Pilot Debrief

ENSTROM F-28F near Twin Falls, ID — 2013-03-27

Final reportWPR13LA167
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Date
2013-03-27
Location
Twin Falls, ID, USA
Airport
TWF
Aircraft
ENSTROM F-28F
Registration
N918DK
Category
Helicopter
Highest injury
None
Fatalities
0
Phase of flight
Approach

Probable cause

A total loss of engine power for reasons that could not be determined because postaccident examination of the airframe and engine did not reveal any anomalies that would have precluded normal operation.

NTSB narrative

The student pilot reported that, during the helicopter's fourth landing, the engine started to sputter and lose rpm. He lowered the collective and added power, and the engine rpm increased. When he raised the collective, the engine lost power again. As he turned the helicopter to land it on the runway, the engine lost total power, and he performed an autorotation to a field. During the landing, one of the helicopter's skids got stuck in soft dirt, and the helicopter subsequently rolled onto its left side. Postaccident examination of the airframe and engine revealed no flight control or fuel system continuity anomalies. The single-drive dual magneto, ignition harness, and spark plugs were removed for further examination. The examination revealed that the left distributor gear was internally timed to the counter clockwise (CCW) marking and that the right distributor gear was internally timed to the clockwise (CW) marking. However, both distributor gears should have been timed relative to the CCW markings in accordance with the magneto manufacturer's Service Support Manual. When one of the distributor gears is timed to the CW markings instead of the CCW markings, a four-teeth difference in timing between the gears can occur. According to the magneto service representative and the magneto manufacturer's magneto specialist, the four-teeth timing difference would only have resulted in faster wear on the magneto's internal components. Given that the magneto was recently overhauled, it is likely that the magneto was operating as designed at the time of the engine loss. The reason for the loss of engine power could not be determined.

Analysis

Primary failure mode
Engine power loss
First missed decision gate
Pilot could have aborted the landing when engine started to sputter.

NTSB coding

Evidence available

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

Docket documents7

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