AD NUMBER: 2007-19-09
MANUFACTURER: Turbomeca
SUBJECT: Airworthiness Directive 2007-19-09
SUMMARY: We are superseding an existing airworthiness directive (AD) by adopting a new AD for the products listed above. This AD results from mandatory continuing airworthiness information (MCAI) provided by the aviation authority of France to identify and correct an unsafe condition onTurbomeca Arriel 2B1 turboshaft engines.

The MCAI states the following: This AD is prompted by several reported cases of rupture of the constant delta pressure valve diaphragm on Arriel 2B1engines, due to the wear of the delta P diaphragm fabric. Rupture can result in the loss of the automatic control mode of the helicopter, accompanied with a deterioration of the behavior of the auxiliary back-up mode (emergency mode).

On a single-engine helicopter, the result may be an emergency landing or, at worst, an accident. This AD supersedes European Aviation Safety Agency (EASA) AD 2007-0006 which required the removal from service of all the delta pressure valve diaphragms logging more than 2,000 hours-since-new.

Since issuance of EASA AD 2007-0006, no further case of rupture of the constant delta pressure valve diaphragm has been reported on Arriel 2 engines. However, about 40 additional diaphragms returning from service have been inspected by Turbomeca, and some signs of wear have been detected on diaphragms having logged less than 2,000 hours.

Based on the inspection results, it has been decided to decrease this limit from 2,000 hours to 1,500 hours in order to further reduce the probability of delta P diaphragm rupture.

We are issuing this AD to prevent forced autorotation landing, or an accident.

FMI: www.faa.gov/regulations_policies/airworthiness_directives/