Summary
We propose to supersede airworthiness directive (AD) 2007-19- 09R1 that applies to Turbomeca S.A. Arriel 2B1 turboshaft engines that do not have modification TU157 incorporated. AD 2007-19-09R1 requires replacement of the hydromechanical metering unit (HMU) with a serviceable HMU. Since we issued AD 2007-19-09R1, we received reports of ruptures on HMU constant delta pressure valves that have less than 2,000 hours in service. This proposed AD would continue to require HMU replacement; reduce the compliance interval; and include the power turbine (C2) cycle consumption rate when determining compliance times. We are proposing this AD to prevent failure of the HMU, which could lead to damage to the engine, and damage to the aircraft.