Air Tractor AT-401 N4542W

Summary

On 19 August 2014 at about 13:40 local time, a Air Tractor AT-401 registered N4542W, operated by Aurora Cooperative, was involved in an accident near Wray, Colorado, United States. One person was on board and one had minor injuries. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

19 August 2014 at 13:40

Classification

Accident

Location

Wray, Colorado, United States

Coordinates

40.1003, -102.2408

Aircraft

Air Tractor AT-401

Registration

N4542W

Category

Airplane

Year built

1989

Engines

1

Operator

Aurora Cooperative

Operating rule

Part 137: Agricultural

Purpose of flight

Aerial Application

Phase of flight

Not recorded

Route

Wray → Wray

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

CEN14LA439

1 person had minor injuries.

A loss of the No. 1 cylinder’s compression due to a stuck exhaust valve caused by a lack of sufficient valve clearance, which resulted in a loss of engine power and a forced landing. Contributing to the loss of engine power were the worn intake and exhaust valves in cylinders No. 3 and 4.

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

Read the full NTSB narrative

During initial climb, the pilot felt a subtle vibration from the engine and noticed the manifold pressure dropping rapidly. When he attempted to increase manifold pressure by opening the throttle, the engine began to vibrate violently and lost all power. The pilot made a downwind forced landing, and the airplane nosed over. The engine was later partially disassembled and examined. A small amount of aluminum and steel filings were recovered from oil drained from the rocker arm sump. A cylinder compression check revealed that the Nos. 1 and 3 cylinders were non-functioning and that the No. 4 cylinder exhibited weak compression. The intake valve in the No. 3 cylinder was found to have a ridge worn on its face, and the valve seat was worn excessively. The No. 1 cylinder's exhaust valve was stuck open and was binding in the valve guide. The exhaust valve clearances for the cylinders were then checked and found to be less than the Pratt and Whitney overhaul limits of 0.003" to 0.0055", with a maximum wear limit of 0.010". Most likely, the engine lost power due to the stuck exhaust valve.

Quoted verbatim from the NTSB record.