Stinson 108 - 3 N6152M accident near North Las Vegas, Nevada

Probable cause

The partial loss of engine power due to a degraded cylinder exhaust valve seal, which resulted in low cylinder compression.

NTSB analysis

According to the private pilot, after an uneventful departure in high-density altitude conditions for the personal cross-country flight, he made a left crosswind turn in the airport traffic pattern as instructed by an air traffic controller. When the airplane was about 800 ft above ground level and near the departure end of the runway, the airplane stopped climbing, which was accompanied by a vibration. The airplane likely stopped climbing due to a partial loss of engine power and the high-density altitude conditions. The pilot lowered the airplane's nose to increase airspeed and continued the turn to land on the runway, but when the airplane started to sink, he decided to land on a tarmac located straight ahead. The airplane touched down, with a tailwind, about halfway down the tarmac. The pilot deployed full flaps but was unable to slow the airplane before it impacted a fence and then nosed over.

A postaccident examination of the engine revealed that the No. 1 cylinder exhaust valve seal was degraded, which prevented the valve from seating properly and likely resulted in low cylinder compression and a partial loss of engine power. Further, testing of the magnetos revealed that the primary ignition lead for the No. 6 cylinder was inoperative, which likely resulted in the engine running roughly after the partial loss of power.

Text from the NTSB. Open the NTSB docket for WPR15LA223 for the full record.