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###### Department of Transportation

###### Federal Aviation Administration

          - 14 CFR Part 25
          - [Docket No. FAA-2017-0636; Notice No. 25-17-02-SC]

# AGENCY:

Federal Aviation Administration (FAA), DOT.

# ACTION:

Notice of proposed special conditions.

# SUMMARY:

This action proposes special conditions for 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 proposed 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:

Send your comments on or before December 18, 2017.

# ADDRESSES:

Send comments identified by docket number FAA-2017-0636 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 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).                    

*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:

Ian Won, FAA, Airframe and Cabin Safety Section, AIR-675, Policy and Innovation Division, Transport Standards Branch, Aircraft Certification Service, 1601 Lind Avenue SW., Renton, Washington 98057-3356; telephone 425-227-2145; facsimile 425-227-1360.

# SUPPLEMENTARY INFORMATION:

## 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 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.

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 § 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 § 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 § 11.38, and they become part of                           ( print page 50582)                        the type certification basis under § 21.101.                

## Novel or Unusual Design Features

The Model 777-8 and 777-9 airplanes will incorporate the following novel or unusual design features: CFRP wings with folding wingtips.

                    Boeing proposes to incorporate this on-ground wingtip-fold capability to reduce the wingspan from 235 to 212 feet when folded. These folding wingtips, when extended into the flight-deployed position, provide improved aerodynamic performance and efficiency, and comply with Code E [1]                                          gate compatibility when folded during ground operations.                

## Discussion

Boeing proposes adding folding wingtips to their Model 777-8 and 777-9 airplane wings to improve aerodynamic performance and efficiency when the wingtips are extended into the flight-deployed position, while maintaining 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 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 proposed 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 proposed special conditions has the same intent as § 25.679(a)(2). Per § 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 proposed 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 § 25.571, and the system-safety requirements of §§ 25.671 and 25.1309.

These proposed 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 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 Proposed 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 § 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 § 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 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 § 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 § 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                           ( print page 50583)                        tolerance must be considered when showing compliance with § 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 § 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 § 25.415(b)(c). Therefore, in lieu of the equation provided in § 25.415(b), the hinge moment may be calculated from rational wind-tunnel data. The 1.25 factor specified in § 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 § 25.415(e), (f), and (g). Runway roughness, as specified in § 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-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 § 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 § 25.393. Hinge design must meet the requirements of § 25.657.

8. In lieu of § 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 § 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 Renton, Washington, on October 25, 2017.

Victor Wicklund,

Manager, Transport Airplane Directorate, Policy and Innovation Division, Aircraft Certification Service.

# Footnotes

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.                    
        Back to Citation      

[FR Doc. 2017-23698 Filed 10-31-17; 8:45 am]

BILLING CODE 4910-13-P