On 25 November 2014, an Airbus A319 (LZ-FBB) being operated by Bulgaria Air on a scheduled international passenger flight from Sofia to Paris CDG as LZB431 taxiing in after landing at destination crossed a runway on which an Airbus A320 (TC-FBJ) being operated by Freebird Airlines on an international passenger flight from Paris CDG to Istanbul Atatürk as FHY542 was taking off from and overflew the A319 by about 100 feet shortly after becoming airborne. Normal daylight visibility prevailed.
An Investigation was carried out by the French civil aviation accident investigation agency, the BEA, based upon recorded ATC data, particularly but not only recordings from the ground radar system.
It was established that at the time of the conflict, runway 08R was in use for landings and runway 08L for takeoffs. Communications between ATC and both the aircraft involved were carried out in the English language but concurrently, communications between ATC and some other aircraft were being carried out in the French language. One TWR controller, who had held an ATCO licence since 2003 and been qualified in all positions at Paris CDG since 2005, was responsible for both runways. He was being assisted in co-ordination with other positions by another fully qualified controller who had held an ATCO licence since 2008 and been qualified in all positions at Paris CDG since 2011.
Shortly after the A319 had vacated runway 08R on taxiway V5 after landing, TWR instructed it to “hold short of 08 L, holding point S6” which was correctly read back. Eight seconds later, the same controller cleared the A320, which had not yet lined up, for takeoff from runway 08L.
The A319 (red) and A320 (blue) positions just before the A319 was instructed to hold short of runway 08L. [Reproduced from the Official Report]
Forty-five seconds after that, the controller instructed the A319 with the words “number one, keep on taxiing” which the crew read back using the same words as used by the controller. He then immediately instructed an Air France A320 which had just landed on runway 08R and was vacating on taxiway V6 to “taxi behind the 319 Bulgaria on left” and when its crew queried whether they were “cleared to cross”, the controller responded that they were not. This exchange was carried out in French. At this time, the A319 was on taxiway S and heading east towards its intersection with taxiways V6 and S6 and the departing A320 had still not lined up on runway 08L.
The positions of both arriving aircraft (red) and the departing A320 (blue). [Reproduced from the Official Report]
Forty seconds after this exchange with the arriving A320, the arriving A319, which had turned left from taxiway S onto taxiway S6 entered runway 08L from S6 to cross to taxiway T9. One second later, a red level 2 RIMCAS warning was activated with the departing A320 accelerating for takeoff on runway 08L and passing 139 KIAS approximately 1500 metres from the point where the A319 had entered the runway. The relative positions of the three aircraft ten seconds later are shown in the third illustration below.
The positions of the three aircraft ten seconds after the RIMCAS activation. [Reproduced from the Official Report]
Nine seconds later, the departing A320 flew over the S6/T9 intersection by which time the A319 had cleared the runway and had stopped on taxiwayT9.
It was noted that according to the configuration of the RIMCAS, the level 2 warning - which indicates a “critical” situation - would have been activated when the departing A320 was moving at a groundspeed of 20 knots or more and a “moving object” - in this case the A319 - was detected as having crossed one of the holding points protecting the runway.
The Perspectives of those directly involved
The crew of the departing A320 subsequently stated that they had seen the Bulgaria Air A319 for the first time as it approached the holding point S6 by which time they said they “had reached V1”. They added that they expected that “it would come to a halt before entering the runway, its taxiing speed being compatible with this scenario”. However, soon after this, they realised that it was crossing the holding point and as VR had been reached, the Captain decided to continue the takeoff, during which they estimated that they overflew the A319 at an estimated height of about 100 feet (which if correct would have meant clearing the A319 by about 60 feet).
The crew of the arriving A319 subsequently stated that the frequency was very busy with exchanges in both French and English and that after vacating runway 08R, they were initially told to taxi to holding point S6 and hold short of runway 08L but as they were taxiing, the controller had said “Bulgaria 431, number one, keep on taxiing” which they understood as being a clearance to cross the runway whilst reading back the instruction using the controller’s exact words. They added that “after they had crossed the runway, the controller told them that they had not been cleared to cross it” and said that they had not seen the Freebird Airlines A320.
The Captain of the arriving Air France A320 subsequently stated that “when the controller told the Bulgaria Air A319 to keep taxiing, he asked himself if that corresponded to a clearance to cross runway 08L as, being based at Paris-CDG, he knew that normally controllers explicitly gave the crossing clearances”. He added that this was why, when the controller told him to follow the A319, he had asked for confirmation that it included clearance to cross the runway.
The TWR controller had started his shift about twenty minutes earlier and on taking up the TWR position, had asked for and been allocated another controller to assist him by coordinating with other controllers because the approach radar controller was sequencing arriving aircraft at 2.5 nm separation which created a high workload. He noted that shortly before the A319 had landed another approaching aircraft had made a go around because the preceding aeroplane had not vacated the runway. He stated that after the A319 had vacated the runway on V5, he had instructed it to taxi to holding point S6 and when the Air France A320 vacated on V6, he had realised that there was going to be a conflict between the two aircraft at the beginning of taxiway S6 and had decided to give priority to the A319. He had then turned his attention to the next aircraft on approach to runway 08R “as he was not sure that he had cleared it to land”. He then said that when the RIMCAS warning activated, his assisting controller told him that the A319 was in the process of crossing runway 08L but that it was too late to intervene as the departing A320 had begun to rotate. He added that “he had not had any misgivings about the intention of the Bulgaria Air flight, as the read back had been correct and the aeroplane was taxiing slowly to the holding point”.
The Assisting Controller had started his shift 2 hours 40 minutes prior to the event under investigation and until moved to assist the TWR controller when the latter took over that position, he had been in the approach radar position. He stated that “the traffic was quite heavy with reduced separations between aircraft on final approach (which) required increased monitoring of inbound aeroplanes and late landing clearances”. He stated that he had seen the arriving A319 taxiing but that it had been “difficult to see if it was going to stop or not, as it was taxiing slowly”. When the RIMCAS Warning occurred and he saw it crossing the holding point, he alerted the TWR controller “specifying that it was too late to act”. He was of the opinion that “if the TWR controller had not been busy with the close arrivals, he could have taken the time to clarify about the crossing” but noted that “the TWR controller had not asked him to call the approach radar controller to ask for greater separations and he had not done this himself, as the period of peak traffic was coming to an end”.
Published Information and Procedures
It was noted that the AIP entry for Paris CDG states that “aircraft vacating runway 08R/26L or 09L/27R after landing must NEVER cross RWY 08L/26R or RWY 09R/27L without first receiving specific ATC clearance”.
It was also noted that:
- to increase the chances that an aircraft taking off on the inner runway will have become airborne before reaching an aircraft which has just cleared the outer runway after landing and enters the inner runway, the taxiways closest to the centre of the runway - in the case of runway 08L the crossings from S5 to T8 and from S4 to T7 (marked in red on the illustrations above) were permanently closed.
- the longitudinal profile of runway 08L is not level and its first 500 metres are about 26 feet higher than its far end which can make it difficult for pilots crossing the runway from taxiway S6 (or S7 and S9) to see an aircraft at the beginning of its takeoff.
- the AIS phraseology guide stipulates the following controller phraseology:
- Managing priorities when taxiing: “Rapidair 3245, give way to Citron Air coming from your right, taxi holding point runway 27 via B7.”
- Holding short of a runway and then crossing a runway: “Rapidair 3245, hold short of runway 18” followed by “Rapidair 3245, cross runway 18 right.”
- Crossing a runway without holding: “Rapidair 3245, keep taxiing, cross runway 18 right.”
The Conclusion of the Investigation was formally documented as follows:
An inadequate phraseology was used to deal with the taxiing priorities between Air France flight 1089 and Bulgaria Air flight 431. The message “Bulgaria 4 3 1, number one, keep on taxiing” was not in fact accompanied by a reminder that the crew must hold short of runway 08L. This message led to an erroneous interpretation by the crew of the Bulgaria Air flight who understood it as a clearance to cross the runway.
The crew of the Air France flight had the meaning of this message clarified. The crew of the Bulgaria flight were not able to understand the exchanges in French between the controller and the crew of the Air France flight. The controller did not connect the question from the crew of the AFR1089 flight with a possible ambiguity as to the meaning of the phraseology that he had used to manage priorities.
In addition, the configuration of the Paris-CDG runways can make it difficult for crews to detect an aeroplane taking off, notably when they cross a runway. The crew of flight LZB431 thus entered runway 08L without seeing flight FHY542 taking off. The RIMCAS alarm was triggered due to the conflict. The controllers considered that it was then too late to intervene.
The Final Report was published in English on 23 July 2019 along with the initial and definitive publication in French.