Wind Shear on Short Final
Approach control for runway 30. A B777 is 4 NM final at 1,000 ft. The LLWAS shows a 30 kt shift between the centerfield and threshold sensors, and the current wind is 330/20G35. An aircraft ahead reported a +15/-10 kt shear at 500 ft. A thunderstorm is 8 NM northwest and moving southeast at 15 kt. The next arrival is 8 NM behind. ATIS is 20 minutes old and still advertises calm wind. The B777 crew has not reported the shear.
1. Do you allow the B777 to continue the approach? Justify your decision.
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The approach may continue only with a clear warning and a low threshold for go-around. The LLWAS shift, gust spread, pilot report and nearby storm together indicate a significant wind-shear threat. Issue: 'B777, wind shear warning, wind 330/20 gust 35.' The crew must be told that a go-around will be supported and that a shear encounter is possible below 500 ft. If the crew reports an unstable approach or a significant airspeed loss, instruct a go-around immediately. The controller should not pressure the crew to continue simply because the next arrival is 8 NM behind; safety and stabilised approach criteria take precedence.
2. What do you do about the ATIS, the following arrival and the thunderstorm information?
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The ATIS is stale and misleading; it must be updated with the current wind, gust, LLWAS warning and thunderstorm location before more arrivals are sequenced. Pass the same wind-shear warning to the following aircraft and anticipate that it may need delaying vectors or a holding pattern. Coordinate with the meteorological office and adjacent sectors about the storm's movement, and pass the pilot report to the next controller. If the storm affects the approach path, be prepared to change runway or suspend arrivals rather than continue to feed aircraft into a known shear zone.
3. If the B777 goes around and reports severe shear, what separation and sequencing actions follow?
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Acknowledge the report, give missed-approach instructions and keep the aircraft clear of the storm cell. Do not immediately turn the aircraft back into the same approach; vector it away from the shear area and obtain crew intentions. The following arrival at 8 NM must be held or given delaying vectors until the situation is assessed, because a go-around will disrupt the sequence and may conflict with the missed-approach path. Record the pilot report for the met office and SMS, and advise the tower and approach supervisor that the approach may need to be suspended.