Norwegian authorities are investigating what they describe as a “serious aviation incident,” after a Sikorsky S-92A suffered an oil leak that forced the crew to declare mayday before landing safely.
The incident took place on Sept. 25, 2020, as the Bristow Norway-operated aircraft returned to Sola from the West Elara oil installation. About 25 to 30 nautical miles southwest of Sola, as the aircraft was making a descent from 7,000 feet to 1,000 feet, its crew received a caution that the oil pressure on the main gearbox had dropped below 45 psi.
Shortly afterwards, the caution “INPUT/AA #1 HOT” came on, and the crew followed the emergency checklist to put the left engine back to idle.
The oil pressure continued to drop to below 35 psi, and the oil cooler automatically switched off. As the aircraft continued its approach to Sola, the oil temperature rose and the caution “INPUT/ACC #2 HOT” came on. The oil reached a peak temperature of 214 C.
The crew declared mayday as they continued to descend to 200 feet, and were preparing to ditch in the sea if the oil pressure disappeared completely.
However, the aircraft was able to land normally at Sola, and it was followed to a standstill by the airport’s fire and rescue department.
The Norwegian Safety Investigation Authority arrived that evening to begin their investigation into the incident, and found about four liters of oil missing from the main gearbox. The main gearbox normally contains about 30 liters of oil.
Investigators found some oil spill on the left engine and left side of the main gearbox, and there was oil on the outside of the helicopter, particularly on the left side of the fuselage.
They noted that the oil appeared to come from the left engine input to the main gearbox area, but there were no signs of leakage in the oil cooler or its hose connections.
An indicator that warns of a high pressure difference across the oil filter had come out, but the investigators saw no particles during an initial visual inspection of the oil filter, and they found no metal particles on the main gearbox’s magnetic plugs.
The main gearbox has been removed and is to be sent to Sikorsky for further analysis.
The NSIA said it will continue its investigation with help from the U.S. National Transportation Safety Board.
