AD Amdt-39-16322
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Aviat | Various | Airworthiness Directives; Turbomeca Arriel 2B1 Turboshaft Engines |
| engine | Turbomeca | Arriel 2B1 | Airworthiness Directives; Turbomeca Arriel 2B1 Turboshaft Engines |
Unsafe Condition
The risk of wear of the delta-P diaphragm fabric due to pressure fluctuations in the HMU system, which could lead to the loss of automatic control mode coupled with deteriorated performance of the backup mode, potentially resulting in the inability to continue safe flight, forced autorotation landing, or an accident.
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Required Actions
Replace the hydromechanical metering unit (HMU) with a serviceable HMU before the HMU accumulates 1,500 hours-since-new, hours-since-last-overhaul (HSO), or since incorporation of Turbomeca Service Bulletin (SB) No. 292 73 2105, whichever occurs later. Thereafter, replace the HMU with a serviceable HMU at every 1,500 hours-since-new, since last overhaul, or since incorporation of Turbomeca SB No. 292 73 2105, whichever occurs later. A serviceable HMU must be fitted with a new constant delta P diaphragm in accordance with Turbomeca Mandatory Service Bulletin (MSB) No. 292 73 2818.
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Compliance Time
Within 1,500 hours-since-new, hours-since-last-overhaul (HSO), or since incorporation of Turbomeca Service Bulletin (SB) No. 292 73 2105, whichever occurs later.
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Affected Aircraft
Turbomeca ARRIEL 2B1 turboshaft engines that do not incorporate modification TU157, installed on, but not limited to, Eurocopter AS 350 B3 and EC 130 B4 helicopters.
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Source: Official FAA Source ↗
Retrieved: Apr 6, 2026
Rights: U.S. Government Public Domain
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