Wake Turbulence Spacing Behind a Heavy on Final
At 14:20 UTC, tower at a single-runway international aerodrome (runway 18R, 3,400 m, dry) is sequencing arrivals in a light wind of 180/05 kt. A Boeing 747-8 has just landed and is rolling out at high speed. The next arrival, a Cessna 172, is established on final at 3.0 NM and has already been cleared to land. A Boeing 737-800 is 9 NM behind the Cessna. The Cessna pilot reports the preceding Boeing in sight and asks to continue, saying 'no turbulence felt.' There is no secondary runway, no crosswind, temperature 31°C, and the 747-8 is still on the runway. The tower controller must decide whether the spacing complies with ICAO wake turbulence separation minima and how to manage the 737-800 behind.
1. State the wake turbulence category of each aircraft and the minimum separation between the Boeing 747-8 and the Cessna 172. Was 3.0 NM compliant, and what immediate instruction should the tower controller issue?
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Categories: the Boeing 747-8 is Heavy; the Cessna 172 is Light. Under ICAO Doc 4444 arrival wake turbulence minima, a Light aircraft following a Heavy aircraft on the same approach requires 6 NM. The spacing is therefore 3 NM against a 6 NM minimum and is not compliant.
The Cessna pilot's visual report does not by itself reduce the wake turbulence minimum. Visual separation may only be used where State procedures permit the pilot to maintain own separation and the pilot explicitly accepts that responsibility; here the safe, defensible decision is to remove the conflict. Issue: Cessna 172, go around, I say again, go around, traffic was a Boeing 747-8 heavy, wake turbulence; climb straight ahead to 3,000 ft, contact approach 120.4. Ensure the 747-8 vacates and warn the 737-800 of the go-around traffic.
2. How should the controller sequence the Boeing 737-800 behind, and what wake turbulence separation applies to it?
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The 737-800 is Medium. A Medium aircraft following a Heavy aircraft requires 5 NM wake turbulence separation. At 9 NM behind the Cessna, the 737 is about 12 NM behind the 747-8 once the Cessna's 3 NM is added, so the 5 NM minimum is satisfied. The controller should not rush the 737: the runway must be vacated by the 747-8 before the 737 lands, and the go-around Cessna must be separated from the 737.
Practical sequence: keep the 737 on the approach, pass traffic information on the go-around Cessna, and instruct the 737 to reduce to final approach speed or hold at an intermediate level if the runway is still occupied. Phraseology: Boeing 737, traffic a Cessna 172 going around, maintain 160 kt until 5 NM, runway 18R. Reassess the 5 NM minimum at the threshold, not just at the initial call.
3. The Cessna pilot disregards the go-around, lands, and reports a severe wake encounter at 50 ft. What must the controller do?
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Treat the report as an in-flight emergency. Confirm the Cessna is safely on the ground, keep the runway clear, and ask for intentions and injuries: Cessna 172, roger wake encounter, are you able to vacate via taxiway Charlie, any injuries? Alert RFFS as a precaution and give the Cessna priority taxi to the apron. Do not let the 737-800 land until the Cessna has vacated and the runway is inspected if debris is suspected.
Record the occurrence: time, location (50 ft), reported severity, preceding aircraft type and spacing. Notify the duty supervisor and safety office, preserve radar and flight-data recordings, and submit an ATS occurrence report. The event may indicate a procedural failure, so the report should state that the landing clearance was issued at 3 NM behind a Heavy aircraft and that a go-around was instructed.