Flybe DH8D at Belfast on Jan 11th 2018, on initial climb autopilot targets 0 feet altitude

Last Update: November 8, 2018 / 19:53:05 GMT/Zulu time

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Photo of Flybe G-ECOE, De Havilland Dash 8 (400) — Flybe G-ECOE, De Havilland Dash 8 (400) (Photo credit: 225driver / Flickr / License: CC by-nd)

Incident Facts

Date of incident
Jan 11, 2018

Classification
Report

Airline
Flybe

Flight number
BE-130

Departure
Belfast City, United Kingdom

Destination
Glasgow, United Kingdom

Aircraft Registration
G-ECOE

Aircraft Type
De Havilland Dash 8 (400)

ICAO Type Designator
DH8D

A Flybe de Havilland Dash 8-400, registration G-ECOE performing flight BE-130 from Belfast City,NI to Glasgow,SC (UK) with 44 passengers and 4 crew, was in the initial climb out of Belfast City's runway 22 through about 1350 feet AGL, the aircraft was already accelerating for cleaning up the flaps and had entered instrument meteorological conditions at 163 KIAS, when the autopilot began to gradually pitch the aircraft down at a rate of about 1.2 degrees/second. The crew was reading the after takeoff checklist, the aircraft in the meantime changed the attitude from 10 degrees nose up to 8 degrees nose down and began to descent after reaching 1500 feet AGL. At 1300 feet AGL the EGPWS sounded "Don't sink!". The captain immediately disconnected the autopilot and pitched the aircraft up to arrest the sink rate that had already reached 4300 feet per minute with the airspeed having increased to 235 KIAS. The EGPWS sounded "PULL UP!", after reaching a minimum height of 928 feet AGL. The commander stabilized the aircraft at 200 KIAS and 8 degrees nose up in a steady climb while increasing engine power. At 1900 feet AGL the commander engaged the autopilot again, the aircraft however began to immediate pitch down again and the captain disconnected the autopilot a second time. The captain selected the flight director to IAS mode which de-selected the ALT mode, and the remainder of the flight was uneventful.

The British AAIB released their bulletin reporting: "After landing, the crew briefly discussed the incident, but neither were certain why the aircraft had descended when the autopilot had been initially engaged." The AAIB concluded the causes of the serious incident were:

Prior to pushback, the crew had selected the FD modes without entering a target altitude. This caused one mode to default to alt instead of alt sel, which was not detected by the crew.

Due to the DES being carried out whilst backtracking the runway, there was reduced time available in which to complete all required checks which, when combined with a sense of urgency, led to the crew not seeing the incorrect FD modes displayed on the FMA.

During the line-up checks, the PF noticed that alt sel was not displayed on the FMA. When alt sel was selected, the crew did not confirm that ga, hdg, and alt sel were displayed on the PFD. Instead alt mode was active and displayed which led to a target altitude of 0 ft amsl being set, resulting in a descent when the autopilot was engaged. Timely warnings of the hazardous flight path were provided by the EGPWS, and prompt corrective action by the PF returned the aircraft to safe flight.

The AAIB analysed:

Despite this high level of activity, the ‘Line Up’ checks did cause the PF to identify that alt sel was not selected but he did not see that alt was active instead of ga. The PF was also expecting to pitch the aircraft to about 15º nose-up instead of the 10º nose-up that the FD bar would have indicated with ga mode selected. It is possible that this was a reason why he did not notice that the FD bars were showing about 0º pitch on the PFD.

If the hdg, alt sel and alt modes are selected on the ground, subsequently as the aircraft climbs after takeoff above the target altitude, the FD vertical guidance bar will progressively move to a nose-down pitch attitude. Upon engagement of the autopilot, the aircraft will pitch down to follow the FD vertical guidance bar to descend to the target altitude. For this incident this target altitude would have been set to about 0 ft amsl.

When the aircraft pitched down as the autopilot was engaged, neither pilot initially noticed the change in pitch attitude but the “don’t sink” and “pull up” EGPWS warnings alerted the crew to the situation. The PF reacted promptly in accordance with the trained sequence of actions and returned the aircraft to a safe flight path. During the event the aircraft lost about 500 ft in 18 seconds, with a maximum rate of descent of 4,300 ft/min and having reached a minimum height of 928 ft agl.

When the autopilot was re-engaged, the aircraft again pitched nose-down but this was identified by the crew. They engaged IAS mode which replaced the alt mode and with alt sel also selected the aircraft climbed and levelled at the cleared altitude of 3,000 ft.