On 23 August 2013, a Eurocopter AS 332 L2 Super Puma helicopter being operated by CHC Scotia on a contract commercial passenger flight from the Borgsten Dolphin drilling platform to Aberdeen was about to complete a non precision approach to runway 09 at Sumburgh in day Instrument Meteorological Conditions (IMC) when, already below the applicable instrument approach minima, a sudden and rapid descent from low altitude occurred which resulted in the helicopter striking the sea surface about 1.7nm west of the airport. The airframe became inverted on impact but remained afloat. Four of the 18 occupants died and 14 survived, three of whom, including the aircraft commander, sustained serious injuries. The airframe subsequently broke up and became partially submerged.
The track of the accident flight (in red) and the two preceding ones (in yellow)[Reproduced from the Official Report]
An Investigation was carried out by the UK AAIB. Recovery of significant parts of the wreckage including the tail boom containing the Combined Voice and Flight Data Recorder (CVFDR) was completed on 29 August. The CVFDR was found to contain a complete record of the accident flight and some items of avionics equipment, identified as containing potentially useful Non Volatile Memory content were retrieved from the recovered wreckage and their data recovered. A radar record of the approach was available which was found to continue until just before impact.
It was found that the 51 year-old aircraft commander had 10,504 total flying hours which included 1894 hours on type. He had been employed by CHC on offshore operations for 16 years and was familiar with operations into Sumburgh. The 40 year old First Officer was found to have joined CHC just over a year earlier following experience flying small single-engine, single pilot helicopters and had qualified as a line pilot on the accident type in late February 2013.
It was established that the aircraft had been en route from the Borgsten Dolphin Platform to Aberdeen and had been planning to land at Sumburgh only to refuel. On nearing Sumburgh, it had been radar vectored onto the final approach track for the LOC/DME approach to runway 09 (see the corresponding chart included below). The Sumburgh Airport weather conditions passed to the crew by ATC half an hour prior to the accident were a surface visibility of 2800 metres in mist and cloud SCT/200 feet and BKN/300 feet and these were found to correspond to the conditions promulgated in the METAR timed three minutes after the accident had occurred. The aerodrome elevation was noted as being 21 feet amsl.
It was established that the aircraft commander had been PF for the accident flight and had flown the approach entirely in IMC with the AP in 3-axes using V/S Mode. MDA for the approach was 300 feet. It was found that "although the approach vertical profile was maintained initially, insufficient collective pitch control input was applied by the commander to maintain the approach profile and the target approach airspeed of 80 kt". As a result, insufficient engine power was available and airspeed reduced continuously as the approach continued. Despite the First Officer's 100 above (MDA) call and automated CHECK HEIGHT call outs at MDA both verbally acknowledged by the commander, descent continued below MDA. As airspeed continued to reduce, the First Officer "drew the commander's attention to the airspeed which was now about 35 knots and the helicopter was descending at 1000fpm". The commander acknowledged and "began to increase the collective" but shortly after the automated 100 feet above the surface automated call out had occurred, control was lost and water impact at around 1800 fpm occurred. Shortly before impact, the First Officer armed the helicopter's Emergency Floatation System so that although it had "rolled upside down and rapidly filled with water" on impact, it had remained afloat. The four fatalities included two who "did not escape from the upturned fuselage" and two died before being rescued.
Both pilots were interviewed during the Investigation but “neither pilot was able to explain exactly what had happened during the latter stages of the approach to Sumburgh, nor why it had happened". The Commander "stated he had no recollection of events between the time the helicopter passed 4 DME and just before impact, when he caught sight of the sea surface and attempted a recovery" and that "it had been his intention to carry out up to two approaches at Sumburgh and then decide on where to divert". The Investigation found that during the accident flight, there was "no attempt to obtain an up-to-date weather report for Scatsta, the nominated alternate airport, or any other potential alternate airport during the accident sector, even though the weather at Sumburgh was deteriorating" and that "the approach was commenced without the crew having established that there was an available alternate with acceptable weather" when in fact, the nominated alternate, Scatsta was no longer viable due to poor weather conditions. However, the Investigation did subsequently estimate that the helicopter had had sufficient fuel available at the time of the accident to reach Wick or Kirkwall (although not Inverness or Aberdeen). At that time, the weather conditions at Wick were favourable for a diversion.
The Sumburgh LOC/DME Approach Chart used by the accident aircraft crew[Reproduced from the Official Report]
Noting that, although the First Officer had raised the possibility of a diversion due to the deteriorating weather at Sumburgh, the Investigation found that the Commander had "expressed several times the view that a diversion would not be necessary and they were likely to be landing at Sumburgh" which, it was considered, "suggests that, despite his earlier briefing, he had not formulated an alternative plan and his focus had narrowed to landing at Sumburgh". The possibility that there was any previous case of the Commander continuing an onshore approach to land in weather below the applicable approach minima was examined and it was found that during the year preceding the accident, there was no evidence of this in respect of his 29 approaches to Sumburgh or his 267 approaches to Aberdeen.
The Investigation noted that the First Officer had stated after the accident that "he did not consider that he had received training on the specific duties of the Pilot Not Flying (PNF) in respect of how to monitor the progress of an approach, or of how to monitor the other pilot during an instrument approach". He had also stated that "he considered that he had not received guidance as to when, as PNF, he should look outside during an approach to acquire the visual references required for landing".
Having established that there was "No evidence....of a causal or contributory fault with the helicopter either before or during the accident flight" the Investigation focussed on the operational aspects and the post crash response. A review of the recorded flight data by the helicopter manufacturer concluded that the loss of control had been a direct consequence of combination of a nose-high attitude, low airspeed, high rate of descent and high power which had placed the helicopter in a Vortex Ring entry condition (also known as “settling with power”). The Investigation concurred with this explanation of the loss of control and noted that, given the limited height available at that point, recovery to controlled flight would have been "difficult, if not impossible".
It was noted that the helicopter was not fitted with a GPWS/TAWS, nor was it required to be. It was also noted that similar helicopter types operating in the UK Offshore sector, such as the Airbus Helicopters EC225, were fitted with a Honeywell Mk XXII EGPWS compliant with the applicable RTCA/DO-309 standard for 'HTAWS' and certified by EASA.
Operation of the helicopter at the time of the accident was noted as having been subject to an AOC issued under JAR-OPS 3 with oversight of the Operator being the sole responsibility of the UK CAA who, in that capacity, had therefore approved the CHC Operations Manual (OM). The Investigation found variously that:
- The OM did not provide a sufficiently detailed description of how to carry out a Non-Precision Approach and evidence from FDM data indicates that a variety of techniques were used by pilots.
- The Commander’s decision to fly the Non-Precision Approach using a reducing airspeed meant that there were two parameters changing during the approach. These were: a) the vertical speed, controlled through the autopilot, and b) the airspeed, controlled through manual collective pitch adjustment. This method increased the risk that any significant period of inattention to either parameter would lead to an undesired approach profile.
- At the time of the accident, the operator’s SOPs did not mandate the use of 4-axes mode for Non-Precision Approaches, but provided the crew with a choice as to whether to use 3-axes or 4 axes modes. The use of automation was therefore not optimised and this safety barrier was ineffective.
- The evidence suggests that the appropriate flight instrument displays were not being monitored adequately in the latter stages of the approach. There is evidence from similar accidents to both fixed wing and rotary wing aircraft, with both highly automated and non-automated flight decks, that pilot monitoring of the airspeed in particular, can be overlooked. While there are potential technological solutions to this problem (for example, low energy alerting systems, as recommended by the NTSB) improved pilot training may also be beneficial.
- In respect of SOPs, the operator identified, in their SMS, the need to ‘maintain procedures for allowing the comparison of standard operating procedures (SOPs) with those actually achieved in everyday line flight’, but it had not implemented an effective method for achieving this. Thus, there was limited evidence to confirm that SOPs were complied with routinely during everyday line operations.
- The fact that an aircraft manufacturer can make a significant input into the operating procedures for their aircraft is reflected in the certification requirements for fixed wing aircraft, which require manufacturers to provide comprehensive operational guidance in the form of an FCOM or similar. Given that the use of appropriate autopilot modes to manage the flight path of the helicopter is a factor in this accident, more comprehensive information from the manufacturer on how the helicopter should be operated has the potential to provide more adequate and effective SOPs. The Rotorcraft Flight Manual (RFM) for the accident helicopter did not provide information and guidance for the use of the autopilot system fitted to the helicopter and neither was it an airworthiness requirement. At the present time, out of the large public transport helicopter types, only the EC225 has a manufacturer-provided FCOM.
- At the time of this accident, North Sea helicopter operators had in place voluntary Operational Flight Data Monitoring (OFDM) programmes. Such a programme was also found to be a contractual requirement of some of its clients. There was no regulatory requirement at the UK or European level for such programmes. Although the coverage of the CHC OFDM programme was considerable, it was found not to monitor day to day performance in respect of a number of operating standards which had been central to the progress towards loss of control on the investigated approach.
In respect of the accident sequel - the evacuation of the occupants and survivability issues generally, the Investigation found that whilst the water impact was survivable, different specifics had led to the four fatalities:
- one had died in the life raft from a chronic heart condition which was probably exacerbated by the stress of the evacuation.
- one had managed to escape from the helicopter cabin but drowned prior to, or immediately after, reaching the surface of the water.
- one had been incapacitated by a head injury during or immediately following the impact with the water probably drowned without regaining consciousness.
- one had died as a result of being unable to successfully escape from the cabin.
In respect of those who evacuated successfully and survived, it was found that:
- The EBS hybrid re-breathers worn by the passengers functioned correctly but were not used by most of them either because they were unaware of the air supply that was available within them, or because they were unable to locate or deploy the mouthpiece.
- Passengers exited the cabin through window openings. A number of window panes were displaced during the initial impact and others were removed by the passengers. The majority of passengers who removed window panes reported that this was not easy and was significantly harder than they experienced during training.
- There had been a significant delay (almost an hour) in arrival on scene of the airport 'Fast Rescue Craft' due to launching complications although this had not affected the outcome of the rescue due to the arrival of SAR helicopters on the scene which were used to winch all the survivors on board and transfer them to a casualty reception centre at the airport.
The Investigation formally identified the following Causal Factors:
- The helicopter’s flight instruments were not monitored effectively during the latter stages of the non-precision instrument approach. This allowed the helicopter to enter a critically low energy state, from which recovery was not possible.
- Visual references had not been acquired by the Minimum Descent Altitude and no effective action was taken to level the helicopter, as required by the operator’s procedure for an instrument approach.
In addition, the following four Contributory Factors were identified:
- The operator’s SOP for this type of approach was not clearly defined and the pilots had not developed a shared, unambiguous understanding of how the approach was to be flown.
- The operator’s SOPs at the time did not optimise the use of the helicopter’s automated systems during a Non-Precision Approach.
- The decision to fly a 3-axes with V/S mode, decelerating approach in marginal weather conditions did not make optimum use of the helicopter’s automated systems and required closer monitoring of the instruments by the crew.
- Despite the poorer than forecast weather conditions at Sumburgh Airport, the commander had not altered his expectation of being able to land from a Non-Precision Approach.
The Investigation "determined that the causal and contributory factors identified in this accident are unlikely to be particular to this flight crew and therefore appropriate safety action should be taken in order to prevent future similar accidents".
Extensive Safety Action was taken on various issues highlighted by the Investigation whilst it was in progress by CHC Scotia, the UK CAA and Eurocopter (since renamed 'Airbus Helicopters') and is detailed at various points in the Official Report.
A total of 28 Safety Recommendations were made as a result of the Investigation as follows:
On 18 October 2013, two Recommendations were made as follows:
- that Highlands & 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. [2013-021]
- that the Civil Aviation Authority (CAA) review the risks associated with the current water rescue provision for the area of sea to the west of Sumburgh Airport and take appropriate action. [2013-022]
A further 26 Recommendations were made at the conclusion of the Investigation as follows:
- that the European Aviation Safety Agency introduces a requirement for instrument rated pilots to receive initial and recurrent training in instrument scan techniques specific to the type of aircraft being operated. [2016-001]
- that the European Aviation Safety Agency reviews the existing research into pilot instrument scan techniques, particularly with respect to glass cockpit displays, with a view to addressing shortcomings identified in current instrument scan training methods. [2016-002]
- that the Civil Aviation Authority reviews the methods used by UK North Sea helicopter operators for confirming compliance with their Standard Operating Procedures (SOPs), to ensure they are effective. [2016-003]
- that the Civil Aviation Authority reviews the Standard Operating Procedures of helicopter operators supporting the UK offshore oil and gas industry, to ensure their procedures for conducting Non-Precision Approaches are sufficiently defined. [2016-004]
- that the European Aviation Safety Agency amends the Certification Specifications for Large Rotorcraft (CS 29) to align them with the Certification Specifications and Acceptable Means of Compliance for Large Aeroplanes (CS 25), with regard to the provision of operational information in Flight Manuals. [2016-005]
- that the European Aviation Safety Agency requires manufacturers of Large Rotorcraft to develop Flight Crew Operating Manuals for public transport types already in service.[2016-006]
- that the Civil Aviation Authority expedites the requirement for companies operating helicopters in support of the UK offshore oil and gas industry to establish a Helicopter Flight Data Monitoring (HFDM) programme.[2016-007]
- that the European Aviation Safety Agency considers establishing a European Operators Flight Data Monitoring forum for helicopter operators to promote and support the development of Helicopter Flight Data Monitoring programmes. [2016-008]
- that the European Aviation Safety Agency collaborates with National Aviation Authorities and helicopter operators to develop and publish guidance material on detection logic for Helicopter Flight Data Monitoring programmes. [2016-009]
- that the Civil Aviation Authority, in co-operation with UK offshore helicopter operators, initiates a review of existing Helicopter Flight Data Monitoring programmes to ensure that operating procedures applicable to approaches are compared with those actually achieved during everyday line flights. [2016-010]
- that the Civil Aviation Authority expedites the publication of the Helicopter Safety Research Management Committee report into improving warning envelopes and alerts. [2016-011]
- that the Civil Aviation Authority supports the ongoing development of Helicopter Terrain Awareness Warning Systems, following the publication of the Helicopter Safety Research Management Committee report into improving warning envelopes and alerts. [2016-012]
- that the European Aviation Safety Agency requires the installation of Helicopter Terrain Awareness Warning Systems to all helicopters, used in offshore Commercial Air Transport operations, with a Maximum Certificated Take-off Mass (MCTOM) of more than 3,175 kg, or a Maximum Operational Passenger Seating Configuration (MOPSC) of more than nine, manufactured before 31 December 2018. [2016-013]
- that the European Aviation Safety Agency introduces a requirement for the installation of cockpit image recorders, in aircraft required to be equipped with Flight Data and Cockpit Voice Recorders, to capture flight crew actions within the cockpit environment. [2016-014]
- that the European Aviation Safety Agency introduces a requirement to install image recorders, capable of monitoring the cabin environment, in aircraft required to be equipped with Flight Data Recorder and Cockpit Voice Recorders. [2016-015]
- that the European Aviation Safety Agency instigates a research programme to provide realistic data to better support regulations relating to evacuation and survivability of occupants in commercial helicopters operating offshore. This programme should better quantify the characteristics of helicopter underwater evacuation and include conditions representative of actual offshore operations and passenger demographics. [2016-016]
- that, the European Aviation Safety Agency (EASA) applies, where technically feasible, the regulatory changes introduced by the EASA Rulemaking Task RMT.120 are applied retrospectively to helicopters currently used in offshore operations. [2016-017]
- that the European Aviation Safety Agency amends the Certification Specifications for rotorcraft (CS 27 and 29) to require the installation of systems for the automatic arming and activation of flotation equipment. The amended requirements should also be applied retrospectively to helicopters currently used in offshore operations. [2016-018]
- that the European Aviation Safety Agency amends the Certification Specifications for Large Rotorcraft (CS 29), certified for offshore operation, to require the provision of a side-floating capability for a helicopter in the event of impact with water or capsize after ditching. This should also be applied retrospectively to helicopters currently used in offshore operations. [2016-019]
- that the European Aviation Safety Agency amends the Certification Specifications for Large Rotorcraft (CS 29), certified for offshore operation, to ensure that any approved cabin seating layouts are designed such that, in an emergency (assuming all the exits are available), each exit need only be used by a maximum of two passengers seated directly adjacent to it. [2016-020]
- that the European Aviation Safety Agency amends the Certification Specifications for Large Rotorcraft (CS 29), certified for commercial offshore operations, to include minimum size limitations for all removable exits, to allow for the successful egress of a 95th percentile-sized offshore worker wearing the maximum recommended level of survival clothing and equipment. [2016-021]
- that the European Aviation Safety Agency amends the Certification Specifications for Large Rotorcraft (CS 29), certified for use in commercial offshore operations, to require a common standard for emergency exit opening mechanisms, such that that the exit may be removed readily using one hand and in a continuous movement. [2016-022]
- that the European Aviation Safety Agency amends the operational requirements for commercial offshore helicopters to require the provision of compressed air emergency breathing systems for all passengers and crew. [2016-023]
- that the European Aviation Safety Agency (EASA) amends the operational requirements for commercial offshore helicopter operations, to require operators to demonstrate that all passengers and crew travelling offshore on their helicopters have undertaken helicopter underwater escape training at an approved training facility, to a minimum standard defined by the EASA. [2016-024]
- that the European Aviation Safety Agency amends the design requirements for helicopters to ensure that where life rafts are required to be fitted, they can be deployed readily from a fuselage floating in any attitude. [2016-025]
- that the European Aviation Safety Agency requires that, for existing helicopters used in offshore operations, a means of deploying each life raft is available above the waterline, whether the helicopter is floating upright or inverted. [2016-026]
Three Special Bulletins were published during the course of the Investigation to report progress - on 5 September 2013, 18 October 2013 and 22 January 2014 - and the Final Report was published on 15 March 2016.