Special Conditions: Gulfstream Aerospace LP (GALP) Model G250 Airplane, Interaction of Systems and Structures, 41041-41045 [2011-17533]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 76, Number 134 (Wednesday, July 13, 2011)]
[Rules and Regulations]
[Pages 41041-41045]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2011-17533]



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Federal Register / Vol. 76, No. 134 / Wednesday, July 13, 2011 / 
Rules and Regulations

[[Page 41041]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM460; Special Conditions No. 25-439-SC]


Special Conditions: Gulfstream Aerospace LP (GALP) Model G250 
Airplane, Interaction of Systems and Structures

ACTION: Final special conditions; request for comments.

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SUMMARY: These special conditions are issued for the Gulfstream 
Aerospace LP (GALP) Model G250 airplane. This airplane will have a 
novel or unusual design feature associated with a fly-by-wire (FBW) 
flight control system that governs the yaw and roll axes. The 
applicable airworthiness regulations do not contain adequate or 
appropriate safety standards for this design feature. 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 airworthiness standards.

DATES: The effective date of these special conditions is July 1, 2011. 
We must receive your comments by August 29, 2011.

ADDRESSES: You must mail two copies of your comments to: Federal 
Aviation Administration, Transport Airplane Directorate, Attn: Rules 
Docket (ANM-113), Docket No. NM460, 1601 Lind Avenue, SW., Renton, 
Washington, 98057-3356. You may deliver two copies to the Transport 
Airplane Directorate at the above address. You must mark your comments: 
Docket No. NM460. You can inspect comments in the Rules Docket 
weekdays, except Federal holidays, between 7:30 a.m. and 4 p.m.

FOR FURTHER INFORMATION CONTACT: Carl Niedermeyer, Transport Airplane 
Directorate, Aircraft Certification Service, 1601 Lind Avenue, SW., 
Renton, Washington 98057-3356; telephone (425) 227-2279; e-mail 
carl.niedermeyer@faa.gov; facsimile (425) 227-1149.

SUPPLEMENTARY INFORMATION: The FAA has determined that notice of, and 
opportunity for prior public comment on, these special conditions are 
impracticable because these procedures would significantly delay 
issuance of the design approval and thus delivery of the affected 
aircraft. In addition, the substance of these special conditions has 
been subject to the public-comment process in several prior instances 
with no substantive comments received. The FAA therefore finds that 
good cause exists for making these special conditions effective upon 
issuance.

Comments Invited

    We invite interested people to take part in this rulemaking by 
sending 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 
about these special conditions. You can inspect the docket 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 preamble 
between 7:30 a.m. and 4 p.m., Monday through Friday, except Federal 
holidays.
    We will consider all comments we receive by the closing date for 
comments. We may change these special conditions based on the comments 
we receive.
    If you want us to acknowledge receipt of your comments on these 
special conditions, include with your comments a self-addressed, 
stamped postcard on which you have written the docket number. We will 
stamp the date on the postcard and mail it back to you.

Background

    On March 30, 2006, GALP applied for a type certificate for their 
new Model G250 airplane. The G250 is an 8-10 passenger (19 maximum), 
twin-engine airplane with a maximum operating altitude of 45,000 feet 
and a range of approximately 3,400 nautical miles. Airplane dimensions 
are 61.69-foot wing span, 66.6-foot overall length, and 20.8-foot tail 
height. Maximum takeoff weight is 39,600 pounds and maximum landing 
weight 32,700 pounds. Maximum cruise speed is mach 0.85, dive speed is 
mach 0.92. The avionics suite will be the Rockwell Collins Pro Line 
Fusion.

Type Certification Basis

    Under the provisions of 14 CFR 21.17, GALP must show that the Model 
G250 airplane meets the applicable provisions of part 25 as amended by 
Amendments 25-1 through 25-117.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., 14 CFR part 25) do not contain adequate or 
appropriate safety standards for the Model G250 airplane because of a 
novel or unusual design feature, special conditions are prescribed 
under the provisions of Sec.  21.16.
    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 novel or 
unusual design feature, the special conditions would also apply to the 
other model.
    In addition to the applicable airworthiness regulations and special 
conditions, the Model G250 airplane must comply with the fuel-vent and 
exhaust-emission requirements of 14 CFR part 34 and the noise-
certification requirements of 14 CFR part 36; and the FAA must issue a 
finding of regulatory adequacy under Sec.  611 of Public Law 92-574, 
the ``Noise Control Act of 1972.''
    The FAA issues special conditions, as defined in 14 CFR 11.19, in 
accordance with Sec.  11.38, and they become part of the type-
certification basis under Sec.  21.17(a)(2).

Novel or Unusual Design Features

    The Model G250 will incorporate the following novel or unusual 
design features:
    The GALP Model G250 airplane has an FBW flight control system that 
governs the yaw and roll axes. The current rules are inadequate for 
considering the effects on structural

[[Page 41042]]

performance of this system and its failures.

Discussion

    Active flight control systems are capable of providing automatic 
responses to inputs from sources other than the pilots. Active flight 
control systems have been expanded in function, effectiveness, and 
reliability to the point that FBW flight controls, without a manual 
backup system to override FBW system failures, are becoming standard 
equipment. As a result of these advancements in flight controls 
technology, the current safety standards contained in Title 14 Code of 
Federal Regulations (14 CFR) part 25 do not provide an adequate basis 
to address an acceptable level of safety for airplanes so equipped. 
Instead, certification of these systems has been achieved by issuance 
of special conditions under the provisions of Sec.  21.16.
    For example, stability augmentation systems (SASs), and to a lesser 
extent load alleviation systems (LASs), have been used on transport 
airplanes for many years. Past approvals of these systems were based on 
individual findings of equivalent level of safety with existing rules 
and on special conditions. Advisory Circular 25.672-1 was issued on 
November 11, 1983, to provide an equivalent means of compliance under 
the provisions of Sec.  21.21(b)(1) for SAS, LAS, and flutter control 
systems (FCSs), another type of active control system.
    Although autopilots are also considered active control systems, 
their control authority historically has been limited such that the 
consequences of system failures could be readily counteracted by the 
pilot. Now, autopilot functions are integrated into the primary flight 
controls and are given sufficient control authority to maneuver the 
airplane to its structural design limits. This advanced technology, 
with its expanded authority, requires a new approach to account for the 
interaction of control systems and structures.
    The usual deterministic approach to defining the loads envelope 
contained in 14 CFR part 25 does not fully account for system 
effectiveness and system reliability. These automatic systems may be 
inoperative or may operate in a degraded mode with less than full-
system authority. Therefore, it is necessary to determine the 
structural factors of safety and operating margins such that the joint 
probability of structural failures, due to application of loads during 
system malfunctions, is not greater than that found in airplanes 
equipped with earlier-technology control systems. To achieve this 
objective, it is necessary to define the failure conditions with their 
associated frequency of occurrence to determine the structural factors 
of safety and operating margins that will ensure an acceptable level of 
safety.
    Earlier automatic control systems usually provided two states: 
fully functioning, or totally inoperative. These conditions were 
readily detected by the flight crew. The new active flight control 
systems have failure modes that allow the system to function in a 
degraded mode without full authority. These degraded modes are not 
readily detectable by the flightcrew, therefore monitoring systems are 
required on these new systems to provide an annunciation of degraded 
system capability.
    In these special conditions, and in the current standards and 
regulations, the term ``any'' is used. Use of this term has 
traditionally been understood to require the applicant to address all 
items covered by the term, rather than addressing only a portion of the 
items. The use of the term ``any'' in these special conditions 
continues this traditional understanding.

Applicability

    As discussed above, these special conditions are applicable to the 
GALP Model G250 airplane. Should GALP apply at a later date for a 
change to the type certificate to include another model incorporating 
the same novel or unusual design feature, the special conditions would 
apply to that model as well.

Conclusion

    This action affects only certain novel or unusual design features 
on the GALP Model G250 airplane. It is not a rule of general 
applicability and it affects only the applicant who applied to the FAA 
for approval of these features on the airplane.
    The FAA has determined that prior public notice and comment are 
unnecessary and impracticable, and good cause exists for adopting these 
special conditions upon issuance.

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 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 GALP Model G250 airplane.

Interaction of Systems and Structures

    For airplanes equipped with systems that affect structural 
performance, either directly or as a result of a failure or 
malfunction, the influence of these systems and their failure 
conditions must be taken into account when showing compliance with the 
requirements of Subparts C and D of 14 CFR part 25.
    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.
    1. The criteria defined herein only address the direct structural 
consequences of the system responses and performance. They cannot be 
considered in isolation but should be included in the overall safety 
evaluation of the airplane. These criteria may, in some instances, 
duplicate standards already established for this evaluation. These 
criteria are only applicable to structure the failure of which could 
prevent continued safe flight and landing. Specific criteria that 
define acceptable limits on handling characteristics or stability 
requirements, when operating in the system degraded or inoperative 
mode, are not provided in these special conditions.
    2. Depending upon the specific characteristics of the airplane, 
additional criteria may be required that go beyond the criteria 
provided in these special conditions to demonstrate the capability of 
the airplane to meet other realistic conditions such as alternative 
gust or maneuver descriptions for an airplane equipped with a load-
alleviation system.
    3. The following definitions are applicable to these special 
conditions.
    (a) Structural performance: Capability of the airplane to meet the 
structural requirements of 14 CFR part 25.
    (b) Flight limitations: Limitations that can be applied to the 
airplane flight conditions following a detectable in-flight occurrence 
and that are included in the airplane flight manual (AFM; e.g., speed 
limitations, avoidance of severe weather conditions, etc.).

[[Page 41043]]

    (c) Operational limitations: Limitations, including flight 
limitations, that can be applied to the airplane operating conditions 
before dispatch (e.g., fuel, payload, and Master Minimum Equipment List 
limitations).
    (d) Probabilistic terms: The probabilistic terms (probable, 
improbable, extremely improbable) used in these special conditions are 
the same as those used in Sec.  25.1309.
    (e) Failure condition: This term is the same as that used in Sec.  
25.1309. However, these special conditions apply only to system-failure 
conditions that affect the structural performance of the airplane 
(e.g., system-failure conditions that induce loads, change the response 
of the airplane to inputs such as gusts or pilot actions, or lower 
flutter margins).

Effects of Systems on Structures

    The following criteria will be used in determining the influence of 
a system and its failure conditions on the airplane structure.
    4. System fully operative. With the system fully operative, the 
following apply:
    (a) Limit loads must be derived in all normal operating 
configurations of the system from all the limit load conditions 
specified in 14 CFR part 25, subpart C (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 changes in control-surface limits, rate of 
displacement of control surface, thresholds, or any other system 
nonlinearities must be accounted for in a realistic or conservative way 
when deriving limit loads from limit conditions.
    (b) The airplane must meet the strength requirements of part 25 
(static strength, 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 when it can be shown that the airplane has 
design features that will not allow it to exceed those limit 
conditions.
    (c) The airplane must meet the aeroelastic stability requirements 
of Sec.  25.629.
    5. System in the failure condition. For any system failure 
condition not shown to be extremely improbable, the following apply:
    (a) At the time of occurrence. Starting from 1-g level-flight 
conditions, a realistic scenario, including pilot corrective actions, 
must be established to determine the loads occurring at the time of 
failure and immediately after the failure.
    (1) For static-strength substantiation, these loads, multiplied by 
an appropriate factor of safety that is related to the probability of 
occurrence of the failure, are ultimate loads to be considered for 
design. The factor of safety is defined in Figure 1.
[GRAPHIC] [TIFF OMITTED] TR13JY11.014

    (2) For residual strength substantiation, the airplane must be able 
to withstand two-thirds of the ultimate loads defined in paragraph 
5(a)(1) of these special conditions. For pressurized cabins, these 
loads must be combined with the normal operating differential pressure.
    (3) 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 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.
    (4) 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.
    (b) For the continuation of the flight. For the airplane in the 
system-failed state, and considering any appropriate reconfiguration 
and flight limitations, the following apply:
    (1) The 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. Sec.  25.331 and 25.345.
    (B) The limit gust and turbulence conditions specified in 
Sec. Sec.  25.341 and 25.345.
    (C) The limit rolling conditions specified in Sec.  25.349, and the 
limit unsymmetrical conditions specified in Sec. Sec.  25.367, and 
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. Sec.  
25.473 and 25.491.
    (2) For static-strength substantiation, each part of the structure 
must be able to withstand the loads in paragraph 5(b)(1) 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.

[[Page 41044]]

[GRAPHIC] [TIFF OMITTED] TR13JY11.015

Qj = (Tj)(Pj)
Where:

Qj = Probability of being in failure condition j
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 14 CFR part 25, subpart C.

    (3) For residual-strength substantiation, the airplane must be able 
to withstand two thirds of the ultimate loads defined in paragraph 
5(b)(2) of these special conditions. For pressurized cabins, these 
loads must be combined with the normal operating differential pressure.
    (4) If the loads induced by the failure condition have a 
significant effect on fatigue or damage tolerance, then their effects 
must be taken into account.
    (5) 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] TR13JY11.016

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:

Qj = Probability of being in failure condition j
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''.

    (6) 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).
    (c) 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.

Failure Indications

    6. For system-failure detection and indication, the following 
apply:
    (a) The system must be checked for failure conditions, not 
extremely improbable, that degrade the structural capability below the 
level required by 14 CFR part 25, or which 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, in lieu of detection-and-
indication systems to achieve the objective of this requirement. These 
inspections should be Certification Maintenance Requirements (CMR; see 
Advisory Circular 25.19). These CMRs must be limited to components that 
are not readily detectable by normal detection-and-indication systems, 
and where service history shows that inspections will provide an 
adequate level of safety.
    (b) The existence of any failure condition, not extremely 
improbable, during flight that could significantly affect the 
structural capability of the

[[Page 41045]]

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 14 CFR part 25, 
subpart C below 1.25, or flutter margins below V'', must be signaled to 
the crew during flight with required crew action specified in the AFM.
    7. Dispatch with known failure conditions. If the airplane is to be 
dispatched in a known system-failure condition that affects structural 
performance, or that affects the reliability of the remaining system to 
maintain structural performance, then the provisions of these special 
conditions must be met, including the provisions described in these 
special conditions in paragraph 4 for the dispatched condition and 
paragraph 5 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 1E-3 per hour.

    Issued in Renton, Washington, on July 1, 2011.
Jeffrey E. Duven,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 2011-17533 Filed 7-12-11; 8:45 am]
BILLING CODE 4910-13-P