AD 96-21-13 Airworthiness Directives; LITEF GmbH Attitude Heading System (AHRS) Unit Model LCR-92, LCR-92S, and LCR-92H

Models named: LCR-92S, P/N 141852-1000, -1100, -2000, -2100, -3000, -3100, -3200, Model LCR-92H, P/N 141450-1000. Read the applicability below — it usually turns on serial or part numbers too.

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.

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 deg. 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 deg. bank angle, self alignment will occur with a variable slewing rate. Verification of heading accuracy should be accomplished utilizing cross checking of other available [[Page 55563]] heading systems. If a fixed heading error and/or a heading OFF flag is present, then realignment can be performed by either the switch or by the MAG/DG/MAG switch at bank angles less than approximately 5 deg..'' 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 SB 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), Revision A, 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. Issued in Fort Worth, Texas, on October 10, 1996. Eric Bries, Acting Manager, Rotorcraft Directorate, Aircraft Certification Service. [FR Doc. 96-26960 Filed 10-25-96; 8:45 am] BILLING CODE 4910-13-U