Belgian investigators have disclosed that an SAS Airbus A320neo had accelerated to 127kt before aborting take-off from Brussels after its crew realised the aircraft was on a short taxiway.

Bound for Copenhagen at night on 5 February, the flight was running late – around 90min behind schedule – and as the crew prepared to taxi, they briefed the possibility of an intersection take-off from runway 07R rather than the full-length roll intended.

Initially the tower controller instructed the jet to taxi to the holding point near the threshold of 07R, by heading south on the Inner taxiway and turning right onto taxiway Z which runs parallel to the runway.

As the aircraft taxied, the crew again discussed requesting the intersection take-off, but were pre-empted by the tower controller who independently asked whether they could depart from intersection C6.

The crew accepted this and were cleared to shift to the Outer taxiway, and continue heading south along taxiway C6 to the intersection.

Preliminary findings from the Belgian air accident investigation unit state that, as the aircraft moved onto the Outer taxiway, the crew received a “line up and wait” instruction – and the red stop-bar at C6 was extinguished.

The A320neo’s captain remarked in the cockpit that “the red line disappeared”.

There appears to have been no additional cue about the runway location from other aircraft; no flight had departed 07R since an Etihad Airways A350 which took off as the A320neo was still moving away from its gate.

When the A320neo reached the final section of the Outer taxiway, the crew “apparently mistook” this for taxiway C6, says the inquiry, the captain mentioning to the first officer that the jet was “at Charlie six” and “cleared to enter [the runway]”.

But when the aircraft turned left to line up, it was actually lining up on the short link taxiway E1, which continues east as F2 and then V1 – a total distance of 1,200m. The crew received take-off clearance as it turned onto the taxiway, and the jet accelerated with full flex thrust.

The captain looked outside as the first officer monitored instruments. But when the captain did not respond immediately to the standard ‘100kt’ callout – apparently concerned about the “increasingly narrow” forward view – the first officer looked up and “immediately recognised” that the jet was not on a runway, the inquiry says.

“No, this is wrong,” the first officer stated, before repeatedly urging “stop”. The captain aborted the take-off roll almost immediately.

At the point when braking was applied and the thrust-reversers were engaged the aircraft was travelling at 127kt. It had covered about 800m of the combined 1,200m taxiway distance before it began to slow.

“Observing the end of the taxiway and a fence approaching, the first officer instructed a right turn,” the inquiry states. The jet subsequently came to a halt.

Beyond the end of E1-F2-V1 is a fenced 300m section of ground adjacent to the airport’s fuel storage farm, past which was a service road and a highway.

None of the 158 occupants as injured. Passengers disembarked and were transferred back to the terminal, while the aircraft was towed about 90min later and underwent a service check the following day.

Investigators have yet to reach conclusions regarding the circumstances which led to the error.

But they state that the crew had identified the configuration of runway 07R and 07L as potentially confusing during the inbound flight to Brussels, and had mentioned stopping and clarifying if in doubt during taxiing.

According to the inquiry the A320neo was fitted with a take-off surveillance function – known as TOS1 – as standard, but not the TOS2 variant which verifies that the aircraft if positioned on the intended runway.

Nor was the aircraft equipped with the Honeywell runway overrun prevention system developed for Airbus jets.

But SAS, the inquiry says, has initiated the process of acquiring airport moving-map functionality which displays the aircraft’s real-time position on the airport and enhances pilots’ situational awareness.