Pilot Debrief

ROBINSON HELICOPTER R22 BETA near Spearman, TX — 2025-02-07

Final reportCEN25LA093
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Date
2025-02-07
Location
Spearman, TX, USA
Aircraft
ROBINSON HELICOPTER R22 BETA
Registration
N7191B
Category
Helicopter
Highest injury
Minor
Fatalities
0

Probable cause

Improperly torqued intake manifold bolts that allowed unmetered air to enter the engine, resulting in an overly lean fuel-air mixture, eventual failure of the No. 3 cylinder intake valve, and a total loss of engine power.

NTSB narrative

The pilot reported that, while performing an aerial inspection of a fence, he heard a loud bang come from the engine and the helicopter began to shake and lose altitude. The shaking stopped momentarily but then started again and the engine lost total power. The pilot performed a forced landing, during which the helicopter impacted cedar trees and then rolled several times down a hill. The helicopter sustained substantial damage to the fuselage, tail boom, and main rotor gearbox. A postaccident inspection of the engine revealed that the No. 3 cylinder intake valve head was burned and chipped specifically on the combustion face, margin, and seat face. Additionally, the bolts that secured the intake manifold system to the engine block were loose. A review of maintenance records revealed that all four engine cylinders were removed for overhaul and reinstalled about 8 months before the accident due to low compression. According to the pilot, who was also the owner of the helicopter, about one month before the accident (about 360 hours after the cylinders were overhauled), the No. 1 cylinder was replaced due to the intake valve head being burned. According the engine manufacturer, when engine cylinders are removed and/or reinstalled, the bolts that secure the intake manifold system to the engine block need to be removed to manipulate the cylinders. It is likely that when the cylinders were removed 8 months before the accident for overhaul and reinstallation, the bolts that secured the intake manifold system to the engine block were not properly torqued when the cylinders were reinstalled. The loose intake manifold system likely allowed unmetered air into the engine, resulting in an overly lean fuel/air mixture, which resulted in damage to both the No. 1 and No. 3 cylinder intake valves. The damage to the valves would likely result in poor combustion and a decrease in engine performance.

NTSB coding

Evidence available

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

Docket documents6

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