Document ID: FAA-2016-6137-0001
Agency: faa
Document Type: Proposed Rule
Title: Special Conditions: The Boeing Company Model 787-10 Airplane; Aeroelastic Stability Requirements, Flaps-Up Vertical Modal-Suppression System
Posted Date: 2016-09-20T04:00Z

[Federal Register Volume 81, Number 182 (Tuesday, September 20, 2016)]
[Proposed Rules]
[Pages 64360-64364]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2016-22547]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2016-6137; Notice No. 25-16-05-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.

[[Page 64361]]

ACTION: Notice of proposed special conditions.

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SUMMARY: This action proposes special conditions 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. 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 November 4, 2016.

ADDRESSES: Send comments identified by docket number FAA-2016-6137 
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), 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: 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: 

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 July 30, 2013, Boeing applied for an amendment to type 
certificate no. T00021SE to include the new Model 787-10 airplane. This 
airplane is a stretched-fuselage derivative of the 787-9, currently 
approved under type certificate no. T00021SE, with maximum single-class 
seating capacity of 440 passengers. The 787-10 has a maximum takeoff 
weight of 560,000 lbs and is powered by two General Electric GEnx-1B/P2 
or Rolls-Royce Trent 1000 engines.

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 or similar 
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 features:
    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 compensate for a flutter-damping 
margin deficiency of the airplane and 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,

[[Page 64362]]

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 to compensate for a flutter-damping margin deficiency for Sec.  
25.629 compliance, and the FAA intends to take a conservative approach 
in the technology's application. The FAA considers the use of this new 
active modal-suppression system for flutter compliance to be 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.
    The stretched body of the 787-10 degrades the 3Hz symmetric wing, 
nacelle, and body aeroelastic mode relative to the 787-9. The 3Hz 
aeroelastic mode of the 787-10 airplane without the F0VMS system does 
not meet the damping margin criteria of AC 25.629-1B within the 
operational envelope, as well as the design envelope, of the airplane. 
The 3Hz mode is not predicted to flutter, but has a lack of adequate 
flutter-damping margin for the airplane. Boeing has determined that 
typical methods of improving the flutter characteristics of the 
airplane, such as increasing the torsional stiffness of the wing or 
adding wingtip ballast weights, do not meet their business objectives. 
Consequently, Boeing is adding a new F0VMS system to the Normal mode of 
the Model 787-10 airplane PFCS to satisfy the flutter-damping margin 
requirements of Sec.  25.629, and means-of-compliance provisions 
contained in AC 25.629-1B. The F0VMS system will be active in certain 
parts of the flight envelope when the flaps are retracted. The F0VMS 
system is a feedback-control system that adds damping to the system's 
3Hz mode by oscillating the elevators symmetrically. When the elevators 
are expected to be ineffective due to blowdown or other limitations, 
the flaperons are applied to augment or supplant elevator-control 
input. However, the flaperons are not as effective as the elevators in 
providing additional damping to the 3Hz mode.
    The F0VMS system will be an integral part of the PFCS Normal mode 
and use existing hardware, including inertial and air-data sensors. As 
such, the F0VMS system is expected to be as reliable as the Normal mode 
itself. In other words, any failures that would cause a loss of the 
F0VMS function would also cause a loss of the Normal mode. FAA issue 
paper SA-17, ``Command Signal Integrity,'' requires that the 
probability of an automatic change from Normal mode to a degraded mode 
of the PFCS should occur with a frequency less than 10-7 per 
flight hour, irrespective of flight phase. This reliability is 
acceptable for the F0VMS system meeting the flutter-damping margins of 
Sec.  25.629 and AC 25.629-1B, and the requirements of these special 
conditions. The F0VMS function is only available in the PFCS Normal 
mode, and not available in the Secondary or Direct modes. However, the 
PFCS Secondary and Direct modes include a simplified modal-suppression 
function, which provides additional damping margin.
    In addition to the Model 787-10 airplane needing the F0VMS 
functionality for flutter compliance, this functionality will also be 
used for active nacelle gust-load alleviation (NGLA), because the low 
damping exhibited by the 3Hz mode adversely affects nacelle gust loads. 
Therefore, the Boeing Model 787-9 airplane NGLA system will not need to 
be carried over to the Model 787-10 airplane.
    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 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 certain novel or unusual design features 
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 Proposed Special Conditions

0
Accordingly, the Federal Aviation Administration (FAA) proposes the 
following special conditions 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.

[[Page 64363]]

[GRAPHIC] [TIFF OMITTED] TP20SE16.024

    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.

[[Page 64364]]

[GRAPHIC] [TIFF OMITTED] TP20SE16.025

    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 September 9, 2016.
Michael Kaszycki,
Assistant Manager, Transport Airplane Directorate, Aircraft 
Certification Service.
[FR Doc. 2016-22547 Filed 9-19-16; 8:45 am]
 BILLING CODE 4910-13-P