Summary
On 25 May 2006, a Piper PA-32RT-300 (registration G-RHHT) operated by a private pilot made a precautionary landing in a wheat field at Fox Heading Lane, St Johns, Spalding, Lincolnshire. The aircraft had departed from Fenland Airfield for a flight to its home base at Sywell. The pilot reported lower than expected climb rate and a vibration transmitted through the control column during the takeoff climb. The landing was successful with no damage to the aircraft or injuries to the two occupants.
Background
The aircraft had been fitted with a newly overhauled Lycoming IO-540-K1G5D piston engine in May 2006. Several test flights were conducted without incident. On the return flight from Fenland to Sywell, the pilot noticed the climb rate was not as good as usual and a vibration was present. The engineering company that performed the overhaul advised the pilot that some power and vibration anomalies could be expected with a newly overhauled engine. The engine was ground tested and the pilot proceeded.
Takeoff Attempt
The pilot calculated the aircraft weight and determined sufficient takeoff distance was available on Runway 36 at Fenland. After a takeoff run of approximately 400 metres, the indicated airspeed was 50-55 kt and the aircraft did not appear to accelerate normally. Judging insufficient distance to stop, the pilot selected two stages of flap, rotated at 55-60 kt, and held the aircraft in ground effect while it accelerated to 60-65 kt. Thereafter, the aircraft did not continue accelerating. After being airborne for about 300 metres, the occupants realized the aircraft was not climbing. Approaching a row of trees, they decided to land immediately in the wheat field ahead. The landing was successful.
Subsequent Findings
The aircraft was recovered and examined by the engineering company. Later that day, the aircraft was declared fit to fly, and a further flight was conducted with the engineer, a well-qualified pilot, accompanying. The takeoff and climb were successful, but the incident pilot still considered climb performance below expectations. Over the following days, several hours were flown with power settings above 75%. Climb performance varied and vibration was intermittently present. Another pilot also experienced poor takeoff performance and vibration. A subsequent flight of six hours at 75% power seemed to rectify the performance. Once more than 20 hours had been accumulated on the overhauled engine, takeoff and climb performance appeared normal.
Engine Behaviour Discussion
New or overhauled engines that have not been extensively run at high power on a test plant require a significant period of higher-than-normal cruise power in flight to run in the piston rings and cylinder bores. This process creates a better fit, reducing oil consumption and friction. Prior to this, oil consumption is high, and oil passing the rings can cause plug fouling during ground running and low-power flight. A single cylinder may suffer more than others. Incomplete combustion from a fouled plug leads to loss of peak combustion pressure, reducing torque contribution; this may be less obvious on a six-cylinder engine like G-RHHT than on a four-cylinder type. High-power operation can burn off oil fouling, but prolonged reduced-power running may allow fouling to return. The incident and subsequent performance issues were consistent with an engine undergoing the running-in process.