Description

On 4 February 2020, an Airbus A350-900 (F-HREV) being operated by French Bee with an augmented flight crew on a scheduled international passenger flight from San Francisco to Paris Orly as FBU711 was passing 1,400 feet QNH on an ILS 25 approach at destination in day VMC when an unexpected predictive windshear warning occurred and the Captain ordered a go around in response. After the go around stop altitude was then significantly exceeded and an ATC heading instruction was ignored, the Captain took over and eventually regained control of the aircraft in accordance with ATC instructions and a second approach to the same runway was completed without further event.

Investigation

An Investigation was carried out by the French Civil Aviation Accident Investigation Agency, the BEA. Information was available from the aircraft flight data maintenance recorder and from ATC and from statements made by the flight crew. Relevant CVR data was overwritten.

The 41 year-old Captain had joined the operator three years previously as a First Officer and had been promoted to Captain in June 2019. He had a total of approximately 8,000 hours flying experience which included just over 2,000 hours on the A330/A350 with around 600 hours as Captain. The 45 year-old First Officer had been employed by the operator about 18 months prior to the investigated event and had over 8,600 hours flying experience of which a little over 1,200 hours were on the A330/A350. The 50 year-old Relief Pilot had joined the operator in 2016 and had around 11,700 hours flying experience of which over 3,400 hours were on the A340/350. She had boarded the flight at San Francisco and was occupying one of the flight deck supernumerary seats for the final part of the journey. A member of the cabin crew subsequently occupied the second flight deck supernumerary seat to observe the approach. 

What happened

With the First Officer as PF, the aircraft was established on the runway 25 ILS and configured for landing with the runway in sight with the AP and A/THR engaged. Passing 1,400 feet QNH (approximately 1,100 feet agl) the AP was disconnected and four seconds later, at 1,350 feet, an unexpected predictive windshear warning ‘GO AROUND, WINDSHEAR AHEAD’ (see point 1 on the illustration below) was annunciated. In response, the Captain called for a go-around and the First Officer responded by pitching up to around 8° and moving the thrust levers forward to the TOGA position. After a few seconds, the Captain requested that the ‘GA SOFT’ mode be engaged and the First Officer complied with the FD command bars then indicating a corresponding reduction in target pitch attitude. However, as the AP was not re-engaged, the aircraft continued to climb at a greater pitch than that now indicated on the FD as the landing gear was retracted and the flaps reselected to CONF3. ‘LVR CLB’ was then annunciated on the Flight Mode Annunciator (FMA) to remind the PF to move the thrust levers to the ‘CL’ detent but no such action occurred. ATC were advised of the go around and confirmed clearance to climb to the standard missed approach altitude of 2,000 feet as already set. 

Altitude acquisition (ALT*) was annunciated passing 1,750 feet, and following the Captain’s call of “SPEED, ALT STAR”, the First Officer was thereby prompted to move the thrust levers to the ‘CL’ detent. Recognising that the aircraft was going to exceed the selected altitude, the Captain and the Relief Pilot both reminded the First Officer to stabilise the aeroplane at 2,000 feet but he did not react. Just over half a minute after the windshear warning had prompted commencement of the go around, the aircraft continued climbing through 2000 feet (point 2 on the illustration below) at 1,800 fpm and 167 KCAS. The flaps were retracted to ‘CONF1’ and FD command bars indicated an increased nose-down input but pitch remained stable at around 8° nose-up. Six seconds after flying through 2,000 feet, the altitude alert began to sound continuously and the final stage of flap was retracted around 10 seconds later. The climb above 2000 feet continued as the aircraft overflew the runway 25 threshold.

The ground track of the aircraft and that of the conflicting traffic during the event. [Reproduced from the Official Report]

As the runway 25 threshold was approached, the First Officer used his sidestick to level off around 2,800 feet. The FCU (Flight Control Unit) altitude knob was pulled which engaged ‘OP DES’ and the ‘THR IDLE’ modes but although the /A/THR was thereby set to flight idle, since the AP was not engaged, no descent followed and the aircraft altitude was unchanged. As the aircraft overflew the runway 25 threshold, ATC instructed the flight to turn left onto 180° and advised of traffic which had just taken off from runway 24 at Orly 4 nm away at one o’clock. When reading this instruction back, the Captain also advised ATC that they had climbed to 3,000 feet and were now in the process of descending back to 2,000 feet as cleared. However, although HDG mode was engaged with the selected heading set to 180°, since neither AP was engaged, there was no consequent turn.

The Captain stated that (only) at this time had he become aware that the aircraft was too high, that the First Officer was not reacting to either his requests or those of ATC and that there was other traffic in the vicinity. The recorded flight data showed that he had then put his hand on the sidestick and that a few seconds later the speedbrakes were extended by one of the pilots, “probably the First Officer” without a callout. The Captain then engaged his AP and, as the aircraft began the instructed left turn and resumed its descent towards the selected altitude of 2,000 feet, announced that he had control (point 3 on the illustration above).

Shortly after this, he saw that the lowest selectable speed (VLS) was increasing and reported having heard a warning about this given by the Relief Pilot. Almost immediately, a three second long low energy alert ‘SPEED, SPEED, SPEED’ was annunciated and at the same time recorded radar data showed that the aircraft had come into sufficient proximity with another company aircraft which had just taken off from runway 24 to activate the STCA on the ATC display (point 4 on the illustration above).

The Captain responded to the low energy alert by selecting a target speed of 260 knots and moving the thrust levers to TOGA and then began to make inputs on his sidestick. The TOGA thrust position automatically retracted the speedbrakes even though the control lever remained in the extended position and this triggered a Master Caution which continued for the next 38 seconds. At the same time, returning to manual control disengaged AP1 (and both FDs at a time where the speed was below VLS with the OP DES mode engaged).

The controller then repeated their instruction to the flight to turn left onto heading 180° but there was no response. Nevertheless the turn had begun when the Captain had earlier had his AP engaged. The controllers in the TWR then reported having seen the aircraft fly over the control tower 650 metres to the right of the runway 25 centreline - at this time it was descending through 2,500 feet. The left turn continued and as the selected altitude of 2,000 feet was approached, the thrust levers were moved from TOGA detent FLX/MCT and then to the CL position. 

The aircraft then flew through the 2,000 ft descending at 2,200 fpm with the speed increasing through 235 KCAS (point 5 on the illustration above). As this occurred, the separation from the other notified traffic reduced to 1.69 NM with 75 feet but the two flight paths were not convergent. The Captain subsequently stated that he had heard the Relief Pilot requesting that he re-engage the AP and as the aircraft descended through 1,850 feet, the First Officer selected his AP upon which the Captain then disengaged it and engaged his own. As the aircraft went from a 10° left bank to wings level, the Captain stated “everybody silent, I’m the only one giving orders”.

As the descent continued through 1,800 feet with the required 2000 feet still set, the altitude alert began to sound continuously again. The Captain selected a heading of 198° and reduced the target speed to 220 knots. Half a minute after the repeated ATC request to turn onto 180° which had still not been answered, the Captain transmitted to ATC that the flight was turning towards heading 180° and received the response “thank you, for your information the traffic is very close, so I suggest you turn very quickly”. Ten seconds later, the Captain engaged the ‘OP CLB’ mode and the A/THR changed from ‘SPEED’ mode to ‘THR CLB’ mode.

After the Captain disengaged his AP in descent through 1600 feet, the minimum altitude reached was 1,550 feet (point 6 on the illustration above) and at this time, the controller instructed the flight to climb to 3,000 feet. There was no readback but the target altitude was changed from 2,000 feet to 3,000 feet. A repeat of the instruction did elicit a readback from the Captain as the turn onto a heading of 180° was completed. 

The Captain then re-engaged his AP as the requested climb was completed at up to 3,100 fpm and at a speed of up to 281 knots KCAS. The First Officer then said that he “felt able to resume an active role (and was) ready to take over radio communications” and completed the remainder of the flight as PM.

Discussion

After approximately four minutes had elapsed since the predictive windshear warning had occurred, the aircraft reached and then maintained 3,000 feet at 220 KCAS. The controller then asked why they had carried out a go-around and were told that it had been due to windshear. ATC stated that no other aircraft had reported windshear before or after the investigated event. Radar vectors for a second ILS 25 approach were then provided and a normal landing followed without further event.

An assessment of the meteorological conditions concluded that it was unlikely that there had been windshear at the time of the first or second approaches or in between them. The First Officer subsequently stated that “there had been moments when his mind went blank, although he had not been aware of it at the time and could only partially remember what happened”. However, he confirmed that he had initially sought to manage the flight path thinking that the AP was engaged but “could no longer remember the modes engaged or the position of the command bars on his FD”. He also stated that he had not heard any of the calls made by the Captain or the Relief pilot or the altitude alerts and ATC instructions although he said that “at the time he had not felt unwell or lost consciousness”. He added that once the Captain stated that he had control, he had completely “let go” and stated that “his brain was working in slow motion (and) he could not remember the low energy alert”.

The Investigation concluded that after being surprised by the unexpected go around, the First Officer had been subtly incapacitated for a short period and that both the Captain and the Relief Pilot occupying one of the supernumerary crew seats in the flight deck had been slow to recognise this and its consequences for flight path control.

An examination of the applicable Airbus procedure for a predictive windshear alert which was in use at French Bee at the time of the event was presented as a memory drill with only the accompanying notes explaining that it was discretionary if it was suspected to be false.

No evidence was found from analysis of the crew’s roster or their statements about their off duty activity prior to the investigated event which indicated that tiredness could have been a contributory factor in what occurred.

It was noted that the configuration of the non-parallel configuration of the two runways at Paris Orly means that any go around there will require a turn if an aircraft making a go around is to remain clear of other runway climbout. The fact that traffic separation achieved in this way was accompanied by an initial stop altitude of 2000 feet was noted to complicate matters and it was noted that this was “an old procedure” and it had not been possible to find the justification for such a low stop altitude. 

Three Contributory Factors to the initial flight path deviation were documented as follows:

• The cognitive incapacitation of the PF, which by definition was difficult for the crew to identify. It was not possible to fully establish the reasons for this. However, the following factors may have contributed to its appearance:
  • the surprise effect linked to the unexpected triggering of the predictive  windshear warning;
  • the initiative taken by the PM Captain, without conferring, with respect to the management of the flight during the go-around phase;
  • the workload associated with the go-around.
• The presence of several elements of a typical scenario identified in the 2013 BEA Aeroplane State Awareness During Go-Around (ASAGA) study:
  • the surprise effect linked to a disruptive element, without any forewarning;
  • carrying out the go-around in manual flight control at an altitude close to             
  • the stabilisation altitude;    
  • a complex missed approach procedure with a low stabilization altitude and a turn.
• The time taken for the PM to take over control. 

Two Contributory Factors which may have contributed to the triggering of the low energy alert and to descending below the published missed approach stabilisation altitude were also documented as follows:

• the cognitive incapacitation of the First Officer, which led to his intervening on the flight systems such as the speedbrakes and AP without calling this out;
• the Captain’s high workload as he had to manage the flight alone in a dynamic phase, which included the interactions with the ATC to manage the conflict with a departing aeroplane.

One Safety Recommendation was issued as a result of the Investigation as follows:

• that the Direction des Services de la Navigation Aérienne (DSNA) study the feasibility of increasing the published missed approach altitude at Orly airport. [FRAN 2021-004]

Safety Action taken by Airbus as a result of the event in January 2021 whilst the Investigation was still in progress was noted as a complete revision of the procedure to be followed in the event of a predictive windshear alert on the A350. This involved “withdrawing the memory items from the FCOM [Flight Crew Operations Manual] and replacing them with a description of a “technique” in the FCTM [Flight Crew Training Manual]”. This change was justified in particular on the basis that a response to a predictive windshear warning is less critical than that necessary in the event of a reactive windshear warning which remains a memory recall procedure. It was noted that the introductory note to the new “technique” now made it clear that a predictive windshear warning could be ignored if there are no other signs of possible windshear conditions and the reactive windshear system is operational.

The Final Report was published simultaneously in both English translation and in the definitive French language version on 13 July 2021.

Related Articles

• Airborne Wind Shear Warning Systems
• Missed Approach
• Go Around
• Augmented Flight Crew
• Autopilot
• Flight Director
• Startle Effect
• Pilot Incapacitation

Further Reading

• Study on Aeroplane State Awareness during Go-Around, BEA France, August 2013