On Monday, 21 April, 2008 at 15:05 UTC a serious aircraft incident took place in Riga FIR, in the vicinity of Liepaja (N56:31:07; E021:05:31) : Air Baltic flight BT165T – Virgin Atlantic flight VIR301 airprox.
Virgin Atlantic flight VIR301 Airbus A340 was en route from Indira Gandhi Intl (DEL), Delhi, India to Heathrow Airport (LHR), London, EN, GB, cruising at FL 380.
Air Baltic flight BT165T Boeing B757-200 (YL-BDC) was en route from London – Gatwick (LGW) on a reciprocal track at FL390 to Riga Intl (RIX).
Air Baltic flight BT165T got issued clearance from the Riga ATC WEST-COMBINED sector controller (hereinafter ATCO) direct to FAP Vekas of CTR Riga International airport.
The crew declared readiness to descend from FL390 to FL170 and had issued clearance from ATCO descend to FL170 despite that the same time with opposite heading at FL 380 was cruising Virgin Atlantic flight VIR301.
Clearance was read back by the crew of Air Baltic flight BT165T and Boeing 752 started descending.
At 15:05:06 the two aircraft passed each other with opposite headings in the vicinity of LIEPAJA (N56:31:07; E021:05:31) in the RIGA Flight Information Region and the separation standard between the two aircraft was infringemented.
The crew of Virgin Atlantic flight VIR301 Airbus A340 received the traffic alert and collision-avoidance system (TCAS) resolution advisory (RA) to descend as a result of the Boeing 752, Air Baltic flight BGT165T traffic ahead of them.
The circumstances leading to this serious incident were following:
- At the time of the incident the traffic was handled by an air traffic controller-student of ANS Training Center who was on an on-the-job training period.
- The air traffic controller on duty had about at the working position and coordinated the traffic by ground communication with adjacent Riga ATCC MALMO AoR sector controller.
- During communication air traffic controller on duty did not control actual situation in the airspace between above mentioned aircraft.
- The student cleared Boeing 757-200 Air Baltic flight BTI65T to descend from FL390 to FL170 despite the opposite heading at FL 380 was cruising Virgin Atlantic flight VIR301.
- Air traffic controller on duty started to handle the traffic after completing communication with MALMO controller and perceiving that there is conflict situation tried to contact with crew of Boeing 752, three times issuing heading change for the aircraft but the crew did not answer.
- After that controller on duty issued heading change for the aircraft Airbus A340-600, but at that time resolution advisory (RA)”DESCEND, DESCEND” was annunciated, the PIC of Airbus A340- 600 disengaged the Autopilot and followed the RA. After a while the RA reduced to a Monitor Vertical Speed RA and then Clear of Conflict.
At the time of the incident, vertical separation between Air Baltic flight BT165T – Virgin Atlantic flight VIR301 decreased to 700 feet, horizontal separation was to 4.0 nautical miles.
The conflicting traffic was in sight for aircrafts crews, so Boeing 752, flight BTI65T and Airbus A340-600, Flight VIR301 passed each other by right side. Visual meteorological conditions existed at the time.
The source or origin of an event that played the major role that caused this incident was human factor – air traffic student controller error- the fact that the air traffic controller – student who handled an air traffic due to lack a experience did not estimate time of passing as well as did not predict consequences and issued instruction for BT165T to descend to FL 170 that potentially can lead to conflict between VIR cruising at FL 380 and BT165T cruising at FL390.
Contributing causes :
- The fact that before conflict controller-student can not get consultation from air traffic controller on duty because he was busy with communication of adjacent ACCC Malmo AoR Sector controller;
- The ATC controller on duty did not recognise that separation would be infringed if the BT165T pilots were cleared to descend their aircraft to FL170, until after separation was infringed;
- The fact that crew of Boeing 752, Flight BTI65T for instructions to change heading of the aircraft with a design to prevent conflict situation did not answer on triple ATCO voice callings.