TCU Veto on a Converging Departure
At 14:20 UTC, SBXX Tower is running a single runway with a long departure queue. A B738 (MTOW 79 t, wake category M) is lined up and cleared for take-off on runway 09 with an initial climb to 5000 ft, heading 090. At the same moment, an A320 (wake category M) on approach to the reciprocal runway 27 has gone around and is climbing on heading 270 at 4000 ft, 6 NM west of the threshold, requesting vectors back for another approach. The tower controller's radar display is certified for 5 NM separation but the minimum radar separation in the TMA is 3 NM. The area controller has not yet accepted handover of the departing B738. Wind is calm, visibility 10 km. The tower controller decides to let both aircraft continue and to issue traffic information only.
1. Evaluate the tower controller's decision to continue both movements with traffic information only. Identify the separation standard that applies and the specific risk.
Read the worked answer
The decision is unsafe and likely non-compliant. The two aircraft are on reciprocal headings (090 and 270) in the same TMA, both climbing/level in the same altitude band (the go-around aircraft is at 4000 ft, the departure will pass 4000 ft shortly). Traffic information alone does not discharge the controller's duty when the controller is providing an ATS surveillance service and the aircraft are under the controller's control in the same airspace.
Key reasoning points:
- The applicable standard is radar separation: 3 NM within the TMA, subject to the surveillance system's capability. The tower's display is certified for 5 NM, so the controller cannot apply 3 NM on that display; the effective minimum is 5 NM unless the separation is delegated to an approach/area controller whose display supports 3 NM.
- Reciprocal tracks are converging head-on. At typical departure and go-around climb speeds (approximately 250 kt closing at 500 kt), 6 NM of initial track distance closes in well under a minute - less than the time needed to coordinate a handover.
- Wake turbulence is not the primary issue here (both are category M), but the go-around aircraft is low and slow and may be unstable; the departure may need to be stopped on the runway if the go-around cannot be vectored clear.
- The correct action is to delay the departure clearance until the go-around aircraft is vectored away from the departure corridor, or to issue an immediate turn to the go-around aircraft (e.g., heading 180 or 360 to open the tracks) before the departure rolls. Traffic information is an adjunct, not a substitute for separation.
2. The area controller refuses handover because the departure's Mode C is intermittent and the flight plan shows a cruising level of FL340. What coordination should the tower controller perform before the departure becomes airborne?
Read the worked answer
The tower controller must resolve the handover before releasing the departure, because an aircraft that is airborne without an accepted handover is in a coordination gap.
Steps:
- Establish voice coordination with the area controller (not just a data message) and state the constraint: intermittent Mode C, requested initial level 5000 ft, and the go-around traffic in the TMA.
- Confirm the assigned level and any restriction. The area controller may accept the aircraft with a temporary level restriction (e.g., maintain 5000 ft until radar identification and Mode C verified) rather than refusing the handover outright.
- If the area controller still cannot accept, the tower must not release the departure into airspace where no unit has accepted control. The tower controller should hold the aircraft on the ground or, if already rolling, issue a stop or an early turn and coordinate a holding instruction.
- Record the coordination (time, unit, content) and advise the approach controller of the go-around aircraft's status so the two streams are deconflicted.
The judgement point: a refusal of handover is a red flag, not a formality. The controller must not 'push' the aircraft into the next unit's airspace and sort it out later.