AF11 - Incident: France B773 at Paris on Apr 5th 2022

An Air France Boeing 777-300, registration F-GSQJ performing flight AF-11 from New York JFK,NY (USA) to Paris Charles de Gaulle (France), was on final approach to Paris' runway 26L established on localizer and cleared to land descending through about 1500 feet when the crew was heard on tower frequency audibly in distress, alarm sounds in the background, one of the pilots calling "Stop! Stop!", "Stop it!", tower instructed the crew to stop the approach at 1500 feet. When the aircraft descended through 1200 feet significantly having veered to the left off the localizer the autopilot disconnect wailer can finally be heard on the radio transmission, the crew manages to go around from about 1150 feet. While climbing out and levelling off at 4000 feet the crew reported they had problems with the aircraft not following commands, the aircraft did not follow the commands. The crew requested runway 27R under radar vectoring, positioned for an approach to 27R and landed without further incident.

The aircraft is still on the ground in Paris about 10.5 hours after landing.

According to ADS-B data transmitted by the aircraft was at 1725 feet MSL about 4.17nm before the runway threshold (glideslope at 1768 feet MSL). The aircraft subsequently began to deviate to the left.

On Apr 6th 2022 the French BEA reported they rated the occurrence a serious incident and opened an investigation. The aircraft suffered a "flight control instability", control stiffness and trajectory oscillations. CVR and FDR data have been downloaded on Apr 5th 2022 and are being analysed.

On Apr 15th 2022 the French BEA reported the aircraft was on an ILS approach to runway 26L in manual control when the crew perceived de-stabilization of the aircraft and initiated a go around however had difficulties maintaining the flight path during the go around. Both pilots acted simultaneously on the flight controls. Once the situation had stabilized the aircraft returned for a safe ILS landing on runway 27R. The occurrence category is still undetermined.

On Apr 27th 2022 the BEA released a press release describing the investigation update stating, the first officer was pilot flying, the captain pilot monitoring. The crew performed an ILS approach to runway 26L. The BEA wrote:

On final, the aeroplane was established on the localizer and glideslope ILS beams. At 07:49, the crew were cleared to land. They configured the aeroplane for landing, the selected speed was 140 kt. The crew then carried out the “Landing” checklist. At 07:50:20, when the aeroplane was at an altitude of 1,670 ft, the PF continued the approach in manual flight: he disconnected the autopilot (AP), leaving the auto throttle (AT) and the flight directors (FD) activated. He then made inputs on the controls for around 15 seconds. The aeroplane followed the movement of the controls and stayed on the ILS path, the left and right roll being less than 2°. In the subsequent ten seconds, there were less inputs on the wheel. The co-pilot than made inputs on the control column and wheel with a greater frequency, the amplitude was still small, the aeroplane followed the commands, the left and right roll being less than 3°. At 07:51:06, the co-pilot expressed his astonishment with respect to the aeroplane’s bank angle. The roll inputs were amplified and the average position of the wheel was at around 6° to the left. The aeroplane turned left with a small bank angle. The captain voiced his surprise with respect to the deviation from the flight path.

At 07:51:12, when the aeroplane was at an altitude of 1,115 ft, banked 7° to the left, with the wheel oriented 16° to the left, the crew carried out a go-around. Up until the go-around, the flight path had remained within the operator’s stabilization criteria. The recorded parameters show that the two pilots then simultaneously made inputs on the controls.

In the following second, the position of the wheel reached a maximum value of 27° to the left. One second later, the roll reached a maximum value of 15° to the left and the nose-up attitude was 12°.

At 07:51:16, the captain commented that the plane was going left. The control columns were then desynchronized8 for 14 seconds due to opposing forces. The captain held the control column in a slightly nose-down position while the co-pilot made several, more pronounced, nose-up inputs. Two brief episodes of wheel desynchronization were also observed.

At 07:51:20, the go-around switches were pushed again increasing the thrust to the maximum thrust available.

At 07:51:23, the pitch reached a maximum value of 24°.

At 07:51:25, the co-pilot called out “Positive climb” and retracted the landing gear. The configuration warning was displayed and the associated aural warning (siren) sounded. The two pilots continued to simultaneously make inputs on the controls. The captain made more pronounced nose down inputs for a few seconds.

At 07:52:06, the captain was the sole person making inputs. The crew completed the go-around actions.

The crew analysed the situation without perceiving the antagonistic inputs made on the controls and the desynchronizations of the control channels. They considered that they could use the AP again and carry out a new approach.

The co-pilot became the PF again. The captain informed the controller that there had been a problem on the flight controls and asked to join the final for runway 27R. The approach and landing took place without further incident.

The sustained input on the controls led to the PTT button and the AP disconnect switch being involuntarily pressed, the latter action causing several activations of the associated warning.

No failure warning was activated during the occurrence10. No anomaly was observed on the aeroplane.

At this stage, the analysis of the parameters does not show inconsistencies, in particular between the movements of the controls and the movements of the aeroplane. The validation and the analysis of the parameters are continuing. Particular attention will be given to reproducing the forces applied to the controls and to the relationship between these forces and the movements of the controls.

On Jan 16th 2024 the BEA released their final report concluding the probable causes of the serious incident were:

During the ILS approach to runway 26L, without external visual references, in manual flight, the PF expressed his surprise regarding the aeroplane’s bank angle and flew a missed approach a few seconds later.

On the PF verbalizing his surprise about the aeroplane’s bank angle, the captain, PM, placed his hand on the wheel at the same time as the pilot aborted the approach. It is possible that the copilot then felt an unusual resistance in the controls when he pulled on the control column to reach the go-around pitch attitude. Already surprised by the bank angle before aborting the approach and feeling an unusual resistance in the controls, he possibly increased his pull input and the aeroplane’s pitch attitude became too steep.

The captain then acted, most probably by reflex action, on the control column to reduce this pitch attitude without taking back the controls and making the procedure call-out, based on the principle of only one pilot having the controls. The two pilots then simultaneously made inputs on the controls. The pitch controls were desynchronized for 12 s due to opposing forces. Two brief episodes of roll desynchronization were also observed. During this phase, 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.

The controls were synchronized again after the captain explicitly called “push push”.

When the captain made the standard "I have the controls” call-out (designed to inform the other pilot of the transfer of tasks between the PF and the PM), about 53 s after the approach had been aborted, the forces recorded on the right-hand control column became zero and the flight path was stabilized. After recovering control of the flight path, the crew carried out a new approach to runway 27R without further incident.

The investigation was not able to identify the factors which contributed to affecting the co-pilot’s sensations. He had believed that it would be difficult to maintain a stabilized approach.

The following factors may have contributed to the simultaneous inputs on the controls:

- the PM’s reflex action on the controls during the banked go-around, probably linked to the deflection of the wheel and the unusual pitch attitude;

- failure to formalise the transfer of control;

- the absence of any warning about the effects of simultaneous actions on the controls in the manufacturer's and operator's documentation for this type of aeroplane;

- the lack of information on the possibility of desynchronization of the controls in the event of opposing inputs in the documentation available to pilots;

- a lack of knowledge about the systems resulting from this lack of information;

- the conviction that simultaneous inputs on the controls would be quickly perceived by crews on this type of aeroplane.

The BEA analysed:

The crew of the Boeing 777 registered F-GSQJ, operated by Air France, were carrying out scheduled flight AF011 between - New York JFK (United States) and Paris-Charles de Gaulle, on 5 April 2022. Take-off was at 01:16. The captain, in the left seat, was the PM, and the co-pilot, in the right seat, was the PF.

During the ILS approach to runway 26L, without external visual references, in manual flight, the PF expressed his surprise about the aeroplane’s bank angle and flew a missed approach at 2.1 NM from the runway threshold. The aeroplane was 0.13 dots to the left of the localizer and 0.4 dots above the glide, in a left bank of 6°. The two pilots then simultaneously made inputs on the controls for 53 s. The pitch controls were desynchronized for 12 s due to opposing forces. Two brief episodes of roll desynchronization were also observed. After recovering control of the flight path, the crew carried out a new approach to runway 27R without further incident.

The analysis covers the following points:
- the perception of each crew member during the approach;
- simultaneous inputs on controls;
- knowledge and perception of flight control system.

Simultaneous control inputs

When the approach was aborted, the parameter relating to the force being applied to the left control column, which until then had been zero, changed. The captain specified in his statement, that by placing his hand on the control, without exerting force, he was better able to perceive the PF's actions.

The investigation was not able to determine whether the PM's action on the control column hindered the PF in reaching the pitch attitude. The pitch rate and attitude parameters show that the PF pulled the control with more force and that the aeroplane took a steeper pitch attitude than that expected for a go-around.

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. It was at this point that the first signs of simultaneous, opposing inputs on the controls were detected.

Five seconds after the start of the missed approach, the controls were desynchronized, with the co-pilot making pitch-up inputs and the captain pitch-down inputs.

During this phase, 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. Crew cooperation was severely disrupted for about 50 s. The division of tasks was no longer respected and the verbal exchanges did not correspond to any standard call-outs.

When the captain called out "push push", the co-pilot reduced the force he was applying. The inputs in the same direction on the control columns brought the desynchronization to an end. At the same time, the pitch attitude passed below the go-around reference pitch attitude. The captain then called out “stop stop”. The co-pilot applied force in the nose-up direction again while the captain continued to apply force in the nose-down direction. The forces were less and remained below the desynchronization threshold.

When the captain called out "I have the controls", about 53 s after the approach had been aborted, the forces recorded on the right-hand control column became zero and the flight path was stabilized.

Knowledge and perception of system

The investigation revealed that crews had little knowledge of the breakout mechanisms. A certain number of pilots were aware of the existence of this system and often only associated it with a jammed control. The description of the system in the FCOM was limited to an explanation about the risk of a control jamming.

The manufacturer's and operator's documentation did not explicitly mention the effects of simultaneous actions on the controls, and this point was not covered in training. This might be explained by the fact that the flight control system on this aeroplane links the left-side and rightside controls, providing each pilot with both tactile and visual indications of the other pilot's inputs. The possibility of simultaneous inputs on the controls thus seemed to be considered marginal on aeroplanes with conventional flight controls. Operators did not seem to systematically monitor for simultaneous control inputs in their flight analyses.

However, the operator's post flight analysis showed a dual input rate of 0.4 per 1,000 flights on the Boeing 777. This rate is comparable to that reported on the operator's Airbus fleet.

The documentation provided to the pilots did not therefore allow them to reasonably envisage that, in the event of antagonistic control inputs exceeding the breakout mechanism's activation threshold, the controls would be desynchronized and the control surface would react according to the mean control positions. The behaviour of the aeroplane during this phase of simultaneous control inputs could not be anticipated.

Tests carried out on the AP0 simulator showed that pilot perception on control input response may become different during the control desynchronization phase due to altered sensitivity and nonlinear response in the controls. Some pilots who carried out the tests described it as difficult to anticipate what the other pilot was doing, while others would immediately recognize the desynchronization and call for one pilot on the controls to regain synchronization. Moreover, the FCTM warned that the jamming of controls is a difficult situation to identify.

However, the tests showed that as soon as one of the two pilots called out “you have control” and released the control, accurate pilot perception of control response returned instantly with synchronisation.

Related Flight: AF11, Twitter: #AF11, Air France News