Conflicting Traffic During a Radar Vectors Approach
Bahrain Approach is providing radar control to an inbound Airbus A321 on a heading of 240 degrees, descending to 4,000 ft, cleared for a vectors ILS approach to Runway 30R. A second aircraft, a Gulfstream G650, is on a heading of 090 degrees at 5,000 ft, cleared to descend to 4,000 ft, and is being vectored for the same runway behind the A321. The controller observes the G650's Mode C indicating 4,800 ft and descending. The A321 is at 4,200 ft. The radar display shows the two aircraft 4.5 NM apart laterally and closing. The controller's radar has a 5-second update rate; the last position update was 3 seconds ago. The G650 pilot reports a TCAS traffic advisory.
1. What separation standard applies here, and does the controller have a loss of separation?
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Under ICAO Doc 4444 radar separation, aircraft established on the same or crossing tracks within controlled airspace where radar separation is applied must be separated by at least 5 NM laterally or 1,000 ft vertically. The two aircraft are 4.5 NM apart laterally and the vertical separation is 4,200 ft versus an indicated 4,800 ft (Mode C), which is only 600 ft - below the 1,000 ft minimum. Therefore both lateral and vertical minima are breached, and separation has been lost. The controller must act immediately: issue an avoiding action to both aircraft, for example a turn to increase lateral spacing and a level-off or climb/descent to restore vertical separation. The controller should also inform the G650 crew of the traffic and acknowledge the TCAS TA. The 5-second radar update rate and 3-second-old data mean the displayed 4.5 NM could already be less; the controller must not wait for the next sweep before acting.
2. What should the controller say to both aircraft, and what follow-up is required after the event?
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The controller should issue clear, concise avoiding instructions to both aircraft. To the A321: 'Turn right heading 300 degrees, maintain 4,000 feet' or a climb/descent as appropriate to restore vertical separation. To the G650: 'Turn left heading 030 degrees, maintain 5,000 feet' or level off at 5,000 ft. The instructions must be unambiguous and prioritised over the approach sequence. The controller should also advise each aircraft of the other's position and altitude. After separation is restored, the controller must file an occurrence report under the State's safety reporting system, recording the positions, altitudes, instructions issued, and the TCAS TA. The event should be reviewed for systemic causes - for example, whether the descent clearance to the G650 was issued too early, whether the radar update rate was adequate, and whether the approach sequence was over-committed. The controller should not attempt to hide the event; voluntary reporting supports safety management.