This article gives an overview of the specific safety issues that arise from offshore helicopter operations and mitigation measures that are intended to increase the chances of survival in case of ditching.
The term “offshore operations” is used to describe situations where not only a part of the flight takes place over large bodies of water but when most of the flight, including the main objectives, are to be completed away from dry land. Driven by industry demand, the use of helicopters in offshore operations has increased greatly in the recent years. Because of their VTOL and hover capabilities, helicopters are often used to support:
Construction and maintenance of offshore wind farms;
Construction and maintenance of offshore oil and gas platforms;
Various ship operations;
Various authorities (e.g. coast guard).
The main offshore tasks performed by helicopters are:
Moving people to and from their workplaces on offshore facilities and vessels;
Search and rescue missions (e.g. it is often faster to send a helicopter to reach a person that has fallen overboard than to use the vessel they have fallen from).
There are a number of risks associated with offshore helicopter operations:
Offshore helicopter operations are often conducted in adverse weather.
Winds are generally stronger over water than over land, thus making the helicopter harder to control.
Offshore wind turbines pose a serious threat to helicopters due to their large moving rotor blades (with a length ranging from 30m to 50m).
High chance of ditching – many system malfunctions have the potential to result in a ditching.
VTOL capabilities are usually limited to helipads, which restricts one of the main inherent helicopter advantages.
Autorotation (which can otherwise be a very helpful safety feature) offers limited benefits compared to onshore situations.
Safety systems are often destroyed or disabled on impact.
Harsh conditions in water can easily cause a helicopter to capsize.
Harsh conditions and destroyed or disabled safety and rescue systems reduce the chances of survivors being saved.
Most fatalities are caused by drowning as occupants are often unable to leave the helicopter in time.
Research has shown that the main reasons for fatalities in offshore operations are drowning and exposure. Impact damage is usually survivable by the occupants. Therefore, the main focus when discussing safety improvement falls on the increase of post-impact survival rates. There are a number of mitigation measures that are already implemented or are being considered. The most notable of them are:
Use of floats – these are intended to keep the helicopter upright after ditching long enough to provide safe occupant egress.
Automatic activation of float systems upon sensing water immersion that would not require pilot interaction. During flight over water, the possibility the automatic float activation being disabled should be minimized.
Use of life-rafts and life jackets – these are intended to increase survivability after leaving the helicopter. Life-rafts should be externally deployable regardless of whether the aircraft is upright or inverted.
Use of standard, high-visibility fabric colours and contrasting stripes to assist aircraft search-and-rescue.
Tear-resistant fabric for float construction. Float bag design should provide a means to minimize the likelihood of tear propagation between compartments.
Hand-holds on the floats to supplement personal flotation, regardless of helicopter orientation. Handhold/life lines should be installed where practical and feasible to allow person to hold on to an upright or inverted rotorcraft.
Side floating helicopters concept – if the helicopter remains on its side, there are still doors and hatches above the water. Therefore, research is being done on systems that can prevent total inversion.
All apertures in the passenger compartment suitable for the purposes of underwater escape should be equipped so as to be usable in an emergency.
Emergency breathing systems – there are a number of systems that can provide a limited supply of oxygen to occupants that is supposed to be enough for them to safely egress a ditched (and inversed) helicopter. There are several issues however, e.g. these devices should be placed in such a way that they remain accessible in all situation but at the same time do not hinder occupant egress.
Accidents and Incidents
The following events in the SKYbrary database relate to offshore helicopter operations:
AS3B, vicinity Sumburgh Airport Shetland Islands UK, 2013: On 23 August 2013, the crew of a Eurocopter AS332 L2 Super Puma helicopter making a non-precision approach to runway 09 at Sumburgh with the AP engaged in 3-axes mode descended below MDA without visual reference and after exposing the helicopter to vortex ring conditions were unable to prevent a sudden onset high rate of descent followed by sea surface impact and rapid inversion of the floating helicopter. Four of the 18 occupants died and three were seriously injured. The Investigation found no evidence of contributory technical failure and attributed the accident to inappropriate flight path control by the crew.
EC25, vicinity Bergen Norway, 2016: On 29 April 2016, an Airbus H225 en route from an offshore platform to Bergen was in the cruise at 2,000 feet when the main rotor head and its mast suddenly detached after which it crashed on a small island. The wreckage caught fire before it ended up in the sea. All 13 occupants died. The continuing Investigation has already concluded that “the accident most likely was the result of a fatigue fracture in one of the second stage planet gears” although it has noted that “what initiated the fatigue fracture has not yet been determined”.
EC35, Sollihøgda Norway, 2014: On 14 January 2014, the experienced pilot of an EC 135 HEMS aircraft lost control as a result of a collision with unseen and difficult to visually detect power lines as it neared the site of a road accident at Sollihøgda to which it was responding which damaged the main rotor and led to it falling rapidly from about 80 feet agl. The helicopter was destroyed by the impact which killed two of the three occupants and seriously injured the third. The Investigation identified opportunities to improve both obstacle documentation / pilot proactive obstacle awareness and on site emergency communications.
A319 / AS32, vicinity Marseille France, 2016 (On 27 June 2016, an Airbus A319 narrowly avoided a mid-air collision with an AS532 Cougar helicopter whose single transponder had failed earlier whilst conducting a local pre-delivery test flight whilst both were positioning visually as cleared to land at Marseille and after the helicopter had also temporarily disappeared from primary radar. Neither aircraft crew had detected the other prior to their tracks crossing at a similar altitude. The Investigation attributed the conflict to an inappropriate ATC response to the temporary loss of radar contact with the helicopter aggravated by inaccurate position reports and non-compliance with the aerodrome circuit altitude by the helicopter crew.)
AS32 / B734, Aberdeen UK, 2000 (For reasons that were not established, a Super Puma helicopter being air tested and in the hover at about 30 feet agl near the active runway at Aberdeen assumed that the departure clearance given by GND was a take off clearance and moved into the hover over the opposite end of the runway at the same time as a Boeing 737 was taking off. The 737 saw the helicopter ahead and made a high speed rejected take off, stopping approximately 100 metres before reaching the position of the helicopter which had by then moved off the runway still hovering.)
AS32, en-route, North Sea Norway, 1998 (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 mistake was realised quickly enough for the crew to recover control of the helicopter.)
AS32, en-route, North Sea UK, 2002 (On 28th February 2002, an Aerospatiale AS332L Super Puma helicopter en route approximately 70 nm northeast of Scatsa, Shetland Islands was in the vicinity of a storm cell when a waterspout was observed about a mile abeam. Soon afterwards, violent pitch, roll and yaw with significant negative and positive ‘g’ occurred. Recovery to normal flight was achieved after 15 seconds and after a control check, the flight was completed. After flight, all five tail rotor blades and tail pylon damage were discovered. It was established that this serious damage was the result of contact between the blades and the pylon.)
AS32, en-route, near Peterhead Scotland UK, 2009 (On 1 April 2009, the flight crew of a Bond Helicopters’ Eurocopter AS332 L2 Super Puma en route from the Miller Offshore Platform to Aberdeen at an altitude of 2000 feet lost control of their helicopter when a sudden and catastrophic failure of the main rotor gearbox occurred and, within less than 20 seconds, the hub with the main rotor blades attached separated from the helicopter causing it to fall into the sea at a high vertical speed The impact destroyed the helicopter and all 16 occupants were killed. Seventeen Safety Recommendations were made as a result of the investigation.)
NIM / AS32, vicinity RAF Kinloss UK, 2006 (On 17 October 2006, at night, in low cloud and poor visibility conditions in the vicinity of Kinloss Airfield UK, a loss of separation event occurred between an RAF Nimrod MR2 aircraft and a civilian AS332L Puma helicopter.)