Document ID: FAA-2017-0636-0006
Agency: faa
Document Type: Rule
Title: Special Conditions: The Boeing Company Model 777-8 and 777-9 Airplanes; Folding Wingtips
Posted Date: 2018-05-18T04:00Z

[Federal Register Volume 83, Number 97 (Friday, May 18, 2018)]
[Rules and Regulations]
[Pages 23209-23212]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2018-10576]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2017-0636; Special Conditions No. 25-726-SC]

Special Conditions: The Boeing Company Model 777-8 and 777-9 
Airplanes; Folding Wingtips

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for The Boeing Company 
(Boeing) Model 777-8 and 777-9 airplanes. These airplanes 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 folding wingtips. 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: Effective June 18, 2018.

FOR FURTHER INFORMATION CONTACT: Ian Won, FAA, Airframe and Cabin 
Safety Section, AIR-675, Policy and Innovation Division, Transport 
Standards Branch, Aircraft Certification Service, 2200 South 216th St., 
Des Moines, Washington, 98198-6547; telephone 206-231-3217.

SUPPLEMENTARY INFORMATION:

Background

    On April 19, 2017 (for the Model 777-8 airplane), and May 12, 2015 
(for the 777-9 airplane), Boeing applied for an amendment to Type 
Certificate (TC) No. T00001SE to include the new Model 777-8 and 777-9 
airplanes. These airplanes are constructed with new carbon-fiber-
reinforced plastic (CFRP) wings with folding wingtips.

[[Page 23210]]

    The Model 777-9 airplane, a derivative of the Model 777-300ER 
airplane currently approved under TC No. T00001SE, is a stretched-
fuselage, large, twin-engine airplane with seating for 408 passengers 
and a maximum takeoff weight of 775,000 pounds.
    The Model 777-8 airplane, a shortened-body derivative of the Model 
777-9 airplane, is a large, twin-engine airplane with seating for 359 
passengers and a maximum takeoff weight of 775,000 pounds.

Type Certification Basis

    Under the provisions of title 14, Code of Federal Regulations (14 
CFR) 21.101, Boeing must show that the Model 777-8 and 777-9 airplanes 
meet the applicable provisions of the regulations listed in TC No. 
T00001SE, or the applicable regulations in effect on the date of 
application for the change, except for earlier amendments as agreed 
upon by the FAA.
    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 777-8 and 777-9 airplanes 
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, or should any other model already included on 
the same type certificate be modified to incorporate the same novel or 
unusual design feature, these special conditions would also apply to 
the other model under Sec.  21.101.
    In addition to the applicable airworthiness regulations and special 
conditions, the Model 777-8 and 777-9 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 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.  21.101.

Novel or Unusual Design Features

    The Boeing Model 777-8 and 777-9 airplanes will incorporate the 
following novel or unusual design features: CFRP wings with folding 
wingtips.
    Boeing will incorporate this on-ground wingtip-fold capability to 
reduce the wingspan from 235 to 212 feet when folded. These folding 
wingtips comply with Code E gate \1\ compatibility when folded during 
ground operations.
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    \1\ A Code E gate is designed to accommodate aircraft wingspans 
between 170.6 ft. (52m) and 213.3 ft. (65m), and outer main-gear 
wheel spans between 29.5 ft. (9m) and 45.9 ft. (14m). Boeing 777 
airplanes are in this gate-code category.
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Discussion

    Boeing will add folding wingtips to their Model 777-8 and 777-9 
airplane wings to maintain Code E gate compatibility when folded during 
ground operations. This wing-folding feature will be operable on the 
ground only. Boeing has no plan to carry fuel in the folding sections 
of the wings.
    Boeing has determined that a catastrophic event could occur if the 
Model 777-8 and 777-9 airplane wingtips are not properly positioned and 
secured for takeoff and during flight. In service, numerous takeoff 
operations with improper airplane configurations have occurred due to 
failures of the takeoff warning systems, or inadvertent crew actions. 
For these special conditions, a parallel is drawn between taking off 
with gust locks engaged and taking off with the wingtips folded, as 
either condition could result in a catastrophic event. Consequently, 
the FAA has determined that the level of safety in protecting a 
misconfigured airplane from takeoff with wingtips folded should be the 
same as taking off with the gust locks engaged. Therefore, condition 2 
of these special conditions has the same intent as Sec.  25.679(a)(2). 
Per Sec.  25.1309, the applicant must show that such an event is 
extremely improbable, must not result from a single failure, and that 
appropriate alerting must be provided for the crew to manage unsafe 
system-operating conditions. In addition, the applicant must ensure 
that the wingtips are properly secured during ground operations to 
protect ground personnel against bodily injury.
    Factors to be considered when showing compliance to these special 
conditions include, but are not limited to:
     With wingtips in the folded position, the conventional 
airplane-wingtip-position lights may have reduced visibility due to the 
upward position of the wingtips, possibly impacting ground-operation 
safety. Light placement may require special consideration to retain the 
current ground-operation safety, and mitigate any adverse impact this 
light position may have on pilot visibility during night-lighting 
conditions.
     Due to upward wingtip positioning on the ground, 
significant loads may be imposed by wind gusts combined with taxi speed 
during the transition from the unfolded to the folded position.
     The FAA issued Policy Statement No. PS-ANM-25-12, 
``Certification of Structural Elements in Flight Control Systems,'' to 
address structural elements in systems that act as both structure and 
as part of a system. This policy provides additional guidance on the 
appropriate application of the fatigue and damage-tolerance 
requirements of Sec.  25.571, and the system-safety requirements of 
Sec. Sec.  25.671 and 25.1309.
    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.

Discussion of Comments

    Notice of Proposed Special Conditions No. 25-17-02-SC for the 
Boeing Model 777-8 and 777-9 airplanes was published in the Federal 
Register on November 1, 2017 (82 FR 50581). The FAA received responses 
from four commenters.

Commenter 1: Air Line Pilots Association (ALPA)

    ALPA stated that the special conditions should require 
demonstration of ground-handling effects due to the folding wingtips, 
and implementing a robust flight-test procedure to evaluate the effects 
of the folding wingtips during landing rollout and taxi under high 
crosswind and gust conditions, to ensure no exceptional piloting skill 
is required during these operations. ALPA also suggests including, 
within the Boeing Model 777 series airplane flight manual, the 
crosswind conditions under which the folding wingtips were studied.
    The FAA notes that demonstration of acceptable handling qualities 
is required by special condition 5 as written. The method of compliance 
demonstration, and associated documentation, is outside the scope of 
these special conditions, and the special conditions remain adopted as 
proposed.

Commenter 2

    One commenter suggested various means for the applicant to address 
the special conditions, for example, the need for additional power cut 
outs that are separate circuits. The FAA partially agrees with the 
commenter, noting that special conditions are performance standards 
that may be satisfied by various means, including those the commenter 
proposed. However, the method of compliance demonstration is outside 
the scope of these special

[[Page 23211]]

conditions. Therefore, the special conditions remain adopted as 
proposed.

Commenter 3

    One commenter expressed concern that the special conditions may be 
confusing to the United States Congress. The FAA responds that special 
conditions are part of the Executive Branch rulemaking process, which 
is independent of the United States Congress lawmaking process. Special 
conditions are unique to aircraft certification and, therefore, are 
written with the aerospace-industry audience in mind. The special 
conditions remain adopted as proposed.

Commenter 4

    One commenter stated concern over the applicability of these 
special conditions to future models on the Boeing Model 777 airplane 
type certificate. Should Boeing apply at a later date for a change to 
the type certificate to include another model incorporating the same 
novel or unusual design feature, these special conditions would apply 
to that model as well. The FAA responds that these special conditions 
provide requirements for a safe design for folding wingtips on future 
Model 777 airplane derivatives, as well as on the current Model 777 
airplanes. These special conditions will ensure that future models 
incorporating the same novel or unusual design feature meet the level 
of safety equivalent to that established in the regulations.
    The commenter suggested that the 1.25 factor specified in Sec.  
25.415(d) be applied to the portion of the system that is isolated in-
flight, and is not critical for safe flight and landing. The FAA 
disagrees with the comment. The structure the commenter addressed has 
no impact on safety of flight. Additionally, the special conditions 
require that the wingtips must have a means by which to safeguard 
against unlocking from the extended, flight-deployed position in-flight 
because of failures, including the failure of any single structural 
element. The special conditions remain adopted as proposed.
    The commenter suggested that the airplane must demonstrate 
acceptable handling qualities during rollout in a crosswind 
environment, as the wingtips transition from the flight-deployed to 
folded position, and transitioning from the folded to the flight-
deployed position, as well as during the unlikely event of asymmetric 
wingtip folding. The FAA agrees with the comment, but it is the FAA's 
position that the special conditions, as proposed, indicate that the 
airplane must exhibit acceptable handling qualities under normal and 
asymmetric operation. The special conditions remain adopted as 
proposed.
    The commenter suggested that the FAA repeat the Sec.  25.675 text 
in special condition 6, in lieu of only referencing Sec.  25.675 in the 
special condition. The FAA finds that the special condition has the 
same legal effect either way, and finds no advantage to repeating the 
text of Sec.  25.675 in special condition 6.

Applicability

    As discussed above, these special conditions are applicable to 
Boeing Model 777-8 and 777-9 airplanes. Should Boeing apply at a later 
date for a change to the type certificate to include another model 
incorporating the same novel or unusual design 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 airplanes. It is not a rule of general 
applicability.

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 Boeing Model 777-8 and 777-9 
airplanes.

    Note: The term ``latch'' refers to the mechanism that allows the 
wingtip to carry flight loads in the down (flight-deployed) 
position. The term ``lock'' refers to the mechanism that prevents 
disconnection of the latch when the wing tip is down.

    1. More than one means must be available to alert the flightcrew 
that the wingtips are not properly positioned and secured prior to 
takeoff. Each of these means must be unique in their wingtip-monitoring 
function. When meeting this condition, the applicant must add a 
function to the takeoff warning system, as required by Sec.  
25.703(a)(1) and (2), to warn of an unlocked or improperly positioned 
wingtip, including indication to the flightcrew when a wingtip is in 
the folded position during taxi.
    2. In addition to a takeoff warning in accordance with Sec.  
25.703, a means must be provided to prevent airplane takeoff if a 
wingtip is not properly positioned and secured for flight.
    3. The applicant must consider the effects of folding-wingtip 
freeplay when evaluating compliance to the design load requirements of 
14 CFR part 25, subpart C, and the aeroelastic stability (including 
flutter, divergence, control reversal, and any undue loss of stability 
and control as a result of structural deformation) requirements of 
Sec.  25.629. Thus, the effects of normal wear, and other long-term 
durability conditions (such as corrosion) of the folding-wingtip 
operating mechanism on freeplay, and its impact on loads and 
aeroelastic stability, must be considered. Where freeplay limitations 
are required to ensure aeroelastic stability, acceptable freeplay 
limits and freeplay check procedures must be established. If 
lubrication is required to control excessive wear, lubrication 
intervals must be established. These procedures and limitations must be 
documented in accordance with Sec.  25.1529. The freeplay-check and 
mechanism-lubrication intervals, if required, must be documented as a 
certification maintenance requirement (CMR). Guidance for CMRs can be 
found in Advisory Circular 25-19A, ``Certification Maintenance 
Requirements.'' The effects of freeplay on wing-joint torsional and 
bending stiffness, as well as wing frequencies, must be evaluated when 
showing compliance to loads and aeroelastic stability requirements. 
Also, the effects of freeplay on fatigue and damage tolerance must be 
considered when showing compliance with Sec.  25.571.
    4. The folding wingtips and their operating mechanism must be 
designed for 65 knot, horizontal, ground-gust conditions in any 
direction as specified in Sec.  25.415(a). Relevant design conditions 
must be defined using combinations of steady wind and taxi speeds 
determined by rational analysis utilizing airport wind data. The 
folding wingtip is not a control surface as specified in Sec.  
25.415(b). Therefore, in lieu of the equation provided in Sec.  
25.415(b), the hinge moment may be calculated from rational wind-tunnel 
data. The 1.25 factor specified in Sec.  25.415(d) need not be applied 
to the portion of the system that is isolated in flight and is not 
critical for safe flight and landing. The folding-wingtip system must 
be designed for the conditions specified in Sec.  25.415(e), (f), and 
(g). Runway roughness, as specified in Sec.  25.491, must be evaluated 
separately up to the maximum relevant airplane ground speeds. All of 
the above conditions must be applied to the folding wingtips in the 
extended (flight-

[[Page 23212]]

deployed), folded, and transient positions.
    5. The airplane must demonstrate acceptable handling qualities 
during rollout in a crosswind environment, as wingtips transition from 
the flight-deployed to folded position, as well as during the unlikely 
event of asymmetric wingtip folding.
    6. The wingtip-fold operating mechanism must have stops that 
positively limit the range of motion of the wingtips. Each stop must be 
designed to the requirements of Sec.  25.675.
    7. The wingtip hinge structure must be designed for inertia loads 
acting parallel to the hinge line. In the absence of more rational 
data, the inertia loads may be assumed to be equal to KW as referenced 
in Sec.  25.393. Hinge design must meet the requirements of Sec.  
25.657.
    8. In lieu of Sec.  25.1385(b): The forward position lights must be 
installed such that they consist of a red and a green light spaced 
laterally as far apart as practicable, and installed forward on the 
airplane, so that, with the airplane in the normal flying position and 
with the wingtips in the folded position for ground operations, the red 
light is on the left side and the green light is on the right side at 
approximately the level of the wingtips in the takeoff configuration. 
Each light must be approved and must meet the requirements of Sec.  
25.1385(a) and (d). The lights must not impair the vision of the 
flightcrew when the wingtips are in the folded and transient positions.
    9. The applicant must include design features that ensure the 
wingtips are properly secured during ground operations, to protect 
ground personnel from bodily injury as well as to prevent damage to the 
airframe, ground structure, and ground support equipment.
    10. The wingtips must have means to safeguard against unlocking 
from the extended, flight-deployed position in flight, as a result of 
failures, including the failure of any single structural element. All 
sources of airplane power that could initiate unlocking of the wingtips 
must be automatically isolated from the wingtip-fold operating system 
(including the latching and locking system) prior to flight, and it 
must not be possible to restore power to the system during flight. The 
wingtip latching and locking mechanisms must be designed so that, under 
all airplane flight-load conditions, no force or torque can unlatch or 
unlock the mechanisms. The latching system must include a means to 
secure the latches in the latched position, independent of the locking 
system. It must not be possible to position the lock in the locked 
position if the latches and the latching mechanisms are not in the 
latched position, and it must not be possible to unlatch the latches 
with the locks in the locked position.

    Issued in Des Moines, Washington, on May 11, 2018.
Victor Wicklund,
Manager, Transport Standards Branch, Policy and Innovation Division, 
Aircraft Certification Service.
[FR Doc. 2018-10576 Filed 5-17-18; 8:45 am]
 BILLING CODE 4910-13-P