On 8 July 2010, an Airbus A319 being operated by Easyjet on a scheduled passenger flight from London Gatwick to Milan Malpensa in day Visual Meteorological Conditions (VMC) with line training in progress lost separation against crossing traffic at FL320, a Lufthansa Boeing 737-300 being operated on a scheduled passenger flight from Nice to Frankfurt, when the A319 descended below its cleared level.
The Investigation was delegated by the French BEA to the Swiss AAIB. It was noted that the conflict had occurred in Class ‘A’ airspace. The Investigation was based upon R/T and radar recordings, mode ‘S’ data and the statements of the flight crew members and the air traffic controllers. It was specifically noted that “the EasyJet company did not provide the AAIB with data from the flight data recorders”.
It was noted that the commander of the A319 was a Training Captain engaged in line training an inexperienced First Officer but the Investigation did not establish which pilot had been designated as PF. It was established that conflict had occurred in day VMC.
It was established that shortly after the A319 crew had been re-cleared on a radar heading from FL370 to FL330 which, although it had been correctly read back had actually been set on their Flight Management System as FL320, the crew had reduced their rate of descent below the minimum 2000 fpm required in conjunction with their descent clearance without permission to do so from ATC because they had received a TCAS TA against traffic below at FL360 and wished to avoid a TCAS RA. Shortly after this, the aircraft was transferred to the next sector. The crew checked in and gave their cleared level as FL320 but the controller did not notice this and simply re-iterated their cleared level as FL330.
Almost immediately, an Short Term Conflict Alert (STCA) Alert was generated as the aircraft descended through FL326 and into potential conflict with the Boeing 737 crossing below at FL320. This was followed less than half a minute later by a TCAS RA ‘CLIMB’ annunciation for the 737, which was actioned accordingly. At almost the same time, the A319, having reached FL320, called ATC to say there was traffic ahead at the same level and was given an emergency turn right onto heading 190°. The 737 RA was only brief and led to a climb of only 300 feet. The A319 received only a TCAS TA. The two aircraft reached their closest proximity on divergent tracks 31 seconds after the TCAS RA had been received by the 737, a lateral distance of 2.2 nm and an altitude difference of 125 feet.
The Investigation considered that “the flight crew of the A319 (twice) showed that they were responding to the traffic advisories in a manner more pronounced than that of preparing for a possible resolution advisory”. It was considered that this inappropriate concern with responding the TCAS TAs had “disrupted the attention of the pilots” in respect of both the original mis-setting of the cleared level and the failure to notice subsequently that this setting did not correspond to the one re-iterated when checking in with the new sector. It was noted that the pilot SOPs for verifying that a new cleared level has been correctly set involves a cross check of the displays on both pilots’ PFDs and that “this operation was clearly not carried out” and represented “a failure to apply the pilot procedure relating to changes in flight levels”.
It was noted that at the time of the event, access to down-linked Mode ‘S’ parameters was not available at Geneva ACC but that implementation had subsequently commenced.
The Cause of the investigated serious incident was determined as:
“the dangerous convergence of an aircraft descending below its cleared flight level, to the same level occupied by an aircraft crossing on a perpendicular route”.
Contributory Factors were identified as:
- An incorrect flight level entered into the flight management system by the flight crew of the EasyJet A319
- The (second) controller not realising that the crew had reported an incorrect cleared flight level during the initial contact on his frequency.
- During this contact, the EasyJet flight crew did not carry out the appropriate verification of the flight level which they correctly read back.
The Final Report no. 2145, serious incident (AIRPROX) was completed on 30 October 2012 and approved by the Swiss AIB on 8 November 2012.