History of Flight
On September 4, 2014, at 2005 Pacific daylight time, a Eurocopter AS 350 B3, registration N217HP, landed hard during a practice autorotation at Lincoln Regional Airport/Karl Harder Field, Lincoln, California. The helicopter was operated by the California Highway Patrol (CHP) as a public aircraft on a training flight. The commercial pilot and flight instructor (CFI) were not injured. The helicopter sustained substantial damage. The flight departed Auburn Municipal Airport, Auburn, California, about 1952. Visual meteorological conditions prevailed; no flight plan was filed.
The purpose was to provide recurrent emergency procedure and night vision goggle (NVG) training. The pilot was in the right seat; the CFI in the left. After a preflight inspection and checks, they departed for Lincoln, performed a full landing, then initiated a practice autorotation with power recovery on Runway 15.
The CFI rolled the twist grip to MIN to start the autorotation. The pilot lowered the collective, and at about 50 feet above ground level (agl), the pilot began to flare. The CFI returned the twist grip to VOL; they heard the engine respond and the CFI announced "power recovery." The pilot held the flare at about 25 ft agl, then increased collective to prevent rotor overspeed. The helicopter ballooned; he lowered the collective. Forward speed decayed, and as he raised the collective, the low rotor speed horn sounded and the helicopter descended rapidly. He pulled up collective, but the helicopter hit the ground hard. The pilot's NVG goggles flipped down, blocking forward vision; the CFI took control, pulling the cyclic full aft, and the helicopter came to rest.
Post-accident, the CFI noted rotor speed about 360 RPM (below normal) and amber GOV and TWT GRIP caution lights on. The twist grip was in the VOL detent. After jiggling and cycling the grip, the lights remained on. He then turned the start selector to IDLE then back to FLT, and the lights extinguished. Examination revealed the tailboom bent downward, aft bulkhead wrinkling, and skid spread.
Personnel Information
Both crew members were full-time CHP pilots. The CFI held a commercial pilot certificate with helicopter and instrument helicopter ratings, and a flight instructor certificate. He reported 3,943 total flight hours, with 2,943 as pilot-in-command in the accident make and model, and 79 hours in the 30 days prior. His most recent flight review was August 27, 2014, in the same model.
The pilot held a commercial pilot certificate with helicopter and instrument helicopter ratings. He reported 2,988 total flight hours, 2,635 as pilot-in-command in the same model, and 42 hours in the prior 30 days. His most recent flight review was June 14, 2014, in the accident make and model.
Aircraft Information
The helicopter, serial number 3628, was manufactured in 2002 and equipped with a Turbomeca Arriel 2B engine. It was maintained under a continuous airworthiness program; the last inspection occurred 12 flight hours prior to the accident.
Additional Information
The flight manual specified that power recovery in autorotation training should be initiated about 70 ft agl, and after returning the twist grip to VOL, the pilot should confirm the amber GOV and TWT GRIP lights extinguish. The CFI did not recall the status of these lights during recovery; checking them was not typically part of his scan during the maneuver. The CHP Chief Helicopter Pilot noted that minimal time at 70 ft prioritizes flying over light checks, and that the fleet's lights sometimes do not extinguish immediately.
Ten months after the accident, Airbus Helicopters issued Safety Information Notice 2896-S-00 for AS 350 B, BA, BB, B1, B2, B3, D models, updating the power recovery initiation to 200 ft agl.
The helicopter was equipped with a GPS-based flight track recorder; data matched the pilots' statements.
Tests and Research
Engine control principles: In AUTO mode, power is set by rotating twist grip to VOL; MIN is for training. In mixed mode (between MIN and VOL), amber lights are on and engine response to load changes is reduced. A functional check of the left twist grip found it could be moved past the VOL detent, causing the amber lights to briefly extinguish then illuminate again; this was a known fleet issue.
Maintenance records showed that Alert Service Bulletin AS350-67.00.43 (issued November 28, 2013) had been complied with about 46 flight hours prior, modifying engine control logic to prevent idle-power events during recoveries. Compliance was confirmed.
The Vehicle and Engine Multifunction Display (VEMD) recorded no over limits or failures. The Digital Engine Control Unit (DECU) was tested; it had a PAN 3 error from a prior maintenance event, but no accident-related errors.
The engine passed bench tests. The hydro mechanical unit (HMU) failed a dynamic limiter acceleration test; the P3 capsule screw was out of adjustment by 1/2 turn. After adjustment, the unit performed within specifications. The HMU had been overhauled about 50 flight hours prior, with correct adjustment at that time.
A failure-mode analysis duplicated the post-accident inability to resume flight speeds by declutching the throttle input lever, but only under a specific sequence of non-standard procedures. Turbomeca representatives stated declutching could have occurred due to the hard landing, but no tests confirmed this.
No probable cause was stated in the source.