DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2017-0522; Directorate Identifier 2015-SW-068-AD]
RIN 2120-AA64

Airworthiness Directives; Northrop Grumman LITEF GmbH LCR-100
Attitude and Heading Reference System Units

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: We propose to adopt a new airworthiness directive (AD) for
Northrop Grumman LITEF GmbH LCR-100 Attitude and Heading Reference
System (AHRS) units installed on various aircraft. This proposed AD
would require removing certain LCR-100 AHRS units from service. This
proposed AD is prompted by test results showing loss of or invalid
data. The proposed actions are intended to prevent an unsafe condition
on these products.

DATES: We must receive comments on this proposed AD by August 4, 2017.

ADDRESSES: You may send comments by any of the following methods:

Federal eRulemaking Docket: Go to http://www.regulations.gov. Follow
the online instructions for sending your comments electronically.

Fax: 202-493-2251.

Mail: Send comments to the U.S. Department of
Transportation, Docket Operations, M-30, West Building Ground Floor,
Room W12-140, 1200 New Jersey Avenue SE., Washington, DC 20590-0001.

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

Examining the AD Docket

You may examine the AD docket on the Internet at http://www.regulations.gov
by searching for and locating Docket No. FAA-2017-0522; or in
person at the Docket Operations Office between 9 a.m. and 5
p.m., Monday through Friday, except Federal holidays. The AD docket
contains this proposed AD, the European Aviation Safety Agency (EASA)
AD, the economic evaluation, any comments received, and other
information. The street address for the Docket Operations Office
(telephone 800-647-5527) is in the ADDRESSES section. Comments will be
available in the AD docket shortly after receipt.

For service information identified in this proposed rule, contact
Northrop Grumman LITEF GmbH, Customer Service--Commercial Avionics,
Loerracher Str. 18, 79115 Freiburg, Germany; telephone +49 (761) 4901-
142; fax +49 (761) 4901-773; email ahrs.support@ng-litef.de. You may
review the referenced service information at the FAA, Office of the
Regional Counsel, Southwest Region, 10101 Hillwood Pkwy, Room 6N-321,
Fort Worth, TX 76177.

FOR FURTHER INFORMATION CONTACT: Nick Rediess, Aviation Safety
Engineer, Boston Aircraft Certification Office, Engine & Propeller
Directorate, 1200 District Avenue, Burlington, Massachusetts 01803;
telephone (781) 238-7159; email nicholas.rediess@faa.gov.

SUPPLEMENTARY INFORMATION:

Comments Invited

We invite you to participate in this rulemaking by submitting
written comments, data, or views. We also invite comments relating to
the economic, environmental, energy, or federalism impacts that might
result from adopting the proposals in this document. The most helpful
comments reference a specific portion of the proposal, explain the
reason for any recommended change, and include supporting data. To
ensure the docket does not contain duplicate comments, commenters
should send only one copy of written comments, or if comments are filed
electronically, commenters should submit only one time.

We will file in the docket all comments that we receive, as well as
a report summarizing each substantive public contact with FAA personnel
concerning this proposed rulemaking. Before acting on this proposal, we
will consider all comments we receive on or before the closing date for
comments. We will consider comments filed after the comment period has
closed if it is possible to do so without incurring expense or delay.
We may change this proposal in light of the comments we receive.

Discussion

We propose to adopt a new AD for Northrop Grumman LITEF GmbH LCR-
100 AHRS units with a part number 145130-2000, 145130-2001, 145130-
7000, 145130-7001, or 145130-7100. These units are installed on various
airplanes and helicopters and are often used to supply attitude and
heading data to Primary Flight Displays (PFDs), autopilots, and other
avionics. These units may be installed as part of a type-certificated
design, an FAA supplemental type certificate, or a field approval.
Northrop Grumman LITEF GmbH discovered the erroneous behavior of an
AHRS unit during laboratory testing. The erroneous behavior occurs when
the unit's continuous built-in test detects a failure and then does not
correctly reset. When this occurs, the analog outputs of attitude and
heading data freeze and the transmission of digital outputs of attitude
and heading stops. The effect of the errors depends on how the AHRS
unit outputs are used in a particular installation. For instance, if
the AHRS unit analog outputs are used by a PFD without any automatic
comparison with another source of data, the PFD will display misleading
information, which could lead to loss of control of the aircraft. Other
installations using the analog outputs might include an automatic
comparison feature that detects and provides an alert if the attitude
and heading data is frozen. A similar situation would occur in
installations that use the digital outputs since the erroneous behavior
would be detected. This proposed AD would only be applicable to
installations of the AHRS units using analog outputs for the display of
primary flight information or for input to an autopilot without
automatic output comparison since these installations do not provide
any warning indication of the erroneous behavior.

EASA, which is the Technical Agent for the Member States of the
European Union, has issued EASA AD No. 2015-0093, dated May 27, 2015,
to correct an unsafe condition for certain part-numbered Northrop
Grumman LITEF GmbH LCR-100 AHRS units. EASA states these units are
known to be installed on, but not limited to, Pilatus PC-12, Learjet
31A, Cessna 560XL, RUAG (Dornier) 228 series, and PZL Mielec M28 (Sky
Truck) airplanes; and Bell Helicopter Textron, Inc., 412EP, Bell
Helicopter Textron Canada 407, and Sikorsky S-76C helicopters. EASA
advises that laboratory tests of the AHRS units discovered that when
the built-in test detects failures and resets the system, the units are
not executing the system reset properly. According to EASA, this
results in a freeze of analog attitude and heading output data without
detection or warning to the pilot. EASA states that installations vary,
but if there is no automatic comparison of analog output to detect unit
failure, this condition, if not corrected, could lead to undetected
attitude and heading errors, possibly resulting in loss of control of
the aircraft.

This proposed AD would also affect AD 2010-26-09 (75 FR 81424,
December 28, 2010), which applies to Sikorsky Model S-76A, B, and C
helicopters with an AHRS unit P/N 145130-7100 installed. Since this
proposed AD would require the removal of P/N 145130-7100, compliance
with this AD would make AD 2010-26-09 no longer valid for those
Sikorsky helicopters.

FAA's Determination

We are proposing this AD because we evaluated all known relevant
information and determined that an unsafe condition exists and is
likely to exist or develop on other products of this same type design.

Related Service Information

We reviewed Northrop Grumman LITEF GmbH Service Bulletin No.
145130-0017-845, Revision D, dated April 1, 2015 (SB 145130-0017-845).
SB 145130-0017-845 specifies returning the applicable part numbered
AHRS units to certain repair stations for modification. The modified
AHRS units, which have new part numbers, have an additional watchdog
circuit in the electronic board that eliminates frozen analog outputs
and digital output interruptions.

Proposed AD Requirements

This proposed AD would require removing certain part-numbered LCR-
100 AHRS units that use analog outputs for primary flight information
display or autopilot functions without automatic output comparison from
service. This proposed AD would also prohibit installing those LCR-100
AHRS units on any aircraft.

Differences Between This Proposed AD and the EASA AD

This proposed AD would only apply to certain part-numbered AHRS
units that use analog outputs for primary flight information display or
autopilot functions without automatic output comparison. The EASA AD
applies to all of these part-numbered units regardless of the type of
installation. The EASA AD requires inserting a temporary revision into
the flight manual for analog without automatic output comparison
installations until the AHRS unit is replaced with a modified unit.
This proposed AD would not require temporarily revising the flight
manual. The EASA AD requires replacing the AHRS units with particular
part-numbered modified units, while this proposed AD would require
removing the AHRS units from service instead.

Costs of Compliance

We estimate that this proposed AD would affect 50 aircraft of U.S.
Registry. We estimate that operators may incur the following costs in
order to comply with this AD. Labor costs are estimated at $85 per
work-hour, and typical installations consist of two AHRS units.
Replacing two AHRS units would take about 4 work-hours and $62,630 for
required parts, for a total cost of $62,970 per aircraft and $3,148,500
for the U.S. fleet.

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.

We are issuing 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

We 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, I certify this proposed regulation:

1. Is not a "significant regulatory action" under Executive Order 12866;

2. Is not a "significant rule" under the DOT Regulatory Policies
and Procedures (44 FR 11034, February 26, 1979);

3. Will not affect intrastate aviation in Alaska to the extent that
it justifies making a regulatory distinction; and

4. Will not have a significant economic impact, positive or
negative, on a substantial number of small entities under the criteria
of the Regulatory Flexibility Act.

We prepared an economic evaluation of the estimated costs to comply
with this proposed AD and placed it in the AD docket.

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 (AD):