Engine Failure Leads to Forced Landing of Air Tractor in South Africa

Casualties unknown • At a soccer field approximately 5 NM north of FAMU, ZA

An agricultural spraying mission ended in a forced landing near Mkuze after a mechanical engine failure caused severe vibrations and power loss.

What happened

On 18 April 2011, an Air Tractor 401, registration ZS-PGT, was conducting commercial aerial crop spraying operations near Monzi. The flight proceeded normally through five spray runs, but during the sixth pass, the aircraft was suddenly struck by intense vibrations. The pilot, flying at an altitude of only 50 to 100 feet above the ground, initially suspected a malfunction in the spray pump and attempted to mitigate the issue by closing the spray valve and deactivating the pump.

However, the shaking intensified, and the engine subsequently lost power. In an attempt to maintain altitude, the pilot increased engine power, but the aircraft could not sustain its height. Seeking an emergency landing site, the pilot identified a nearby soccer field. During the approach, the aircraft struck a line of trees bordering the field, leading to a heavy impact and a ground loop. While the aircraft sustained substantial damage to its wings, undercarriage, and engine, the pilot escaped the wreckage without any injuries.

The investigation

SACAA AIID investigators examined the wreckage and the engine components to determine the source of the vibration and subsequent power loss. The engine was transported to an overhaul facility for a complete teardown. The investigation also included a review of the aircraft's maintenance logs, the pilot's training records, and the meteorological conditions at the time of the accident.

Findings

  • The investigation established that the aircraft suffered a contained engine failure.
  • Metallurgical analysis of the engine components revealed that the piston rods for cylinders #5 and #6 had failed.
  • The failure was traced to a fatigue mechanism initiated by wear in the main bearing pins.
  • It was determined that this wear resulted from extended use and that the components should have been replaced during the previous engine overhaul.
  • Although the aircraft had recently undergone maintenance to address a low compression issue in cylinder #5, the underlying fatigue in the bearing pins remained undetected until the catastrophic failure occurred.

Probable cause

The engine failed due to a contained mechanical failure involving the breakage of the #5 and #6 piston rods, which led to an unsuccessful forced landing.

Frequently asked questions

What happened in the 2011-04-18 Air Tractor 401 accident near At a soccer field approximately 5 NM north of FAMU, ZA?

An agricultural spraying mission ended in a forced landing near Mkuze after a mechanical engine failure caused severe vibrations and power loss.

What aircraft was involved and where did it happen?

The accident on 2011-04-18 involved a Air Tractor 401, registration ZS-PGT, at At a soccer field approximately 5 NM north of FAMU, ZA.

What was the probable cause of the accident?

The engine failed due to a contained mechanical failure involving the breakage of the #5 and #6 piston rods, which led to an unsuccessful forced landing.

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