
withstand 1g level flight loads acting simultaneously with the maximum
limit torque loads imposed by each of the following:
(1) Sudden engine deceleration due to a malfunction which could
result in a temporary loss of power or thrust.
(2) The maximum acceleration of the engine.
(b) For auxiliary power unit installations, the power unit mounts
and adjacent supporting airframe structure must be designed to
withstand 1g level flight loads acting simultaneously with the maximum
limit torque loads imposed by each of the following:
(1) Sudden auxiliary power unit deceleration due to malfunction or
structural failure.
(2) The maximum acceleration of the power unit.
(c) For engine supporting structure, an ultimate loading condition
must be considered that combines 1g flight loads with the transient
dynamic loads resulting from each of the following:
(1) Loss of any fan, compressor, or turbine blade.
(2) Where applicable to a specific engine design, any other engine
structural failure that results in higher loads.
(d) The ultimate loads developed from the conditions specified in
paragraphs (c)(1) and (c)(2) are to be multiplied by a factor of 1.0
when applied to engine mounts and pylons and multiplied by a factor of
1.25 when applied to adjacent supporting airframe structure.
5. Design Roll Maneuver Requirement
In lieu of compliance to Sec. 25.349(a), the following special
conditions are proposed.
The following conditions, speeds, and cockpit roll control motions
(except as the motions may be limited by pilot effort) must be
considered in combination with an airplane load factor of zero and of
two-thirds of the positive maneuvering factor used in design. In
determining the resulting control surface deflections, the torsional
flexibility of the wing must be considered in accordance with Sec.
25.301(b):
(a) Conditions corresponding to steady rolling velocities must be
investigated. In addition, conditions corresponding to maximum angular
[[Page 10947]]
acceleration must be investigated for airplanes with engines or other
weight concentrations outboard of the fuselage. For the angular
acceleration conditions, zero rolling velocity may be assumed in the
absence of a rational time history investigation of the maneuver.
(b) At VA, sudden movement of the cockpit roll control
up to the limit is assumed. The position of the cockpit roll control
must be maintained until a steady roll rate is achieved and then must
be returned suddenly to the neutral position.
(c) At VC, the cockpit roll control must be moved
suddenly and maintained so as to achieve a roll rate not less than that
obtained in paragraph (2).
(d) At VD, the cockpit roll control must be moved
suddenly and maintained so as to achieve a roll rate not less than one-
third of that obtained in paragraph (2).
Issued in Renton, Washington, on March 1, 2007.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. E7-4306 Filed 3-9-07; 8:45 am]
BILLING CODE 4910-13-P
