Description

On 16 January 2013, an Augusta 109E helicopter (G-CRST) owned by Castle Air was being operated by Rotormotion on a daylight positioning flight from Redhill to Elstree under callsign Rocket 2 prior to an intended revenue charter flight was unable to land at the intended destination due to freezing fog. The pilot subsequently requested and received acceptance for a diversion to the London Heliport when nearby. Shortly afterwards, it hit the jib of a crane on a high rise building under construction and the main body of the aircraft fell, with attendant debris, to the ground where the impact triggered an explosion and fire. The sole occupant of the helicopter and one other person on the ground were killed and several others were seriously injured.

Investigation

An Investigation was carried out by the Aircraft Accident Investigation Branch (UK) (AAIB). ATC radar and R/T recordings, CCTV and the record of text messages to and from the pilot involved whilst airborne were obtained to assist. No CVR or FDR was fitted or required to be fitted to the accident helicopter. An AAIB Special Bulletin was published on 23 January 2013 to advise on the initial assembly of relevant evidence. Subsequently, it was concluded that there was no evidence of any technical defect which might have been causal or contributory to the accident outcome and as a result, this was considered "unlikely" and the Investigation focussed on the operational and regulatory context in which the collision had occurred.

It was established that the aircraft had left its base at Redhill Aerodrome south of London to position to Elstree aerodrome in north London despite pilot awareness of widespread freezing fog there and across the general area. Upon finding, after the 14 minute flight, that a landing at Elstree was not possible, the pilot had then set course for a return to Redhill via the London Eye on an ATC clearance “not above 1500 feet VFR or SVFR if required”. When asked by ATC almost immediately after accepting that clearance if he’d like an IFR clearance, he responded with “I have good VMC on top here, that’s fine”.

At this time, the just-issued weather report for London City Airport, about 10 nm to the east of the southerly track being flown, included a cloud base of 100 feet agl and a visibility of 700 metres. This was typical of the general aftercast for the London area at the time of the accident provided by the UK Met Office which stated that “much of the area was prone to widespread low cloud, poor visibility and patches of freezing fog" with "cloud bases...in the range of 100 feet to 400 feet agl at 0800 hrs and visibility...generally below 4,000 metres, with several areas of London…reporting freezing fog with visibility of approximately 700 metres.”

Four minutes later, abeam the London Eye at a radar-recorded altitude of 1570 feet amsl and having already asked about the possibility of diverting to the London Heliport at Battersea, the pilot had reported being able to see and identify his surface location and the adjacent River Thames as he approached the former Battersea Power Station and suggested he could “head down to (the river)” tracking southwest as a means of getting to Battersea. However, ATC instructed him to take up a hold on the river between Vauxhall and Westminster Bridges whilst they checked if the Heliport would be able to accept him. As the approved manoeuvring commenced with a right turn to head downriver again, a descent which reached approximately 570 feet amsl was begun before a climb back to approximately 770 feet amsl as Vauxhall Bridge was approached.

Having been assured by the controller working the helicopter that it was "visual with the river", the TWR controller at the Heliport agreed to accept the diversion and the pilot was so advised and cleared to go there along the river. By this time, almost at Vauxhall Bridge heading eastbound, the pilot began a 180° turn to the right whilst taking the frequency change to TWR at the heliport. A few seconds later, impact with the crane attached to a high rise building under construction approximately 275 metres from the south east end of Vauxhall Bridge occurred. This position was approximately 2 nm to the east north east of the London Heliport, the relative positions being shown on the first diagram below.

The radar-derived final part of the track of the helicopter on the right and the London Heliport at the lower left (the earlier northbound track towards Elstree is on the left). Reproduced from the Official Report

The final stages of the flight are shown in the second illustration taken from the Official Report and also based on radar track data.

The radar-derived final track and altitude of the final stages of the flight. Reproduced from the Official Report

The collision initially resulted in the separation of the helicopter’s main rotor blades from the main rotor head followed by damage to the fuselage structure above the cabin and then separation of the main rotor head and main gearbox from the upper fuselage. The latter fell to the ground separately from the rest of the helicopter. The vertical stabiliser and tail rotor separated from the tail boom as the cabin of the helicopter made contact with a building shortly before it hit the ground where the impact led to further extensive damage and a severe post-impact fire fed by the approximately 500kg of Jet A1 on board followed. Part of the crane boom also fell to the ground but the remainder was only partly severed. Impact of all falling items led to considerable collateral impact damage.

It was noted that eye witness evidence collected was generally consistent with the top of the crane and the top of the building to which it was attached being in and out of cloud around the time of the impact. Some witnesses claimed to have seen the helicopter flying 'in' the cloud or appearing to emerge from it. It appeared that the crane and/or the building to which it was attached could well have been in, or transiently obscured by, cloud at the time of the impact. CCTV footage also supported this probability.

It was also noted that a NOTAM was current in respect of the crane, identifying it as having a maximum height not above 800 feet amsl and “lit at night extending to 770 ft amsl”. Lighting only at night was in accordance with prevailing regulatory requirements. At the time of the accident, the crane was not in use and the crane jib was therefore parked in the 'minimum jib position' at a 65° angle above the horizontal giving a total height from the ground to the tip of the jib of 723 feet.

Analysis of all available evidence indicated that the helicopter had "struck the crane at a point where its separation from the building was approximately 105 ft." It was noted that the pilot was required to maintain separation of at least 500 feet from the building in accordance with Rule 5 of the UK "Rules of the Air Regulations" and that this must be achieved by means of a visual assessment of distance which is likely to vary between individuals. However, the view was taken that "105 ft is significantly less than 500 ft and was considered to be outside the bounds of variability" and that therefore "the pilot flew too close to the building not because he misjudged 500 ft separation but because he either did not see the building or because he disregarded Rule 5".

With the assistance of the helicopter manufacturer, the observed radius of the right hand turn made in order to begin the requested holding track eastbound along the river was compared with the maximum bank angle which was possible with the autopilot engaged. It was found that this turn had been "flown tighter than is possible by the autopilot, suggesting that it was flown manually". It was also concluded that the subsequent erratic height-keeping along the river indicated that the autopilot had not been used to control altitude at that point either.

The conduct of the pilot was reviewed in respect of his decision making and the use of text messaging whilst flying, including whilst flying manually. The purpose of the positioning flight from Redhill to Elstree was to pick up two passengers and take them to the north of England. The pilot was aware before departing that there was fog at Elstree and was considered to have had "a safe contingency plan" to return to Redhill. However, it was nevertheless concluded that there were two specific risks which invited explicit mitigation:

• The flight was likely to be conducted to a large degree above fog or cloud
• There was no instrument approach procedure at Elstree and any intention to descend to minimum safe altitude in cloud, while looking for a clear area into which the helicopter could descend further, would have involved the possibility of icing if entering visible moisture conditions’.

The later decision to divert to the London Heliport rather than return to Redhill which led to "increasingly challenging circumstances" on account of the prevailing adverse weather conditions relative to this intention was also considered. It was noted that after the pilot sent a text message to the client waiting at Elstree indicating his intention to return to Redhill, he received a reply pointing out that London Heliport was open which was immediately followed by his request to ATC to confirm this was the case. Once he knew that this option may be possible but ahead of confirmation, he had begun descent in conditions where "there was widespread freezing fog over London" and knowing that he "had been unable to see the heliport when he overflow it 14 minutes earlier" heading north. It was therefore considered likely "that he knew that the flying conditions he would encounter at low level would be close to the limits for flight under VFR". It was further noted that "the pilot did not know the current weather conditions at London Heliport when the helicopter began to descend. The fact that the heliport was open indicated only that there was at least 1,000 m visibility and a 600 ft agl cloud base". Circumstantial evidence that finding a hole to descend to the river and be able to hold over it clear of cloud once there was not straightforward was considered to have included an incursion into Restricted Area 157 and entry into Class A airspace when taking an indirect route rather than a direct track to a location which the pilot had claimed to ATC was in sight less than two minutes before the collision. It was concluded that the final minutes of the flight had been conducted in "conditions that were probably marginal for flight under Special VFR." Overall, it was considered that whilst it was unknown if the pilot had periodically reviewed his plan to proceed to the heliport, "he did not change his decision despite the increasingly challenging circumstances".

The question of airspace use requirements, air traffic service provision and information on obstructions in the context of achieving required lateral or vertical clearances from the latter was reviewed in depth. In respect of the responsibilities of a pilot on a Special VFR clearance, which by default the accident flight was obliged to operate when VFR conditions no longer existed, it was noted that “when operating on a Special VFR clearance, the pilot must ...remain at all times in conditions which enable him to determine his flight path and to keep clear of obstructions.” However, the practicalities of this in a complex and dynamic urban environment in which the combination of airspace access restrictions and the need to avoid obstructions was already potentially demanding was found to be in some respects questionable. It was noted that, although parts of central London were affected by airport safeguarding requirements, these were not intended to address issues relating to the presence of either temporary or permanent obstructions other than for airport safeguarding purposes. In this matter, it was concluded that "there is no effective system in place to anticipate the potential effects of new obstacles on existing airspace arrangements when the obstacles are outside safeguarded areas".

Relevant international developments in supporting the safe operation of helicopters over large urban areas were reviewed. NTSB recommendations in respect of HEMS operations in the USA and the FAA response to them were noted, in particular the FAA conclusion that "most of the safety issues identified applied equally to commercial passenger operations as they did to HEMS operations and that the majority of the proposed safety changes should be applied across the industry". However, it was noted that whilst the FAA regulatory response following this conclusion has been focused on improving pre flight operational risk assessment for all helicopter operations, their response on the fitting of Helicopter Terrain Awareness and Warning Systems (HTAWS), already required for turbine-powered fixed-wing aircraft with six or more passenger seats, has been limited to extending this requirement (with effect from April 2015) only to HEMS helicopters.

The Investigation concluded that changes similar to the FAA requirements on pre-flight risk assessment and VFR flight planning should be considered in relation to the decision to accept a flight, to continue operation in adverse weather conditions, to low level flight in the vicinity of terrain or obstacles and in the case of "short notice or en route changes to flight objectives and planning". It was considered too that a process such as the EHEST Pre-departure Risk Assessment Tool and in the particular case of the accident being investigated, the existence of a version applicable to single pilot passenger transport flights, might also have positive safety benefits. It was considered that the use of such a tool might have prompted the pilot of the accident helicopter to seek management approval before accepting the flight and that its use might also have resulted in the two elevated risk factors identified by the Investigation being recognised and corresponding risk-mitigation being put in place before any departure.

The Investigation also took the view that the case for restricting the requirement for HTAWS to HEMS operations was not clear given the circumstances in which this accident had occurred and that HTAWS may well be an equally beneficial safety improvement in respect of UK commercial helicopter operations.

In respect of any regulatory changes which would require action at the European level, there was a concern that whilst European regulations are routinely reviewed against those in the US for standardisation purposes, the process of rulemaking in Europe requires "a review and consultation period of typically five years or more prior to implementation" whereas "some of the changes made by the FAA are directly relevant to this accident and could provide immediate safety benefits".

The Investigation formally identified two Causal Factors relevant to the Accident:

1. The pilot turned onto a collision course with the crane attached to the building and was probably unaware of the helicopter’s proximity to the building at the beginning of the turn.
2. The pilot did not see the crane or saw it too late to take effective avoiding action.

One Contributory Factor was also identified:

• The pilot continued with his decision to land at the London Heliport despite being unable to remain clear of cloud.

Ten Safety Recommendations were made as a result of the Investigation as follows:

1. that the Civil Aviation Authority require UK Air Navigation Service Providers to assess the effect of obstacles, notified through the UK Aeronautical Information Regulation and Control cycle, on operational procedures relating to published VFR routes near those obstacles, and modify procedures to enable pilots to comply simultaneously with ATC instructions, and the Air Navigation Order and Commission Implementing Regulation (EU) 923/2012 as applicable. [2014-025]
2. that the Civil Aviation Authority require UK Air Navigation Service Providers to assess the effect of obstacles, notified through the UK Aeronautical Information Regulation and Control cycle, on operational procedures for controlling non-IFR flights within the Control Areas and Control Zones surrounding UK airports, and modify procedures to enable pilots to comply simultaneously with ATC instructions, and the Air Navigation Order and Commission Implementing Regulation (EU) 923/2012 as applicable. [2014-026]
3. that the Department for Transport implement, as soon as practicable, a mechanism compliant with Regulation (EU) 73/2010 and applicable to the whole of the UK for the formal reporting and management of obstacle data, including a requirement to report data relating to newly permitted developments. [2014-027]
4. that the Department for Transport remind all recipients of the Office of the Deputy Prime Minister Circular 01/2003 that they are requested to notify the Civil Aviation Authority:
   • whenever they grant planning permission for developments which include an obstacle
   • about obstacles not previously notified
   • about obstacles previously notified that no longer exist. [2014-028]
5. that the Scottish Government remind all recipients of Planning Circular 2/2003 that they are requested to notify the Civil Aviation Authority:
   • whenever they grant planning permission for developments which include an obstacle
   • about obstacles not previously notified
   • about obstacles previously notified that no longer exist. [2014-029]
6. that the Department for Transport implement measures that enable the Civil Aviation Authority to assess, before planning permission is granted, the potential implications of new en-route obstacles for airspace arrangements and procedures. [2014-030]
7. that the Civil Aviation Authority review Federal Aviation Regulations Part 135 Rules 135.615, VFR Flight Planning, and 135.617, Pre-flight Risk Analysis, to assess whether their implementation would provide safety benefits for those helicopter operations within the UK for which it is the regulatory authority. [2014-031]
8. that the European Aviation Safety Agency review Federal Aviation Regulations Part 135 Rules 135.615, VFR Flight Planning, and 135.617, Pre-flight Risk Analysis, in advance of the scheduled regulatory standardisation programme, to assess whether their immediate implementation would provide safety benefits for helicopter operations within Europe. [2014-032]
9. that the Civil Aviation Authority assess whether mandating the use of Helicopter Terrain Awareness and Warning Systems compliant with Technical Standard Order C194 or European Technical Standard Order C194 would provide safety benefits for helicopter operations within the UK for which it is the regulatory authority. [2014-033]
10. that the European Aviation Safety Agency assess whether mandating the use of Helicopter Terrain Awareness and Warning Systems compliant with Technical Standard Order C194 or European Technical Standard Order C194 would provide safety benefits for helicopter operations within Europe. [2014-034]

The Final Report of the Investigation was published 9 September 2014.

Related Articles

• Controlled Flight Into Terrain (CFIT)
• Freezing Fog
• Continuation Bias

Further Reading

• UK CAA AIC: P 067/2013, Helicopter Flight in Degraded Visual Conditions presents guidance to support better decisions about whether to fly when adequate visual reference may not be available given the handling characteristics of the helicopter and the pilots' own training and experience. Accident Example 6 in this AIC is an accident for which both a detailed summary article and access to the full Official Investigation Report are available on SKYbrary.