Procedural separation when radar coverage is lost in the eastern lowlands
The Santa Cruz approach radar (SRE) fails at 18:40 UTC. Two IFR aircraft are in the terminal area: flight BOV 720, a 737-800 inbound from the east descending through FL150 on the VOR/DME approach transition, and flight BOV 314, an ATR 42 outbound to the north climbing through FL110. Both are in communication with approach. The controller has a flight progress strip for each, a VHF/HF link, and no surveillance. The 737's last reported position was 40 NM east, estimating the initial approach fix in 9 minutes. The ATR reported 25 NM north, estimating the en-route boundary in 6 minutes. There is a third aircraft, a medevac Learjet 35, requesting priority inbound from the south at FL200, 50 NM out.
1. With radar lost, what separation standard now applies between BOV 720 and BOV 314, and is the current situation compliant?
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Without radar, the controller must apply procedural separation. The primary tool is vertical separation: 1,000 ft below FL290 and 2,000 ft at or above FL290 (or the applicable metric equivalent). Lateral separation can be achieved by ensuring the aircraft are on different airways or on tracks separated by the prescribed angular or distance criteria, and longitudinal separation by time (typically 10 minutes at the same level on the same track, or 15 minutes if the following aircraft is faster, unless a reduction is authorized by the appropriate authority).
Current situation: BOV 720 is descending through FL150, BOV 314 climbing through FL110. They are 4,000 ft apart vertically and on diverging tracks (one east-west inbound, one northbound outbound). That is compliant provided the controller stops the 737's descent at a level that keeps at least 1,000 ft from the ATR's cleared level and does not allow the ATR to climb into the 737's level. The risk is that both are on climb/descent profiles converging on the same terminal area, and without radar the controller cannot verify their actual positions between reports.
Actions: freeze the levels, confirm each aircraft's cleared level and estimate, and require position reports at the next compulsory reporting point. Do not use the last radar positions as if they were current; they are now historical. If the tracks will cross, apply vertical separation before the crossing, not after.
2. The Learjet 35 requests priority inbound at FL200. How should the controller integrate it without surveillance, and what does 'priority' entitle it to?
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Priority means the controller must give the medevac precedence in sequencing and, where necessary, hold or delay other traffic to accommodate it. It does not mean the controller can suspend separation standards. The Learjet still needs a clearance, a level, and separation from the other two aircraft.
Integration steps:
- Establish the Learjet's position and estimate by procedural report, since there is no radar. At FL200, 50 NM south, it is above both other aircraft.
- Keep it high as long as possible. FL200 is 5,000 ft above the 737's current FL150 and 9,000 ft above the ATR's FL110, so vertical separation is already satisfied. The danger is the Learjet's descent: if it descends to approach levels while the 737 is still on the transition, the controller must sequence them vertically or longitudinally.
- Sequence the 737 first if it will reach the IAF in 9 minutes, then the Learjet behind it, using time-based longitudinal separation at the same level, or keep the Learjet at a higher level until the 737 is established.
- Coordinate with the area control centre for the Learjet's handover and with the tower for the priority landing.
- Inform the other aircraft that a medevac is being given priority, so they expect delays.
The controller must also consider that the ATR is outbound and climbing; if the Learjet descends through the ATR's level, the climb must be capped until the Learjet is clear.