The Boeing 767-300F that overran runway 30 at Miami on 6 September crossed the threshold at 105ft – twice the typical height – and touched down 3,750ft beyond it, according to preliminary National Transportation Safety Board data.

Runway 30 spans 9,360ft, but a displaced threshold of 945ft means the 21 Air twinjet landed roughly halfway down the available pavement. Groundspeed at touchdown was 160kt, recorded 13s after the aircraft passed the threshold.

The aircraft did not immediately settle on its landing gear. The weight-on-wheels sensor switched "intermittently" between 'air' and 'ground' for about 7s, the inquiry states. Only once the sensor achieved a stable 'ground' status did 2,730ft of runway remain.

Flight-data recorder information shows the speedbrakes stayed stowed, with no change in the speedbrake handle position, and the thrust-reversers did not deploy. Investigators have yet to confirm how the alternating air-ground status affected the aircraft's systems.

Braking interrupted by go-around attempt

The crew manually applied wheel brakes at 146kt groundspeed, but released the pedals 8s later at 120kt, when the thrust levers were advanced to go-around power with just 930ft of runway left. Flaps, which had been set to 30° about 10s before touchdown, began retracting to 25°.

Four seconds later, at 117kt, the thrust levers were retarded to idle and the brakes were re-applied. By then only 415ft of runway remained. The jet overran at 113kt.

It struck the localiser and approach lighting system at the far end of the runway and travelled 1,200ft beyond the paved surface. During that run it hit a van carrying seven occupants on the perimeter road, fatally injuring five of them. The aircraft then broke through a perimeter fence, crossed a highway and struck a sports utility vehicle, seriously injuring its sole occupant, before coming to rest next to a parking lot.

Both pilots, the only people on board, escaped with minor injuries.

Crew experience

The captain, who was the flying pilot, had held a 767 type rating for about four months at the time of the accident. He had logged roughly 150h on the model across the five months since 21 Air hired him. The first officer had been type-rated on the 767 for about 17 months and had 800h on type.

The aircraft was operating a service from San Juan on behalf of retailer Amazon. Amazon suspended operations with 21 Air in the wake of the accident.

The NTSB has not reached conclusions on the occurrence. It says the analysis will include an aircraft performance study to "refine" the sequence of events and assess the physical state of the aircraft during the approach and landing. The question of whether the intermittent air-ground signal delayed spoiler, brake and reverser activation – and how much stopping distance that cost on a runway already half-consumed at touchdown – will be central to that work.