Wsk Pzl Mielec M-18A N92640

Summary

On 25 July 2011 at about 18:17 local time, a Wsk Pzl Mielec M-18A registered N92640, operated by Forest Air Services Inc, was involved in an accident near Anderson, Indiana, 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

25 July 2011 at 18:17

Classification

Accident

Location

Anderson, Indiana, United States

Coordinates

40.1475, -85.5408

Aircraft

Wsk Pzl Mielec M-18A

Registration

N92640

Category

Airplane

Engines

1

Operator

Forest Air Services Inc

Operating rule

Part 137: Agricultural

Purpose of flight

Aerial Application

Phase of flight

Not recorded

Route

Marion → Marion

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

CEN11LA512

Nobody was injured.

The fatigue failure of the propeller governor speeder spring, which resulted in the pilot’s inability to control engine output power.

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

Read the full NTSB narrative

The pilot was marking a field in preparation for an aerial application when he experienced what he thought was an engine failure. He stated that the engine was still running, but it was not producing power. The pilot pushed the power lever forward; the engine power did not increase, but the engine temperature increased. He stated that the engine was idling fast and that he forced the airplane into a bean field about 150 to 200 yards ahead of a tree line. The pilot ground looped the airplane before contacting the trees. A postaccident examination of the engine did not reveal any anomalies. A bench test of the propeller governor revealed that the maximum speed was above the nominal limit and the minimum speed was below the nominal limit. The control lever position was set higher than the specified position, which indicated that the governor had been adjusted in an attempt to regulate the propeller speed. X-rays and a teardown revealed that the propeller governor speeder spring was fractured. A metallurgical examination revealed a preexisting fatigue crack that, over time, resulted in the failure of the spring. The failed speeder spring would have resulted in a loss of oil pressure to the propeller piston, which allowed the propeller blades to rotate to a high blade angle, which then decreased the engine speed and overall power output of the engine. Maintenance records showed the propeller governor was overhauled on May 19, 2009. The speeder springs did not have serial numbers, and, therefore, the maintenance history of the speeder spring could not be determined.

Quoted verbatim from the NTSB record.