81 FR 51086 - Special Conditions: Gulfstream Aerospace Corporation Model GVII-G500 Airplanes; Interaction of Systems and Structures Through a Three-Axis Fly-by-Wire System

DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration

Federal Register Volume 81, Issue 149 (August 3, 2016)

These special conditions are issued for the Gulfstream Aerospace Corporation (Gulfstream) Model GVII-G500 airplane. This airplane will have a novel or unusual design feature when compared to the state of technology envisioned in the airworthiness standards for transport-category airplanes. This design feature is a fly-by-wire flight-control system that governs the pitch, yaw, and roll axes of the airplane. 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.

[Federal Register Volume 81, Number 149 (Wednesday, August 3, 2016)]
[Rules and Regulations]
[Pages 51086-51090]
From the Federal Register Online  [www.thefederalregister.org]
[FR Doc No: 2016-18448]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2015-7294; Special Conditions No. 25-628-SC]


Special Conditions: Gulfstream Aerospace Corporation Model GVII-
G500 Airplanes; Interaction of Systems and Structures Through a Three-
Axis Fly-by-Wire System

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions; request for comments.

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SUMMARY: These special conditions are issued for the Gulfstream 
Aerospace Corporation (Gulfstream) Model GVII-G500 airplane. This 
airplane will have a novel or unusual design feature when compared to 
the state of technology envisioned in the airworthiness standards for 
transport-category airplanes. This design feature is a fly-by-wire 
flight-control system that governs the pitch, yaw, and roll axes of the 
airplane. 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: This action is effective on Gulfstream on August 3, 2016. We 
must receive your comments by September 19, 2016.

ADDRESSES: Send comments identified by docket number FAA-2015-7294 
using any of the following methods:
     Federal eRegulations Portal: Go to http://www.regulations.gov/and follow the online instructions for sending your 
comments electronically.
     Mail: Send comments to Docket Operations, M-30, U.S. 
Department of Transportation (DOT), 1200 New Jersey Avenue SE., Room 
W12-140, West

[[Page 51087]]

Building Ground Floor, Washington, DC 20590-0001.
     Hand Delivery or Courier: Take comments to Docket 
Operations in Room W12-140 of the West Building Ground Floor at 1200 
New Jersey Avenue SE., Washington, DC, between 9 a.m. and 5 p.m., 
Monday through Friday, except Federal holidays.
     Fax: Fax comments to Docket Operations at 202-493-2251.
    Privacy: The FAA will post all comments it receives, without 
change, to http://www.regulations.gov/, including any personal 
information the commenter provides. Using the search function of the 
docket Web site, anyone can find and read the electronic form of all 
comments received into any FAA docket, including the name of the 
individual sending the comment (or signing the comment for an 
association, business, labor union, etc.). DOT's complete Privacy Act 
Statement can be found in the Federal Register published on April 11, 
2000 (65 FR 19477-19478), as well as at http://DocketsInfo.dot.gov/.
    Docket: Background documents or comments received may be read at 
http://www.regulations.gov/ at any time. Follow the online instructions 
for accessing the docket or go to Docket Operations in Room W12-140 of 
the West Building Ground Floor at 1200 New Jersey Avenue SE., 
Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, 
except Federal holidays.

FOR FURTHER INFORMATION CONTACT: Walt Sippel, FAA, Airframe and Cabin 
Safety Branch, ANM-115, Transport Airplane Directorate, Aircraft 
Certification Service, 1601 Lind Avenue SW., Renton, Washington 98057-
3356; telephone 425-227-2774; facsimile 425-227-1320.

SUPPLEMENTARY INFORMATION: The FAA has determined that notice of, and 
opportunity for prior public comment on, these special conditions is 
impracticable because 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 
publication in the Federal Register.

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 will consider all comments we receive by the closing date for 
comments. We may change these special conditions based on the comments 
we receive.

Background

    On March 29, 2012, Gulfstream applied for a type certificate for 
their new Model GVII-G500 airplane. This transport-category, twin-
engine airplane will be a business jet capable of accommodating up to 
19 passengers. The maximum takeoff weight is 91,000 lbs.

Type Certification Basis

    Under title 14, Code of Federal Regulations (14 CFR) 21.17, 
Gulfstream must show that the Model GVII-G500 airplane meets the 
applicable provisions of 14 CFR part 25, as amended by Amendments 25-1 
through 25-129.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., part 25) do not contain adequate or appropriate 
safety standards for the Model GVII-G500 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 or similar 
novel or unusual design feature, the special conditions would also 
apply to the other model under Sec.  21.101.
    In addition to the applicable airworthiness regulations and special 
conditions, Model GVII-G500 airplanes 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. The FAA must issue a 
finding of regulatory adequacy under section 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 GVII-G500 airplane will incorporate the following novel 
or unusual design feature:
    A fly-by-wire flight-control system that governs the pitch, yaw, 
and roll axes of the airplane.

Discussion

    Active flight-control systems are capable of providing automatic 
responses to inputs from sources other than pilots. Active flight-
control systems have been expanded in function, effectiveness, and 
reliability such that fly-by-wire flight controls, without a manual 
backup system to address system failures, are becoming standard 
equipment. As a result of these advancements in flight-control 
technology, the current safety standards contained in 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 through special conditions. Advisory circular 25.672-1 was issued 
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 flight-control system.
    Although autopilots are also considered active flight-control 
systems, their control authority has historically 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 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; 
either fully

[[Page 51088]]

functioning or totally inoperative. The flightcrew readily detected 
these conditions. The new active flight-control systems have failure 
modes that allow the system to function in a degraded mode without full 
authority. The flightcrew do not readily detect these degraded modes. 
Therefore, monitoring systems are required on these new systems to 
provide an annunciation of degraded system capability.
    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.

Applicability

    As discussed above, these special conditions are applicable to the 
Gulfstream Model GVII-G500 airplane. Should Gulfstream apply at a later 
date for a change to the type certificate to include another model 
incorporating the same novel or unusual design feature, these special 
conditions would apply to that model as well.

Conclusion

    This action affects only a certain novel or unusual design feature 
on one model series of airplane. It is not a rule of general 
applicability.
    The substance of these special conditions has been subjected to the 
notice and comment period in several prior instances and has been 
derived without substantive change from those previously issued. It is 
unlikely that prior public comment would result in a significant change 
from the substance contained herein. Therefore, good cause exists for 
adopting these special conditions upon publication in the Federal 
Register.
    The FAA is requesting comments to allow interested persons to 
submit views that may not have been submitted in response to the prior 
opportunities for comment described above.

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 Gulfstream Model GVII-G500 
airplane.
    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 14 CFR part 25, subparts C and D.
    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 studies that go beyond the criteria provided in these 
special conditions may be required to demonstrate the airplane's 
capability 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 an in-flight occurrence, and that 
are included in the airplane flight manual (e.g., speed limitations, 
avoidance of severe weather conditions, etc.).
    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: Terms such as probable, improbable, and 
extremely improbable, as 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

    1. General. The following criteria will be used in determining the 
influence of a system and its failure conditions on the airplane 
structure.
    2. 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 conditions specified in 
14 CFR part 25, subpart C (or defined by special conditions or 
equivalent level of safety 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 
nonlinearity (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 14 CFR 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 
that 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.
    3. 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 1g level flight 
conditions, a realistic scenario, including pilot corrective actions, 
must be established to determine the loads occurring at the

[[Page 51089]]

time of failure and immediately after the failure.
    i. 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, below.
[GRAPHIC] [TIFF OMITTED] TR03AU16.000

    ii. For residual-strength substantiation, the airplane must be able 
to withstand two thirds of the ultimate loads defined in special 
condition 3.a.(i). 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 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.
    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:
    i. 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:
    1. The limit symmetrical maneuvering conditions specified in 
Sec. Sec.  25.331 and 25.345.
    2. the limit gust and turbulence conditions specified in Sec. Sec.  
25.341 and 25.345.
    3. 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).
    4. the limit yaw-maneuvering conditions specified in Sec.  25.351.
    5. the limit ground-loading conditions specified in Sec. Sec.  
25.473 and 25.491.
    ii. For static-strength substantiation, each part of the structure 
must be able to withstand the loads in special condition 3.b.(i), 
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, 
below.
[GRAPHIC] [TIFF OMITTED] TR03AU16.001

Where:

Qj = (Tj)(Pj)
Qj = Probability of being in failure mode j
Tj = Average time spent in failure mode 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.

    iii. For residual-strength substantiation, the airplane must be 
able to withstand two-thirds of the ultimate loads defined in paragraph 
3.b.(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 their effects 
must be taken into account.
    v. Freedom from aeroelastic instability must be shown up to a speed 
determined from Figure 3, below. 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).

[[Page 51090]]

[GRAPHIC] [TIFF OMITTED] TR03AU16.002

V' = Clearance speed as defined by Sec.  25.629(b)(2).
V'' = Clearance speed as defined by Sec.  25.629(b)(1).

Where:

Qj = (Tj)(Pj) where:
Qj = Probability of being in failure mode j
Tj = Average time spent in failure mode j (in hours)
Pj = Probability of occurrence of failure mode j (per 
hour)

    Note: If Pj is greater than 10-3 per 
flight hour, then the flutter clearance speed must not be less than 
V''.

    vi. Freedom from aeroelastic instability must also be shown up to 
V' in Figure 3, above, for any probable system-failure condition, 
combined with any damage required or selected for investigation by 
Sec.  25.571(b).
    b. 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.
    4. Failure indications. 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 that 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 
certification-maintenance requirements 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 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.
    5. 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 of special condition 2 
for the dispatched condition, and special condition 3 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.

    Issued in Renton, Washington, on July 27, 2016.
Victor Wicklund,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 2016-18448 Filed 8-2-16; 8:45 am]
 BILLING CODE 4910-13-P