What happened
On 23 September 2009, a Dornier 328-100, registration D-CIRT, was being repositioned from Dundee to Germany for maintenance and potential sale. The flight, conducted as a non-revenue commercial operation, began its takeoff from Dundee at 1406 hrs. Shortly after becoming airborne, the crew observed an amber caution light, which quickly extinguished. As the aircraft climbed to 1,500 ft, the right engine's oil pressure began to fluctuate, accompanied by EICAS messages regarding the right-hand engine alternator.
As the aircraft reached 3,000 ft, the left engine's oil pressure also began to fluctuate, followed by a red master warning and an audible alarm. Fearing a total loss of power in either engine, the commander decided to return to the airport. During the climb, the crew experienced significant system malfunctions, including a loss of oil pressure on the left engine. Due to a misunderising of ATC instructions, the crew believed they were returning to Dundee, but were actually being vectored toward RAF Leuchars. The crew, unfamiliar with the Leuchars airfield, landed safely at 1418 hrs.
The investigation
An AAIB field investigation examined the aircraft's flight data and maintenance records. While there was no external evidence of leaks, the left engine had lost approximately seven quarts of oil, and the right engine had lost four quarts. Post-flight engine tests showed high oil consumption and vapour venting from the engine breathers.
Engine inspections revealed that the oil cavities and gearboxes in both engines had become over-pressurised, forcing oil out through the vent system. Further disassembly of the air-switching valves revealed that the pistons, rings, and inner valve housings were heavily corroded. This corrosion prevented the valves from transitioning correctly from P3 to P2.5 bleed air as engine speed increased.
Findings
- The failure of both engine air-switching valves to operate normally caused the engine oil cavities to become over-pressurised.
- This over-pressurisation forced oil to be purged overboard through the engine vent system.
- Corrosion on the valve components was caused by the prolonged storage of the aircraft in environments exposed to saline moisture.
- The crew's decision to land at the nearest suitable airfield was prompted by the simultaneous engine malfunctions.
- A lack of effective communication regarding the crew's intentions prevented the situation from escalating further.