What happened
On 25 May 2006, a private Piper PA-32RT-300, registration G-RHHT, departed from Fenland Airfield for a flight to Sywell. During the takeoff roll on Runway 36, the pilot noted that the aircraft was not accelerating normally, reaching only 50-55 kt after approximately 400 metres. Fearing insufficient remaining runway to stop, the pilot deployed two stages of flap and rotated the aircraft at 55-60 kt.
While the aircraft entered ground effect and accelerated to roughly 60-65 kt, it failed to achieve a sustained climb. As the aircraft approached a line of trees, the crew decided to perform an immediate landing in a nearby wheat field. The landing was completed without any damage to the aircraft and with no injuries to the two occupants.
The investigation
The investigation examined the aircraft' and the recent maintenance history of the engine. The aircraft had been fitted with an overhauled Lycoming IO-540-K1G5D piston engine in May 2006. Following the incident, the aircraft was inspected by an engineering firm.
During subsequent flights, the pilot reported intermittent vibration and inconsistent climb performance. An engineer accompanied the pilot on a follow-up flight, noting that the issues persisted. However, after a six-hour flight was conducted at power settings above 75%, the performance and vibration issues appeared to resolve. The investigation focused on the behavior of newly overhauled engines during the initial run-in period.
Findings
- The aircraft's takeoff performance was hindered by potential spark plug fouling caused by the recent engine overhaul.
- Newly overhauled engines often experience high oil consumption as rings and cylinder bores seat, which can lead to oil passing into the combustion chambers.
- This oil can cause fouling of the spark plugs, particularly during low-power operations or ground running.
- In a six-cylinder engine, the loss of power from a single fouled cylinder may not be immediately obvious, but it can result in reduced climb rates and engine vibration.
- Sustained high-power operation is required to increase combustion temperatures enough to burn off such deposits and stabilize engine performance.