incident to the Boeing-777 registered F-OREU operated by Air Austral and the Airbus A330 registered 3B-NCL operated by Air Mauritius on 03/01/2024 near Mauritius

1. Synopsis

On Wednesday 03 January 2024 an AIRPROX event happened between an Air Mauritius A330 aircraft and an Air Austral B777 aircraft.

The occurrence has been observed over the Region of Black River Gorges National Park at 18:21 hrs. local time on Wednesday 03 January 2024 between Air Mauritius flight MAU 293 and Air Austral flight REU 121.

The Air Mauritius aircraft was operating the flight between Roland Garros Airport (Reunion) (FMEE) and SSR International Airport (FIMP), flight MAU 293. Air Mauritius flight contacted the SSR International Airport approach at 18:10 hrs. and the latter cleared the flight for an approach to land on runway 32 facing Northwest on a descent / approach path called EPTEK 2 F and had just left flight level 100 (10,000ft), also cleared to descend to flight level 60 by the controller. The estimated time of arrival at SSR International Airport was 18:43 hrs. The Standard Arrival Route (STAR) approach procedure includes geographical reference points on a defined heading and at a defined altitude, which must be strictly complied with by the crews, which, after analyzing the Air Mauritius approach flight, was the case.

The Air Austral flight a Boeing 777 was departing from SSR International airport to Roland Garros Airport, flight REU 121. The flight was cleared by the tower Air Traffic Controller at 18:09 hrs. to Roland Garros Airport (Reunion) based on a Standard Instrument Departure (SID) Route called SOBAT two Bravo, via SID, flight level 180 (18 000 ft.) and take off at 18:17 hrs. on runway 32 at SSR International Airport, following by a first climb to 4000 ft. and left turn after takeoff. The REU 121 flight continued its climb to find itself at the time of the AIRPROX event at 18:21 hrs., less than 5 nautical miles from the trajectory of the flight MAU 293. The Air Austral pilot announced to ATC that he had a TCAS resolution advisory at flight level 080 (8000ft.). The pilot announced that he was resuming his normal flight path. Investigation demonstrate that the aircraft was at flight level 080 at that particular point whereas, according to the published procedure, it should not have been above flight level 070.

At 18:41 hrs., both aircraft flying within a circle of less than 5 nautical miles, all directions combined, had an activation of the automatic system called TCAS (Traffic alert & Collision Avoidance System) and thus avoided a possible collision between both aircraft. The approach controller was informed by both crew, who were authorised to continue their approach and departure as per the SID and STAR procedure.

4. Conclusion

1) The crew of Air Mauritius MAU 293 complied fully with the trajectories, waypoints and reference levels of the published chart "Standard Arrival Route" Reference AD2-FIMP 37.2. The only deviation from the descent profile occurred at the time of the AIRPROX event, when the Pilot in Command (PF) deviated manually upward. The crew resumed control of the aircraft after the event, returning it to its initial descent path. (see MAU 293 flight profile in annex 1)

2) With regard to Air Austral flight REU 121, it should be noted that the flight's parameters and FDR data were not available. However, according to ATC and flight trajectory data, it is clear that the crew of REU 121 did not comply with the procedure published constraints in the "Standard Departure Chart - Instrument" reference AD2 -FIMP-35.2 (SOBAT TWO Bravo Departure). The Boeing was at waypoint MP 603 at flight level 080 when it should not have been flying above flight level 070 over this waypoint, hence the proximity alert with the Air Mauritius flight descending in the same area between flight level 100 and flight level 060. (see REU 121 Flight profile in annex 2)

3) In recap, Air Mauritius was flying above flight level 080 when its path was crossed by REU 121, which was also flying around flight level 080 when it should have been below flight level 070 with a separation of 1000 feet or more.

4) It should also be noted that the tower controller, on receiving the read back of the ATC clearance given to the crew of Air Austral flight REU 121, did not ensure that the read back was incomplete; “REU121 CLEAR TO ROLAND GARROS SOBAT TWO BRAVO FLIGHT PLAN ROUTE CLIMB VIA SID FL180”

“VIA SID” was omitted from the read back of the REU 121 flight crew and this "VIA SID" means respecting the waypoints on the route and at the maximum / minimum altitude or level (to comply with all altitude/flight level and speed restrictions of the departure).

5) Traffic information was not given to none of the two aircraft by the approach controller. One of the main reasons for giving traffic information is to raise pilots’ situational awareness.

6) Even though the air traffic services have a TCAS RA procedure, which is to be used in case aircraft report a TCAS RA, this was not properly implemented.

4.1 Findings.

1. Error from the PM (Captain Pilot) who press twice the ALT switch cancelling the second altitude constraint of the departure SOBAT Two Bravo.

2. REU 121 did not comply with all altitude/flight level and speed restrictions of the departure (SID).

3. Clearance “read back” by the PM was incomplete.

4. The tower controller did not inform the Air Austral pilot of an incomplete “read back”.

5. The Approach controller did not give Traffic Information to none of the aircraft.

4.2 Causes/Contributing Factors.

1. Approximately twenty minutes before, the runway in use was changed from RWY 14 to RWY 32, forcing the Air Austral crew to reprogram a SID while calculating limiting performance under stress with the time pressure of the “white worm” due to the aircraft's delay.

2. The Air Austral co-pilot (PF) was flying for the first time on MRU- RUN route and on Mauritius Airport procedures.

3. A departure clearance at 4000ft. amended on initial climb to FL180.

4. The co- pilot has been instructed by the Captain pilot to be the Pilot Flying and to fly the departure and climb manually increasing the Pilot Monitoring (PM) workload on the initial climb.

5. Specific PBN phraseology used by Mauritian air traffic control authorising a climb via the SID phraseology which is the subject of a bulletin (The Air Austral crew learnt about it afterwards from a colleague) which should have been included in the flight file, and which was not in the REU flight file, but present in flight files of flights 108/109 and 102/103 (information source: Air Austral Pilot report (PIREP)).

6. An error of the Captain (Pilot Monitoring), when setting the cleared flight level, he pressed the switch twice, hence deleting a constraint in the FMC which limits the climb on the SID to cross the way point MP603 at or below flight level 70. (information source: Air Austral Pilot report (PIREP)).

7. The lack of compliance with SID’s numerous altitude constraints on runway 32, and never operated by this Air Austral flying crew.

8. Human factors issues;

 additional stress due to Pilot Flying manually for practicing for the first time. (reported by the Captain).

 Error from the PM (Captain Pilot) who press twice the ALT switch.

5. Safety Recommendations

5.1 Flight Operations

1. SIDS AND STARS CONSTRAINTS (Recommendations for operators at SSR International Airport – to be inserted in their Operations Manual Parts A and D)

Operators on SSR International Airport shall inform their crews to read back the departure / arrival clearance correctly, as per ICAO DOC 4444. E.g “Climb via SID or Descend via STAR”, which means that ALL altitude constraints on the SID/STAR shall be adhered to.

Altitude change shall be acknowledged verbally and confirmed by both flight crew members. Once the clearance is acknowledged verbally and confirmed by both flight crew members, PF shall set correct altitude on the AFS Control panel. Actions done by the PF shall be cross-confirm by the PM.

During the cockpit preparation, the PF shall set the initial expected altitude, SID altitude or MSA on the FCU as applicable. Once the departure clearance is received, the crew must verify and set the new altitude/FL on the FCU if different from what was set at preparation stage.

When the FMGS preparation is completed for departure or arrival, the PM must cross-check all constraints with the relevant SID/STAR chart. He/she may include the speed and altitude restrictions in the departure/arrival briefing if required during the threat and error management briefing

The PM shall ensure that he/ she has the correct MFD/FMS page with SPD/ALT selected on their side and check the display of the correct cleared FL/ALT on the PFD whenever the FCU FL/ALT has been changed.

2. Particular surveillance via SAFA should be carried out on aircraft operating at SSR International Airport, regarding PBN arrival and departure procedures.

5.2 Air Traffic Services

1. Air traffic controllers should always pay close attention to the read back from the flight crews, they should listen not just heard. If a controller does not ensure that a read back is correct, this could become into a serious incident or even an accident.

2. Recurrent training should be delivered to air traffic controllers, ensuring that one of the topics be when and how to provide aircraft with traffic information, by doing so pilots situational awareness will be raised.

3. The air traffic services should ensure through the ATC Supervisor on duty, that air traffic controllers provide traffic information whenever there is eventual conflicting traffic.

4. Even though most air traffic controllers are familiar with the air traffic services TCAS RA procedure, theoretical and practical training should be delivered to all controllers on this matter. This type of training should be addressed in recurrent training.