Incident Overview
On 28 July 2006, an incident involving a reduction of the prescribed separation occurred between two commercial aircraft in the Prague Flight Information Region (FIR LKAA). The aircraft were an MD-82 (registration OY-KHE) operating as Scandinavian Airlines flight SAS 1666 and an A319 (registration D-AILK) operating as Germanwings flight GWI 2727. The event took place approximately 10 km northeast of the OKG navigational aid at flight level 324.
Sequence of Events
SAS 1666 departed from Munich (EDDM) at 11:54 UTC en route to Copenhagen (EKCH). After entering the Prague FIR, the crew contacted the area control center (SWM EC) at 12:01:22, reporting flight level 280 and a heading of 014° to avoid thunderstorm activity. At 12:02:29, the controller instructed the crew to climb to FL 310, which they acknowledged and initiated. Shortly thereafter, at 12:03:51, the controller issued a further instruction to climb to FL 340 with a vertical rate exceeding 1500 ft/min. The crew acknowledged while passing FL 302.
According to radar data, the climb was interrupted at FL 322 at 12:05:27 without notification to ATC. The controller queried the crew at 12:05:56 regarding their ability to increase the climb rate due to conflicting traffic (GWI 2727). The crew reported a problem maintaining vertical speed. The controller then issued a left turn instruction of 20° to maintain separation.
Meanwhile, GWI 2727 had departed from Warsaw (EPWA) at 10:50 UTC en route to Stuttgart (EDDS). The crew contacted the same controller at 11:58:32 at FL 340 approaching the KONAR waypoint. At 12:03:29, the controller instructed them to descend to FL 320. At 12:05:00, the crew received an expedited descent instruction. At 12:06:23, after coordination with other sectors, the controller issued a further descent to FL 300 at maximum vertical rate.
The Short Term Conflict Alert (STCA) activated at 12:06:14. The closest approach occurred at 12:06:57, with a vertical separation of approximately 800 ft and a horizontal distance of 4.26 nautical miles. The crew of SAS 1666 received a TCAS Resolution Advisory (RA) requiring a climb, which they executed at 300 ft/min. The RA cleared after about 2 seconds. The crew did not report the RA to ATC.
After the conflict, SAS 1666 was instructed to proceed direct to KILNU and later transferred to ACC Rhein at 12:08:18. GWI 2727 was transferred to ACC Rhein at 12:07:38 and left the Prague FIR at 12:10:54.
Aircraft and Crew Information
The MD-82 (OY-KHE) was manufactured by McDonnell Douglas/Boeing, USA. The A319 (D-AILK) was manufactured by Airbus Industries. Both aircraft were operated under standard airline procedures. The crew of SAS 1666 reported that at FL 320 the Ram Air Temperature (RAT) reached -18°C, leading to a suspected engine inlet icing condition. They engaged engine anti-icing, but the vertical climb rate decreased. No injuries or aircraft damage occurred.
Meteorological Conditions
According to the Czech Hydrometeorological Institute, the region was under a weak pressure field over central Europe. Visibility was greater than 10 km, with scattered cumulus and towering cumulus clouds bases at 2500–4000 ft, and scattered layers above 10,000 ft. Strong thermal turbulence was present. The crew of SAS 1666 reported a wind of 240°/45 kt at FL 320, visibility of 500 m (likely in cloud), light turbulence, and cumulonimbus clouds. Thunderstorm activity was confirmed by ATC communications, with other traffic requesting course deviations due to CB cells north of OKG.
Aftermath
The incident was reported to the Air Accidents Investigation Institute (ÚZPLN) by the Czech Air Navigation Services Provider. The institute notified the Swedish authority (responsible for SAS) and conducted an investigation in accordance with Annex 13. The final report was issued on 28 May 2007. No explicit probable cause was stated in the available sections of the report.