France A319 at Marseille on Jun 27th 2016, near collision with helicopter
Last Update: December 19, 2018 / 18:58:49 GMT/Zulu time
An Eurocopter AS532 Cougar Helicopter was nearing Marseille Aerodrome at 1500 feet MSL with the intent to join the traffic pattern, however, its transponder had failed and wasn't operating. As such ATC had only primary radar contact with the helicopter. While near the entry point into the traffic pattern the helicopter slowed and hovered, as result primary radar contact was also lost.
As result both flight crews remained unaware of the presence of the other aircraft. The flight pathes crossed, the minimum separation between the two aircraft reduced to 240 feet vertically and 0.19nm horizontally. Only after the aircraft had crossed the A319 flight crews established visual contact and became aware of the other aircraft.
Both aircraft landed without further incident.
On Dec 19th 2018 the French BEA released their final report in French only (Editorial note: to serve the purpose of global prevention of the repeat of causes leading to an occurrence an additional timely release of all occurrence reports in the only world spanning aviation language English would be necessary, a French only release does not achieve this purpose as set by ICAO annex 13 and just forces many aviators to waste much more time and effort each in trying to understand the circumstances leading to the occurrence. Aviators operating internationally are required to read/speak English besides their local language, investigators need to be able to read/write/speak English to communicate with their counterparts all around the globe).
The final report concludes the probable causes of the serious incident were:
- failure by ATC to apply separation measures towards the Cougar operating without transponder in dense air traffic at an aerodrome where IFR and VFR traffic mixes based on air traffic information and visual contact between crews.
- non-compliance with traffic pattern altitudes by the Cougar crew
- lack of information provided by the Cougar crew to ATC to enter hovering and inaccurate position reports to ATC leading to ATC developing a wrong mental picture of the traffic situation and thus providing inaccurate traffic information to other aircraft
- lack of information available to ATC of conditions, under which radar echos are not being displayed
Contributing to the serious incident were:
- the absence of an overall strategy to sequence VFR and IFR traffic on arrival
- the present workload did not permit ATC to sufficiently anticipate the arrival of the Hop! flight
- excessive flexibility in management of the parallel runways
- high load on the tower frequency due to density of traffic, aggravated by the use of non-standard phraseology, which did not permit the Hop! crew to intervene or benefit from a timely traffic information
- possible overconfidence by ATC and the Cougar crew, which was based in Marseille, which could have resulted in less rigor in the accuracy of position reports and use in air traffic management
The BEA analysed:
The Cougar was intended to become number 2 behind a Lufthansa A320 for approach to Marseille's runway 31R. The Tower controllers were aware of the loss of transponder by the Cougar and were confident that the primary radar return as well as the crews' position reports would be sufficient to ensure proper tracking of the flight. At the same time approach control informed the Air France A319 that they were number 2 for the approach to 31R behind the Lufthansa A320 15nm ahead of them, no speed or other restrictions were given to the A319. The A319 thus assumed their only reference would be the A320, however, both the Cougar and the A319 became number 2 for the approach at that point. Both the A319 and the Cougar crew thus began to adjust their progress to remain properly visually separated behind the A320.
The helicopter began hovering near the entrance point into the visual approach to runway 31R, which caused the loss of the primary radar return being displayed. The controller failed to locate the helicopter, but knowing the large helicopter would be easily seen this was no cause for alert to them, no failover actions were initiated.
The tower controller was mentally tracking the Cougar, but being unaware that the helicopter had started hovering he believed the helicopter was much further down the final approach. When the crew finally announced they were reaching the entry point into the approach tower controller, trying to permit planned departures out of runway 31R, redirected the helicopter to runway 31L. At the same time the controller made a mental image that the approach path runway 31R was clear. In reality however the helicopter was about 2nm northeast of the approach path to runway 31R and was about to cross the path about a minute later.
Just before the helicopter crossed the approach path runway 31R and 31L the crew made a visual scan to their left to ensure safety of the helicopter before turning right, but were unable to detect the A319 which was in their 10 o'clock position above them, the crew would have needed to scroll further back. The A319 was presenting the nose to the Cougar and was difficult to spot, the lack of contrast between the blue sky and white aircraft did not facilitate visual detection, too. The A319 crew was not yet on tower frequency, hence the Cougar crew remained unaware of the A319. When the A319 reported on tower frequency, there was no reply by tower, who was engaged in communications with other crews. The controller regards response to the A319 as not urgent as in his mental picture the approach path to runway 31R is clear and the A319 is far out with no conflicting traffic. When the A319 reaches the final approach, the crew slightly above the nominal height while reducing their speed, the tower frequency is busy preventing the crew to repeat their log in call. With their mental image that their only reference was the Lufthansa A320 ahead of them that they had in sight since joining the approach, the visual detection of the helicopter was even more difficult, the closing speed of about 300 knots does not permit the concept of "look and see". The crew does not get information about the helicopter via the TCAS display due to the failed transponder of the helicopter, does not get traffic information due to the congested tower frequency. A short gap in the tower transmissions permitted the crew to finally repeat their log in call, now tower responds providing traffic information about the helicopter on approach to runway 31L. At that point the helicopter was actually crossing the extended center line runway 31R at 1500 feet MSL and the A319 overflew the helicopter by a narrow margin acquiring visual contact too late to initiate any evasive maneouver. The helicopter crew did not establish visual contact with the A319.
The BEA concluded the analysis: the collision was "luckily" avoided.
The BEA analysed with regards to the Cougar's transponder that a second transponder on board of the aircraft would likely have prevented the loss of secondary radar returns and as such would have permitted other aircraft to see the Cougar on their TCAS display as well as enabling short term collision alerts at the ATC control desks.
The BEA analysed with respect to the loss of primary radar echo display due to the helicopter hovering that the filter criteria to process radar returns are not effective. A 2006 study had concluded that helicopters operating in or out of airfields were lost from primary radar displays occasionally, however, this possibility had not been brought to the attention of the Marseille controllers, who believed the primary radar return would enable them to sufficiently track the Cougars flight path.
The BEA analysed with respect to the control zone, that the approaches happen in Class D airspace where separation is visually ensured by providing air traffic information to IFR and VFR traffic to assist visual detection of the traffic. A crew is such not permitted to turn final unless they have visually identified the traffic ahead on final as well as the traffic on the parallel runway. This practise, although legally mandated, appears fragile, particularly in dense traffic. In many situations it is difficult to acquire and maintain visual contact with other aircraft at any time.
The BEA analysed that the tower frequency was active for about 80% of the time around the time of the occurrence, which is a very high use of the frequency. A review of the radio exchanges showed that the use of non-standard phraseology contributed significantly to the congestion of the tower frequency.
The BEA analysed that the fact the Cougar crew was based in Marseille permitted to develop habits and levels of mutual trust between controllers and crew. Crews are familiar with the terrain around the aerodrome resulting in less vigilance with respect to speed and trajectory, controllers in turn may be less vigilant in tracking the trajectories. The habits may also permit less formal phraseology to emerge. While those adoptions may work out well in daily routine, they may cause faults in an unexpected event.
This article is published under license from Avherald.com. © of text by Avherald.com.
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