France A318 at Toulon on Dec 20th 2019, aircraft intercepted false glide slope
Last Update: October 18, 2021 / 15:26:46 GMT/Zulu time
The French BEA rated the occurrence an incident and opened an investigation.
On Sep 3rd 2021 the BEA released their final report in French only and a (French) video showing an animation of the approach and go around based on the FDR. An English translation of the final report is to be expected in due time, the AVH is going to summarize the English version of the report when it is being released.
On Oct 18th 2021 the BEA released their final report concluding the probable causes of the incident were:
The following factors may have contributed to a false glide slope signal being captured, followed by the AutoPilot (AP) increasing the pitch attitude and the activation of the flight envelope protections:
- The underestimation of the threat that a strong tailwind represents during the approach, mentioned for the landing phase during the approach briefing and insufficiently taken into account thereafter. Several factors may explain this underestimation:
-- The presence of other threats possibly perceived as more serious, such as windshear, might have overshadowed this threat.
-- The risk linked to a tailwind is often taken into account for landing and less so for the approach.
-- In the flight file, the reported wind for the approach was a tailwind of 25 kt. The threat was therefore not easily identifiable during flight preparation.
- Insufficient monitoring of the glide path by the PM and the PF during the approach.
- Not taking into account the controller’s suggestion to fly a missed approach.
- The crew not having an objective in terms of altitude and distance to the threshold and not carrying out the checks at the key points of the approach, in particular on passing the Final Approach Point (FAP).
- The two pilots having had little exposure, in training and line flying, to the interception of the glide slope from above despite their aviation experience.
The BEA analysed:
The threat linked to the presence of a tailwind was mentioned by the crew during the approach briefing. However, this threat concerned the landing and not the approach phase.
The crew’s statements show that this threat during the approach was not sufficiently taken into account. Several factors may explain this underestimation:
- The presence of other threats which may have appeared more serious, such as windshear, might have overshadowed the tailwind during approach threat.
- The risk linked to a tailwind is often taken into account for landing and less so for the approach. This is particularly the case for this flight; as the crew had to land with a tailwind on a wet runway, the threats linked to the landing performance were more prominent than those linked to the glide path.
- In the flight file, it was indicated that there was a tailwind of 25 kt on the approach path, which is a lower value than that actually encountered in flight. The threat was thus not easily identifiable during flight preparation.
Due to the strong tailwind during the approach and the flight speed, less than 2 min 30 s elapsed between the moment the crew, at 12 NM from the runway, decided to continue the direct approach for runway 05 without flying a holding pattern, and the AP acquiring the false glide slope signal. During this period, the crew tried to intercept the glide slope from above and prepared the aeroplane for landing. With this workload, the tailwind during the approach threat, of little prominence in the initial assessment, was forgotten or not taken into account.
Recovery of the Upset situation
Following the Low energy alert, the PF selected TOGA thrust which engaged the FD SRS mode, and resumed manual control. When the pitch reached 30°, he made a nose-down input, initially less than that indicated by the FD, and then held the pitch at values of around 15° which was consistent with following the FD command bars in SRS mode in the conditions of the day.
The Air France documentation specifies that when the pitch exceeds 25°, the aeroplane is in an Upset situation. In this case, the Upset recovery techniques should be applied. In case of an excessive nose-up pitch, the technique specifies the following PF actions:
- Recognise and confirm the situation.
- Disconnect the AP and A/THR and resume manual control.
- Make a nose-down input of sufficient amplitude to enter a nose-down attitude.
- Adjust thrust.
- Adjust roll without exceeding a bank angle of 60°.
- Return to level flight with a sufficient speed.
The PF’s initial reaction corresponded to the first items of the recovery technique. Subsequently, holding the pitch at around 15°, corresponded more to the FD commands being followed than carrying out the recovery technique. The consequence of this was to prolong the low speed (below VLS) situation. Fully complying with the Upset recovery technique linked to an excessive nose-up pitch might have contributed to the crew getting out of the aircraft's low-energy situation faster.
Aircraft Registration Data New!
This article is published under license from Avherald.com. © of text by Avherald.com.
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