A319 / AS32, vicinity Marseille France, 2016
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|On 27 June 2016, an Airbus A319 narrowly avoided a mid-air collision with an AS532 Cougar helicopter whose single transponder had failed earlier whilst conducting a local pre-delivery test flight whilst both were positioning visually as cleared to land at Marseille and after the helicopter had also temporarily disappeared from primary radar. Neither aircraft crew had detected the other prior to their tracks crossing at a similar altitude. The Investigation attributed the conflict to an inappropriate ATC response to the temporary loss of radar contact with the helicopter aggravated by inaccurate position reports and non-compliance with the aerodrome circuit altitude by the helicopter crew.|
|Actual or Potential
|Air-Ground Communication, Airworthiness, Human Factors, Loss of Separation|
|Type of Flight||Public Transport (Passenger)|
|Take off Commenced||Yes|
|ENR / APR|
|Aircraft||AEROSPATIALE AS-332 Super Puma|
|Type of Flight||Aerial Work|
|Take off Commenced||Yes|
|ENR / APR|
|Location - Airport|
|Tag(s)||Aircraft-aircraft near miss,|
Event reporting non compliant,
Inadequate Airport Procedures,
Delayed Accident/Incident Reporting
Procedural non compliance
|Tag(s)||Accepted ATC Clearance not followed,|
See and Avoid Ineffective,
Released to Own Separation,
Lateral Navigation Error,
VFR Aircraft Involved
|Contributor(s)||Component Fault in service|
|Safety Net Mitigations|
|Damage or injury||No|
|Causal Factor Group(s)|
Air Traffic Management
|Group(s)||Air Traffic Management|
On 27 June 2016, an Airbus A319 (F-GRHX) being operated by Air France on a scheduled passenger flight from Bordeaux to Marseille as HOP25PG and an Airbus Helicopters AS 532 Cougar (F-ZWBS) being operated under VFR on a test flight prior to delivery came into close proximity whilst visually positioning in Class ‘D’ airspace to land on runways 31L and 31R at Marseille in day VMC. Neither aircraft was aware of the other until the helicopter had crossed beneath the A319 at which point the A319 reported having sighted it. After the minimum separation of 0.19 nm laterally and 240 feet vertically, both aircraft subsequently completed their respective approaches and landed without further event.
There was a delay in the reporting of the event to the French Civil Aviation Accident Investigation Agency, the BEA, who, after being so informed determined that a Serious Incident Investigation was required. The A319 CVR data had been overwritten but the relevant QAR data was provided by Air France on 2 July 2016. Airbus Helicopters provided a copy of the relevant CVFDR on 5 July 2016.
It was noted that the A319 flight crew consisted of a 44-year-old Captain acting as PF who had a total of 11,752 hours flying experience including 5,292 hours on type and a 33 year-old First Officer who had a total of 4,457 hours flying experience including 3,761 hours on type. Both pilots were based at Marseille. The Cougar helicopter was being flown by a 49-year-old Airbus Helicopter’s test pilot with a total of 9,175 hours flying experience of which 1,100 hours were on type, who was accompanied by a company flight test engineer. The 55-year-old TWR controller involved had been working at Marseille since 2011 and had been qualified for all TWR and APP positions there since 2014. His 31-year-old assistant had been at Marseille since 2007 and had been qualified to control in all TWR and APP positions there since 2009.
It was established that on first contact with the destination APP controller, the A319 had been advised to expect an ILS Z approach to runway 31R. A few minutes later, the A319 reported field in sight and requested a visual approach which was acknowledged. Approximately 3½ minutes later, the Cougar, which was operating under VFR and had advised its previous frequency that its transponder had failed earlier in the flight and indicated that it was returning to the airport and tracking towards the ‘E’ reporting point (see blue position 1 on the illustration of both aircraft tracks below), was transferred to TWR having acknowledged a request to descend to an altitude of 1500 feet. After being informed by TWR that only a primary radar contact was showing, it was asked to join the circuit on right base for runway 31 and report when it had visual contact with an inbound Lufthansa A320 which was 12nm from the field on an ILS approach in order to position on final behind it.
Shortly after this, the Cougar crew reported visual with the A320 and after confirming that it should be in their 10 o’clock at 5 nm, the TWR controller asked them to self position behind it which was read back. Straight after this exchange, the APP controller cleared the A319 to descend to 5000 feet and fly heading 090° and informed the crew that they were “number two behind an aircraft in their 12 o’clock at about 15nm” (the Lufthansa A320) which they acknowledged saying they “had the traffic on the TCAS”. The TWR controller advised a light aircraft in the circuit which had reported left hand downwind for runway “31” to expect 31L and report visual with the A320 on 9nm final in order to position behind it which the pilot read back.
Half a minute later, the A319 crew reported visual contact with the A320 ahead to APP and were advised to expect visual final behind that traffic. At this time, the TWR controller asked the Cougar crew to report on final 31R behind the A320 and advised them of the light aircraft downwind for the parallel runway (31L). Meanwhile, the APP controller was clearing the A319 (now in red position 3 on the illustration) to make a left hand visual approach to runway 31R subject to the A320 ahead being in sight. The Cougar had, unknown to the controller, begun to hover (blue positions 3 and 4) at an altitude of approximately 1850 feet at which point, its primary radar return ceased. When the TWR controller realised this and advised the crew, they reported that they were at the ‘EA’ reporting (shown on the above illustration) when they were in fact almost 2nm southwest of it. Ten seconds later, the APP controller advised the A319 crew that they could turn base at their discretion and transferred the flight to TWR.
The A319 crew called TWR on left base (red position 5) and confirmed contact with the number 1 traffic (the A320). The tower controller did not reply but cleared the A320 to land and the asked the Cougar crew if they were visual with the light aircraft on final for 31L. The Cougar crew replied (at blue position 6) that they were not and stated that they were at the ‘MS’ waypoint (on the illustration and on the 31R extended centreline at 3.9nm) whereas their position was actually 2nmm east northeast of it. The TWR controller, based on this erroneous position report asked the Cougar crew to “make a small dog leg to the left” for runway 31L and position behind the light aircraft which had just passed the ‘MS’ reporting point and confirm visual contact. CVR data from the Cougar showed that for the next 1½ minutes, conversation between the Cougar crew members were solely concerned with the search for visual contact with the light aircraft. During this time, with the Cougar still northeast of the 31R extended centreline (at blue position 7), the TWR controller again reminded its crew to report visual with the light aircraft who responded with a request for its position and were advised that it was established on a long final for runway 31L.
With the A319 at red point 8 on the illustration immediately above and approximately 20 seconds from crossing the Cougar’s fight path, the A319 crew, having received no response to their initial call on the TWR frequency, again called and reported that they were “arriving on final for runway 31R”. The TWR controller responded by asking them to report short final for 31R and advised of two aircraft on the parallel approach, a light aircraft followed by a helicopter. During this transmission the A319 crossed the Cougar’s flight path and after its completion the A319 crew reported that a helicopter had just flown right to left across and below their track in ‘dangerous’ proximity. The TWR controller then told the Cougar crew (at blue position 10), who were still discussing only the location of the light aircraft they were to follow on their 31L visual approach, that in the absence of radar contact, it was difficult for him to provide traffic information. He informed them of the presence of an A319 at the MS reporting point on final for runway 31R but the Cougar crew did not reply. The Investigation established that the time of non reply coincided with their visual acquisition of the light aircraft they had been looking for followed a few seconds later by their first sighting of the A319 to their north with separation now increasing from the earlier unseen minimum of 0.19 NM horizontally and 240 ft vertically.
The TWR controller then cleared the A319 to land on 31R and advised the Cougar crew that he now regained radar contact on their aircraft and subsequently cleared them to land on 31L.
Why it happened
The effect of the temporary loss of a primary radar return from the Cougar when its single transponder had failed earlier in its flight created a situation which ATC resolved by relying on its position reports to separate it from other traffic which was also manoeuvring visually. The TWR controller was aware of the failure of the Cougar’s transponder earlier in the flight but initially had primary radar returns from it. When these were lost in the vicinity of the ‘EA’ reporting point, the TWR controller considered that despite this now total loss of radar contact, its reported position at the ‘EA’ reporting point meant that it “could be integrated in the traffic, even with respect to the visual approach in progress”. His assessment of the situation was that the Cougar approach could be fitted in between those of the A320 and the A319. Then, still without primary radar contact he accepted the subsequent report from the Cougar that it had reached the ‘MS’ reporting point on the 31R extended centreline at face value given that it was from a locally-based professional crew. This report and a desire to fit in departures from runway 31R led him to alter his initial plan to make the Cougar number 2 for 31R behind the A320 and ask it to continue to final for 31L, positioning number 2 to the light aircraft in a left hand circuit. However, since the ‘MS’ position report was incorrect and the Cougar was still east of both final approach tracks, its flight path to a 31L final then took it across the final approach track for 31R and into conflict with the A319, whose crew did not see it until after it had passed below them. It was noted that the failure of the transponder on the Cougar meant that no anti-collision system was triggered.
The Investigation considered that although the APP controller had coordinated in the normal way with the TWR controller to obtain his acceptance for the A319 visual approach, this communication and approval did not occur within any overall strategy to ensure the organisation of all traffic and each controller had thus sequenced the traffic in their own sector “without really taking into account the traffic in progress or expected in the adjacent airspace”. It was also noted that the ANSP OM did not specify any local restrictions on runway use, leaving “the choice of runway assignment strategy to the duty controllers and the tower manager”. The Investigation particularly noted in the context of the investigated conflict that there are no restrictions in runway assignment for VFR flights which “is done according to the traffic and the needs of the tower controllers regardless of the inbound sector of a VFR flight”. It was observed that “whilst such a practice allows a certain flexibility", it can also, as in the present case, lead to flights crossing paths on the final approach centrelines, by applying the “see and avoid” principle which “does not always guarantee safety” and “can also lead to aircraft overtaking each other on the parallel centrelines at small distances and may cause, in addition to a possible wake turbulence problem, a feeling of insecurity among the users”.
It was found that the TWR frequency was busy for 80% of the time between the arrival of the Cougar on frequency and the completion of its landing and it was noted that this “very high degree of congestion” had delayed both the Cougar crew and the A319 crew from establishing initial two way contact with the TWR controller. In addition, “an examination of the radio exchanges established that the use of non-standard phraseology, in French, also largely contributed to increasing the time spent on the frequency”. It was considered that “this can be explained by a propensity for French parties to talk more without there being a real need or added value for the traffic management, sometimes even to the detriment of the precision and conciseness of the messages”.
The cause of the loss of a primary radar return from the Cougar was initially its entry into a hover which was not known to ATC. The fact that this then led to a period of almost 4 minutes until returns reappeared well after the hover had been discontinued was attributed by the Marseille ANSP technical department to a series of circumstances which were a consequence of the radar configuration rather than as a result of any malfunction of it. It was noted that some patchiness in primary radar cover in the vicinity of Marseille which particularly affected helicopter movements had been identified by a study by the DGAC (French CAA) in 2006, but that this finding had not been brought to the attention of controllers.
The Investigation also identified the fact that the crews involved in the investigated event were all based at Marseille. The consequence of this “base effect” was summarised as follows:
- On an airport such as Marseille with dense traffic, the wish to optimise traffic and keep it fluid may lead the various actors to operate with lower safety margins. Progressively, skills are developed, habits created and the levels of mutual trust between operators are re-enforced. Locally-based crews, for example, become familiar with the terrain and may be less vigilant with respect to the path or speed adopted. The controllers may also monitor the flying of these paths to a lesser degree and reduce internal coordination. These habits also lead to less formal language being adopted on the frequency with more implicit elements or digressions. This event thus underlines the fragilities in the current approach practices at the airport. Adaptations which work well on a daily basis may be deficient on an unplanned event occurring, if there is not a real awareness of the associated risk and of the need to switch to another mode of operation.
- Here the risk caused by the Cougar transponder failure was probably underestimated. The excessive confidence in the primary radar (in the absence of information about its limitations) as well as confidence in the crew reporting (reinforced by the fact that it was a professional crew) may have led the controllers to overestimate the possibility of knowing the position of the aircraft.
Four Causal Factors were identified in combination as having led to the near collision as follows:
- No segregation measures being taken by the air traffic control with respect to the Cougar which had to operate without a transponder, in dense airport traffic where the compatibility of IFR and VFR traffic is based on traffic information and visual contact between crews.
- Non-compliance with the aerodrome circuit altitude by the Cougar crew.
- Cougar crew not advising that they were bringing the helicopter into hover and an inaccuracy in their position reports which meant that the controller constructed an erroneous mental representation of the situation and thus provided unsuitable traffic information.
- Controllers not being given information about the existence of zones where primary radar returns are not displayed.
Five Contributory Factors were also identified:
- The absence of an overall sequencing strategy for inbound VFR and IFR traffic.
- Work load which did not allow the tower controller to sufficiently anticipate the arrival of the HOP (A319) flight.
- Excessive flexibility in the management of parallel runways.
- Very busy tower frequency due to the density of the traffic and the use of non-standard phraseology which did not allow the HOP flight crew to contact the controller and meant that they did not obtain traffic information in due time.
- Possible overconfidence between the Tower controllers and the Cougar crew, professionals based at the same airport, which may have led to less rigorous practices in providing accurate position reports and in the use of these reports for traffic management.
Safety Action taken as a result of the event whilst the Investigation was in progress was noted to have included but not been limited to the following:
- The Marseilles ANSP introduced a ban on visual approaches in situations where any aircraft has a transponder failure and a ban on any takeoff without a transponder. In such circumstances, an inbound aircraft which has a transponder failure must be held clear until the runway circuit is free.
- Airbus Helicopters - introduced a requirement to inform ATC in the event of a transponder failure in flight and thereafter follow the published VFR tracks scrupulously with prior ATC clearance to be requested if any need to leave a published altitude, for example due to turbulence, arises.
- Air France - temporarily suspended visual approaches at Marseille until safety action taken by the ANSP and Airbus Helicopters had restored their confidence in the operational safety of such approaches
Five Safety Recommendations were made as a result of the Investigation as follows:
- that the DNSA (the French ANSP) establish a procedure so that when justified by the density and/or complexity of traffic in the airspace, spatial and temporal segregation measures are implemented by the air traffic control for any flight with a transponder failure until it can be safely integrated in the traffic. [FRAN2018-011]
- that the DNSA ensure that the Marseille-Provence controllers are informed of the performance restrictions or limitations of their display equipment and in particular, the primary radar. [FRAN2018-012]
- that the DNSA assess the need for an extension of the action detailed in recommendation FRAN2018-012 to other air traffic units.[FRAN 2018-013]
- that the DNSA ensure that procedures are implemented in the Marseille-Provence tower and approach units so that flights are managed as part of a shared traffic sequencing strategy. [FRAN 2018-014]
- that the DNSA study the implementation, at Marseille-Provence, of work methods to safely sequence traffic on one of the two parallel runways. [FRAN 2018-015]
Two Safety Lessons relevant to aircraft operating in Class ‘D’ airspace and identified as a result of the Investigation were as follows:
- Approach Speed:
- It is important that crews adopt speeds compatible with the “see and avoid” principle when manoeuvring in airspace where both IFR and VFR flights are permitted.
- Accuracy of Position Reports:
- It is essential for safety that crews provide accurate and reliable reports and that any change to the flight path is indicated to air traffic control.
The Final Report in English translation was completed on 22 January 2019 and published on 28 February 2019. The definitive French language Final Report was completed on 19 December 2018 and published in French on 21 December 2018.
- Loss of Separation
- Operation without a Transponder or with a Dysfunctional Transponder
- ATC Loss of Transponder Signal
- An aircraft without transponder – Guidance for Controllers
- Communication Guide for General Aviation VFR Flights
- Non-Standard Phraseology
- Air-Ground Voice Communications
- Frequency Congestion
- Visual Flight Rules (VFR)
- Instrument Flight Rules (IFR)
- Aircraft without Transponder – Mitigations
- Transponder failure types
- Impact of transponder failure on safety barriers
- Airborne Collision Avoidance System (ACAS)
- Standard Operating Procedures (SOPs)
- Base Effect