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, 41428-41433 [07-3689]
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Federal Register / Vol. 72, No. 145 / Monday, July 30, 2007 / Rules and Regulations
4. In § 1210.515 revise paragraph (b)
to read as follows:
I
§ 1210.515
Levy of assessments.
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(b) The import assessment shall be
uniformly applied to imported
watermelons that are identified by the
numbers 0807.11.30 and 0807.11.40 in
the Harmonized Tariff Scheudle of the
United States of any other number used
to identify fresh watermelons for
consumption as human food. The U.S.
Customs Service (USCS) will collect
assessments on such watermelons at the
time of entry and will forward such
assessment as per the agreement
between USCS and USDA. Any
importer or agent who is exempt from
payment of assessments may submit the
Board adequate proof of the volume
handled by such importer for the
exemption to be granted.
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Dated: July 23, 2007.
Lloyd C. Day,
Administrator, Agricultural Marketing
Service.
[FR Doc. E7–14615 Filed 7–27–07; 8:45 am]
BILLING CODE 3410–02–P
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
effects of certain conditions on these
novel or unusual design features, such
as the effects of high intensity radiated
fields (HIRF). The applicable
airworthiness regulations do not contain
adequate or appropriate safety standards
for these design features. These special
conditions contain the additional safety
standards that the Administrator
considers necessary to establish a level
of safety equivalent to that established
by the existing standards. Additional
special conditions will be issued for
other novel or unusual design features
of the Boeing Model 787–8 airplanes.
DATES: Effective Date: August 29, 2007.
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:
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.
14 CFR Part 25
Type Certification Basis
[Docket No. NM362 Special Conditions No.
25–354–SC]
Under provisions of 14 Code of
Federal Regulations (CFR) 21.17, Boeing
must show that Boeing Model 787–8
airplanes (hereafter referred to as ‘‘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’’.
The FAA issues special conditions, as
defined in § 11.19, under § 11.38 and
they become part of the type
certification basis under § 21.17(a)(2).
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: Final special conditions.
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AGENCY:
SUMMARY: These special conditions are
issued 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
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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 § 21.101.
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 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 special conditions are
identical or nearly identical to those
previously required for type
certification of the Model 777 series
airplanes.
Most of these 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.
Special conditions are 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.
These special conditions require that
the airplane meet the structural
requirements of subparts C and D of 14
CFR part 25 when the airplane systems
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Federal Register / Vol. 72, No. 145 / Monday, July 30, 2007 / Rules and Regulations
are fully operative. The special
conditions also require that the airplane
meet these requirements considering
failure conditions. In some cases,
reduced margins are allowed for failure
conditions based on system reliability.
jlentini on PROD1PC65 with RULES
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. This feature of this design is
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 flight crew 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 situations.
These 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 and 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 transmitter and use of
sensitive avionics/electronics and
electrical systems to command and
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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, special
conditions are needed for the 787. These
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 this 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
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 ...........
Average
50
50
50
100
50
50
100
100
700
700
2000
3000
3000
1000
3000
2000
600
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.
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41429
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
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 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 25.306
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.
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Federal Register / Vol. 72, No. 145 / Monday, July 30, 2007 / Rules and Regulations
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
adopted and thus warrant special
conditions. These special conditions
contain design criteria recommended by
ARAC.
jlentini on PROD1PC65 with RULES
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.
These special conditions differ from
current requirements in that they
require that the roll maneuver result
from defined movements of the cockpit
roll control as opposed to defined
aileron deflections. Also, these special
conditions require an additional load
condition at design maneuvering speed
(VA), in which the cockpit roll control
is returned to neutral following the
initial roll input.
These special conditions differ from
similar special conditions applied to
previous designs. These special
conditions are limited to the roll axis
only, whereas previous special
conditions also included pitch and yaw
axes. Special conditions are 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 conditions are needed for the
pitch axis because the applicant’s
proposed method for the pitch
maneuver takes into account effects of
an electronic flight control system.
Discussion of Comments
Notice of Proposed Special
Conditions No. 25–06–15–SC for the
787 was published in the Federal
Register on March 12, 2007 (72 FR
10941). Only one comment was received
and it addressed proposed Special
Conditions No. 5.
1 A nonlinearity is a situation where output does
not change in the same proportion as input.
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Comment on Special Conditions No. 5.
Design Roll Maneuver Requirement
Requested change: The commenter,
an individual, stated that the paragraph
dealing with § 25.349(a) in the proposed
special conditions is a little confusing.
Paragraphs (c) and (d) of the proposed
special conditions both refer to
‘‘paragraph (2)’’. But there are no
numbered paragraphs in proposed
Special Conditions No. 5. The
commenter thought that the reference
was to paragraph (2) of § 25.349(a), but
since § 25.349(a) is superseded by the
special conditions, the commenter
suggested that this may cause confusion.
FAA response: The reference to
paragraph (2) in the proposed special
conditions was an error and we thank
the commenter for pointing it out. The
reference should have been ‘‘paragraph
(b).’’ We have revised the final special
conditions accordingly. Otherwise, all
special conditions are adopted as
proposed.
Applicability
As discussed above, these 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 on the same type
certificate incorporating the same novel
or unusual design features, these special
conditions would apply to that model as
well.
Conclusion
This action affects only certain novel
or unusual design features of the 787. It
is not a rule of general applicability.
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Reporting
and recordkeeping requirements.
I The authority citation for these
special conditions is as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701,
44702, 44704.
The Special Conditions
Accordingly, pursuant to the authority
delegated to me by the Administrator,
the following special conditions are
issued as part of the type certification
basis for the Boeing Model 787–8
airplane.
I
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
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14 of the Code of Federal Regulations.
The following criteria must be used for
showing compliance with these special
conditions 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 these special
conditions are 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 structure 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
or inoperative mode are not provided in
these special conditions.
(b) Depending on the specific
characteristics of the airplane,
additional studies may be required that
go beyond the criteria provided in these
special conditions 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 these special conditions.
(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 these special
conditions 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 these special
conditions, however, applies only to
system failure conditions that affect
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Federal Register / Vol. 72, No. 145 / Monday, July 30, 2007 / Rules and Regulations
41431
(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.
(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
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
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.
(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.
(ii) For static strength substantiation,
each part of the structure must be able
to withstand the loads in paragraph
(f)(2)(i) of these special conditions
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.
jlentini on PROD1PC65 with RULES
Note: Although failure annunciation
system reliability must be included in
probability calculations for paragraph (f) of
these special conditions, there is no specific
reliability requirement for the annunciation
system required in paragraph (g) of the
special conditions.
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Figure 2
Factor of Safety For Continuation of
Flight
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.
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ER30jy07.000</GPH>
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.
Federal Register / Vol. 72, No. 145 / Monday, July 30, 2007 / Rules and Regulations
(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).
(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 § 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
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
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Jkt 211001
Figure 3
Clearance Speed
V′=Clearance speed as defined by
§ 25.629(b)(2).
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Sfmt 4700
V″=Clearance speed as defined by
§ 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″.
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 these special conditions
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.
E:\FR\FM\30JYR1.SGM
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ER30jy07.002</GPH>
jlentini on PROD1PC65 with RULES
(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
these special conditions. 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.
ER30jy07.001</GPH>
41432
Federal Register / Vol. 72, No. 145 / Monday, July 30, 2007 / Rules and Regulations
2. Electronic Flight Control System:
Control Surface Awareness
In addition to compliance with
§§ 25.143, 25.671, and 25.672, the
following special conditions apply.
(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.
jlentini on PROD1PC65 with RULES
4. Limit Engine Torque Loads for
Sudden Engine Stoppage
In lieu of § 25.361(b) the Boeing
Model 787–8 must comply with the
following special conditions.
(a) For turbine engine installations,
the engine mounts, pylons, and adjacent
supporting airframe structure must be
designed to withstand 1g level flight
VerDate Aug<31>2005
16:39 Jul 27, 2007
Jkt 211001
41433
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.
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
(b).
(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 (b).
5. Design Roll Maneuver Requirement
In lieu of compliance to § 25.349(a),
the Boeing Model 787–8 must comply
with the following special conditions.
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
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 the limit is
AGENCY:
PO 00000
Frm 00011
Fmt 4700
Sfmt 4700
Issued in Renton, Washington, on July 18,
2007.
Stephen P. Boyd,
Acting Manager, Transport Airplane
Directorate, Aircraft Certification Service.
[FR Doc. 07–3689 Filed 7–27–07; 8:45 am]
BILLING CODE 4910–13–M
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA–2007–27359; Directorate
Identifier 2006–NM–042–AD; Amendment
39–15136; AD 2007–15–07]
RIN 2120–AA64
Airworthiness Directives; Boeing
Model 747–100, 747–100B, 747–200B,
747–200C, 747–200F, 747–300, 747SR,
and 747SP Series Airplanes
Federal Aviation
Administration (FAA), Department of
Transportation (DOT).
ACTION: Final rule.
SUMMARY: The FAA is adopting a new
airworthiness directive (AD) for certain
Boeing Model 747–100, 747–100B, 747–
200B, 747–200C, 747–200F, 747–300,
747SR, and 747SP series airplanes. This
AD requires repetitive high frequency
eddy current inspections for cracks of
the fuselage skin at stringer 5 left and
right between stations 340 and 350, and
corrective actions if necessary. This AD
results from reports of fatigue cracks in
the fuselage skin near stringer 5 between
stations 340 and 350. We are issuing
this AD to detect and correct fatigue
cracking of the fuselage skin near
stringer 5. Cracks in this area could join
together and result in in-flight
depressurization of the airplane.
DATES: This AD becomes effective
September 4, 2007.
The Director of the Federal Register
approved the incorporation by reference
of a certain publication listed in the AD
as of September 4, 2007.
E:\FR\FM\30JYR1.SGM
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]]>Agencies
[Federal Register Volume 72, Number 145 (Monday, July 30, 2007)]
[Rules and Regulations]
[Pages 41428-41433]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 07-3689]
=======================================================================
-----------------------------------------------------------------------
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. NM362 Special Conditions No. 25-354-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: Final special conditions.
-----------------------------------------------------------------------
SUMMARY: These special conditions are issued 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). The applicable
airworthiness regulations do not contain adequate or appropriate safety
standards for these design features. These special conditions contain
the additional safety standards that the Administrator considers
necessary to establish a level of safety equivalent to that established
by the existing standards. Additional special conditions will be issued
for other novel or unusual design features of the Boeing Model 787-8
airplanes.
DATES: Effective Date: August 29, 2007.
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:
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 Code of Federal Regulations (CFR) 21.17,
Boeing must show that Boeing Model 787-8 airplanes (hereafter referred
to as ``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''.
The FAA issues special conditions, as defined in Sec. 11.19, under
Sec. 11.38 and they become part of the type certification basis under
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 Sec. 21.101.
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 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 special conditions are identical or nearly identical
to those previously required for type certification of the Model 777
series airplanes.
Most of these 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. Special conditions are 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.
These special conditions require that the airplane meet the
structural requirements of subparts C and D of 14 CFR part 25 when the
airplane systems
[[Page 41429]]
are fully operative. The special conditions also require 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. This feature of this design is 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 flight crew 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 situations.
These 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 and 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 transmitter 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, special
conditions are needed for the 787. These 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 this 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 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 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 25.306 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.
[[Page 41430]]
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 special conditions. These
special conditions contain design criteria recommended by ARAC.
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.
---------------------------------------------------------------------------
These special conditions differ from current requirements in that
they require that the roll maneuver result from defined movements of
the cockpit roll control as opposed to defined aileron deflections.
Also, these special conditions require an additional load condition at
design maneuvering speed (VA), in which the cockpit roll
control is returned to neutral following the initial roll input.
These special conditions differ from similar special conditions
applied to previous designs. These special conditions are limited to
the roll axis only, whereas previous special conditions also included
pitch and yaw axes. Special conditions are 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
conditions are needed for the pitch axis because the applicant's
proposed method for the pitch maneuver takes into account effects of an
electronic flight control system.
Discussion of Comments
Notice of Proposed Special Conditions No. 25-06-15-SC for the 787
was published in the Federal Register on March 12, 2007 (72 FR 10941).
Only one comment was received and it addressed proposed Special
Conditions No. 5.
Comment on Special Conditions No. 5. Design Roll Maneuver Requirement
Requested change: The commenter, an individual, stated that the
paragraph dealing with Sec. 25.349(a) in the proposed special
conditions is a little confusing. Paragraphs (c) and (d) of the
proposed special conditions both refer to ``paragraph (2)''. But there
are no numbered paragraphs in proposed Special Conditions No. 5. The
commenter thought that the reference was to paragraph (2) of Sec.
25.349(a), but since Sec. 25.349(a) is superseded by the special
conditions, the commenter suggested that this may cause confusion.
FAA response: The reference to paragraph (2) in the proposed
special conditions was an error and we thank the commenter for pointing
it out. The reference should have been ``paragraph (b).'' We have
revised the final special conditions accordingly. Otherwise, all
special conditions are adopted as proposed.
Applicability
As discussed above, these 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 on the same type certificate
incorporating the same novel or unusual design features, these special
conditions would apply to that model as well.
Conclusion
This action affects only certain novel or unusual design features
of the 787. It is not a rule of general applicability.
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Reporting and recordkeeping
requirements.
0
The authority citation for these special conditions is as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.
The Special Conditions
0
Accordingly, pursuant to the authority delegated to me by the
Administrator, the following special conditions are issued 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 these special conditions 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 these special conditions are 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 structure 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 or inoperative mode are not provided in these
special conditions.
(b) Depending on the specific characteristics of the airplane,
additional studies may be required that go beyond the criteria provided
in these special conditions 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 these special
conditions.
(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 these special conditions 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 these special conditions,
however, applies only to system failure conditions that affect
[[Page 41431]]
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 these
special conditions, there is no specific reliability requirement for
the annunciation system required in paragraph (g) of the special
conditions.
(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] TR30JY07.000
(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 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 these
special conditions 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.
Figure 2
Factor of Safety For Continuation of Flight
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.
[[Page 41432]]
[GRAPHIC] [TIFF OMITTED] TR30JY07.001
(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 these special conditions. 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[min] and
V[sec] may be based on the speed limitation specified for the remainder
of the flight using the margins defined by Sec. 25.629(b).
Figure 3
Clearance Speed
V[min]=Clearance speed as defined by Sec. 25.629(b)(2).
V[sec]=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[sec].
[GRAPHIC] [TIFF OMITTED] TR30JY07.002
(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 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 these
special conditions 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.
[[Page 41433]]
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 conditions apply.
(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 Boeing Model 787-8 must comply with
the following special conditions.
(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 Boeing Model 787-8
must comply with the following special conditions.
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
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 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 (b).
(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 (b).
Issued in Renton, Washington, on July 18, 2007.
Stephen P. Boyd,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 07-3689 Filed 7-27-07; 8:45 am]
BILLING CODE 4910-13-M
