The operator of the Battersea Heliport in London warned authorities of the danger of flying helicopters near a Thames River construction site four years before an AgustaWestland AW109 collided with a building crane in the St. George Wharf development on Jan. 16, 2013, according to the UK’s Air Accidents Investigation Branch. Cloud ceilings were low and visibility poor on the morning of the accident. The crash sent the fuselage plummeting to the street below during the height of the morning rush hour, killing both the pilot and a pedestrian.

While the pilot was cited as responsible for being unable to remain clear of clouds while flying near the tall buildings, the heliport operator had previously expressed concern to the UK’s Civil Aviation Authority that new high-rise developments along the Thames River represented a hazard to flight.

The crane and the building to which it was attached were not listed in the obstacle database available to the AW109 pilot on the morning of the accident.