Air France A319 and Easyjet Switzerland A319 near Mulhouse on Jun 29th 2010, near collision and TCAS reversal

Last Update: October 8, 2013 / 16:25:26 GMT/Zulu time

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Incident Facts

Date of incident
Jun 29, 2010

Classification
Report

Airline
Air France

Flight number
AF-7343

Aircraft Registration
F-GRHA

Aircraft Type
Airbus A319

ICAO Type Designator
A319

An Air France Airbus A319-100, registration F-GRHA performing flight AF-7343 from Basel/Mulhouse (Switzerland/France) to Paris Orly (France), was climbing out of Basel/Mulhouse's runway 15 following LUMEL 5T standard instrument departure route, the first officer (ATPL, 3,643 hours total, 3,481 hours on type) was pilot flying and the captain (ATPL, 6,667 hours total, 2,289 hours on type) pilot monitoring. The air traffic controller instructed the aircraft to climb to FL110.

An Easyjet Switzerland Airbus A319-100, registration HB-JZQ performing flight DS-1058 from Palma Mallorca,SP (Spain) to Basel/Mulhouse (Switzerland/France), was descending towards Basel with a training captain occupying the right hand seat being pilot flying (ATPL, 9,418 hours total, 4,374 hours on type) and a captain under supervision (ATPL, 7,090 hours total, 3,350 hours on type) being pilot monitoring, when about one minute after instructing AF-7343 to climb to FL110 the air traffic controller instructed DS-1058 to descend to FL110 and direct to ALTIK waypoint, the crew requested to deviate 10 degrees to the right to avoid a storm cell which was approved with the instruction to report as soon as they were able to proceed direct to ALTIK.

Another 75 seconds later the crew of AF-7343 requested a heading of 230 degrees turning to their left to avoid a storm cell, which was approved as well with the instruction to report as soon as they were able to proceed direct to MOROK waypoint.

About 10 seconds after that instruction DS-1058 reached FL110 and levelled off, while AF-7343 was climbing through FL100 at more than 3000 feet per minute rate of climb. The controller informs DS-1058 that a visual approach as requested would not be possible.

At that time, 27 seconds after the instruction to AF-7343, both TCAS began to highlight the crossing traffic, the pilot monitoring on AF-7343 announced "TCAS, you fly, Flight Directors Off" and both flight directors were disengaged. 3 seconds later a short term collision alert activated at the radar console of the air traffic controller. The controller instructed AF-7343, at that point at FL106, to maintain FL100, the pilot flying disconnects the autopilot and pushes the nose from 4.6 degrees nose up to 2.1 degrees nose up. 2 seconds later the TCAS issues "maintain vertical speed, crossing maintain" resolution advisory to the crew of AF-7343 indicating a climb rate greater than 1500 fpm green and vertical speeds below 1500 fpm climb red. The pilot flying increased the pitch to 6.7 degrees nose up, the pilot monitoring radioed "TCAS climb" to ATC.

At the same time the crew of DS-1058 received a "Monitor vertical speed" with all vertical speeds to climb marked red and descent speeds between 0 and -1500 fpm marked green. The autopilot is being disconnected, the pitch angle changes from 2.8 degrees to 5.3 degrees immediately after. Autothrust is disengaged, 2 seconds after the nose up the nose is pushed down to 5.6 degrees nose down producing a vertical acceleration of -0.19G, DS-1058 reaches a maximum of 11050 feet standard pressure setting, thrust levers are moved into the idle detent. The TCAS resolution advisory changes to "DESCEND, DESCEND CROSSING", 2 seconds the resolution advisory changes to "CLIMB, CLIMB NOW". The pilot flying pulls the nose up to 13.8 degrees nose up producing a vertical acceleration of +2.04G and initiates a turn to the left rolling to a 30 degrees of bank angle, the aircraft reaches a minimum of 10,870 feet on standard pressure setting, the thrust levers are placed into the TOGA detent and the aircraft reaches a climb rate of 2500 fpm.

At the same time AF-3743 received a revised TCAS resolution advisory "DESCEND, DESCEND NOW", the pilot flying pushes the nose down to 5.3 degrees nose down, the pilot monitoring announced "TCAS descend" to ATC. The aircraft reaches a maximum of 11,040 feet on standard pressure setting before beginning to descend. 20 seconds after the first resolution advisories both crews receive "adjust vertical rate" resolution advisories.

The aircraft reach the point of mimimum lateral separation at 0.29nm with a vertical separation of already 1760 feet 23 seconds after the first RAs, 36 seconds after the first RAs both TCAS announce "clear of conflict".

Both aircraft continued to their destinations for safe landings.

The French BEA reported that the minimum lateral separation with both aircraft at the same altitude was 2.2nm at a closing speed of 500 knots (15 seconds to possible collision). The occurrence was rated a serious incident, the BEA released their final report into the serious incident concluding:

The serious incident was caused by the slip of the air traffic controller trainee, who cleared AF-7343 to climb to FL110 although he planned and shortly afterwards cleared DS-1058 to descend to and the non-detection of the slip by the controller instructor.

Contributing factors were:

- the radar displays were unreliable at the time of the serious incident
- the controllers were not familiar with an environment of standard control procedures with unreliable radar and deviations due to weather
- the role of the controller instructor as "interlocutor" between controller and coordinator which was not conducive to supervise the trainee
- it is possible that the vertical speed of AF-7343 played a role in the sequence of TCAS resolution advisories

The further loss of separation evidenced by the TCAS resolution advisory reversal followed as conjunction of:

- the initiation of descent by AF-7343 as result of the trainee's instruction to maintain FL100 after the aircraft had already climbed above FL100, the instruction occurred prior to the TCAS resolution advisory "maintain vertical speed, crossing maintain" with the intention to maintain the current high rather than a reduced rate of climb
- a brief nose up input by the pilot flying of DS-1058 while disconnecting the autopilot to follow the "monitor vertical speed" resolution advisory intended to instruct the crew to not climb

The flight attendant on board DS-1058, already working in the cabin, received a minor injury as result of vertical accelerations of increasing magnitude following the responses by the pilot flying to the successive TCAS resolution advisories.

Inadequacy of the equipment with respect to configuration and capabilities to handle traffic levels resulted in radar system malfunctions. Inadequate coordination of service and down times did not support the detection of these anomalies during safety studies conducted prior to the serious incident.

The BEA stated: "The risk of collision is characterized by the issue of dual TCAS resolution advisories and the short term collision alert".

The BEA analysed that the controllers continued to monitor the radar displays although they could not be certain that the image displayed was reliable.

The controller instructor was taking a position between the trainee and the radar coordinator to facilitate exchanges between the two stations. Due to that position he did not hear the trainee's instruction to descend to FL110 and thus could not determine the coherence of the trainee's actions.

The instructor and trainee had never controlled the standard departure and arrival procedures to Basel/Mulhouse prior to their work shift. The trainee felt uneasy about how to work in that environment but verbalised his uneasiness only after the end of the serious incident.

The trainee had noticed the descending aircraft while watching the radar screens and intended to have that aircraft, DS-1058, descend to FL110, but then made a mental slip clearing AF-7343 to FL110 instead of the intended FL100, and believed he had cleared AF-7343 to FL100. A minute later he then carried out his intended instruction to descend DS-1058 to FL110.

The BEA analysed further that the uncertainty of the radar display and the standard control procedures in use due to the unreliable radar added to the workload of the controllers and helped to develop confusion over the actual position of aircraft. The fallback control procedures to cover unreliable radar image had been inconclusively discussed prior to the occurrence as safety net (with arguments raised that the safety net was unsafe), following the occurrence the Direction des Services de la Navigation Aérienne found it necessary to engage in a reflection on training of control procedures and associated instructions on a national level.

The BEA reported that in May and June anomalies occurred on the radar screens, that slowed the radar screens to a point where aircraft positions could not be detected. The BEA analysed those malfunctions were serious. Such a malfunction may have contributed to the sequence of events resulting in the loss of separation on Jun 29th.

Those failures of the radar visual systems were introduced when portions of the airspace formerly controlled by ACC East were transferred to the approach sector of Basel Mulhouse a few months earlier.

Before the transfer took place a safety study had been conducted but was held to the "operational level" aiming to keep the sectors operating. The study did not expand to include safety aspects of possibly arising scenarios. Notwidthstanding the shortcomings of the safety study the work identified the necessity to upgrade the radar display units. This had to be done quickly to ensure a timely transfer. The study thus did not expand into the installation and configuration of the new radar display units and was not included in a review of the general system. Therefore shortcomings were not detected that arose from the standard configuration prepared at the factory. As result of that standard configuration several unwanted events were not monitored and recorded including but not limited to the slow down of the display units.

In addition the time pressure to install the new units led to regulatory gaps especially of post installation security checks.
Incident Facts

Date of incident
Jun 29, 2010

Classification
Report

Airline
Air France

Flight number
AF-7343

Aircraft Registration
F-GRHA

Aircraft Type
Airbus A319

ICAO Type Designator
A319

This article is published under license from Avherald.com. © of text by Avherald.com.
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