French investigators have revealed that a Nouvelair Airbus A320 may have passed less than 10ft above a waiting EasyJet A320 during the recent landing conflict at Nice, after conducting its approach to the wrong runway.

The inquiry into the extraordinary 21 September incident states that the Nouvelair A320 did not actually touch down on runway 04R after overflying the EasyJet aircraft, although its crew received an automated 20ft height callout before climbing away for a go-around.

French investigation authority BEA has confirmed, in preliminary findings, that the Nouvelair crew had been cleared to land on runway 04L but instead lined up with the parallel 04R.

BEA says the approach was conducted in darkness and it has highlighted a significant difference in illumination between the runways, stating that 04R’s lights are “much brighter” at night than those for 04L.

Arriving from Tunis, the Nouvelair crew was cleared directly to the BISBO waypoint, south of the airport, to avoid weather. They opted then to use a slightly different RNP approach to 04L.

The EasyJet crew, at the same time, had been cleared by the ground controller to taxi and hold short of 04L, in preparation to cross it to reach the departure runway 04R.

BEA says the crew had remarked about poor visibility conditions on the ground.

Just after the tower had cleared the Nouvelair crew to begin their RNP approach to 04L – an instruction read back correctly – the EasyJet crew switched to the tower radio frequency and was cleared to cross 04L.

“The [EasyJet] crew checked that there was no aircraft on final [to 04L] before crossing,” says BEA.

Although the crew, after crossing 04L, was cleared to line up on 04R they asked to wait at holding point W3 because the cabin was not fully prepared.

Some 3min later the tower controller cleared the Nouvelair crew to land on 04L, and this was also read back correctly. After heading north to the airport from BISBO, the jet descended through the missed-approach point at 2,000ft and commenced a right turn to 040° to align with the runway heading.

The captain, who was flying, reported having the runway in sight.

As the aircraft turned, passing through 1,000ft, the tower controller instructed the EasyJet flight – now ready to depart – to line up and hold on 04R.

Around 40s later the Nouvelair jet aligned with the axis of 04R, descending through 527ft at 1.8nm from the threshold. As the EasyJet aircraft moved into its path on 04R, it triggered an initial runway incursion alert in the tower from the Nice surface-movement system.

BEA says a second, more urgent, alert sounded about 15s later when the Nouvelair A320 was 1nm from the runway.

As the EasyJet crew turned left onto the threshold stripes of 04R, the first officer noticed the Nouvelair jet on final.

“He expressed his surprise at the perceived flightpath,” says BEA. “However, the crew did not identify any conflict.”

The tower controller contacted the Nouvelair flight to confirm runway 04L, and received a confirmation from the crew who reported that they were on short final for 04L. The controller then cleared the aircraft to land.

At the time, however, the inbound jet was actually 0.7nm from 04R and descending through 200ft. BEA says the crew received automatic height callouts for 100ft, 50ft, 40ft and 30ft.

The inquiry states that the aircraft’s radio altimeter reading suddenly dropped from 39ft to 10ft, before reverting to 24ft.

BEA believes this interruption represents the moment that the descending A320 overflew the EasyJet aircraft, which was stationary and aligned with the 04R centreline.

Airbus data shows the fuselage height of an A320 is just under 20ft while that of the vertical fin is about 39ft – indicating extremely close margins between the two aircraft.

The 20ft callout and thrust ‘retard’ instruction also sounded as the tower controller ordered the Nouvelair crew to conduct a go-around.

BEA says the main landing-gear of the jet “did not touch the runway” before it climbed away.

It says the EasyJet crew requested to return to the apron, while the Nouvelair crew was vectored for an approach to 04L where the A320 landed about 16min after the go-around.

BEA is still probing the circumstances of the conflict. It has noted that Nice’s runway configuration – using the northern runway for landing and the southern for take-off – is one which “differs from the current practice” of using the runway adjacent to terminal buildings for departures.

“This choice of reversing the direction of the two runways reduces the impact of noise pollution from departing flights over urban areas,” it states.

BEA will assess the lighting levels of the runways but has already pointed out that the lights for 04R appear much brighter than those for 04L at night. It adds that the precision-approach path indicator lamps for 04L are situated on the right-hand side of the runway, differing from the typical left-hand PAPI installation.