Helicopter pilots have one of the most demanding jobs in aviation.
The flying itself is usually totally hands-on, totally visual, involves flying relatively close to the ground during the en-route phase, and frequently involves flying extremely close to buildings or other obstructions on the approach to the destination landing point.
This was certainly true of the task for the pilot flying the Agusta Westland AW109E when it hit a crane over Vauxhall, just south-west of London's West End, at precisely 07:59:29 on 16 January.
The UK Air Accident Investigation Branch has just published an interim Special Bulletin releasing some of the facts established so far about the accident, but providing no analysis.
The weather was foggy over London below about 1,500ft and, at the time of the collision, the helicopter had been cleared to fly "not above 1,500ft", because that area of central London is beneath the main approach path to Heathrow airport. Crossing traffic has to stay low.
Back to the early morning before the flight:
The pilot, Capt Peter Barnes, reported to his base at Redhill aerodrome, at 06:30, knowing his task was to fly to Elstree aerodrome to pick up a client.
That entails a 20min flight more or less due north across central London. Barnes knew that Elstree was in freezing fog, but he made the decision to go and have a look anyway.
He knew he had some personal advantages on a day when the weather made his task a marginal one. He knew it would involve continual risk assessment, mainly because of the poor visibility at low level, but he was extremely experienced, fully capable of flying on instruments, and he was piloting a twin-engined aircraft with a cockpit equipped for IFR (instrument flight rules) flying.
On departure from Redhill for Elstree, air traffic control cleared him to fly across London "not above 1,000ft", on a track that would pass over Battersea heliport. He was flying under SVFR (special visual flight rules, which means "in sight of the surface and clear of cloud"). But in a text message he sent just after passing Battersea, he said "Can't see Batts", so we know he was not continuously in sight of the surface.
When he got to Elstree he made his first obvious risk-assessment decision: Elstree visibility was not good enough to land. He made the decision to return to Redhill, and asked for clearance to re-cross London. Thames Radar gave him permission to fly "not above 1,500ft" via the London Eye.
When the helicopter was established en route, flying south at 1,500ft, about 8min before the collision with the crane, ATC asked Barnes if he wanted an instrument flight rules (IFR) radar-guided transit, but he replied: "I have good VMC on top here, that's fine." VMC is visual meteorological conditions. In other words, he was flying above the fog with good visibility at that height and did not want help.
At 07:55, Barnes' client texted him: "Battersea is open".
In the same minute, Barnes texted back to base: "Can't get in Elstree hdg back assume still clear". Base texted back, still at 07:55, about 4min before the collision with the crane, "Yes its still fine here". That was the last text Barnes either sent or received, but ten texts altogether had been sent or received by Barnes during this flight.
Guessing what the client had in mind, Barnes asked ATC whether he could head to Battersea, and the controller told him he'd check and get back to him. At 07:57 Barnes told ATC: "I can actually see Vauxhall" and proposed that he could join the prescribed helicopter route along the Thames river. He was told: "Hold over the river for the minute between Vauxhall and Westminster bridges and I'll call you back."
The map below shows the remainder of the flight.
Barnes did not hold over the river in the area instructed but headed for a position on the river more or less where Battersea heliport is, and began descending from 1,500ft to an altitude below 1,000ft, going as low as 570ft. Over the river opposite Battersea, Barnes turned right in a loop through more than 180deg, and headed along the river to the east.
At 07:59:10 ATC called, clearing him to Battersea, and providing him with the frequency, 122.9mHz, to call the heliport. He never made the call.
Fatally, Barnes turned right to reverse his heading along the Thames, and tracked south of the river's southern bank into the area of high rise construction at St George's Wharf. This construction work had been accurately Notamed, so Barnes should have been aware of it, and probably was.
It would have been better if he had turned left, but the commander's seat in a helicopter is on the right side of the cockpit, so you can see better into the turn if you go right than left.
But at that point, in poor visibility, with a 180deg turn to carry out, a frequency change to make on his radio, the river and buildings to watch as he turned, and Battersea heliport to find visually, he was probably overloaded.
If Barnes had seen the crane in time he would not have hit it.
Witnesses on the ground testify that the top of the building and the crane were invisible in fog. The precise horizontal visibility at the height the helicopter was flying at impact is unknown and may remain so.
When the AAIB publishes its final report, expect to see expressions like "continued VFR flight into IMC" (instrument meteorological conditions). And although the pilot was not texting just before the accident, there may be some recommendations about the practice of communicating like this while flying, especially for a solo pilot.