On 3 May 2012, a Sikorsky S76C (G-WIWI) being operated on a passenger charter flight from the London Heliport at Battersea to a private landing site at Peasmarsh discontinued an initial night approach at destination in Instrument Meteorological Conditions (IMC) but during the subsequent manoeuvring for a second attempt at a visual transition almost descended into terrain before climbing away and diverting without further event to a licensed aerodrome.
A Field Investigation was carried out by the UK AAIB. The event was not appropriately reported to the Operator and notification of it as a Serious Incident was delayed accordingly. The Investigation was provided with Flight Data Recorder (FDR) data from the CVFDR fitted to the helicopter but the voice data from this recorder had been overwritten. The Non Volatile Memory of the Honeywell MKXXII EGPWS fitted was a useful source of data on the Alerts and Warnings generated during the event and the ground track at the time but data from the Digital Video Recording System (DVRS) which provides a recording of EFIS display screens, had been overwritten due to delay in the disclosure of the event.
It was noted that the 55 year old aircraft Commander was an experienced helicopter pilot with nearly 5000 hours on the S76 but that although the Co-pilot was also a qualified commander and with plenty of experience, he had only 185 hours on the S76.
The programme for the days flying involved positioning from the Operator's base at London Stansted to a private landing site at Peasmarsh, a small settlement just to the north west of the small town of Rye, to collect passengers, taking them to the London Heliport and waiting there until they were ready to return to Peasmarsh before positioning back to Stansted. Both pilots were familiar with the landing site at Peasmarsh. The Co-pilot had been PF for the initial positioning flight and had briefed that the MSA in the vicinity of Peasmarsh was 1250 feet amsl and that he intended to descend to this altitude slightly to the north-west of the landing site to gain visual contact with the ground and if this was achieved, he would then continue with a visual approach and land. The approach was executed as briefed.
The return flight from London took off at 2235 local time. The Commander was PF and had "assessed from the available information that the chances of being able to make a successful approach at Peasmarsh were good, but he retained Lydd (approximately 9nm to the ESE), as an alternate destination". It was reported that no formal briefing for the approach and landing had been given but the pilots had agreed that "they would follow the same routine for the arrival at Peasmarsh as they had done earlier". Initially, the flight proceeded in IMC at 2100 feet amsl below controlled airspace. The weather at Lydd was checked and had clearly deteriorated a little from earlier on. When asked by the Co-pilot what his plan was for the destination approach, the Commander said that he "intended to descend to 500 feet with the aim of achieving visual contact with the landing site" but the Co-pilot did not query on what datum the 500 feet value was to be based and assumed that it would be above the highest obstacle near the site.
The flight proceeded with the AP engaged towards an FMS waypoint inserted at 3 nm west of the landing site. This position had been chosen because an approach from the west would provide the best view of both the lit helipad in the north east corner of a large field surrounded by mature trees and a triangular arrangement of three lights in the middle of the field. Approaching it, forward visibility was sufficiently limited to require flying on instruments although the Commander "recalled that the Co-pilot had stated he had visual contact with the ground beneath". He reported having set 600 feet on the altitude pre-select, begun a descent towards Peasmarsh using the FD and AP and selected the landing gear down. The Co-pilot subsequently recalled "informing the commander of his concerns that the helicopter was below the safety altitude without sufficient visual references" but had taken the view that "rather than pressing this point, his better option was to support the commander as effectively as he could, even though he believed that the commander’s actions were flawed".
Ground contact remained intermittent as the descent continued and forward visibility was poor. The Co-pilot reported having focussed his attention on his flight instruments and moving map display so as to give a running commentary of height, speed and the distance to run to the landing site. The Co-pilot stated that he had become aware that at 350 feet agl, the landing site was only about 30 seconds flying time away. During a subsequent interview, he recalled that at this point they were still “in the bottom of the cloud” and that he had considered calling for a go around or taking control of the helicopter to do so himself. Soon afterwards, the Commander caught sight of the landing site but assessed that the helicopter was too high and too fast to continue the approach straight in. As they flew over the site at approximately 300 feet agl and 35 KIAS, the Commander noted that the driver who was meeting the passengers had parked his car near the helipad. He was able to see the lights of the small town of Rye about 3nm away and it appeared that towards Lydd on lower terrain, the visibility was rather better and the cloud base higher.
He decided to maintain height whilst making an orbit to the right to position for a further approach from the west and disconnected the AP. He reported having been flying by a combination of reference to the instruments and outside cues but as the helicopter turned through a westerly heading, it began to descend and an Terrain Avoidance and Warning System (TAWS) 'CAUTION TERRAIN' occurred followed by a 'WARNING TERRAIN' as it approached 100 feet agl. but neither pilot recalled being aware of these activations at the time.
After a brief climb, a further descent occurred and the Commander recalled seeing the three lights in the middle of the field "begin to flicker". The Co-pilot, who was monitoring his instruments, saw that the helicopter was descending and reported beginning to speak to highlight this when he saw the radio altimeter “winding down towards zero extremely quickly” but found himself momentarily unable to continue, expecting the helicopter to crash.
Simultaneously, the commander reported realising that the lights were flickering because his view of them was becoming obstructed intermittently by the tops of the trees around the field and commenced an 'aggressive' climb by rolling level, making cyclic control inputs to arrest the rate of descent, pitching to 20°nose-up and raising the collective lever to apply 'blowaway' or maximum power. A rate of climb of 1300 fpm was achieved within six seconds. It was considered that the Commander’s control inputs were "swift, aggressive, and co-ordinated". As the recovery commenced, both pilots heard an Terrain Avoidance and Warning System (TAWS) 'TAIL TOO LOW' Warning. It was noted from the Non Volatile Memory data downloaded from the EGPWS computer that this Warning occurred only 20 seconds after the WARNING TERRAIN which both pilots had been unaware of. The minimum radio height recorded was 2 feet agl to a accuracy of +/- 2 feet.
The recovery climb was continued into IMC and a diversion to Lydd completed without further event. The helicopter was then positioned back to Stansted where they went into an office and completed post-flight paperwork which did not include an ASR or MOR.
The EGPWS GPS ground track of the Helicopter during the go around and subsequent descent to near ground impact in light blue - returns from radar for the initial arrival from the west and the go around and eventual departure to the north are shown in dark pink.. [Reproduced from the Official Report]
No indication was found that there had been any "unusual pressure… to complete the proposed series of flights should conditions prove unfavourable" had been placed upon the pilots by their employer, the passengers or anybody else.
It was noted that during the orbit for a second approach, the helicopter had "turned towards higher ground, worse weather and less cultural lighting". As the orbit continued with the commander’s visual references reduced to the triangle of lights in the centre of the field, it was considered that maintaining both orientation and situational awareness would have become challenging. It was surmised that the descent close to the ground during the orbit could have been a result of intentional control inputs by the commander in an endeavour to remain visual below a lowering cloud base or alternatively the result of degraded spatial awareness.
No technical reason could be found to explain how EGPWS warnings could be recorded without being presented to the pilots. If the audio inhibit switch had been selected prior to the approach, then no audible warnings would have been issued but neither pilot believed that the inhibit switch had been selected and both had recalled hearing the 'TAIL TOO LOW' Warning. It was considered that "the earlier audible alerts may have also been announced, but not ‘heard’ by the pilots, because of inattentional deafness or the effects of overload on the pilots’ capacity to process auditory cues". However, since the 'WARNING TERRAIN' annunciation had bee followed temporarily by a climb, it was considered possible that either they had assimilated and reacted to the EGPWS warnings, but later did not recall doing so, or that the commander became aware of the close approach to terrain independently of the warning and had begun to react to avoid it at the same time the warning was issued.
It was found that the Operator had its main base at Oxford and operated a small fleet of Eurocopter EC135/EC155 and Sikorsky S76 helicopters from various UK bases. Although the minimum flight crew for an S76 for both for Visual Flight Rules (VFR) or Instrument Flight Rules (IFR) operations is one pilot, the Operator "habitually operated the helicopter with two pilots". The helicopter was certified for flight by day and night and under VFR and IFR.
The Company Operations Manual, which had been "accepted" rather than "approved" by the UK CAA, "did not contain specific procedures for operations at private landing sites". "A senior company official" stated that the "recognised procedure" for landing at a private landing site after an en route transit in IMC above MSA was "to descend to MSA approaching the site and only continue to land if sufficient visual references can be identified". This source further advised that this "recognised procedure" also included the expectation that "if visual contact is not gained, the crew should either continue to their alternate (normally a licensed airfield with instrument approach aids) and make an instrument approach or remain at or above MSA until visual conditions prevail and a visual descent and approach can be carried out".
The Investigation noted that although helicopter EGPWS does incorporate a database of runways which allows 'nuisance' annunciations to be disabled, private landing sites such as that where the event occurred are not included. No mention of visual EGPWS annunciations could be found in the Operations Manual but it did say that "when operating in IMC or at night or in conditions of impaired visibility…..pilots are to be familiar with the corrective actions to be taken in the case of an audio warning" and provided a table of responses such as "reduce rate of descent" in response to a "PULL UP" Warning. No guidance was provided as to the expected response in the event of ‘look ahead’ alerts such as the ‘CAUTION TERRAIN’ and ‘WARNING TERRAIN’ annunciations which occurred during the event.
The formal Conclusion of the Investigation was as follows:
"The descent from above the minimum safe altitude was conducted in reduced visibility and low cloud conditions into an area with limited visual references. The helicopter was therefore brought close to terrain in an environment in which situational awareness could become degraded easily.
The decision to execute an orbit around the landing site, in the circumstances pertaining, further increased the chances of situational awareness becoming degraded, whilst the helicopter was at low height above unlit and undulating terrain.
In the course of the orbit, the commander became spatially disorientated and the helicopter descended towards the tops of trees. Although the EGPWS issued warnings that the helicopter was approaching contact with the ground, the flight crew were not aware of these warnings."
One Safety Recommendation was issued as a result of the Investigation as follows:
- that the Civil Aviation Authority review the regulations that permit a helicopter engaged in public transport operations to descend below MSA for the purpose of landing, when flying in instrument meteorological conditions but not on a published approach procedure.[2014-35]
The Final Report was published on 11 December 2014.