DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2020-0994; Project Identifier AD-2020-00687-T]
RIN 2120-AA64

Airworthiness Directives; Gulfstream Aerospace Corporation
Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: The FAA proposes to adopt a new airworthiness directive (AD)
for certain Gulfstream Aerospace Corporation (Gulfstream) Model GVII-
G600 airplanes. This proposed AD was prompted by a report that a
failure mode in the data concentration network (DCN) software causes the
pitch attitude value to freeze on the primary flight display (PFD) for up
to 20 seconds. This proposed AD would require updating the DCN and flight
deck master operating system (MOS) software. The FAA is proposing this
AD to address the unsafe condition on these products.

DATES: The FAA must receive comments on this proposed AD by April 9,
2021.

ADDRESSES: You may send comments, using the procedures found in 14 CFR
11.43 and 11.45, by any of the following methods:

Federal eRulemaking Portal: Go to https://www.regulations.gov. Follow the
instructions for submitting comments.

Fax: (202) 493-2251.

Mail: U.S. Department of Transportation, Docket
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New
Jersey Avenue SE, Washington, DC 20590.

Hand Delivery: Deliver to Mail address above between 9
a.m. and 5 p.m., Monday through Friday, except Federal holidays.

For service information identified in this proposed rule, contact
Gulfstream Aerospace Corporation, Technical Publications Dept., P.O.
Box 2206, Savannah, GA 31402; phone: (800) 810-4853; email:
pubs@gulfstream.com; website: https://www.gulfstream.com/en/customer-
support/. You may view this service information at the FAA,
Airworthiness Products Section, Operational Safety Branch, 901 Locust,
Kansas City, Missouri 64106. For information on the availability of
this material at the FAA, call (816) 329-4148.

Examining the AD Docket

You may examine the AD docket at https://www.regulations.gov by
searching for and locating Docket No. FAA-2020-0994; or in person at
Docket Operations between 9 a.m. and 5 p.m., Monday through Friday,
except Federal holidays. The AD docket contains this NPRM, any comments
received, and other information. The street address for Docket
Operations is listed above.

FOR FURTHER INFORMATION CONTACT: Myles Jalalian, Aviation Safety
Engineer, Atlanta ACO Branch, FAA, 1701 Columbia Avenue, College Park,
GA 30337; phone: (404) 474-5572; fax: (404) 474-5606; email:
myles.jalalian@faa.gov.

SUPPLEMENTARY INFORMATION:

Comments Invited

The FAA invites you to send any written relevant data, views, or
arguments about this proposal. Send your comments to an address listed
under ADDRESSES. Include "Docket No. FAA-2020-0994; Project Identifier
AD-2020-00687-T" at the beginning of your comments. The most helpful
comments reference a specific portion of the proposal, explain the
reason for any recommended change, and include supporting data. The FAA
will consider all comments received by the closing date and may amend
this proposal because of those comments.

Except for Confidential Business Information (CBI) as described in
the following paragraph, and other information as described in 14 CFR
11.35, the FAA will post all comments received, without change, to
https://www.regulations.gov, including any personal information you
provide. The agency will also post a report summarizing each
substantive verbal contact received about this NPRM.

Confidential Business Information

CBI is commercial or financial information that is both customarily
and actually treated as private by its owner. Under the Freedom of
Information Act (FOIA) (5 U.S.C. 552), CBI is exempt from public
disclosure. If your comments responsive to this AD contain commercial
or financial information that is customarily treated as private, that
you actually treat as private, and that is relevant or responsive to
this AD, it is important that you clearly designate the submitted
comments as CBI. Please mark each page of your submission containing
CBI as "PROPIN." The FAA will treat such marked submissions as
confidential under the FOIA, and they will not be placed in the public
docket of this AD. Submissions containing CBI should be sent to Myles
Jalalian, Aviation Safety Engineer, Atlanta ACO Branch, FAA, 1701
Columbia Avenue, College Park, GA 30337. Any commentary that the FAA
receives which is not specifically designated as CBI will be placed in
the public docket for this rulemaking.

Background

The FAA received a report that on certain Gulfstream Model GVII-
G600 airplanes a failure mode in the DCN software causes the pitch
attitude value to freeze on the PFD for up to 20 seconds.

During implementation of the DCN software update version 10.10.10
for certain Model GVII-G500 airplane configurations ("Block 1"), it
was discovered the software supplier had incorrectly implemented one of
Gulfstream's design requirements. At the time of this discovery on
Model GVII-G500 Block 1 configurations, the DCN software version
10.10.10 had already been implemented on Model GVII-G600 airplanes in
service. This airplane has three independent inertial reference systems
(IRSs), identified as IRS1, IRS2, and IRS3, which are expected to
provide identical pitch data. During flight testing, the GVII-G600 IRS1
was found to indicate a slightly different pitch from IRS2 and IRS3, at
the same actual airplane pitch attitude. A DCN embedded function was
created to correct the very minor pitch difference between IRS1, IRS2,
and IRS3. DCN software version 10.10.10 implemented the new embedded
function which computes a "PITCH_DELTA correction factor" (pitch
difference correction factor) between the IRS pitch angles being used
by the PFDs. The system calculates pitch correction based in part on
the IRS1 pitch angle. If the IRS1 is lost, it causes the embedded
function to invalidate the "PITCH_DELTA output." During this failure
mode, the pitch attitude value freezes on the display for up to 20
seconds, which results in temporarily incorrect pitch indications. The
effect is evident only if the pitch of the airplane changes during the
20 second reset window. After 20 seconds, the system returns to normal.
The standby flight display and heads up display are unaffected by this
failure mode and continue to display the correct pitch attitude.

There is not an alert or annunciation that informs the flight crew
of a stale (frozen) pitch display or potentially misleading flight
information.

This condition, if not addressed, could result in loss of control
of the airplane in certain phases of flight during instrument
meteorological conditions.

Related Service Information Under 1 CFR Part 51

The FAA reviewed Gulfstream GVII-G600 Aircraft Service Change No.
901, Initial Issue, dated May 12, 2020. This service document specifies
procedures for installing the MOS software update part number
EB60001034-0106 and operationally checking the installation.

The FAA also reviewed Gulfstream GVII-G600 Aircraft Service Change
No. 020, Initial Issue, dated May 12, 2020. This service document
specifies procedures for updating the DCN software level to version
10.10.12, updating system software in support of the MOS software
update, and operationally checking the installation.

This service information is reasonably available because the
interested parties have access to it through their normal
course of business or by the means identified in the ADDRESSES section.

FAA's Determination

The FAA is issuing this NPRM after determining the unsafe condition
described previously is likely to exist or develop in other products of
the same type design.

Proposed AD Requirements in This NPRM

This proposed AD would require accomplishing the actions specified
in the service information described previously.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would
affect 43 airplanes of U.S. registry.

The FAA estimates the following costs to comply with this proposed
AD:

Estimated Costs

The FAA has included all known costs in its cost estimate.
According to the manufacturer, however, some of the costs of this
proposed AD may be covered under warranty, thereby reducing the cost
impact on affected operators.

Authority for This Rulemaking

Title 49 of the United States Code specifies the FAA's authority to
issue rules on aviation safety. Subtitle I, section 106, describes the
authority of the FAA Administrator. Subtitle VII: Aviation Programs,
describes in more detail the scope of the Agency's authority.

The FAA is proposing this rulemaking under the authority described
in Subtitle VII, Part A, Subpart III, Section 44701: General
requirements. Under that section, Congress charges the FAA with
promoting safe flight of civil aircraft in air commerce by prescribing
regulations for practices, methods, and procedures the Administrator
finds necessary for safety in air commerce. This regulation is within
the scope of that authority because it addresses an unsafe condition
that is likely to exist or develop on products identified in this
rulemaking action.

Regulatory Findings

The FAA determined that this proposed AD would not have federalism
implications under Executive Order 13132. This proposed AD would not
have a substantial direct effect on the States, on the relationship
between the national government and the States, or on the distribution
of power and responsibilities among the various levels of government.

For the reasons discussed above, I certify this proposed
regulation:

(1) Is not a "significant regulatory action" under Executive
Order 12866,

(2) Would not affect intrastate aviation in Alaska, and

(3) Would not have a significant economic impact, positive or
negative, on a substantial number of small entities under the criteria
of the Regulatory Flexibility Act.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Incorporation by
reference, Safety.

The Proposed Amendment

Accordingly, under the authority delegated to me by the
Administrator, the FAA proposes to amend 14 CFR part 39 as follows:

PART 39--AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701.

Sec. 39.13 [Amended]

2. The FAA amends Sec. 39.13 by adding the following new airworthiness
directive: