AD FAA-2007-27009

We are superseding airworthiness directive (AD) 2007-19-09R1 for all Turbomeca S.A. Arriel 2B1 turboshaft engines that do not have modification TU157 incorporated. AD 2007-19-09R1 required replacement of the hydromechanical metering unit (HMU) with a serviceable HMU. This AD requires HMU replacement; reduction of the compliance interval; and inclusion of the power turbine C2 cycle consumption rate when determining compliance times. This AD was prompted by reports of ruptures on HMU constant delta pressure valves that have less than 2,000 hours in service. We are issuing this AD to prevent failure of the HMU, which could lead to damage to the engine, and damage to the aircraft.