What happened
On 3 October 2005, a Beech Baron 55, registration ZS-JFR, was conducting a flight from Walvis Bay, Namibia, to Mafikeng Aerodrome, South Africa. The aircraft was carrying the pilot and five passengers. During the transit, the pilot observed oil appearing on the trailing edge of the left wing flap and noted that the engine oil pressure had risen to 90psi. Although this pressure remained within the engine's standard operating parameters, the pilot recognized a leak occurring in the number one engine.
Upon establishing communication with the Mafikeng control tower, the pilot declared the engine oil leak and requested permission to land at Mafikeng, despite the aerodrome not being a designated port of entry for the flight. The tower granted clearance, and the aircraft completed a safe landing on Runway 04. Following the arrival, the aircraft was moved into a hangar under the supervision of aerodrome security.
The investigation
Investigators examined the aircraft's maintenance history and the mechanical state of the engines. It was noted that a 50-hour oil change inspection had been completed on 20 September 2005, and the aircraft had flown 20.2 hours since that service. The investigation focused on the source of the oil discharge observed on the wing flap and the cause of the increased oil pressure.
Findings
- The investigation established that the two engine oil dipsticks had been interchanged.
- Because of the swapped dipsticks, the pilot was unaware that the number one engine had been overfilled with oil.
- The excess oil in the engine was forced out through the engine breather and the crankshaft seal, leading to the visible leak on the aircraft's wing.