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ASN Wikibase Occurrence # 17517
Last updated: 6 April 2019
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Date:15-APR-2008
Time:09:23
Type:Silhouette image of generic AS50 model; specific model in this crash may look slightly different
Eurocopter AS 350B2
Owner/operator:Era Helicopters
Registration: N213EH
C/n / msn: 3158
Fatalities:Fatalities: 4 / Occupants: 5
Aircraft damage: Substantial
Category:Accident
Location:1 mile off Glenn Highway, Sheep Mountain, 34 miles E of Chickaloon, AK -   United States of America
Phase: En route
Nature:Domestic Non Scheduled Passenger
Departure airport:Anchorage, AK
Destination airport:Chickaloon, AK
Investigating agency: NTSB
Narrative:
**This report was modified on July 7, 2015. Please see the public docket for this accident to view the original report.**

The commercial pilot was on a Part 135 passenger flight transporting telecommunication technicians to remote sites. A technician was left at one site, and when the helicopter did not return, he contacted his employer. His employer contacted the helicopter operator. Unable to make contact with the helicopter, the operator contacted the FAA, and reported the helicopter overdue. A search for the helicopter was initiated based on a position report from the helicopter's onboard commercial satellite tracking system. A snowstorm in the search area precluded the use of aircraft in the search, and ground searchers were unsuccessful.

A State Trooper helicopter found the crash site the next morning when the weather improved. The pilot and three passengers were found dead; the fourth passenger, the minor stepson of one of the technicians, had head injuries and hypothermia. According to the operator and survivor, after transporting the first technician, the helicopter landed at a rest area near the highway and picked up another technician and his stepson prior to going to the next site. The stepson was in the left front seat, and the three technicians were in the rear seats. The destination site was about 2.5 miles from the rest area across a ravine. A motorist on the highway saw the helicopter depart from the rest area, and then make a steep descent into a ravine. He said he thought the descent was unusual, but he did not see any impact, and thought the helicopter was working in the ravine. He said the visibility was about 2 miles, and it was snowing lightly.

The helicopter impacted terrain approximately in a level attitude in a near vertical descent, about three-quarters of a mile from the rest area. The terrain at the accident site was rough and uneven, covered with trees, high brush, and snow. The accident flight lasted less than 2 minutes. The surviving front seat passenger recalled the liftoff and departure, then said he felt like he was falling, and that the pilot told everyone to "hold on we're going to crash."

The main rotor blades remained attached to the rotor head; two of the blades were resting on the ground, and the third blade was suspended over the ravine. The uncut brush surrounding the two blades resting on the ground and the downward chordwise bend of the suspended blade were consistent with low rotor rpm at final impact.

Examination of the helicopter's engine and drive train revealed damage signatures indicative of an overtorque event. These signatures included a 7 millimeter misalignment of the engine's module 5 drive nut and torsional damage (twisting) of the engine-to-transmission driveshaft, which shortened the driveshaft, allowing the splines at the aft end of the shaft to disengage, disconnecting the engine from the main transmission. The module 5 drive nut misalignment was consistent with the engine free turbine producing power at the time of the drive nut overtorque. The direction of rotational smearing damage observed on a portion of the splines was indicative of the engine continuing to provide power for a short time after the driveshaft twisted and shortened. The directionality of the driveshaft twisting was consistent with an opposing torque load forward (on the transmission side) of the driveshaft, which could have resulted from a main transmission seizure or a main rotor impact event. Disassembly and examination of the main transmission revealed no evidence of a seizure. Therefore, the overtorque likely resulted from one or more main rotor blade strikes occurring while the engine was powering the main rotor system. Further, the overtorque damage likely occurred before the helicopter's final impact in the ravine because the low rotor rpm signatures observed at the accident site indicated that the engine was not powering the main rotor system and that the rotational energy in the system had been significantly dissipated before that impact.

The helicopter's mai
Probable Cause: An in-flight overtorque of the engine-to-transmission driveshaft resulting in disconnection of the main transmission from the engine. The overtorque likely occurred due to an in-flight main rotor blade contact with snow-covered terrain, precluding significant main rotor blade damage and ground scarring. Contributing to the severity of the surviving occupant's injuries was the helicopter operator's failure to properly monitor their satellite flight-following system and to immediately institute a search once the system reported that the helicopter was overdue.

Sources:

NTSB: https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20080421X00524&key=1
FAA register: 2. FAA: http://registry.faa.gov/aircraftinquiry/NNum_Results.aspx?omni=Home-N-Number&nNumberTxt=213EH


Images:


photo: NTSB


photo: NTSB

Revision history:

Date/timeContributorUpdates
22-Apr-2008 10:37 Fusko Added
05-Mar-2010 10:38 harro Updated [Time, Aircraft type, Nature, Source, Narrative]
05-Mar-2010 10:38 harro Updated [[Time, Aircraft type, Nature, Source, Narrative]]
18-Jul-2014 17:43 Dr. John Smith Updated [Time, Location, Departure airport, Destination airport, Source, Narrative]
08-Sep-2014 19:48 Aerossurance Updated [Source, Narrative]
21-Dec-2016 19:14 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
21-Dec-2016 19:16 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
21-Dec-2016 19:20 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
03-Dec-2017 10:45 ASN Update Bot Updated [Operator, Other fatalities, Departure airport, Destination airport, Source, Narrative]

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