Incident Overview
On 2 August 2019, at approximately 08:02 LMT (UTC+2), two aircraft operating in the Warsaw Terminal Manoeuvring Area (TMA) experienced a loss of required separation. The aircraft involved were an ATR-72 500, registration OK-NFU, and a Bombardier DHC-8-402, registration SP-EQI. The incident occurred about 4 NM east of the ELKIR waypoint.
Flight Paths and Conflict
OK-NFU was executing the standard terminal arrival route (STAR) AGAVA4U to EPWA (Warsaw Chopin Airport). The crew contacted Approach Control (APP) Warsaw before AGAVA point, descending to FL190. The APP controller trainee cleared OK-NFU to descend to FL120. Meanwhile, SP-EQI was flying the standard instrument departure (SID) EVINA7G from EPWA, maintaining FL180. The routes crossed at approximately 90 degrees. The ELKIR waypoint on the STAR was located 5 NM from the SID track, providing required horizontal separation.
OK-NFU descended but did not reach FL170 or lower as required by the STAR procedure. The On-the-Job Training (OJT) instructor, supervising the trainee, observed a potential conflict but decided to wait for the trainee to notice. The trainee eventually identified the conflict, indicated by linking the aircraft symbols on the radar display using measurement. At 08:05:20, the PEGASUS-21 system generated a Short-Term Conflict Alert (STCA) predicting a proximate conflict.
Resolution and Separation Values
Due to ongoing radio communication with another aircraft, the trainee could not immediately issue instructions. Shortly after, the trainee directed OK-NFU to turn left to heading 360 and SP-EQI to turn left to heading 120, using urgent phraseology. OK-NFU initiated the turn immediately; SP-EQI began the turn after the trainee repeated the instruction.
The loss of separation occurred at 08:05:58 at ELKIR, with OK-NFU descending through FL178. The minimum recorded separation was 4.3 NM laterally and 600 ft vertically, against required minima of 5 NM and 1000 ft. The trainee's decision was delayed, but the issued headings averted a collision risk. Neither crew reported an ACAS Resolution Advisory (RA). After separation was regained, the trainee instructed both aircraft to resume their own navigation.
Causes and Contributing Factors
The investigation identified two causes: 1. Improper execution of the STAR by the OK-NFU crew — at ELKIR, the aircraft was above FL170. 2. Excessive waiting by the OJT instructor for the trainee to notice the potential conflict and react.
Two contributing factors were noted:
- Low experience of the OJT instructor.
- Low operational experience of the trainee.
Preventive Actions
Following the incident, the Air Navigation Services Provider (PAŻP) proposed several preventive actions:
- The incident was to be discussed with the OJT instructor and trainee within two months.
- The SMS Event Investigation Manager was to inform the operator of OK-NFU about the crew's non-compliance with the altitude constraint at ELKIR.
- The report and related materials were to be provided to the ATS Personnel Training Centre for use in OJT training.
No additional safety recommendations were formulated.