Cessna 150M N714PW

Summary

On 15 July 2024 at about 18:45 local time, a Cessna 150M registered N714PW was involved in an accident near Ritzville, Washington, United States. One person was on board and nobody was injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

15 July 2024 at 18:45

Classification

Accident

Location

Ritzville, Washington, United States

Nearest airport

Pru Fld (33S)

Coordinates

47.1030, -118.3863

Aircraft

Cessna 150M

Registration

N714PW

Category

Airplane

Year built

1977

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Personal

Phase of flight

Not recorded

Route

Spokane → Yakima

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

WPR24LA248

Nobody was injured.

Maintenance personnel’s improper installation of the No. 2 cylinder exhaust valve, which allowed the valve to drop into the cylinder and resulted in a total loss of engine power.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

The pilot was conducting a cross-country flight when he heard a “loud metal sound” followed by a partial loss of engine power. While troubleshooting the rough-running engine, he diverted to a local airport. The airplane then had a total loss of engine power, and the pilot initiated an off-airport landing to an open field. During the landing roll, the nose landing gear collapsed and the airplane impacted terrain, which resulted in substantial damage to the fuselage and both wings. Postaccident examination of the engine revealed mechanical damage to the No. 2 cylinder’s combustion dome and piston face. The keeper halves for the exhaust valve were missing, and the keeper shoulder on the valve stem showed fretting contact damage consistent with relative movement between the keeper halves and the valve stem. Contact wear patterns were also observed on the exhaust valve spring seat. The keepers likely became dislodged during the accident flight, allowing the valve to drop into the combustion chamber, where it was repeatedly impacted by the piston. The valve was then pushed back into the exhaust cavity, where the valve stem impacted the head adjacent to the exhaust valve guide. The fragmentation of the piston and exhaust valve likely led to the loss of engine power. Possible causes for dislodged keepers include improper installation or weak valve springs. The height of the intake and exhaust valve springs were similar, so weak springs are unlikely. Thus, the keepers were likely not installed properly before the accident. With improper installation, failure can be expected relatively soon after installation. Although the last record of work that would require disassembly of the valve to complete (a top overhaul) was dated about 36 years before the accident flight, the engine was reported to have only accrued about 320 hours since repair of the cylinders. It is likely that the keeper halves were not properly seated on the exhaust valve shoulder when the valve was installed. This incorrect installation allowed the keepers to eventually work their way out of position, allowing the valve to drop into the combustion chamber.

Quoted verbatim from the NTSB record.