DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2017-0522; Product Identifier 2015-SW-068-AD; Amendment
39-19621; AD 2019-07-10]
RIN 2120-AA64

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

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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

DATES: This AD is effective May 29, 2019.

ADDRESSES: For service information identified in this final 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.

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 Docket Operations between 9 a.m. and 5 p.m.,
Monday through Friday, except Federal holidays. The AD docket contains
this AD, the European Aviation Safety Agency (EASA) AD, the economic
evaluation, any comments received, and other information. The street
address for Docket Operations (phone: 800-647-5527) is U.S. Department
of Transportation, Docket Operations Office, M-30, West Building Ground
Floor, Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590.

FOR FURTHER INFORMATION CONTACT: Nick Rediess, Aviation Safety
Engineer, Boston ACO Branch, Compliance and Airworthiness Division,
1200 District Avenue, Burlington, Massachusetts 01803; telephone (781)
238-7763; email nicholas.rediess@faa.gov.

SUPPLEMENTARY INFORMATION:

Discussion

On June 5, 2017, at 82 FR 25742, the Federal Register published our
notice of proposed rulemaking (NPRM), which proposed to amend 14 CFR
part 39 by adding an AD that would apply to airplanes and helicopters
with a Northrop Grumman LITEF GmbH LCR-100 AHRS unit part number (P/N)
145130-2000, 145130-2001, 145130-7000, 145130-7001, or 145130-7100
installed that uses analog outputs for primary flight information
display or autopilot functions without automatic output comparison. A
primary flight information display includes any device that displays to
the pilot primary flight information such as attitude, airspeed, and
altitude. Such displays include primary flight displays, standby
instruments, and multifunction displays that provide a secondary
display of primary flight information. The NPRM proposed to require
removing these LCR-100 AHRS units from service and to prohibit
installing them on any aircraft.
These units are often used to supply attitude and heading data to
Primary Flight Displays (PFDs), autopilots, and other avionics.
Northrop Grumman LITEF GmbH discovered erroneous behavior of an AHRS
unit 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
(display of misleading information, providing an alert if the attitude
and heading data is frozen) 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. The NPRM proposed to only apply 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.
The proposed requirements were intended to prevent an AHRS unit's
analog outputs of attitude and heading data freezing without detection
or warning, which could result in misleading attitude and heading
information, anomalous autopilot behavior, and loss of control of the
aircraft.
The NPRM was prompted by AD No. 2015-0093, dated May 27, 2015,
issued by EASA, which is the Technical Agent for the Member States of
the European Union, to correct an unsafe condition for the Northrop
Grumman LITEF GmbH LCR-100 AHRS units. 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, which 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.
The NPRM also advised that the proposed AD would affect AD 2010-26-
09 (75 FR 81424, December 28, 2010) (``AD 2010-26-09''), which applies
to Sikorsky Model S-76A, B, and C helicopters with an AHRS unit P/N
145130-7100 installed. Since the NPRM proposed to require the removal
of P/N 145130-7100, compliance with the proposed would make AD 2010-26-
09 no longer valid for those Sikorsky helicopters.
Since the NPRM was issued, the FAA's Aircraft Certification Service
has changed its organizational structure. The new structure replaces
product directorates with functional divisions. We have revised some of
the office titles and nomenclature throughout this Final rule to
reflect the new organizational changes. Additional information about
the new structure can be found in the Notice published on July 25, 2017
(82 FR 34564).

Comments

After our NPRM was published, we received comments from one
commenter.

Request

The commenter suggested we made an error in the Discussion section
where it states, ``A similar situation would occur in installations
that use the digital outputs since the erroneous behavior would be
detected.'' The commenter states the loss of digital data would be
detected, and therefore the sentence should state instead that a
similar situation would not occur.
We disagree. The commenter is correct that an installation that
uses digital outputs would detect the erroneous behavior and provide an
alert. The ``similar situation'' referred to is the alert provided by
installations that use analog outputs with automatic comparison, which
also detect the attitude and heading data becoming frozen. Because both
types of installations detect the erroneous behavior, they result in a
similar situation. We did not change the AD based on this comment.

FAA's Determination

We have reviewed the relevant information, considered the comment
received, and determined that an unsafe condition exists and is likely
to exist or develop on other products of these same type designs and
that air safety and the public interest require adopting the AD
requirements as proposed.

Differences Between This AD and the EASA AD

This AD only applies 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 AD does not require temporarily revising the flight manual. The
EASA AD requires replacing the AHRS units with particular part-numbered
modified units, while this AD requires removing the AHRS units from
service instead.

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.

Costs of Compliance

We estimate that this AD affects 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 takes 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

This AD will not have federalism implications under Executive Order
13132. This AD will 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 that this AD:
(1) Is not a ``significant regulatory action'' under Executive
Order 12866;
(2) Is not a ``significant rule'' under 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 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.

Adoption of the Amendment

Accordingly, under the authority delegated to me by the
Administrator, the FAA amends 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):