Radar Head Failure in the Middle of the Afternoon Peak
At 1445Z the Santo Domingo approach radar head fails. The display freezes on a coasted picture and the Mode S processor drops flight-plan coupling on about half the tracks; the standby radar at the alternate site is not yet commissioned. Radio communication, telephones and the surveillance feed to the adjacent San Juan CERAP are unaffected. Seventeen IFR aircraft are under control: six on approach to RWY 17, four being vectored downwind, three departures in the climb, two overflights at FL240 and FL260, and two VFR training aircraft. It is the afternoon peak. The second controller position is unstaffed because its incumbent is on a meal break, and the supervisor is in a briefing. The unit's contingency procedure requires reverting to procedural separation, advising all affected aircraft, and notifying adjacent units and the supervisor. The tower is still showing primary radar.
1. State your first five actions in order and justify each one.
Read the worked answer
- Stop trusting the picture. The frozen display keeps presenting plausible track symbols that no longer update; every vector you issue from memory of that picture is a potential loss of separation. The first action is to stop issuing surveillance-based instructions.
- Broadcast to all stations that radar service is terminated and that position reports are required. One transmission covers most of the fleet and stops pilots expecting vectors.
- Get a position from every IFR aircraft - 'say position and estimate next fix' - and write it down. Until each aircraft is positively located, you have no separation at all.
- Call the supervisor and recall the second controller. Seventeen aircraft is not a single-position procedural workload, and the meal break is exactly the kind of normal activity that turns an equipment failure into an incident.
- Coordinate outward: tower (stop departures for a moment), San Juan CERAP (they keep their feed but need to know your capacity has collapsed), and AIS for a NOTAM. Then restrict VFR and reduce the arrival rate before you accept anything new.
The order matters: protect the aircraft first, then get help, then manage the flow.
2. How does separation change, and what do you do with the four aircraft being vectored downwind?
Read the worked answer
Radar separation of 5 nm disappears. Procedural separation applies: vertical separation of 1,000 ft between RVSM-approved aircraft, or longitudinal separation on the same track and level of typically 10 minutes where a navigation aid allows positions to be fixed, and 15 minutes where it does not. Base it on the position reports, not on the last known radar position.
The four downwind aircraft are the hard problem, because 'downwind' only meant something relative to vectors. Options:
- Send them to a published hold or a defined fix they can navigate to and report over, then build a stack with vertical separation.
- Bring them onto the approach one at a time, with the next one only cleared once the preceding aircraft has reported established or landed.
- Use the tower's primary radar as a cross-check, not as a separation tool.
Tell each crew plainly: 'radar service terminated, expect delays, position reports required.' Sequencing four aircraft with no radar will take several minutes each; say so early so the crews can manage fuel.
3. What must be passed to pilots, to adjacent units and in the log, and what human-factors traps do you need to manage in the next ten minutes?
Read the worked answer
To pilots: radar service terminated, position reports required, the applicable QNH, the expected delay, and the runway in use. Keep each transmission standard and short; a non-standard transmission now creates a second problem.
To adjacent units and internally: the supervisor, San Juan CERAP, the tower and ground positions, technical maintenance, and AIS for the NOTAM. The tower needs to stop or meter departures so you are not feeding the approach while you cannot sequence.
In the log: the time of failure, the time of the broadcast, the actions taken, the coordination carried out, the times aircraft were identified by position report, and anything that went wrong. This record also feeds the occurrence report.
Human-factors traps to manage: fixation on the frozen display and trying to 'make it work'; expectation bias, believing a track is where it last was; task saturation from a 17-aircraft procedural workload; and the fatigue and complacency that follow an interrupted break. Countermeasures: get the second controller back, use a deliberate 'stop and think' before each clearance, verbalise your plan to the supervisor, and hand off tasks explicitly rather than assuming someone is covering them.