Double engine failure leads to forced landing of Piper Chieftain in Scotland

Casualties unknown • Field near Stonehaven, Aberdeenshire, GB

A Piper PA-31-350 experienced successive engine failures shortly after takeoff from Wick, resulting in a forced landing in a ploughed field.

What happened

On 9 April 2014, a Piper PA-3-350 Chieftain, registration N66886, was performing a private ferry flight from Wick, Scotland, toward Le Touquet, France. Approximately 25 minutes after departing Wick, the pilot noted a drop in fuel flow and manifold pressure on the right-hand engine. Despite attempts to restart the engine using the standby fuel pump and switching fuel tanks, the engine failed. Shortly thereafter, the left engine also lost power. Unable to maintain altitude or reach the requested diversion to Aberdeen, the pilot performed a forced landing in a ploughed field. There were no injuries to the pilot, though the aircraft was damaged beyond economic repair.

The investigation

The investigation focused on the simultaneous failure of both Lycoming engines. The aircraft had a complex recent history, having been abandoned in Greenland in December 2013 due to low oil pressure indications. Although multigrade oil had been sent to Greenland to rectify this, the engine oil was not actually changed before the aircraft continued its journey through Iceland to Scotland.

Upon inspection of the engines, investigators found severe damage to the No 6 piston in the left engine and the No 3 piston in the right engine. Both pistons exhibited burning and melting consistent with combustion gases escaping past the piston rings into the crankcase, a phenomenon known as 'blow-by'. In the left engine, the damage was so severe that it led to the extrusion of bearing material and the loss of oil, evidenced by a missing dipstick and oil smears on the nacelle.

Findings

  • The engines had been operated in extremely low temperatures in Greenland using an incorrect grade of oil (Aeroshell W100) for such conditions.
  • The engine manufacturer noted that using this specific oil grade without pre-heating during cold-weather starts can cause damage due to inadequate lubrication.
  • The simultaneous failure of both engines was likely a common-mode event, potentially caused by detonation (pre-ignition).
  • Factors that could contribute to such damage include incorrect mixture settings (running too lean), incorrect ignition timing, or contaminated fuel.
  • The left engine suffered more significant oil loss, likely because crankcase pressurisation caused the oil dipstick to be ejected.

Probable cause

The simultaneous failure of both engines was likely caused by detonation, potentially stemming from the use of an incorrect oil grade during previous cold-weather operations or improper mixture settings during the flight.

Frequently asked questions

What happened in the 2014-04-09 Piper PA-31-350 accident near Field near Stonehaven, Aberdeenshire, GB?

A Piper PA-31-350 experienced successive engine failures shortly after takeoff from Wick, resulting in a forced landing in a ploughed field.

What aircraft was involved and where did it happen?

The accident on 2014-04-09 involved a Piper PA-31-350, registration N66886, at Field near Stonehaven, Aberdeenshire, GB.

What was the probable cause of the accident?

The simultaneous failure of both engines was likely caused by detonation, potentially stemming from the use of an incorrect oil grade during previous cold-weather operations or improper mixture settings during the flight.

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