Europa B738 near Palma Mallorca on Apr 20th 2017, near collision with business jet

Last Update: June 4, 2019 / 21:38:51 GMT/Zulu time

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Photo of Air Europa EC-JBK, Boeing 737-800 — Air Europa EC-JBK, Boeing 737-800 (Photo credit: Bram Steeman - Aviation Photography / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Apr 20, 2017

Classification
Incident

Cause
Near collision

Airline
Air Europa

Flight number
UX-6007

Departure
Barcelona, Spain

Destination
Palma Mallorca, Spain

Aircraft Registration
EC-JBK

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

An Air Europa Boeing 737-800, registration EC-JBK performing flight UX-6007 from Barcelona,SP to Palma Mallorca,SP (Spain) with 162 passengers and 6 crew, was maintaining FL120 while maneouvering for the approach to Palma Mallorca.

A Cessna Citation C510 business jet registration EC-LCX had departed Palma Mallorca and had been instructed to climb to FL110, however, climbed above FL110.

Spain's CIAIAC reported a loss of separation occurred 13nm north of Palma Mallorca's aerodrome when both aircraft came to maintain FL120. Both aircraft performed evasive maneouvers, the closest point of separation occured with both aircraft at 11,300 feet (0 feet vertical separation) and 0.9nm horizontal separation at 06:58z.

Both aircraft subsequently continued their flight to their destinations and landed safely.

The CIAIAC opened an investigation into the occurrence.

No position data off the Citation's transponder are available. The position data off the B738 suggest the aircraft received a TCAS RA to descend and descended to about 11,000 feet in response to the resolution advisory before returning to FL120.

On Jun 4th 2019 the CIAIAC released their final report concluding the probable cause of the incident was:

The incident is deemed to have been caused by the failure of the controller to correct a faulty acknowledgment by the crew of EC-LCX.

The CIAIAC analysed:

The controller identified the potential conflict between the flight paths of EC-LCX and AEA6007, and as a result, he correctly planned the instructions to give to ensure vertical separation between them. He instructed AEA6007 to descend to FL120 and hold, and EC-LCX to climb and maintain FL110. He also gave traffic information to both aircraft. The phraseology used and the way in which the messages were made by ATC were clear and in keeping with procedure.

However, the captain of EC-LCX, who was handling communications at the time and was acting as the PM, (incorrectly) acknowledged FL120. This message was also clear. The aircraft’s captain stated that he did not know why he heard the clearance incorrectly, but he indicated that after his acknowledgment, the first officer set FL120 and he replied “check”, just as required by procedure. In other words, both pilots made the same mistake.

However, the captain of AEA6007 heard perfectly that the controller’s instruction entailed stopping the climb of EC-LCX at FL110, and also heard how said aircraft acknowledged FL120. This put him on the alert, since he was holding at FL120 and could see EC-LCX climbing quickly on his left on a flight path that converged with his.

As a result, the possibility that ATC’s instruction was incorrect can be ruled out, and the misinterpretation of the instruction received is confirmed, which caused EC-LCX to climb higher than the level instructed to an incorrect level.

Neither the trainee nor the executive controller, both of whom were responsible for the communications, noticed the incorrect acknowledgment by the crew of ECLCX, even though it was received clearly. This indicates that both controllers were focused on other tasks and were not actively listening to the acknowledgment from the aircraft. Specifically, seconds after the acknowledgment from the crew of ECLCX, the controller under instruction was giving instructions and radar and radio contact to another aircraft that had made contact on the frequency earlier and that he had been unable to reply to until then. As stated, the instructional stage that the trainee controller was in required constant communications between the trainee and the instructor, which forced the latter to focus on multiple areas in order to maintain situational awareness of the traffic while providing the explanations.

...

Aircraft EC-LCX exceeded FL110 at 06:57:16, and 14 seconds later was climbing through 11400 ft. This activated the level change alert which involves a color change in the CFL field of the radar label. However, the controllers did not notice this, since between 06:57:16 and 06:57:47, they were focused on contacting and giving instructions to another aircraft (EZY123M). Both controllers may have believed that the potential conflict between EC-LCX and AEA6007 had been addressed, since they had given instructions that separated them vertically by 1000 ft, along with traffic information to both aircraft, so they did not actively monitor the radar.

Upon detecting the conflict, at 06:57:52, the controller under instruction told ECLCX to turn left heading south. By that point, the aircraft had reached FL120 and the aircraft were some 2.2 NM and 0 ft apart. Thus, both the measure adopted to alter the flight path horizontally and the phraseology used, which included the term “immediately”, were in keeping with procedure. AEA6007 was then instructed to turn right, but its crew reported that they were responding to a TCAS RA. Before that moment, the controller had not been informed by the crew of AEA6007 that they were executing a TCAS RA maneuver, and thus the instruction given to AEA6007 is not deemed incorrect.

The conflict alert system (STCA) had not yet been implemented in the airspace in which the aircraft were flying. According to data provided by the Palestra system, if the STCA had been implemented, the initial visual and aural alert would have been issued at 06:57:22, at which time EC-LCX was climbing through FL113 and the horizontal distance was 4.2 NM. It is estimated that the controllers would have been able to detect the conflict some 30 seconds in advance.

The fact that the navigation service provider implemented the STCA system in April 2018 will very likely help to identify situations such as this one. As a result, it is not necessary to issue an additional safety recommendation.

In the factual section of the report the CIAIAC states that the Boeing received a TCAS resolution advisory to descend, however, in the analysis they stated the TCAS RA was to climb which later was reversed to climb because both aircraft were descending. The Cessna did have ACAS I only which does not produce resolution advisories, the captain of the Cessna thus performed an evasive descent while following the ATC instruction to turn left, the Boeing crew followed the TCAS descent instruction but maintained their heading and did not comply with the ATC instruction to turn right. The CIAIAC concluded the analysis: "The fact that both aircraft executed descent maneuvers caused a change in the direction of the TCAS resolution advisory on board AEA6007, which now instructed the crew to climb. According to QAR data, following this activation, the aircraft started to reduce its descent rate, which caused the vertical separation between the two aircraft to increase. According to radar data, the aircraft came at the closest point of approach within 0.9 NM and 0 ft of each other."

Metars:
LEPA 200800Z 05015KT 020V080 9999 FEW028 14/03 Q1024 NOSIG=
LEPA 200730Z 05017KT 9999 FEW028 14/04 Q1024 NOSIG=
LEPA 200700Z 06010KT 020V090 9999 FEW028 13/03 Q1024 NOSIG=
LEPA 200630Z 06010KT 9999 FEW028 11/05 Q1023 NOSIG=
LEPA 200600Z VRB01KT 9999 FEW028 09/05 Q1023 NOSIG=
LEPA 200530Z 00000KT 9999 FEW028 07/03 Q1023 NOSIG=
LEPA 200500Z VRB01KT 9999 FEW028 06/03 Q1022 NOSIG=
LEPA 200430Z 01002KT CAVOK 06/03 Q1022 NOSIG=
LEPA 200400Z 00000KT CAVOK 06/03 Q1022 NOSIG=