Citation climbed into conflict with 737

[Ref 18-24 June 2019 | Flight International P.12]

Occurrence Date/Time 20 April 2017
Aircraft Type Cessna Citation (EC-LCX) ; 737-800 (EC-JBK)
Flight / Operator Caladero Aviation ; Air Europa
POB  –
Description The Cessna was cleared to climb to 11,000ft but its captain incorrectly read back the clearance as 12,000ft.

At the point where the Cessna levelled off, the two aircraft were “on a collision course

The two aircraft were fitted with collision-alert systems – although the 737 was capable of issuing resolution advisories, the Cessna’s system only provided a traffic alert

The 737’s system instructed the crew to descend and the Cessna’s crew also started to descend, as a discretionary
evasive manoeuvre.

At their closest point, the two jets were 0.9 NM apart, at the same altitude

Result The 737’s collision-avoidance system reversed its descend instruction to a climb order, and the Cessna was told to turn left by air traffic control.


Short-term conflict alert systems had not been implemented in the airspace sector at the time,
and were not in place until a year after the incident.

Contributory factors Both pilots made mistake – the Cessna‘s captain incorrectly read back the clearance while the 737’s captain had overheard “perfectly” the Citation
acknowledgement with no further clarification.

Meanwhile, neither the controllers on duty – a trainee overseen by an instructor – noticed the incorrect altitude acknowledgement

Recommendation Short-term conflict alert systems should be implemented in the dense airspace sector

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