Serious incident to the Bombardier CRJ 1000 registered F-HMLD operated by Hop! on 20/10/2021 on approach to Nantes-Atlantique
Erreur de collationnement du calage altimétrique (QNH), déclenchement d’une alarme MSAW en approche finale
When the crew of F-HMLD were cleared to descend to the first altitude below the transition level and to conduct the approach to runway 21, the PM incorrectly read back the QNH, indicating an altimeter setting of 1021 instead of 1002. This error was not detected by the controller or the PF.
When resetting the altimeter, the crew did not apply the procedure fully, omitting to check the consistency of the QNH provided by the controller against another source of information because of the turbulence experienced during this phase of flight, which was making it difficult for the crew to read the information written on the flight plan.
Due to this QNH error, the aircraft’s path during the approach was approximately 530 ft lower than the published path. However, the procedures and information on the aircraft instruments did not allow the crew to directly identify the path error in a simple way.
The only instrument information that could have allowed the crew to detect this QNH error was the radio altimeter value, which was abnormally low compared to the procedure altitudes, taking into account the altitude of the area overflown. This check was not clearly defined by the standard operating procedures.
The altitude displayed on the radar display, which is a standard altitude, did not allow the controller to easily detect that the aeroplane was not flying the intermediate approach at the published altitude. Moreover, it was not the responsibility of the controller to carry out this check.
The final descent path checks carried out during a RNP Baro-VNAV approach do not enable the crew to detect a path error due to an altimeter setting error. This limitation inherent to RNP Baro-VNAV approaches is a well-known threat, which pilots are regularly reminded of by the operator during their recurrent training or through internal flight safety documents.
As the aircraft was approaching the missed approach point, a MSAW triggered at the LOC controller’s position. The controller informed the crew of this warning, without initially reminding them of the QNH and without using the word “immediately” in the message. Exchanges between the crew and the controller lasted almost 30 s before the crew realised their mistake and corrected the vertical path.
The crew did not perform a go-around as required by the MSAW procedure described in the operations manual. As they had sight of the runway and were aware of bad weather conditions on the missed approach path, they considered it more judicious to continue the approach.
According to the stabilisation criteria, the approach was not stabilised. During the final approach, due to the inherent limitations of the Baro-VNAV function in the event of an altimeter setting error, the crew could not gain awareness of this destabilisation. The crew were only able to perceive this destabilisation on the triggering of the MSAW.
The BEA issues 4 safety recommendations:
- Recommendations FRAN-2023-007, FRAN-2023-008, FRAN-2023-009 et FRAN-2023-010 / Alignment of procedures and phraseology to be used in the event of a terrain alert:
The standard expressions defined by SERA and by the Order of 11 December 2014 relating to the implementation of European Regulation (EU) No 923/2012 establish that in the event of a low altitude warning, the message includes the principle of emergency introduced by the expression “immediately”, and the QNH information. In the event of a terrain alert, the standard expression does not include these elements. The notion of a “terrain alert” is not defined, and the investigation could not determine why the QNH information and the expression “immediately” are not used in this context.
The phraseology defined in the operations manuals and directives used by the French air navigation services differs according to whether the aircraft which triggered the MSAW is being radar vectored or not. This differentiation is consistent with the national regulatory text regarding procedures, but is not consistent with the national texts regarding phraseology.
It would seem that the variations in phraseology identified in the operational documents and reference manuals used by the French air navigation services, are the result of the inconsistencies observed between procedures and phraseology, and between regulations and operating procedures. The BEA did not obtain a clear explanation about these inconsistencies.
This variability in phraseology in the operational documents (operational directives, operations manual) regarding a MSAW is not likely to facilitate air traffic controllers having accurate and unambiguous knowledge of the message to be used in the event of an MSAW.
It was observed that an imprecise alert message was given in this event and in the event involving the Airbus A320 registered 9H-EMU operated by AirHub on 23 May 2022 on approach to Paris-Charles de Gaulle airport (see paragraph 2.9). In both cases, the controllers did not remind the crew of the QNH value, nor did they stress the urgency of the situation by using the word “immediately”.
Consequently, the BEA recommends that:
- whereas the QNH information is crucial for the crew of an aircraft to be able to actually check their altitude;
- whereas using the word “immediately” is important to make the crew aware of the urgency of the situation;
- whereas the variability in the various DSNA documents as regards the provision of these two pieces of information;
the DSNA, without waiting for the other actions expected from EASA and ICAO, ensure that all documents relating to phraseology and MSAW procedures are updated so that:
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- the urgency of the situation is systematically mentioned;
- the crew is systematically reminded of the QNH in the controller’s message in the event of a MSAW. [Recommendation FRAN 2023-007]
In ICAO Doc 4444 (Procedures for Air Navigation Services), as well as in French regulatory texts, the procedure to be applied in the event of a MSAW differs according to whether the aircraft which triggered the warning is being radar vectored or not.
In ICAO Doc 4444 and Doc 9432 (Manual of Radiotelephony), as well as in European and French regulatory texts, the phraseology to be used in the event of a MSAW differs according to whether it is a low altitude warning or a terrain alert. These notions are not otherwise defined in these texts.
The phraseology defined in the operations manuals and directives used by the French air navigation services differs according to whether the aircraft which triggered the MSAW is being radar vectored or not. This differentiation is consistent with the national regulatory text regarding procedures, but is not consistent with the national texts regarding phraseology.
It would seem that the variations in phraseology identified in the operational documents and reference manuals used by the French air navigation services, are the result of the inconsistencies observed between procedures and phraseology, and between regulations and operating procedures.
The BEA questioned the authorities behind the drafting of these texts and did not obtain clear explanations.
This variability in phraseology in the operational documents (operational directives, operations manual) and reference manuals regarding a MSAW is not likely to facilitate air traffic controllers having accurate and unambiguous knowledge of the message to be used in the event of an MSAW.
It was observed that an imprecise alert message was given in this event and in the event involving the Airbus A320 registered 9H-EMU operated by AirHub on 23 May 2022 on approach to Paris-Charles de Gaulle airport (see paragraph 2.9).
This is contrary to what is stated by ICAO in the foreword to Doc 9432, namely “ICAO phraseologies are developed to provide efficient, clear, concise and unambiguous communications.”
Consequently, the BEA recommends that:
- whereas the low altitude warning and terrain alert notions used by ICAO Doc 4444 and ICAO Doc 9432, the SERA European regulation and the French order of 11 December 2014 relating to the implementation of Implementing Regulation (EU) No. 923/2012 to define the phraseology to be used in the event of a MSAW, are not defined in these documents;
- whereas the procedures to be applied by controllers in the event of a MSAW as described in ICAO Doc 4444 and in the national supplement FRA.11002 to the SERA are based on whether the aircraft is being radar vectored and not being radar vectored;
- whereas the QNH information is crucial for the crew of an aircraft to be able to actually check their altitude;
- whereas using the word “immediately” is important to make the crew aware of the urgency of the situation;
EASA, without waiting for the ICAO documents to be updated, develop Guidance Material (GM) designed to clarify in the SERA regulation, the phraseology to be used by controllers to inform crews of a MSAW and ensure that the SERA is updated so that the urgency of the situation is systematically mentioned and the crew is systematically reminded of the QNH in the controller’s message in the event of a MSAW. [Recommendation FRAN 2023-008]
EASA initiate international actions in conjunction with ICAO to also resolve inconsistencies and ambiguities in Doc 4444 and Doc 9432, so that they systematically specify that the urgency of the situation and the QNH information is mentioned, and move towards simple and unified phraseology, if possible. [Recommendation FRAN 2023-009]
ICAO ensure that the inconsistencies between MSAW procedures and phraseology contained in Doc 4444 and Doc 9432 are removed, and ensure that these documents are updated so that the urgency of the situation is systematically mentioned and the crew is systematically reminded of the QNH in the controller’s message in the event of a MSAW. [Recommendation FRAN 2023-010]
The recommendations are being processed
The status of the recommendations is available at SRIS2: click here
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Note: in accordance with the provisions of Article 17.3 of Regulation No 996/2010 of the European Parliament and of the Council of 20 October 2010 on the investigation and prevention of accidents and incidents in civil aviation, a safety recommendation in no case creates a presumption of fault or liability in an accident, serious incident or incident. The recipients of safety recommendations report to the issuing authority in charge of safety investigations, on the measures taken or being studied for their implementation, as provided for in Article 18 of the aforementioned regulation.
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