Intermittent Malfunctions Of The LITEF AHRS

The FAA has issued an emergency Airworthiness Directive (AD) 2010-11-52 prompted by reports of intermittent malfunctions of the LITEF Attitude Heading and Reference System (AHRS) units of the navigation system. This condition, if not corrected, could result in malfunction of the autopilots, inability to reset the autopilots, an uncommanded roll, reduction in rotorcraft functional capabilities, inability of the crew to perform the required tasks, and subsequent loss of control of the helicopter.

The Sikorsky Alert Service Bulletin (ASB) No. 76-34-11, dated May 17, 2010, specifies informing operators of an interim minimum flight crew restriction of two pilots for Instrument Flight Rules (IFR) and night flight for helicopters equipped with LITEF LCR-100, Mod Status 18, AHRS units. The ASB also specifies removing and inspecting the AHRS units to determine if part number (P/N) 145130-7100, Mod Status 18, is installed. Also, the ASB specifies if an AHRS unit with LITEF LCR-100, P/N 145130-7100, Mod Status 18 is installed, identifying the unit with a placard with a different P/N. Finally, the ASB specifies installing 2 placards P/N SS9140-1746 or locally fabricated placards onto the instrument panel.

This unsafe condition is likely to exist or develop on other helicopters of these same type designs. Therefore, this AD requires inspecting the AHRS unit to determine if it is a Mod Status 18. If the nameplate on an AHRS unit is P/N 145130-7100, Mod Status 18, this AD requires installing placards on the instrument panel to prohibit single pilot IFR and single pilot night flight, and reducing airspeeds to 120 KIAS if both autopilots uncouple during IFR or night flight. This AD also requires inserting Active Temporary Revisions into the Limitations section of the applicable Rotorcraft Flight Manual (RFM) to limit the minimum flight crew to two pilots for IFR and night flight and to reduce airspeed to 120 KIAS if both autopilots uncouple during IFR or night flight. This AD does not require installing placards on the AHRS unit as specified in the ASB. The actions must be done by following specified portions of the ASB described previously.

The emergency AD applies to Model S-76A, B, and C helicopters, with LITEF LCR-100, part number (P/N) 145130-7100, Attitude Heading and Reference System (AHRS) Unit, installed, certificated in any category. Compliance is required within 5 days, unless accomplished previously, and any time thereafter when a LITEF LCR-100, part number (P/N) 145130-7100, Attitude Heading and Reference System (AHRS) Unit is installed.

This rule is issued under 49 U.S.C. Section 44701 pursuant to the authority delegated to me by the Administrator, and is effective immediately upon receipt of this emergency AD.

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