Mis-set altitude led Neos 737 to fly low

[Ref Flight International Magazine 5 – 11 May 2020]

Investigators have found that a Neos Boeing 737-800 arriving from Verona on 1 June 2019 – had been vectored to a shortened ­arrival route by approach controllers, which left it above 10,000ft with less than 25nm (46km) to touchdown.

With the aircraft high and fast on the approach the crew was unable to switch the autopilot to vertical navigation mode.

As a result of the shortened approach, the aircraft’s descent was rushed and became unstable. It sank some 250ft below the designated flightpath, travelling with excessive airspeed, and the tower controller instructed the crew to execute a go-around.

“The crew found themselves performing a go-around unexpectedly but did not know why they had been required to do so,” it adds.

Take-off thrust was engaged and the aircraft began to climb. But the altitude setting in the mode-control panel remained at 1,000ft because the crew had omitted to select the go-around altitude of 3,000ft.

The flying pilot manually followed the flight director, which attempted to guide the aircraft to level off at 1,000ft.

As the jet acquired this altitude, the autothrottle mode changed from “go-around” to a mode that maintains the aircraft’s speed, resulting in the thrust levers being back-driven to a lower power setting and causing the landing gear warning horn to sound.

The crew then adjusted the mode-control panel to set the correct go-around altitude of 3,000 ft, but it caused a switch to “vertical speed” mode.

The vertical speed set in the mode-control panel at the time was a descent rate of 300ft/min (1.5m/s), and the jet started to lose height as the pilot continued to ­follow the flight director.

“Neither crew member ­noticed for a significant period that the aircraft was descending during the manoeuvre,” says the inquiry.

The gear-warning horn was still active, owing to the low thrust and flap settings, and was followed by a “too low, gear” warning from the ground-proximity warning system. The jet was descending for 32s, says the inquiry, reaching a minimum of 457ft above ground after passing almost the entire length of the runway.

“The crew then realised that the aircraft was not climbing as expected and adjusted the attitude of the aircraft to begin a climb,” it states, adding that the tower controller almost simultaneously issued an order to climb to 3,000ft.

After climbing away the ­aircraft (I-NEOT) subsequently levelled at 3,000ft and was vectored to another approach, following which it landed without further incident.

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