THE PILOTS of the Super Puma that plunged into the sea off Shetland killing four oil workers failed to observe the speed of the aircraft as it approached Sumburgh airport, an Air Accident Investigation Branch (AAIB) report has said.
The report also told the operator of the airport to improve its water rescue capabilities after it emerged that valuable time was lost in launching its rescue craft.
In a response, Highlands and Islands Airport (HIAL) said that although officially it had no role to play in the rescue, it was its rigid inflatable that was the first vessel on the scene.
In a special bulletin the AAIB detailed the helicopter’s flight history as it approached the airport with 18 people on board in the late afternoon of 23 August.
It said no technical fault that could have caused the tragedy has been found.
The investigation will now focus on the operational aspects of the flight, especially on the effectiveness of pilot monitoring of instruments during the approach, the AAIB said.
The report read: “At approximately 2.3 nm, the commander noted that the airspeed was 80 kt and increased the collective pitch, intending to maintain the speed.
“However, the helicopter’s airspeed reduced below 80kt and continued to reduce, unobserved by the crew.”
The report continued: “There was then an automated audio call of “CHECK HEIGHT”, an acknowledgement by the commander, and then a comment by the co-pilot to draw the commander’s attention to the airspeed.
“At this time the helicopter’s speed was 35kt and reducing.
“Shortly thereafter, there was a second automated audio call of “CHECK HEIGHT”, followed by a “100 FEET” automated call two seconds before impact with the surface of the sea.”
A modelling of the final stages of the flight indicated that “in this condition, the reduced helicopter performance, together with the limited height available, meant that the impact with the sea was unavoidable”.
The report also said: “Examination of the main rotor head and the remains of the main rotor blades revealed evidence of high-speed rotation at impact.
“Similar evidence was found on the tail rotor blades and the tail rotor drive shaft.”
The two safety recommendations made in the report refer to the difficulties the airport’s fire service had in launching its 8.6-metre rigid inflatable rescue craft.
Owing to the tidal conditions on the day, rescue crews were unable to use the slipway nearest the scene of the accident, and had to launch the inflatable from the opposite side of the runway.
It took almost an hour and a six-nautical-mile open-sea transit for the rescuers to reach the survivors in the water, who were just a mile-and-a-half offshore.
Two of the three crew members in the inflatable were injured owing to the difficult sea conditions encountered while heading for the scene of the accident.
Under civil aviation rules, HIAL is only required to respond effectively to incidents within a kilometre offshore.
However, an airport safety survey had shown that owing to tidal conditions the narrow slipway designed to launch the inflatable could only be used in 11 per cent of the cases.
The AAIB said: “It is recommended that the operator of Sumburgh Airport, Highlands and Islands Airports Limited, provides a water rescue capability suitable for all tidal conditions for the area of sea to the west of Sumburgh, appropriate to the hazard and risk, for times when the weather conditions and sea state are conducive to such rescue operations.”
The Civil Aviation Authority meanwhile was advised to review the risks associated with the current water rescue provision for the area and to take appropriate action.
HIAL responded on Friday afternoon by saying that it would consider the comments made but insisted that it had “no role in responding to incidents that occur outwith its limited area of responsibility”
“In this case, given the serious nature of the incident and in spite of the hazardous weather conditions, Sumburgh Airport played an important role in support of the rescue operation.
“The airport’s fast rescue craft was the first waterborne asset on site in support of the rescue effort. We would like to reiterate our thanks to the members of the airport fire service who responded to the incident outwith the airport’s area of responsibility.
“Their professionalism, expertise and courage in operating in difficult environs offshore were crucial in their ability to be the first rescue vessel on the scene in support of the emergency responders to this incident,” an airport spokesman said.
The full AAIB special bulletin can be downloaded here.