Pilot Debrief

EUROCOPTER AS 350 B3 near Parker, AZ — 2010-03-16

Final reportWPR10CA164
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Date
2010-03-16
Location
Parker, AZ, USA
Airport
AZ47
Aircraft
EUROCOPTER AS 350 B3
Registration
N4282
Category
Helicopter
Highest injury
None
Fatalities
0
Phase of flight
Hover

Probable cause

The mechanics' failure to account for all the tools following a maintenance procedure and the pilot's failure to perform a preflight check before a maintenance test flight.

NTSB narrative

The pilot of the helicopter told the lead mechanic that the main rotor blade needed to be balanced. Two mechanics showed up on the morning of the accident and installed the balancing equipment. A test flight was flown. The two men performed the necessary work, which required a second adjustable wrench on the top of the rotor head to hold the bolt while the nut below was removed and later torqued back on. When the work was finished, the men gathered their tools. The pilot asked the lead mechanic if they had gathered all their tools and the mechanic replied "yes." The three men got on the helicopter for a test hover to check their work. As the main rotor speed reach 100 percent, the three occupants heard a "bang." As the helicopter hovered, the two mechanics thought the balancing equipment readings were worse than the first flight, and the vibrations in the aircraft had increased. The pilot landed the helicopter so that the mechanics could make additional adjustments. The mechanics discovered that they were missing the adjustable wrench that had been used on the top of the main rotor head. Postaccident examination revealed that one main rotor blade, the tail boom, and the lower vertical stabilizer had received damage from the unaccounted for wrench.

Analysis

Primary failure mode
Human factors
First missed decision gate
Mechanics should have ensured all tools were accounted for before test flight.

NTSB coding

Evidence available

  • 1 docket document
View NTSB final reportView NTSB docket

Docket documents1

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