The UK Airprox Board investigated a drone near-miss reported by Boeing 737 near Stansted on 13 September 2015. Separation distance reported as 165 feet.
THE B737 PILOT reports passing 4000ft on departure from RW04 at Stansted when the First Officer saw a remotely piloted aircraft pass within 50m and overhead the aircraft by about 5m. The aircraft was purple in colour with a fuselage of about 2m in length, the crew were unable to tell whether it was jet powered or had prop blades. It went from the 12 o’clock position to the 1 o’clock position on a reciprocal track. The incident happened so quickly that there was no time to take avoiding action; however, there was no indication on the flightdeck of an impact. The incident was reported to ATC.
He assessed the risk of collision as ‘High’.
Operating as he was in airspace within which he was not permitted meant that the Board considered that the cause of the Airprox was that the drone operator had flown into conflict with the B737. Unsurprisingly, the incident did not show on the NATS radars and, therefore, the exact separation between the two air-systems was not known; however, the B737 pilot had estimated the separation to be 15ft vertically and 50m horizontally. Basing their assessment on this report, the Board determined that the risk was Category A, separation had been reduced to the minimum and chance had played a major part in events.
Aircraft: Boeing 737
Aircraft altitude: 4000 ft
Separation: 165 feet
Please note that separation distances are solely based on pilot’s judgements and not necessarily accurate since horizontal and vertical separation distances can be hard to judge.