Investigators probing the fatal 28 February crash of a Sikorsky S-92 off the Norwegian coast say the helicopter unexpectedly pitched up to an angle of 30° shortly before its impact with the water.
As part of a training mission, the Bristow Norway crew had deployed an emergency beacon into the sea west of the island of Sotra, to the west of Bergen, which they intended to later locate and retrieve, says the Norwegian Safety Investigation Authority (NSIA) in a 13 May update.
Operating in visual flight rules conditions in darkness without night vision goggles, the crew had activated the S-92’s search and rescue-specific ‘Mark on Top’ mode of its automatic flight control system as they prepared to position the helicopter to recover the beacon.
Mark on Top mode switches the helicopter from straight and level flight to a circuit around a target, such as a beacon or casualty, ending in a hover with the object around 50-100m (164-328ft) away in the two o’clock position.
But analysis of flight-data recorder information and additional data from the S-92’s systems, including its flight-control computer, “indicates that the pitch attitude started to increase abnormally when the helicopter was near the training beacon”, says the NSIA.
At that point the S-92 (LN-OIJ) was at 150ft and its speed was decreasing to around 10kt (18km/h).
“The nose of the helicopter started to rise from the expected 10-12° nose-up attitude to a 30° nose-up attitude over several seconds,” says the report.
Although still “working to determine the cause of the pitch-up manoeuvre”, the NSIA has “not made any unequivocal findings that are believed to affect immediate flight safety”.
The crew unsuccessfully attempted to counter the high nose-up attitude and the helicopter impacted the water, sinking to a depth of 220m (720ft).
One of the six crew members aboard the helicopter, a nurse, died in the crash. Her body was found “floating without a deployed life jacket and any sign of life”, says the NSIA.
While the S-92 was equipped with emergency floats, which were armed, they did not deploy during the “uncontrolled impact with the sea”, says the NSIA.
The design of the system means a power supply is needed to trigger the automatic deployment of the floats. But the uncontrolled nature of the crash meant when the S-92’s main rotor blades hit the surface of the water, the required power was cut, the update says.
It adds that new regulations for helicopters have been published, which “include emergency flotation elements”. The rule change will require the S-92 fleet to be retrofitted to the new standard by August 2025, says the NSIA.
European regulations covering the CS-29 large rotorcraft category in which the S-92 sits, updated in 2023, state that the inflation system “should, where practicable, minimise the possibility of foreseeable damage preventing the operation or partial operation of the [floatation system] (e.g. interruption of the electrical supply or pipework).
“This could be achieved through the use of redundant systems or through distributed systems where each flotation unit is capable of autonomous operation (i.e. through the provision of individual inflation gas sources, electrical power sources and float activation switches).”
