EASA AD 2019-0021

Supersedes an AD that required the inclusion of specified emergency operational procedures in the rotorcraft flight manual. That was prompted by the discovery that certain attitude heading and reference systems (AHRS) used the same “flight/ground” logic signal, instead of independent redundant signals, as required by the original design specification. If both AHRS receive wrong “ground” status in flight, as a result for instance of a single failure, this will generate consistent erroneous computation of the attitudes and vertical speed during helicopter maneuvers with consequent incorrect flight data indications to the flight crew on both primary displays. This condition could lead to increased workload for the flight crew when the upper modes of Automatic Flight Control System are not engaged, possibly resulting in reduced control of the helicopter during high-speed maneuvers in instrumental meteorological conditions. Since issuance of that AD, Airbus Helicopters developed a wiring harness modification to ensure independent sources of “flight/ground” logic signal for both AHRS.  This AD retains the requirement of EASA AD 2017-0077 and requires a wiring harness modification of the AHRS1.