Pilot Debrief

BELL 206 near Tombstone, AZ — 2014-09-12

Final reportWPR14LA374
Sign in to save
Date
2014-09-12
Location
Tombstone, AZ, USA
Aircraft
BELL 206
Registration
N64AW
Category
Helicopter
Highest injury
None
Fatalities
0
Phase of flight
Climb

Probable cause

A partial loss of engine power during cruise flight due to loose “B” nut fittings and a bent tube as a result of maintenance personnel’s inadequate inspection of the nuts during the most recent inspection.

NTSB narrative

The commercial pilot reported that, after initiating a climb for the local flight, he observed that the helicopter was not producing adequate power. He found a suitable landing site and descended toward it. When the helicopter was about 60 to 70 ft above the ground, the helicopter started descending rapidly and impacted the ground hard. During a pressure leak check of the engine, air leaks at three separate "B" nut fittings were found; two of the leaks were at the power turbine governor, and one leak was at the gas producer fuel control. The engine was test run, and it operated; however, it then lost power consistent with the pilot's report. Further examination of the "B" nut fittings revealed that one of the "B" nuts was less than finger tight, the second one was just above finger tight, and the third exhibited breakaway torque within the specified range. The "B" nut fittings were tightened to specifications and rechecked. One of the leaks was still present; the tube was removed, and it was bent near where the leak was found. A new tube was installed, and the engine was run again with no anomalies noted. The engine manufacturer had previously issued several commercial service letters regarding the importance of properly torqueing and aligning the fuel, lubrication, and pneumatic systems tubes and fittings; the service letters contained proper directions, placards, and 100-hour-inspection requirements. The helicopter's most recent 100-hour inspection occurred about 66 hours before the accident. It is likely that the "B" nuts became loose during the approximate 66 hours of operation since the most recent inspection and that maintenance personnel did not adequately inspect the "B" nuts at that inspection and, thus, failed to detect that they were not properly torqued. It could not be determined when the tube became bent.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Pilot could have aborted the climb when power loss was first noted.

NTSB coding

Evidence available

  • Photos
  • 9 docket documents
View NTSB final reportView NTSB docket

Docket documents9

Related mishaps