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ASN Wikibase Occurrence # 213575
Last updated: 25 September 2018
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Date:24-OCT-2015
Time:16:33 LT
Type:Silhouette image of generic AS50 model; specific model in this crash may look slightly different
Eurocopter AS 350B3
Owner/operator:Placer County Sheriff's Department
Registration: N911WL
C/n / msn: 4587
Fatalities:Fatalities: 0 / Occupants: 3
Other fatalities:0
Aircraft damage: Substantial
Location:near Folsom, CA -   United States of America
Phase: Landing
Nature:Training
Departure airport:Sacramento, CA (MCC)
Destination airport:Auburn, CA (AUN)
Narrative:
The purpose of the public helicopter flight was to perform a patrol mission with a tactical flight officer onboard, while the flight instructor also trained the pilot under instruction (PUI), who had recently been hired by the sheriff's department. The plan was to perform a routine patrol mission to introduce the PUI to the operation of the helicopter's systems, then practice autorotations, which the PUI had not previously performed in the accident helicopter make and model.

After the patrol, they practiced a series of uneventful autorotations over flat areas. They then conducted an autorotation to a pinnacle in the middle of a peninsula. The flight instructor was flying the helicopter throughout the maneuver; during the power recovery phase of the autorotation, he applied engine power by moving the throttle twist grip from the idle to the flight position as the helicopter passed through 100 ft. The engine did not respond as he expected, and, unable to reach the pinnacle, he maneuvered the helicopter to a forced landing on downsloping terrain. The helicopter landed hard and tipped forward, resulting in substantial damage to the tailboom and aft fuselage structure. Postaccident examination of the engine and airframe did not reveal any anomalies that would have precluded normal operation, and the engine met its nominal performance parameters during a subsequent test run.

The helicopter's flight manual recommended that autorotation training be conducted within gliding distance of a suitable running landing area. The flight instructor's choice of a raised landing area, which was surrounded by soft and rocky downsloping terrain, did not represent a suitable area for such practice. Additionally, the slope did not allow a sufficient maneuvering envelope for the appropriate control inputs required to safely control the helicopter in the event of a delayed engine response or loss of engine power. Also, although physically close to a town, the location was relatively remote, because accessing the site by road would have required a long on- and off-road drive by first response vehicles around the lake. Therefore, the chosen location placed the crew in additional danger should a more serious accident have occurred.

About 3 months before the accident, the helicopter manufacturer issued a safety information notice regarding the high exposure to accidents and incidents during simulated engine-off landing training. The notice issued a series of procedural updates, including a recommendation that minimal crew be onboard, and that power recoveries should be initiated as the helicopter passed through 200 ft above ground level (agl) rather than 70 ft agl, as recommended in the flight manual. The notice reiterated the need to be prepared to conduct an engine-off landing if power recovery was unsuccessful, along with the reminder that a higher gross weight increases the risk of a hard landing. Therefore, the flight instructor's choice of a power recovery initiation altitude (100 ft) lower than recommended left him with a reduced margin for recovery when the anomaly occurred. Further, the decision to keep the tactical flight officer onboard during the autorotation portion of the training represented an unnecessary risk both to him and the mission. The helicopter was loaded near its maximum gross weight, increasing the risk of a hard landing.

The flight instructor did not hold a valid medical certificate at the time of the accident due to a recent Type 1 diabetes diagnosis. However, as a public operation, the sheriff's department was responsible for oversight of its own operation and allowed the instructor to fly with another pilot present. The instructor was not exhibiting any symptoms of the condition, and there was no evidence to suggest his diagnosis contributed to the outcome of the accident.

Probable Cause: The flight instructor's failure to perform simulated engine failure training in accordance with manufacturer guidance, including his improper recovery from the maneuver, which resulted in an overshoot of the intended landing zone when the engine did not respond as expected; his selection of an unsuitable landing area; and his decision to perform the maneuver near the helicopter's maximum gross weight, which resulted in a hard landing.

Sources:

http://aerossurance.com/helicopters/bad-autorotation-training/
https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20151029X24739&key=1


Revision history:

Date/timeContributorUpdates
22-Jul-2018 18:48 ASN Update Bot Added
18-Aug-2018 15:45 Aerossurance Updated [Time, Location, Phase, Source, Narrative]

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