Description

On 18 February 2009, a Eurocopter EC225 LP Super Puma being operated by Bond Helicopters on a scheduled passenger flight from Aberdeen to the Eastern Trough Area Project (ETAP) Central Production Facility Platform. Whilst en route, weather conditions at the platform deteriorated such that Instrument Meteorological Conditions (IMC) prevailed although there was some visual reference. A night visual approach was attempted during which the helicopter descended and impacted the surface of the sea. It remained upright in an estimated sea state 3 and all 18 occupants were able to evacuate into its liferafts prior to subsequent rescue. There were no injuries.

Investigation

An Investigation was carried out by the UK AAIB. The combined CVFDR was recovered and successfully replayed, making a significant contribution to the available evidence. Two Special Bulletins were issued in early stages of the Investigation.

It was established that the aircraft commander had been PF for the 132nm flight with the cruise being made at FL055 and the AP engaged in four-axis mode. On the basis of the initial destination weather report, the crew had decided to make an Non Precision straight in Airborne Radar Approach (ARA) commencing from an altitude of 1500 feet which had a MAP at 0.75 nm prior to the platform and an MDH of 300 feet on the radio altimeter. Shortly before reaching 1500 feet, Visual Meteorological Conditions (VMC) was regained and since the crew could what appeared to be the ETAP platform it was agreed to make a straight-in visual approach descending on the radio altimeter to a height of 300 feet as necessary to remain clear of any cloud.

Before reaching 1500 feet, the crew visually acquired the lights and flare of the ETAP platform at a range of about 20 nm and decided to make an en-route descent to a height of 300 feet to position the helicopter for a visual approach and landing. However, when low cloud was entered during the descent to 300 feet, a climb to 400 feet was all that was necessary to regain visual contact with the platform. A second descent to 300 ft was initiated at a range of 1.5 nm but, again, the helicopter entered low cloud and a climb was commenced. At 400 feet the platform lights and flare became visible again and the aircraft commander, remaining as PF, continued the approach.

He de-selected the upper modes of the AP at a range of approximately 0.75 nm and also de-selected the 150 feet radio altimeter height call out. Whilst manoeuvring left, the helicopter entered a continuous descent. The First Officer identified and called out the descent but no corrective action was taken. He also called out range and speed. Both pilots could see the platform flare and diffused lights but only the First Officer could see the green perimeter lights of the helideck. The PF became focussed on visually acquiring the helideck which was not visible to him. Neither pilot was aware of the continued descent and neither could see the oval shape defined by the perimeter lighting and so had no means of visually determining the approach path angle. The PF gradually pitched up in order to maintain what he thought was a constant approach angle using the visual picture of the platform relative to his windscreen.

The non-cancellable 100 ft height audio alert did not activate (and it was concluded that this was probably due to a malfunction of the GPWS/TAWS of which the pilots were unaware). The PF reported having had “the sensation that the helicopter was high and fast” and had therefore increased the pitch attitude and both pilots thought that the helicopter was still above the level of the helideck when it impacted the sea surface.

Very soon after thus, the helicopter impacted the surface of the sea with the last vertical acceleration reading on the Flight Data Recorder (FDR) just over 4g. It remained upright and the Helicopter Emergency Floatation Systems (EFS) deployed. With only the emergency exit lights illuminated, the PF located the engine control switches and selected them to ‘off’ whilst shouting to the passengers not to evacuate until the rotors had stopped. Evacuation into both life rafts was accomplished uneventfully.

It was considered that “it was probable that both pilots were subjected to the effects of oculogravic and somatogravic illusions possibly reinforced by the reflection of the platform lights in the surface of the sea”.

The Investigation noted that:

• there was no specified visual approach profile providing the crew with recommended range, height and rate of descent information for the approach.
• there were no minimum heights at which a go-around must be initiated..
• there was no specified procedure for the PM to monitor the approach using the flight instruments.
• The platform helideck lighting was in full compliance with the guidance contained in UK CAA CAP 437.
• The helideck perimeter lighting was visible from below the 166 feet elevation of the deck.
• The apparent GPWS/TAWS malfunction which prevented the 100 feet height alert sounding would also have prevented the 150 feet alert sounding had not been deselected anyway.
• survivable water impacts such as this highlighted various opportunities for safety improvement in respect the safe recovery of survivors.

Although recovered, the helicopter was declared a hull loss because of extensive damage caused by the impact, prolonged salt water immersion and additional damage sustained during the salvage operation.

It was established that the helicopter had been airworthy and there were no open ADDs which might have had a bearing on the accident. However, a transient false TAWS alert was noted as having occurred en route during the accident and it was noted that the ETAP Platform was not in the TAWS database.

The Investigation formally identified the following Causal Factors:

1. The crew’s perception of the position and orientation of the helicopter relative to the platform during the final approach was erroneous. Neither crew member was aware that the helicopter was descending towards the surface of the sea. This was probably due to the effects of oculogravic and somatogravic illusions combined with both pilots being focused on the platform and not monitoring the flight instruments.
2. The approach was conducted in reduced visibility, probably due to fog or low cloud. This degraded the visual cues provided by the platform lighting, adding to the strength of the visual illusions during the final approach.
3. The two radio altimeter-based audio-voice height alert warnings did not activate. The fixed 100 ft audio-voice alert failed to activate, due to a likely malfunction of the GPWS/TAWS, and the audio-voice element of the selectable 150 ft alert had been suspended by the crew. Had the latter not been suspended, it would also have failed to activate. The pilots were not aware of the inoperative state of the TAWS.

In addition, the Investigation also formally identified the following Contributory Factors:

1. There was no specified night visual approach profile on which the crew could base their approach and minimum heights, and stabilised approach criteria were not specified.
2. The visual picture on final approach was possibly confused by a reflection of the platform on the surface of the sea.

A total of 27 Safety Recommendations were issued as a result of the Investigation. Four of these were made during the Investigation and first published in Special Bulletin S4/2009 which was issued on 23 June 2009 as follows:

• that the Civil Aviation Authority review the carriage and use in commercial air transport helicopters of any radio location devices which do not form part of the aircraft’s certificated equipment.

[2009-064]

• that the Civil Aviation Authority advise the European Aviation Safety Agency of the outcome of the review on the carriage and use in commercial air transport helicopters of any radio location devices which do not form part of the aircraft’s certificated equipment.

[2009-065]

• that the European Aviation Safety Agency require manufacturers of Emergency Locator Transmitters (ELT(S)s)/Personal Locator Beacons (PLBs) units to add details, where absent, of the correct use of the antenna to the instructions annotated on the body of such beacons.

[2009-066]

• that the Civil Aviation Authority ensure that all aspects of Emergency Locator Transmitter (ELT(S))/Personal Locator Beacon (PLB) operation, particularly correct deployment of the antenna, are included and given appropriate emphasis in initial and recurrent commercial air transport flight crew training, as applicable.

[2009-067]

The remaining 23 were published at the conclusion of the Investigation:

• that the Civil Aviation Authority re-emphasises to Oil and Gas UK that they adopt the guidance in Civil Aviation Publication (CAP) 437, entitled Offshore Helicopter Landing Areas - Guidance on Standards, insofar as personnel who are required to conduct weather observations from vessels and platforms equipped for helicopter offshore operations are suitably trained, qualified and provided with equipment that can accurately measure the cloud base and visibility, in order to provide more accurate weather reports to helicopter operators.

[2011-049]

• that the Civil Aviation Authority encourages commercial air transport helicopter operators to make optimum use of Automatic Flight Control Systems.

[2011-050]

• that the Civil Aviation Authority ensures that commercial air transport offshore helicopter operators define specific offshore approach profiles, which include the parameters for a stabilised approach and the corrective action to be taken in the event of an unstable approach.

[2011-051]

• that the Civil Aviation Authority commissions a project to study the visual illusions that may be generated during offshore approaches to vessels or offshore installations, in poor visibility and at night, and publicises the findings.

[2011-052]

• that the Civil Aviation Authority (CAA) amends Civil Aviation Publication (CAP) 437 Offshore Helicopter Landing Areas - Guidance on Standards, to encourage operators of vessels and offshore installations, equipped with helidecks, to adopt the new lighting standard, for which a draft specification has been published in Appendix E of CAP 437, once the specification has been finalised.

[2011-053]

• that the Civil Aviation Authority reviews the procedures specified by commercial air transport helicopter operators as to when a crew may or should suspend a radio altimeter aural or visual height warning.

[2011-054]

• that the Civil Aviation Authority reviews commercial air transport offshore helicopter operators’ procedures to ensure that an appropriate defined response is specified when a height warning is activated.

[2011-055]

• that the Civil Aviation Authority reviews the procedures set out by commercial air transport offshore helicopter operators to ensure that a member of the flight crew monitors the flight instruments during an approach in order to ensure a safe flight path.

[2011-056]

• that the International Civil Aviation Organisation introduces a Standard for crash-protected recordings of the operational status of Airborne Collision Avoidance System (ACAS) and Terrain Awareness and Warning System (TAWS) equipment, where fitted, on helicopters required to carry a flight data recorder.

[2011-057]

• that the European Aviation Safety Agency requires that crews of helicopters, fitted with a Terrain Awareness and Warning System, be provided with an immediate indication when the system becomes inoperative, fails, is inhibited or selected off.

[2011-058]

• that the European Aviation Safety Agency reviews the acceptability of crew-operated on /off controls which can disable mandatory helicopter audio voice warnings.

[2011-059]

• that the Civil Aviation Authority reviews the guidance in Civil Aviation Publication (CAP) 562, Civil Aircraft Airworthiness Information and Procedures, Part 11, Leaflet 11-35, Radio Altimeters and AVADs for Helicopters, regarding the pre-set audio height warning that is triggered by the radio altimeter and may not be altered in flight, to ensure that crews are provided with adequate warning to take corrective action.

[2011-060]

• that the European Aviation Safety Agency ensures that helicopter performance is taken into consideration when determining the timeliness of warnings generated by Helicopter Terrain Awareness and Warning Systems.

2011-061

• that the European Aviation Safety Agency reviews the frequency of nuisance warnings generated by Terrain Awareness and Warning System equipment in offshore helicopter operations and takes appropriate action to improve the integrity of the system.

[2011-062]

• that the European Aviation Safety Agency, in conjunction with the Federal Aviation Administration, defines standards governing the content, accuracy and presentation of obstacles in the Terrain Awareness and Warning System obstacle database for helicopters operating in the offshore environment.

[2011-063]

• that the European Aviation Safety Agency establishes the feasibility of recording, in crash protected memory, status indications from each avionic system on an aircraft.

[2011-064]

• that the European Aviation Safety Agency considers amending certification requirements for rotorcraft, that are certified in accordance with ditching provisions, to include a means of automatically inflating emergency flotation equipment following water entry.

[2011-065]

• that the European Aviation Safety Agency modifies European Technical Standard Order (ETSO) 2C70a and ETSO 2C505 to include a requirement for multi-seat liferafts, that do not automatically deploy their Sea Anchor, to include a label, visible from within the inflated liferaft, reminding the occupants when to deploy the Sea Anchor.

2011-066

• that the Federal Aviation Administration modifies Technical Standard Order (TSO) C70a to include a requirement for multi-seat liferafts, that do not automatically deploy their Sea Anchor, to include a label, visible from within the inflated raft, reminding the occupants when to deploy the Sea Anchor.

[2011-067]

• that the European Aviation Safety Agency requires Eurocopter to review the design of the fairings below the boarding steps on AS332 and EC225 series helicopters to reduce the possibility of fairings shattering during survivable water impact and presenting sharp projections capable of damaging liferafts.

[2011-068]

• that the European Aviation Safety Agency, in conjunction with the Federal Aviation Administration, review the design requirements and advisory material for helicopters to require ‘delethalisation’ of the fuselage to prevent damage to deploying and floating liferafts following a survivable water impact.

[2011-069]

• that the European Aviation Safety ensures that a requirement is developed for all emergency equipment, stowed in deployable survival bags, to be capable of being easily accessed and utilised by the gloved hands of a liferaft occupant whilst in challenging survival situations when a liferaft may be subject to considerable motion in cold, wet and dark conditions.

[2011-070]

• that the European Aviation Safety Agency reviews the location and design of the components and installation features of Automatically Deployable Emergency Locator Transmitters and Crash Position Indicator units, when required to be fitted to offshore helicopters, to ensure the reliability of operation of such units during and after water impacts.

[2011-071]

An Investigation was carried out by the UK AAIB. It was established that the Final Report of the Investigation was published on 14 September 2011.

Further Reading

• Controlled Flight Into Terrain (CFIT)
• Helicopter Emergency Floatation Systems (EFS)
• Sea State
• Emergency Breathing Systems (EBS) for Offshore Helicopter Occupants
• Somatogravic and Somatogyral Illusions
• Vestibular System and Illusions (OGHFA BN)
• Terrain Avoidance and Warning System (TAWS)
• UK CAA CAP 437 Offshore Helicopter Landing Areas - Guidance on Standards, February 2013