Compression on Final Behind a Heavy

The gap is 6.0 NM and the required minimum is 5 NM, so there is only 1.0 NM of buffer. A closing rate of 40 kt is about 0.67 NM per minute (40/60). At that rate the 1.0 NM buffer is consumed in roughly 1.5 minutes. The 777 is 6 NM from the threshold at 160 kt, so it needs about 2.25 minutes to reach it, and it will slow further to 140 kt at 4 NM, which increases the closure rate because the A320 is still at 200 kt. Separation would therefore be lost approximately 45 seconds before the heavy touches down, and possibly earlier once the speed reduction takes effect. A 5 NM gap is not a target to defend; it is a floor. The existing clearance cannot stand unchanged. The decision must be taken now, not when the gap reaches 5 NM, because by then the corrective instruction will not have time to take effect.

Sequence the A320 behind the heavy and control the closing rate with speed rather than with vectors, since a vector would take it off the localizer and cost more time. Phraseology: 'JAI 452, reduce speed 160 knots, maintain 5 miles behind heavy Boeing 777.' The word 'reduce' is correct because the aircraft is already at 200 kt; the speed is a limit, not an optional suggestion. Why 160 kt: it removes most of the 40 kt closure immediately. The heavy will still slow to 140 kt at 4 NM, leaving about 20 kt of closure, which over the remaining 1.5 minutes costs roughly 0.5 NM, keeping the gap above 5 NM. Monitor the gap at each mile. If the A320 cannot accept 160 kt, or if the gap falls below 5.5 NM, instruct it to go around: 'JAI 452, go around, fly runway heading, climb 3000 feet.' Do not delay the go-around in the hope that the leader will clear the runway early.

'Minimum fuel' is an advisory, not an emergency declaration. It tells the controller that the aircraft cannot accept any undue delay without becoming fuel-critical; it does not permit a breach of wake turbulence separation. The plan therefore stays the same on the spacing side, but priority handling changes: keep the A320 number one for the runway, give it the shortest practical route to the threshold, and avoid any further speed restriction below its safe approach speed. Inform the tower by landline so the runway is vacated promptly and the next arrival is not delayed. Ask the pilot to state the endurance in minutes so you can judge whether a go-around remains safe. If the fuel situation deteriorates into 'mayday fuel', separation is still maintained, but all other traffic is stopped and the aircraft is given priority. The key judgement is not to trade a wake turbulence guarantee for a fuel advisory; both risks are managed, not swapped.