Background
On 28 April 2001, a Piper PA-28-180 (registration G-AVNP) was being operated on a private flight from Southend Airport to Wickenby Airfield and back. The aircraft was manufactured in 1967 and equipped with a Lycoming O-360-A4A piston engine. The flight crew consisted of two qualified private pilots: one (Pilot A) in the left seat acting as commander for the return leg, and the other (Pilot B) in the right seat. Both pilots had prior experience, with Pilot A holding a lapsed instructor rating and Pilot B studying for a JAR ATPL.
History of the Flight
The aircraft departed Southend with full fuel tanks (50 USG total) earlier that morning. The flight to Wickenby was uneventful, lasting approximately 1.7 hours. After a brief stop, the pilots swapped roles for the return journey. Pre-flight checks indicated both fuel tanks were about 3/4 full, confirmed visually. The aircraft took off from Wickenby at 1555 hrs and routed towards RAF Mildenhall, maintaining contact with London Information. During the flight, regular cruise checks included monitoring engine rpm and applying carburettor hot air to test for induction ice.
While cruising at 1,500 feet agl near the Stansted Control Area, approximately 5 to 10 minutes after the last cruise check, the engine suffered a sudden loss of power. Throttle pumping and carburettor hot air selection did not restore power. The crew prepared for a forced landing and sighted Nayland Airfield ahead. An approach was made to Runway 32, but late on final approach, Pilot A saw a large tree too close to avoid. The right wing struck the tree and separated from the fuselage. The remainder of the aircraft hit the ground in a nose-down attitude and rolled onto its right side, preventing cabin door opening. Pilot B pushed out the left window and released seat belts. A passer-by helped extract Pilot A through the left window, then Pilot B. The emergency services arrived and righted the aircraft; no fire occurred.
Wreckage and Examination
The aircraft was recovered and examined. The left fuel tank contained approximately 10.6 USG of fuel with no significant leakage. The right tank was ruptured, and the fuel selector was found selected to the right tank. The electric fuel pump was functional, and fuel was present in the carburettor float chamber. No airframe anomalies were found. Engine strip examination revealed severe wear on the camshaft lobe operating Nos 3 and 4 inlet valves, and pitting on follower bodies. However, the overhaul agency noted such damage is common in engines nearing overhaul and has not been linked to significant power loss. The engine had 1,881 hours since overhaul and had suffered a propeller strike 427 operating hours earlier, after which the camshaft and followers were replaced. No other engine anomalies were found.
Weather Conditions
A meteorological aftercast indicated an unstable flow from the west-south-west, with a trough line clearing the area and possible showers. Surface temperature was 10°C, dew point 6°C, relative humidity 76%. These conditions fell within the 'float carburettor - severe icing at cruise power' envelope on the standard induction system icing chart.
Conclusion
The investigation concluded that induction system icing was the most likely cause of the power loss, given the ambient weather conditions. The damage to the valve operating mechanism was not considered a factor. Fuel exhaustion was deemed unlikely based on fuel calculations.