Air France has sought to prevent dual pilot inputs to flight controls, after a serious incident involving a Boeing 777-300ER during go-around in low-visibility conditions at Paris Charles de Gaulle.

The aircraft, arriving from New York JFK on 5 April 2022, had been conducting an ILS approach to runway 26L, in daylight but without visual references owing to a low cloud base.

It had been stable on the approach when, at 1,670ft altitude, the crew disengaged the autopilot, leaving the autothrottle and flight directors active.

But as the twinjet descended the first officer, who was flying, became concerned about the bank angle.

French investigation authority BEA found no evidence of any flight-control issue, and confirms that the aircraft’s changes in bank angle corresponded to the first officer’s inputs to the control wheel.

These roll inputs became “amplified”, it says, and the aircraft started turning left after a few seconds of average left-wheel input.

When the aircraft was 2.1nm from the runway, at an altitude of 1,117ft, it was banked 6° left and the first officer called for a go-around.

Air France 777-300ER F-GSQJ-c-Anna Zvereva Creative Commons

Source: Anna Zvereva/Creative Commons

Neither pilot was aware of the possibility of desynchronised flight controls

But as the aircraft’s thrust was increased and the first officer pulled on the control column, the captain – who had previously noticed the deviation from the approach path – also started making control inputs.

BEA says the captain testified to placing his hand on the control, to perceive the first officer’s actions, but the inquiry could not determine whether this subsequently hindered the first officer’s attempts to set the correct nose-up pitch.

“The pitch rate and attitude parameters show that the [first officer] pulled the control with more force and that the aircraft took a steeper pitch attitude than that expected for a go-around,” it states.

“It is likely that, surprised by an unusual pitch rate for an aborted approach, the captain made a reflex input on the control column to limit the variation in nose-up attitude, which he felt was too great.”

BEA says the result of this reflex action resulted in the controls being subject to simultaneous opposing inputs, and 5s after the go-around was initiated the aircraft’s controls desynchronised.

While the two pilots’ flight controls on the 777 are normally synchronised, they will desynchronise if the pilots exert opposing forces of around 220N (50lb).

Simultaneous pilot inputs on the control columns do not trigger any visual or aural alert, and neither pilot was aware of the possibility that the controls could desynchronise, says BEA.

“There was considerable confusion, as neither pilot was aware that he was fighting the other, with the captain initially attributing the extra load in the controls to a jammed control,” it adds.

The pilots made simultaneous inputs for 53s and for 12s the controls were desynchronised. Crew co-operation, says the inquiry, was “severely disrupted” with non-standard call-outs and no proper division of tasks.

Analysis of the event shows the captain made nose-down inputs while the first officer made emphasised nose-up inputs. The aircraft’s pitch reached a maximum of 24°, much higher than the typical 15° for a go-around.

BEA says the captain eventually called out that he had taken control, and he became the sole input pilot. The crew completed the go-around actions and, after control was returned to the first officer, carried out a new approach and landing on 27R, without further incident.

Air France has taken steps to ensure crews have access to Boeing documentation on the control desynchronisation mechanisms, and reinforce the awareness of dual-input risk with training in order to prevent such occurrences on all aircraft in its fleet – whether cockpit dual-input warnings are given or not.

Boeing updated documentation in June last year, states BEA, to point out that pilots should always have a “clear understanding” as to who has control of the aircraft, and recommending that operators establish standardised procedures to transfer this control.

None of the 177 and 15 crew members on board the aircraft (F-GSQJ) was injured.