Introduction
On 11 October 2014, a serious incident involving a loss of separation occurred between a Boeing B735 (flight BTI97H) and a Piper PA-34L (registration YL-GBS) near Riga International Airport (EVRA). The incident was investigated by the Transport Accident and Incident Investigation Bureau of Latvia (TAIIB).
Sequence of Events
The Piper PA-34L departed from Spilve airfield (EVRS) at 13:00 UTC on a training flight. At 13:09:48, the pilot contacted Riga Tower controller on frequency 118.1 MHz, requesting to enter via SARPS and climb to 1500 feet. The controller provided QNH 1018 and squawk 1615.
Meanwhile, the Boeing B735, operating as AirBaltic flight BTI97H, was arriving on final approach to runway 18. At 13:04:04, the crew contacted Riga Approach controller on 129.925 MHz, descending from flight level 110. The Approach controller vectored the aircraft, instructing descent to 2500 feet at 13:11:15, then to 1500 feet at 13:13:38.
At 13:15:00, the Approach controller cleared BTI97H for an ILS approach to runway 18, with a heading of 150 degrees. At 13:16:08, the Boeing was transferred to Tower frequency 118.1 MHz, coming under the Tower controller’s responsibility.
At 13:16:12, the Tower controller instructed YL-GBS to turn right to heading 030 degrees. The Piper pilot acknowledged at 13:16:23. However, the Piper had previously been assigned a turn to heading 30° but deviated from this instruction, coming close to the arriving Boeing.
Separation Data
At 13:15:55, the Boeing was at 1500 feet (crossing 2600 feet) with ground speed 176 knots on a true track of 154 degrees. The Piper was at 1500 feet with ground speed 117 knots on a true track of 245 degrees. The separation was 5.5 nautical miles (NM), and the Short-Term Conflict Alert (STCA) was active. The STCA signal turned off at 13:16:04.
By 13:16:23, the Boeing was crossing 2300 feet on track 156 degrees, while the Piper remained at 1500 feet on track 242 degrees. The separation had reduced to 4.5 NM. The minimum recorded vertical separation was 300 feet, and longitudinal separation was 2 NM.
Reporting and Investigation
The incident was not immediately reported to TAIIB; notification arrived on 22 October 2014 from the ATC service provider. TAIIB initiated an investigation under Annex 13 to the Chicago Convention and EU Regulation 996/2010. The report noted that both aircraft were under the Tower controller's control at the time of the incident. No injuries or aircraft damage were reported.