Pilot Debrief

BEECH S35 near Pagosa Springs, CO — 2015-09-25

Final reportCEN15FA424
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Date
2015-09-25
Location
Pagosa Springs, CO, USA
Aircraft
BEECH S35
Registration
N193Q
Category
Airplane
Highest injury
Fatal
Fatalities
2
Phase of flight
Maneuvering

Probable cause

Improper engine assembly by unknown maintenance personnel, which resulted in the failure of the No. 6 connecting rod due to oil starvation from the shifting of the crankshaft's No. 4 main bearing.

NTSB narrative

On the day before an air race competition, the accident pilot and another pilot decided to execute a practice circuit of the race course in their airplanes. As the two airplanes entered the course, the accident airplane was behind the other airplane. After they passed the first course waypoint, the accident pilot radioed the other pilot and stated that his airplane's engine had lost power and that the airplane was going down. No further communications were heard from the accident airplane. Witnesses observed white smoke coming from the underside of the airplane before they lost sight of it. Examination of the accident site indicated that the pilot was attempting to land on a gravel road when the airplane impacted a steel pole adjacent to the road and traveled about 200 yards before coming to rest inverted. Examination of the engine showed that the No. 6 connecting rod failed due to oil starvation. The oil starvation resulted from movement of the No. 4 main crankshaft bearing to a position where it blocked the oil transfer passage to the No. 6 connecting rod. The engine thru-bolts were improperly torqued by unknown maintenance personnel, and this allowed the No. 4 main bearing movement to occur. In addition, disassembly of the engine revealed that unapproved pistons had been installed. However, the unapproved pistons were not related to the engine failure.

Analysis

Primary failure mode
Engine power loss
First missed decision gate
Pilot could have aborted the maneuver after engine power loss was first noted.

NTSB coding

Evidence available

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

Docket documents9

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