Airworthiness Directive 2001-25-06
one-timeAirworthiness Directives; Sikorsky Aircraft Corporation Model S-76B and S-76C Helicopters
What this AD requires
This amendment adopts a new airworthiness directive (AD) for Sikorsky Aircraft Corporation (Sikorsky) Model S-76B and S-76C helicopters. This action requires modifying the electrical power distribution system to change the source of the 28 volts supplied to Nos. 1 and 2 attitude and heading reference (AHRS) WARN circuits. This amendment is prompted by a ground test simulating loss of the essential bus by pulling both bus tie circuit breakers and switching off both batteries. As a result of this action, both autopilots went off-line. The actions specified in this AD are intended to prevent an AHRS fail signal to both autopilots due to a failure of the essential bus, loss of autopilot functions, and subsequent loss of control of the helicopter.
Which aircraft AD 2001-25-06 applies to
Modify Nos. 1 and 2 AHRS WARN circuits per Sikorsky Aircraft Corporation Alert Service Bulletin No. 76-34-7A (320A), Rev A; model inferred from the Sikorsky S-76 (model 76) bulletin-numbering convention, as the specific 'applies to' clause was not present in the retrieved applicability slice.
Whether AD 2001-25-06 actually applies to your aircraft (by serial and installed parts) and whether it’s already complied with comes from that aircraft’s records.
How AD compliance is recorded
A valid compliance record (14 CFR 43.9) states:
Tailplate reads a tail number’s logbooks and matches every applicable AD — including this one — to its compliance evidence, with recurring next-due dates computed.
Look up a tail number →Read the full directive (Federal Register)Applicability is derived from the FAA directive corpus and is advisory, not a legal airworthiness determination. Compliance is established only from an aircraft’s actual records.