Description

On 20 October 1998, in the North Sea, an Eurocopter AS332L Super Puma operated by Norsk HeliKopter AS, experienced engine failure with autorotation and subsequent lost of height. The crew misidentified the malfunctioning engine and reduced the power of the remaining serviceable engine. However, the error was detected just in time for the crew to recover control of the helicopter.

Synopsis

The following is an extract from the official Investigation Report published by the Aircraft Accident Investigation Board (AAIB), Norway:

“[…]The flight proceeded normally at an altitude of 2 000 ft until the crew at 12:23:04 hours discovered that the torque on the right engine (Tq 2) started to rise and became unstable. The RPM of the gas turbines (Ng 1 and Ng 2) increased correspondingly. No other indications were observed at that time. The crew then noticed an unusual engine noise. The torque indicator was set to indicate separate values for Tq 1 and Tq 2 (crosshatched position). This showed that the torque value on the left engine was correspondingly low. The crew analysed the situation and got the impression that the problem was related to the right engine.”

The crew decreased the power of the right engine to approximately 75-80%.

“The noise from the engine area then increased substantially, and the warning indicator for high Nr [rotor RPM] came on for a short period. Later analysis of the helicopter’s Flight Data Recorder (FDR) showed that the rotor RPM reached 109% for one second before it was stabilised by the Co-pilot. The Ng 1 reached in this period 101.3% and this may explain the high Nr. The collective pitch was then reduced to 7 degrees and the helicopter entered autorotation at a speed of 80 kt.