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ASN Wikibase Occurrence # 30994
Last updated: 27 January 2021
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Date:07-MAR-1998
Time:09:56 PDT
Type:Silhouette image of generic UH1 model; specific model in this crash may look slightly different
Bell UH-1B
Owner/operator:Del Rio Avn
Registration: N204DR
C/n / msn: 401
Fatalities:Fatalities: 0 / Occupants: 1
Other fatalities:0
Aircraft damage: Written off (damaged beyond repair)
Category:Accident
Location:Hollister, California -   United States of America
Phase: Manoeuvring (airshow, firefighting, ag.ops.)
Nature:Agricultural
Departure airport:Hollister, CA
Destination airport:Hollister, CA
Investigating agency: NTSB
Narrative:
The pilot initiated a right turn, then he felt and heard a thump. He lowered the collective and attempted to straighten from the turn. He felt a strong vibration and the nose of the aircraft pitched down.

A ground crewman who witnessed the accident reported that while the helicopter was about 35 feet agl, he saw a large piece of the tail and a rotor blade fly off the ship, followed by the tail rotor hub assembly, the remaining blade, and the 90-degree gearbox. The helicopter began a 360-degree right spiral, made 2 1/2 rotations, and then impacted the ground in a 30-degree nose-down attitude.

He further noted that the engine still seemed to be producing about 60 percent power. The tail and tail rotor gearbox was found about 125 feet from the fuselage. Metallurgical examination of the vertical tail fin, tail rotor gearbox, and tail rotor blades disclosed an area of chafing which wore through the vertical fin's spar and initiated a fatigue crack.

The fatigue crack initiated in an area where the vertical fin driveshaft cover fastened on the left side of the aircraft near the upper end. Chafing had occurred between the cover and the spar, wearing away the spar. According to Bell, the UH-1B requires a daily inspection to visually check the area of the upper vertical fin, per the Aviation Unit Technical Manual, where the fatigue cracking
occurred.

Sources:

http://dms.ntsb.gov/aviation/AccidentReports/wkkdsn45jeuqy3va5zqea5451/X10312011120000.pdf


Revision history:

Date/timeContributorUpdates
27-Sep-2008 01:00 ASN archive Added
31-Oct-2011 14:26 Dr. John Smith Updated [Time, Total fatalities, Total occupants, Other fatalities, Location, Country, Phase, Nature, Departure airport, Destination airport, Source, Damage, Narrative]

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