AD 96-21-13

This amendment adopts a new airworthiness directive (AD) that is applicable to LITEF GmbH Attitude and Heading Reference System (AHRS) Unit Model LCR-92, LCR-92S, and LCR-92H installed on but not limited to Sikorsky Aircraft Model S-76 helicopters, McDonnell Douglas Helicopter Systems Model MD-900 helicopters, Bell Helicopter Textron, Inc. Model 412 helicopters, and Pilatus Model PC-12 airplanes. This action requires either installing a placard adjacent to each primary attitude indicator which states that flight is limited to Visual Flight Rules (VFR) operations only, or modifying and inspecting the AHRS wiring cables, requiring a repetitive inspection of the cable shielding, and inserting a statement into the aircraft flight manual. This amendment is prompted by a field report and verified by laboratory tests that shows there is an unusual AHRS reaction to certain radio frequency signals. The actions specified by this AD are intended to prevent reliance on or to correct the cause of misleading roll and pitch information produced by the AHRS when encountering certain radio frequency signals.

Final rule; request for comments.

96-21-13 LITEF GmbH: Amendment 39-9789. Docket No. 96-SW-12-AD.

Applicability: Attitude and Heading Reference System (AHRS) Model LCR-92, part number (P/N) 124210-1000, -2000, and -3000, Model LCR-92S, P/N 141852-1000, -1100, -2000, -2100, -3000, -3100, and -3200, and Model LCR-92H, P/N 141450-1000, -1100, -2000, -2100, -3000, and -3100, installed in aircraft certificated in any category.

NOTE 1: This AD applies to each aircraft equipped with an AHRS unit identified in the preceding applicability provision, regardless of whether the aircraft has been modified, altered, or repaired in the area subject to the requirements of this AD. For aircraft that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must use the authority provided in paragraph (b) to request approval from the FAA. This approval may address either no action, if the current configuration eliminates the unsafe condition, or different actions necessary to address the unsafe condition described in this AD. Such a request should include an assessment of the effect of the changed configuration on the unsafe condition addressed by this AD. In no case does the presence of any modification, alteration, or repair remove any aircraft from the applicability of this AD.

Compliance: Required within 60 calendar days after the effective date of this AD, unless accomplished previously.

To prevent reliance on or to correct the cause of misleading roll and pitch information produced by the AHRS unit when encountering certain radio frequency levels, accomplish the following:

(a) Perform the procedures contained in paragraph (1) or paragraph (2):

(1) Obliterate Technical Standard Order (TSO) C4c information from the TSO label on the exterior of the AHRS unit and install a placard made of material that is not easily erased, disfigured, or obscured, adjacent to each primary attitude indicator that states:(i) "Flight Limited to Day VFR Operations Only," or

(ii) If the primary attitude instrument(s) have been deactivated, "Flight Limited to VFR Operations Only" or

(2) Modify and inspect the AHRS unit and insert a statement into the operating limitation section of the Airplane or Rotorcraft Flight Manual as follows:

(i) Modify the AHRS wiring cable in accordance with either the Accomplishment Instructions of LITEF Alert Service Bulletin 141450-0000-840-003, dated July 9, 1996, or, for Sikorsky S-76 helicopters, in accordance with the Accomplishment Instructions of Sikorsky Aircraft Alert Service Bulletin No. 76-34-6A (287A), dated September 12, 1996.

(ii) Prior to the first flight after modifying the AHRS wiring cable and thereafter at intervals not to exceed 365 calendar days, using a calibrated bonding meter, inspect the modified AHRS wiring cable for proper shielding, proper bonding of the wiring cable shields, and proper unit grounding. The electrical shielding and grounding resistance should be less than 0.005 ohms. If the electrical resistance of the shielding bond is 0.005 ohms or greater, the cable shielding bond is unacceptable.

(iii) Insert into the operating limitation section of the FAA-approved Airplane or Rotorcraft Flight Manual the following statement:

"Switching from DG to MAG or operation of the switch (MAG mode only) in flight with any bank angle will induce an unannounced heading error. Activation of either switch at bank angles over approximately 5 will induce a large fixed heading error that will not self-align and will force the AHRS into memory with no heading OFF flag appearing for 5 minutes. If switching occurs at less than approximately 5 bank angle, self alignment will occur with a variable slewing rate. Verification of heading accuracy should be accomplished utilizing cross checking of other available heading systems. If a fixed heading error and/or a heading OFF flag is present, thenrealignment can be performed by either the switch or by the MAG/DG/MAG switch at bank angles less than approximately 5 ."

This revision may be accomplished by inserting a copy of this AD into the aircraft flight manual.

(b) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Rotorcraft Standards Staff, FAA, Rotorcraft Directorate. Operators shall submit their requests through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, Rotorcraft Standards Staff.

NOTE 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Rotorcraft Standards Staff.

(c) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the aircraft to a location where the requirements of this AD can be accomplished.

(d) The modification and inspections shall be done in accordance with the Accomplishment Instructions of LITEF ASB No. 141450-0000-840-003, dated July 9, 1996, or, for Sikorsky S-76 helicopters, with the Accomplishment Instructions of Sikorsky Aircraft ASB No. 76-34-6A (287A), dated September 12, 1996. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and CFR part 51. Copies of the LITEF ASBs may be obtained from LITEF GmbH, Postfach 774, 79007 Freiburg, Germany. Copies of the Sikorsky Aircraft ASB may be obtained from Sikorsky Aircraft Corporation, 6900 Main Street, P.O. Box 9729, Stratford, CT 06497-9129. Copies may be inspected at the FAA, Office of the Assistant Chief Counsel, 2601 Meacham Blvd., Room 663, Fort Worth, Texas; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

(e) This amendment becomes effective on November 12, 1996.

The Luftfahrt-Bundesamt (LBA), which is the airworthiness authority for the Federal Republic of Germany, recently notified the FAA that an unsafe condition may exist on aircraft equipped with LITEF GmbH (LITEF) AHRS Unit Model LCR-92, LCR-92S, or LCR-92H. The LBA advises that the AHRS unit may provide misleading roll and pitch information to the attitude indicator, with no failure indication, when exposed to radio frequency levels much lower than the levels to which the AHRS unit was qualified.

LITEF has issued LITEF Alert Service Bulletin (ASB) No. VW/JH 6B751 dated June 12, 1996, which specifies that the AHRS unit should only be used under Day VFR conditions. LITEF has also issued LITEF ASB No. 141450-0000-840-002, dated June 28, 1996, that gives directions for the modification of the AHRS units. The LBA classified this service bulletin as mandatory and issued LBA LTA No. 96-212, dated July 4, 1996, in order to assure the continued airworthiness ofthese AHRS units in Germany. However, LITEF has also issued LITEF ASB No. 141450-0000-840-003, dated July 9, 1996 which supersedes LITEF ASB No. 141450-0000-840-002, dated June 28, 1996. Additionally, Sikorsky Aircraft, a manufacturer that has installed the affected AHRS units on certain of its helicopters, has issued Sikorsky Aircraft ASB No. 76-34-6A (287A), dated September 12, 1996, which provides directions for the modification of the AHRS units on those helicopters.

This AHRS unit is manufactured in Germany and was approved under TSO C4c for operation in the United States under the TSO provisions of 14 CFR part 21 and the applicable bilateral airworthiness agreement. Pursuant to the bilateral airworthiness agreement, the LBA has kept the FAA informed of the situation described above. The affected AHRS units have been installed on U.S. type certificated aircraft, including but not limited to, Sikorsky Aircraft Model S-76 helicopters, McDonnell Douglas Helicopter Systems Model MD-900 helicopters, Bell Helicopter Textron, Inc. Model 412 helicopters, and Pilatus Model PC-12 airplanes. The FAA has examined the findings of the LBA, reviewed all available information, and determined that AD action is necessary for products of this type that were approved for operation in the United States.

Since an unsafe condition has been identified that is likely to exist or develop on other LITEF AHRS units installed on, but not limited to, Sikorsky Aircraft Model S-76 helicopters, McDonnell Douglas Helicopter Systems Model MD-900 helicopters, Bell Helicopter Textron, Inc. Model 412 helicopters, and Pilatus Model PC-12 airplanes registered in the United States, this AD is being issued to prevent reliance on or to correct the cause of misleading roll and pitch information produced by the AHRS when encountering certain radio frequency signals. This AD requires either installing a placard adjacent to each primary attitude indicator that states that flight is limited toDay Visual Flight Rules (VFR) operations only, or if the primary attitude instrument(s) have been deactivated, that states that flight is limited to VFR operations only; or modifying and inspecting the AHRS wiring cables, requiring a repetitive inspection of the cable shielding, and inserting a statement into the aircraft flight manual. The actions are required to be accomplished in accordance with the service bulletins described previously.

Since a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days.

Comments Invited
Although this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this rule by submitting such written data, views, or arguments as they may desire. Communications should identify the Rules Docket number and be submitted in triplicate to the address specified under the caption "ADDRESSES." All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed.

Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket No. 96-SW-12-AD." The postcard will be date stamped and returned to the commenter.

The regulations adopted herein will not have substantial direct effects 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. Therefore, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment.

The FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it is not a "significant regulatory action" under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES."

List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.
Adoption of the Amendment
Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:

PART 39 - AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
Authority: 49 USC. App. 106(G), 40113,44701.

39.13 - [Amended]
2. Section 39.13 is amended by adding a new airworthiness directive to read as follows: