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AD/ARRIEL/31 - Reduction Gear Box Intermediate Pinion
Turbomeca Turbine Engines - Arriel SerieTurbomeca Turbine Engines - Arriel Series
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Turbomeca Turbine Engines - Arriel Series
| AD/ARRIEL/31 | Reduction Gear Box Intermediate Pinion | 3/2009 |
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| Applicability: | Arriel 1B, 1D and 1D1 turboshaft engines, all serial numbers.Note 1: These engines are known to be installed on, but not limited to, EurocopterAS 350 B, AS 350 BA, AS 350 B1 and AS 350 B2 helicopters. |
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| Requirement: | Replace the Reduction Gear Box Intermediate Pinions (P/N 0 292 70 779 0) with Pinions incorporating Turboméca modification TU 232 in accordance with Turboméca Mandatory Service Bulletin 292 72 0276 Version B dated6 November 2008 or later approved revision.Note 2: EASA AD 2009-0002 dated 7 January 2009 refers. |
| Compliance: | No later than 28 February 2011, unless previously accomplished. |
| This Airworthiness Directive becomes effective on 12 March 2009. | |
| Background: | Several events of rupture of the Arriel 1 Reduction Gear Box Intermediate Pinion have been reported in service. The ruptures have been determined to be originated at the pinion teeth root due to increased vibratory stresses. This increase in vibratory stresses is mainly caused by increased teeth wear over engine life time.The rupture of the Reduction Gear Box Intermediate Pinion may result in an overspeed of the Power Turbine and, subsequently, an uncommanded engine in-flight shutdown. This could lead to an emergency autorotation landing on a single-engine helicopter.To reduce the level of vibratory stresses and improve tooth resistance, Turboméca modification TU 232 incorporates the addition of a damping ring below the teeth and a shot peening of the teeth roots. These modifications reduce the risk of incipient fatigue cracks. |
| This AD requires the replacement of all Reduction Gear Box Intermediate Pinions with Pinions incorporating Turboméca modification TU 232. |
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James Coyne
Delegate of the Civil Aviation Safety Authority
27 January 2009