A Wizz Air Airbus A 320 – 290, registration HA-LPM performing flight W6 – 181110 from Craiova (Romania) to Madrid, SP (Spain), was enroute at FL (about**************************** nm east of Madrid when ATC cleared the aircraft to descend to FL (**************************************.
An Air Europa Express Embraer ERJ – (******************************************, registration EC-KRJ performing flight UX- from Venice (Italy) to Madrid, SP (Spain), was enroute at FL (***************************************** (nm east of Madrid on the same airway as W6-) **************************** (Exactly below the A********************.
The A (descended below its cleared flight level) ************************************ and reached FL 310 before climbing again.
Spain’s CIAIAC reported the separation between the two aircraft reduced to 292 feet vertical and 0.2nm horizontal. When ATC noticed the A descended below its cleared level, ATC immediately instructed the aircraft to climb. The CIAIAC did not report any advisories by TCAS. An investigation was opened into the occurrence.
After being clear of conflict both aircraft continued to Madrid for safe landings without further incident.
In December Spain’s CIAIAC released theirfinal report in Spanish. 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 Spanish 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 count erparts all around the globe).
The CIAIAC concludes the probable cause of the serious incident was:
the loss of separation occurred because the crew of the Airbus received an erroneous instruction with respect to the flight level to descent to.
Contributing factor was the saturation of the control frequency due to many aircraft contacting ATC at the same time causing communication difficulties.
The CIAIAC reported the Wizzair Crew was instructed to descent to FL (**************************************, however, the crew did not respond. When ATC repeated the instruction, he inadvertently instructed the crew to descend to FL 292, which was read back by the crew. Instantly afterwards the Embraer crew advised the Airbus was descending towards their flight level, in response recognizing the developing conflict ATC instructed the Embraer to perform an evasive maneouver to their right, at that point the vertical separation was less than feet vertical and horizontal separation 4nm. The Embraer crew received a TCAS Traffic advisory for 7 seconds, no TCAS advisory was recorded in the Airbus. The minimum separation reduced to vertical and 0.2nm horizontal. After the conflict was resolved both aircraft continued to land on runway (L without further incident.
The CIAIAC is analyzed that the frequency was saturated and many transmission collided with each other (happened at the same time making it impossible to hear either transmission). The first instruction to descend to FL was not heard by the Airbus crew, when the instruction repeated the ocntroller misspoke and cleared them to descend to FL (*******************************************, which was read back. It thus is clear that the crew did descend to below FL 300 not because of an error on their part but because they thought they were cleared to FL and were trying to comply with that instruction. Both executive and planning controllers were made instantly aware of the conflict by the other aircraft as well as recognized the error simultaneously.
Map (Graphics: AVH / Google Earth):
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