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ASN Wikibase Occurrence # 166729
 
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Date:03-JUN-2014
Time:19:03
Type:Silhouette image of generic EXEC model; specific model in this crash may look slightly different
RotorWay Exec 162F
Owner/operator:Private
Registration: N78291
MSN: 6109
Fatalities:Fatalities: 0 / Occupants: 2
Aircraft damage: Written off (damaged beyond repair)
Category:Accident
Location:NNW of Merced Rgn'l Airport/Macready Field (KMCE), Merced, CA -   United States of America
Phase: Manoeuvring (airshow, firefighting, ag.ops.)
Nature:Private
Departure airport:Merced, CA (MCE)
Destination airport:Merced, CA (MCE)
Investigating agency: NTSB
Confidence Rating: Accident investigation report completed and information captured
Narrative:
The pilot, who was also the owner/builder of the experimental, amateur-built helicopter, reported that he was conducting a practice autorotation and that, during the landing flare and power recovery, the helicopter yawed left. The pilot applied the right antitorque pedal to correct; however, the helicopter did not respond. The helicopter then began to spin and subsequently landed hard and rolled onto its side. A postimpact fire ensued, which consumed most of the helicopter.

Examination of the tail rotor drive system revealed that the aft tail rotor drive belt remained intact and connected between the tail rotor gearbox and aft pulley and that the majority of the forward belt had been consumed by fire. The center belt had fractured, and subsequent examination of the belt revealed that it exhibited signatures consistent with tensile overload failure.
The pilot/owner reported that the helicopterís center tail rotor drive belt, which was a noncogged design in accordance with the kit manufacturerís recommendation, had failed previously. He chose to replace the failed belt with a cogged belt that had the same dimensions, and he had installed the cogged belt in the airplane less than 3 flight hours before the accident. The cogged belt had slightly different tensioning requirements; however, the owner installed the belt using the tension values required by the noncogged belt, which likely precipitated the cogged beltís tensile overload failure. The cogged belt was also not recommended for pulsation, shock loads, and high-tension configurations, all of which would have been present during the critical power recovery phase when the failure occurred and likely contributed to the beltís failure.

Probable Cause: The helicopter pilot/owner's decision to install a belt type not recommended by the kit manufacturer in the tail rotor drive system using the incorrect tension values, which led to the beltís in-flight failure and the subsequent loss of tail rotor drive during a practice autorotation.

Sources:

NTSB
https://flightaware.com/resources/registration/N78291

Accident investigation:
cover
  
Investigating agency: NTSB
Status: Investigation completed
Duration:
Download report: Final report
Location


Revision history:

Date/timeContributorUpdates
04-Jun-2014 05:56 gerard57 Added
04-Jun-2014 16:33 Geno Updated [Time, Aircraft type, Registration, Cn, Location, Phase, Nature, Source, Narrative]
10-Jun-2014 22:50 Geno Updated [Time, Phase, Nature, Departure airport, Destination airport, Source, Narrative]
21-Dec-2016 19:28 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
29-Nov-2017 15:03 ASN Update Bot Updated [Other fatalities, Nature, Departure airport, Destination airport, Source, Narrative]

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