82 FR 14115 - Special Conditions: The Boeing Company Model 787-10 Airplane; Aeroelastic Stability Requirements, Flaps-Up Vertical Modal-Suppression System

DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration

Federal Register Volume 82, Issue 51 (March 17, 2017)

These special conditions are issued for the Boeing Company (Boeing) Model 787-10 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 flaps-up vertical modal-suppression system, which is in lieu of traditional methods of improving airplane flutter characteristics. 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 82, Number 51 (Friday, March 17, 2017)]
[Rules and Regulations]
[Pages 14115-14117]
From the Federal Register Online  [www.thefederalregister.org]
[FR Doc No: 2017-05326]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2016-6137; Special Conditions No. 25-644-SC]


Special Conditions: The Boeing Company Model 787-10 Airplane; 
Aeroelastic Stability Requirements, Flaps-Up Vertical Modal-Suppression 
System

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 787-10 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 flaps-up vertical modal-suppression 
system, which is in lieu of traditional methods of improving airplane 
flutter characteristics. 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 April 17, 2017.

FOR FURTHER INFORMATION CONTACT: Wael Nour, FAA, Airframe and Cabin 
Safety Branch, ANM-115, Transport Airplane Directorate, Aircraft 
Certification Service, 1601 Lind Avenue SW., Renton, Washington 98057-
3356; telephone 425-227-2143; facsimile 425-227-1320.

SUPPLEMENTARY INFORMATION: 

Background

    On July 30, 2013, Boeing applied for an amendment to Type 
Certificate No. T00021SE to include the new Model 787-10 airplane. This 
twin-engine, transport-category airplane is a stretched-fuselage 
derivative of the 787-9, with maximum seating capacity of 440 
passengers. The 787-10 has a maximum takeoff weight of 560,000 lbs.

Type Certification Basis

    Under the provisions of Title 14, Code of Federal Regulations (14 
CFR) 21.101, Boeing must show that the Model 787-10 airplane meets the 
applicable provisions of the regulations listed in Type Certificate No. 
T00021SE or the applicable regulations in effect on the date of 
application for the change, except for earlier amendments as agreed 
upon by the FAA.
    In addition, the certification basis includes other regulations, 
special conditions, and exemptions that are not relevant to these 
proposed special conditions. Type Certificate No. T00021SE will be 
updated to include a complete description of the certification basis 
for this airplane model.
    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 787-10 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, 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 787-10 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.
    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 Model 787-10 airplane will incorporate the following novel or 
unusual design feature:
    A flaps-up vertical modal suppression system.

Discussion

    The Boeing Model 787-10 will add a new flaps-up vertical modal-
suppression (F0VMS) system to the Normal mode of the primary flight-
control system (PFCS). The F0VMS system is needed to satisfy the 
flutter-damping margin requirements of Sec.  25.629 and the means-of-
compliance provisions in Advisory Circular (AC) 25.629-1B. This system 
will be used in lieu of typical methods of improving the flutter 
characteristics of an airplane, such as increasing the torsional 
stiffness of the wing or adding wingtip ballast weights.
    The F0VMS system is an active modal-suppression system that will 
provide additional damping to an already stable, but low-damped, 3Hz 
symmetric wing, nacelle, and body aeroelastic mode of the airplane. 
This feedback-control system will maintain adequate damping margins to 
flutter. The F0VMS system accomplishes this by oscillating the 
elevators, and, when needed, the flaperons.
    Because Boeing's flutter analysis shows that the 3Hz mode is stable 
and does not flutter, the F0VMS system is not an active flutter-
suppression system, but, rather, a damping-augmentation system. At this 
time, the FAA is not prepared to accept an active flutter-suppression 
system that suppresses a divergent flutter mode in the operational or 
design envelope of the airplane.
    This will be the first time an active modal-suppression system will 
be used for Sec.  25.629 compliance. The use of this new active modal-
suppression system for flutter compliance is novel or unusual when 
compared to the technology envisioned in the current airworthiness 
standards. Consequently, special conditions are required in 
consideration of the effects of this new system on the aeroelastic 
stability of the airplane, both in the normal and failed state, to 
maintain the level of safety intended by Sec.  25.629.
    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. 25-16-05-SC for the

[[Page 14116]]

Boeing Model 787-10 airplane was published in the Federal Register on 
September 20, 2016 (81 FR 64360). One substantive comment was received.
    By letter no. B-H020-REG-16-TLM-68 dated November 1, 2016, Boeing 
stated that they ``. . . recommend that development of future 
requirements for the application of [active modal-suppression system 
for flutter compliance] technology be the subject of an Aviation 
Rulemaking Advisory Committee (ARAC).'' Boeing adds that ``. . . 
standard requirements should be developed which reflect this state-of-
the-art system and apply to all airplane manufacturers. The development 
of these requirements would benefit from the collaborative effort of an 
ARAC.''
    The FAA agrees with Boeing and currently has plans to task ARAC to 
develop recommendations on this subject.

Applicability

    As discussed above, these special conditions are applicable to the 
Boeing Model 787-10 airplane. 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 airplane. 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 787-10 airplanes.
    The following special conditions are proposed to address the 
aeroelastic stability of the 787-10 airplane with the F0VMS system as 
an integral part of the PFCS Normal mode:

Analytical Flutter-Clearance Requirements

    1. The airplane in the PFCS Normal mode (which includes F0VMS) must 
meet the nominal (no failures) flutter and aeroelastic stability 
requirements of Sec.  25.629(b)(1), and the damping-margin criteria of 
AC 25.629-1B, Section 7.1.3.3. Figure 1, below, illustrates the Damping 
versus Airspeed plot.
    a. The aeroservoelastic analysis must take into account the effect 
of the following items:
    i. Significant structural and aerodynamic nonlinearities.
    ii. Significant F0VMS nonlinearities, including control-surface 
rate and displacement saturation, and blowdown.
    iii. The range of design maneuver load factors.
    iv. Control surface freeplay.
    v. Any other items that may affect the performance of the F0VMS 
system in maintaining adequate modal damping margins.
[GRAPHIC] [TIFF OMITTED] TR17MR17.000


[[Page 14117]]


    2. The airplane in the PFCS Normal mode, but with the F0VMS system 
inoperative, must exhibit a damping margin to flutter of 0.015g within 
the VD/MD envelope, linearly decreasing (in KEAS) 
to zero damping margin to flutter at 1.15 VD/1.15 
MD, limited to Mach 1.0. That is, the 3Hz mode should not 
cross the g = 0.015 line below VD, or the g = 0.03 line 
below 1.15 VD, assuming the use of analysis Method 1 of AC 
25.629-1B, Section 7.1.3.3. Figure 2, below, illustrates the Damping 
versus Airspeed plot.
[GRAPHIC] [TIFF OMITTED] TR17MR17.001

    3. The airplane in the PFCS Normal mode (which includes F0VMS) must 
meet the fail-safe flutter and aeroelastic stability requirements of 
Sec.  25.629(b)(2), and the damping-margin criteria of AC 25.629-1B, 
Section 7.1.3.5.
    4. The airplane in the PFCS Secondary and Direct modes must meet 
the fail-safe flutter and aeroelastic-stability requirements of Sec.  
25.629(b)(2), and the damping-margin criteria of AC 25.629-1B, Section 
7.1.3.5.

    Issued in Renton, Washington, on February 10, 2017.
Michael Kaszycki,
Assistant Manager, Transport Airplane Directorate, Aircraft 
Certification Service.
[FR Doc. 2017-05326 Filed 3-16-17; 8:45 am]
 BILLING CODE 4910-13-P