Date: 201304
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Light: Dusk
Aircraft: Eurocopter AS 350/355/EC130 - Astar/Twinstar/Ecureuil
Operator: Air Taxi
Operating under: Part 135
Mission: Other Electronic News Gathering
Flight phase: Cruise
Aircraft component: Indicating and Warning - Hydraulics
Component problem: Design; Malfunctioning
Reporter organization: Air Taxi
Reporter function: Inspector
Reporter qualification: Maintenance Powerplant; Maintenance Inspection Authority; Maintenance Airframe
Human factors: Troubleshooting; Communication Breakdown; Situational Awareness
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural FAR; Inflight Event / Encounter Other / Unknown
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Maintenance Action; General Declared Emergency
Contributing factors: Human Factors; Aircraft; Company Policy
Primary problem: Aircraft

Narrative: During flight; AS-350 helicopter crew experienced an annunciation of Hydraulic System failure. The pilot followed procedures and declared an emergency. The pilot successfully landed the aircraft without incident. Maintenance conducted a quick examination and no visible signs of failure were evident. The AS-350 helicopter was towed back to the hangar and placed in Maintenance to determine the failure.  This aircraft had the same occurrence the previous week. I was not aware of the prior event until I was called asking details and the maintenance performed; to return the aircraft to service.

Callback: Reporter stated that further troubleshooting of the AS-350 helicopter hydraulic system was performed after the second incident. A hydraulic pressure gauge was installed in the pressure line; downstream of the hydraulic pump pressure outlet; to enable monitoring of the hydraulic pressure while the engine; rotor and hydraulic pump were running.  Maintenance personnel identified that the two-position hydraulic system cutoff switch; located on the collective handle; could be inadvertently shifted to an intermediate position; triggering a hydraulic system failure warning annunciation; even though the pressure gauge continued to show stable hydraulic pressure. According to reporter; the hydraulic system reverts to a by-pass mode and the flight control system operates on four accumulators; three for the main rotor and one for the tail rotor; supplying limited pressure to the four servos.The reporter stated that the Pilot Operating Handbook (POH) procedure for this warning in flight requires the hydraulic system cutoff switch to be placed the 'off' position and an emergency to be declared.  The hydraulic system cutoff switch was replaced and no similar incidents have been reported in 240 hours of flight.



Synopsis: A Quality Assurance Inspector reports about two events involving a Eurocopter AS-350 that experienced an inflight Hydraulic System Failure Warning Annunciation; requiring a shutdown of the aircraft's single hydraulic system and an emergency landing. Maintenance troubleshooting noted the hydraulic system was functioning properly; but the 'On/Off' Hydraulic System toggle switch detent on the Pilot's Collective handle was malfunctioning.