Unfavourable tidal conditions meant some rescue workers were delayed in reaching the scene of August’s fatal helicopter crash, air accident investigators have revealed.
A special bulletin relating to the investigation was published on Friday afternoon by the Air Accident Investigation Branch (AAIB) which makes safety recommendations in relation to an airport slipway which can be used “in only 11 per cent of tidal conditions”.
And the interim report states that the crew failed to notice a drop in speed in the minutes before the helicopter which was carrying 18 people, including a pilot and co-pilot, hit the water. Fourteen survived but Duncan Munro, Sarah Darnley, Gary McCrossan and George Allison lost their lives.
The ongoing investigation will focus on the effectiveness of pilot monitoring of instruments during the approach, operational procedures and the training of flight crews.
The slipway is used by the airport fire service’s fast rescue craft (FRC). But on the evening of the crash the rescue craft was not able to launch from it.
Instead an alternative slipway, located on a “soft, sandy beach” was used. However the rescue craft, an 8.6 metre rigid inflatable vessel, became bogged down in the sand and had to be rescued.
The AAIB bulletin states the airport slipway is “shorter and narrower than optimum”.
It adds: “The FRC could not be launched from the slipway near the runway…in response to this accident due to the unfavourable tidal conditions that prevailed.
“An attempt was made to use the alternate launch site, but the FRC became bogged down in the soft sand and had to be recovered.”
Once the craft was launched it had to travel six nautical miles in rough waters around the peninsula to the scene of the crash. Three crew members were injured due to the difficult sea conditions.
This week, prior to the publication of the bulletin, The Shetland Times contacted Sumburgh Airport’s operator Highlands & Islands Airports Limited (HIAL) asking about the suitability of the slipway. But the organisation did not want to comment while the investigation is ongoing.
The AAIB bulletin makes safety recommendations in relation to the slipway. “This accident has highlighted that, in the majority of tidal conditions, the FRC may not be able to respond to aircraft accidents in the sea on the western side of Sumburgh Airport within the available survival time.”
It recommends HIAL provides a water rescue capability suitable for all tidal conditions. And it suggests the Civil Aviation Authority (CAA) review the risks associated with the current water rescue provision and take “appropriate action”.
Examination and analysis of the wreckage has revealed no evidence of a technical fault, although investigation work continues. There is also no evidence of any pre-impact damage to the main rotor gearbox or the engines.
The interim report states that approximately 2.3 nautical miles from the airport the helicopter’s airspeed was 80 knots, which the commander intended to maintain.
“However, the helicopter’s airspeed reduced below 80 kt and continued to reduce, unobserved by the crew.”
At about two nautical miles from the airport there was an automated “check height” message which was acknowledged by the commander.
The co-pilot then drew attention to the airspeed, which was 35 knots and reducing.
That was followed by a second “check height” message and a “100 feet” notification, two seconds before the helicopter hit the water.
“At some point the commander saw the sea, but he was unable to arrest the helicopter’s descent and it struck the surface shortly thereafter, at 17.17 hours. The co-pilot,
realising that the helicopter was about to enter the water, armed the helicopter’s flotation system.
“After striking the surface the helicopter rapidly inverted, but remained afloat, the flotation equipment having successfully deployed.”