Sumburgh disaster
Encyclopedia
The Sumburgh disaster was the crash of a Boeing 234LR Chinook
helicopter
on 6 November 1986 with a loss of 43 passengers and two crew members. The helicopter was on approach to land at Sumburgh Airport
Shetland Islands
returning workers for the Brent oilfield
. At 2.5 miles (4 km) from the runway the helicopter had a catastrophic forward transmission failure which de-synchronised the twin rotor
s causing the blades to collide. The helicopter crashed into the sea and sank.
but had been based at Sumburgh Airport since 3 November 1986 to operate a shuttle service from the Brent oilfield in the East Shetland Basin
. On 6 November the first flight was delayed due to an oil leak from an engine gearbox but was soon rectified and the aircraft left Sumburgh at 08:58 with 40 passengers for the Brent Field. The aircraft visited three platforms with exchanges of freight and passengers then departed Brent Platform C at 10:22 with 44 passengers on board for return to Sumburgh Airport. It transited at a height of 2500 feet (762 m), and as it approached Sumburgh it was cleared to descend to 1000 feet (304.8 m). Reporting 4.5 miles (7.2 km) from the airfield, the controller cleared it to land on helicopter runway 24. Nothing else was heard.
search and rescue helicopter which had just departed Sumburgh Airport reported liferafts in the sea. It then observed a survivor clinging to a substantial piece of wreckage. While they winched the man on board another survivor was noted amongst the floating bodies. With no signs of other survivors the Coastguard helicopter flew the survivors to Lerwick for transfer to hospital. An air and sea search failed to find any more survivors but all the floating bodies were recovered to the airport.
, the MSV Deepwater, started a search for the sunken wreckage at 09:00 the following morning. Sea conditions were rough and the depth of water around 90 metres but the wreckage was located and the cockpit voice recorder
and the cockpit section of the fuselage was recovered. By the evening of 10 November most of the aircraft wreckage had been recovered.
(AAIB) stated that the underlying causes were the inadequacy of a previously accepted test program and the failure of a stringent inspection programme.
in heavy lift, non-passenger capabilities.
CH-47 Chinook
The Boeing CH-47 Chinook is an American twin-engine, tandem rotor heavy-lift helicopter. Its top speed of 170 knots is faster than contemporary utility and attack helicopters of the 1960s...
helicopter
Helicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...
on 6 November 1986 with a loss of 43 passengers and two crew members. The helicopter was on approach to land at Sumburgh Airport
Sumburgh Airport
-Other tenants:*Maritime and Coastguard Agency *Bristow Helicopters*Bond Helicopters -Incidents and accidents:...
Shetland Islands
Shetland Islands
Shetland is a subarctic archipelago of Scotland that lies north and east of mainland Great Britain. The islands lie some to the northeast of Orkney and southeast of the Faroe Islands and form part of the division between the Atlantic Ocean to the west and the North Sea to the east. The total...
returning workers for the Brent oilfield
Brent oilfield
The Brent field is an oil field located in the East Shetland Basin north-east of Lerwick, Shetland Islands, Scotland at the water depth of . The field operated by Shell UK Limited was once one of the most productive parts of the UK's offshore assets but is now nearing the end of its useful...
. At 2.5 miles (4 km) from the runway the helicopter had a catastrophic forward transmission failure which de-synchronised the twin rotor
Helicopter rotor
A helicopter main rotor or rotor system is a type of fan that is used to generate both the aerodynamic lift force that supports the weight of the helicopter, and thrust which counteracts aerodynamic drag in forward flight...
s causing the blades to collide. The helicopter crashed into the sea and sank.
History
The helicopter was normally based at Aberdeen AirportAberdeen Airport
Aberdeen Airport is an international airport, located at Dyce, a suburb of Aberdeen, Scotland, approximately northwest of Aberdeen city centre. 2.76 million passengers used Aberdeen Airport in 2010, a reduction of 7.4% compared with 2009, making it the 15th busiest airport in the UK...
but had been based at Sumburgh Airport since 3 November 1986 to operate a shuttle service from the Brent oilfield in the East Shetland Basin
East Shetland Basin
The East Shetland Basin is a major oil-producing area of the North Sea between Scotland and Norway.Oil produced there is landed at Sullom Voe Terminal in the Shetland Islands.-See also:*Energy policy of the United Kingdom...
. On 6 November the first flight was delayed due to an oil leak from an engine gearbox but was soon rectified and the aircraft left Sumburgh at 08:58 with 40 passengers for the Brent Field. The aircraft visited three platforms with exchanges of freight and passengers then departed Brent Platform C at 10:22 with 44 passengers on board for return to Sumburgh Airport. It transited at a height of 2500 feet (762 m), and as it approached Sumburgh it was cleared to descend to 1000 feet (304.8 m). Reporting 4.5 miles (7.2 km) from the airfield, the controller cleared it to land on helicopter runway 24. Nothing else was heard.
Accident
The crew noticed an increased noise level in the flightdeck followed by a bang. Despite applying full cyclic pitch control the aircraft did not respond and nose-dived towards the sea from a height of 150 feet (46 m). The helicopter hit the sea, broke up and sank. A CoastguardHer Majesty's Coastguard
Her Majesty's Coastguard is the service of the government of the United Kingdom concerned with co-ordinating air-sea rescue.HM Coastguard is a section of the Maritime and Coastguard Agency responsible for the initiation and co-ordination of all civilian maritime Search and Rescue within the UK...
search and rescue helicopter which had just departed Sumburgh Airport reported liferafts in the sea. It then observed a survivor clinging to a substantial piece of wreckage. While they winched the man on board another survivor was noted amongst the floating bodies. With no signs of other survivors the Coastguard helicopter flew the survivors to Lerwick for transfer to hospital. An air and sea search failed to find any more survivors but all the floating bodies were recovered to the airport.
Recovery
A diving support vesselDiving support vessel
A diving support vessel is a ship that is used as a floating base for professional diving projects.Commercial Diving Support Vessels emerged during the 1960s and 1970s when the need arose for diving operations to be performed below and around oil production platforms and associated installations in...
, the MSV Deepwater, started a search for the sunken wreckage at 09:00 the following morning. Sea conditions were rough and the depth of water around 90 metres but the wreckage was located and the cockpit voice recorder
Cockpit voice recorder
A cockpit voice recorder , often referred to as a "black box", is a flight recorder used to record the audio environment in the flight deck of an aircraft for the purpose of investigation of accidents and incidents...
and the cockpit section of the fuselage was recovered. By the evening of 10 November most of the aircraft wreckage had been recovered.
Cause
The accident was caused by the failure of a modified bevel ring gear in the forward transmission which allowed the twin rotors to collide when synchronisation was lost. The Air Accidents Investigation BranchAir Accidents Investigation Branch
The Air Accidents Investigation Branch investigates air accidents in the United Kingdom. It is a branch of the Department for Transport and is based on the grounds of Farnborough Airport near Aldershot, Rushmoor, Hampshire.-History:...
(AAIB) stated that the underlying causes were the inadequacy of a previously accepted test program and the failure of a stringent inspection programme.
Safety recommendations
The board made three recommendations:- Certification procedures be reviewed so that all modifications to vital components are adequately scrutinised and tested before approval and more closely monitored after their introduction into service.
- The Civil Aviation AuthorityCivil Aviation AuthorityThis is a list of national and supra-national civil aviation authorities.-See also:* Air route authority between the United States and the People's Republic of China* National Transportation Safety Board -External links:****...
should report on the progress that has been made towards the early incorporation of a specification for suitable condition monitoring systems into airworthiness requirements for helicopters and indicate the time scale and scope of likely developments.
- Requirements relating to the ADELT (Automatically Deployable Location Transmitter) equipment, including location, crashworthiness, protection and power supplied, be reviewed in the light of the accident. (The beacon did not operate due to impact damage to the aft part of the aircraft).
Aftermath
The oil industry decided that the Chinook was too big for the offshore support task and the remaining Chinooks were withdrawn and sold. All surviving aircraft now operate with Columbia HelicoptersColumbia Helicopters
Columbia Helicopters, Incorporated, or CHI, is an aircraft manufacturing and operator company based in Aurora, Oregon, United States. They are known for operating tandem rotor helicopters; in present times, exclusively the Boeing Vertol 107 and Boeing 234. These helicopters are used in...
in heavy lift, non-passenger capabilities.