Preliminary inquiries by Portuguese investigators indicate that a serious loss of roll control by an Air Astana Embraer 190 was “consistent” with “possible disturbance” during earlier maintenance work.

Investigation authority GPIAA says the crew battled severe instability during flight – to the extent that they considered ditching in the sea – before restoring a degree of control by engaging direct flight-control law, and trying to avoid roll inputs.

“The crew realised that the ailerons were behaving erratically and therefore any command for the aircraft roll was kept to its minimum,” says the inquiry.

Flight KC1388, a ferry service to Almaty via Minsk, started experiencing roll oscillations immediately after taking off from Alverca air base at 13:31 on 11 November, following a maintenance visit to specialist OGMA.

GPIAA says the crew felt the aircraft was “not responding adequately” to commands, and tried to counter the oscillations with controls for all three axes.

The autopilot could not be engaged, says the inquiry, and the crew did not understand the reason for the instability – there was no indication of a system malfunction, only continuous alarms in response to excessive flight attitudes.

GPIAA says the crew were subjected to “intense” g-forces, and needed “considerable effort” to minimise the oscillations, using “crossed commands” and generating high structural loads during some of the recovery manoeuvres.

While the pilots asked Lisbon air traffic control several times for headings to direct the jet towards the ocean, for a possible ditching, they were unable to maintain those headings.

GPIAA has yet to detail the extent of the attitudes experienced by the aircraft, but flight-data recorder traces suggest that control-column roll commands resulted in an opposite-direction response.

The inquiry says the decision to engage direct law on the flight controls improved the situation “considerably” – although roll control remained difficult and normal operation was not restored. The crew was also facing problems from poor weather conditions.

After the pilots regained control over altitude and heading, as well as better visual references, the Embraer was intercepted by two Portuguese Air Force Lockheed Martin F-16s which supported the jet as it diverted to Beja airport.

Its crew carried out two unstable approaches to Beja, executing go-arounds on both occasions, and had intended to land on runway 19R during the third approach. The aircraft drifted, however, and touched down on the parallel runway 19L.

“All on board were physically and emotionally shaken,” says the inquiry, adding that one of the six occupants sustained a leg injury.

While information on the in-flight upset is still being gathered, the investigation states: “Evidence that was possible to collect [initially] suggests the existence of failures in the aircraft roll controls configuration, consistent with possible disturbance during maintenance actions.”

Source: Cirium Dashboard