Engine power loss leads to forced landing in wheat field near Anstey

Casualties unknown • Ansty, near Westside, Leicester, GB

A Quad City Challenger II experienced a sudden engine failure during a flight to assess a potential airstrip, resulting in an intentional stall and landing in a crop.

What happened

On 26 May 2003, a Quad City Challenger II, registration G-MZEA, was conducting a private flight near Leicester to evaluate a farmer's field for use as a new airstrip. While the aircraft was at approximately 1000 feet, the engine suffered a sudden loss of power.

The pilot initially identified an alternative field for an emergency landing but determined the distance was too great and feared an impact with trees during the approach. Consequently, the pilot executed a 6/0-degree turn toward a different field, which necessitated an intentional stall to reach a wheat crop. The resulting landing was heavy, causing damage to the nose wheel and the left main landing gear. Both the pilot and the passenger, who were secured in four-point harnesses, escaped the aircraft without injury.

The investigation

Following the incident, investigators examined the aircraft's Hirth 2706 piston engine. During the recovery process, it was discovered that a spark plug had been ejected from one of the engine cylinders. The plug was found still attached to its respective plug cap.

Further inspection of the aluminium cylinder head showed that the spark plug had been gradually loosening over an unspecified period. The investigation established that the plug had reached a state where only the final three or four threads were holding it in place. Continuous engine vibration then wore down these remaining threads until the plug was no longer held by the cylinder head and was subsequently expelled.

Findings

  • The engine failure was caused by the ejection of a spark plug from the cylinder head.
  • Vibrational forces caused the spark plug to work loose over time, progressively wearing the remaining threads in the aluminium cylinder head.
  • The pilot had not checked the security of the spark plugs for approximately 27 flight hours, with the last known disturbance to the plugs occurring roughly one year prior to the accident.
  • No specific manufacturer recommendations were in place requiring periodic security checks of the spark plugs for this engine type.

Probable cause

The engine lost power because a spark plug worked loose due to vibration, eventually wearing away the remaining threads in the cylinder head until it was ejected.

Frequently asked questions

What happened in the 2003-05-26 QUAD CITY CHALLENGER II MICROLIGHT accident near Ansty, near Westside, Leicester, GB?

A Quad City Challenger II experienced a sudden engine failure during a flight to assess a potential airstrip, resulting in an intentional stall and landing in a crop.

What aircraft was involved and where did it happen?

The accident on 2003-05-26 involved a QUAD CITY CHALLENGER II MICROLIGHT, registration G-MZEA, at Ansty, near Westside, Leicester, GB.

What was the probable cause of the accident?

The engine lost power because a spark plug worked loose due to vibration, eventually wearing away the remaining threads in the cylinder head until it was ejected.

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