Microburst and gust front on short final at Abuja
At Abuja (DNAA, elevation 1,129 ft) at 1700 local, a multicell thunderstorm is 8 nm west of runway 22. ATIS reports wind 240/12 kt, but the tower reports a gust front with wind 310/25 gust 40 kt and an alert of a 20 kt loss at 500 ft. You are on 3 nm final in an A320, landing mass 64 t, flaps 3, autothrust in managed speed. The preceding aircraft went around after reporting severe turbulence and a 25 kt airspeed loss. The runway is dry, braking action good, and there is 20 minutes holding fuel. Storm tops are 45,000 ft, the freezing level is 14,000 ft, and hail has been reported. The captain asks whether to continue, what escape maneuver to fly if a microburst is encountered, and what reports should be made after landing.
1. Interpret the wind information and the pilot report. What phenomenon is most likely, and what is the immediate threat to the approach?
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- ATIS wind 240/12 kt versus tower wind 310/25 gust 40 kt is a 70° shift with a large gust increase. That is consistent with a thunderstorm gust front or outflow boundary, not ordinary surface heating.
- The 20 kt loss at 500 ft, and the preceding aircraft's 25 kt loss and severe turbulence, point to a microburst or strong downdraft. A microburst produces a sharp headwind increase followed by a tailwind, so airspeed and climb performance collapse close to the ground.
- For runway 22, heading 220, wind 310 is about 90° across the runway. The gust to 40 kt is a strong crosswind and may exceed the aircraft crosswind limit; more importantly, the shear is in the last 500 ft.
- The immediate threat is low-level wind shear with possible microburst. Continuing on 3 nm final would put the aircraft into the most dangerous phase of flight with a known severe shear report.
2. As captain at 3 nm, what do you do? If a microburst is encountered, describe the escape maneuver.
Read the worked answer
- Go around. At 3 nm the aircraft is still in the approach phase, with holding fuel and a known shear report. There is no requirement to continue. Apply go-around thrust, pitch to the go-around attitude, establish a positive climb, and follow ATC instructions away from the storm.
- Do not attempt to land short or accept a large crosswind and shear with a 25 kt loss report. The preceding aircraft's experience is direct evidence that the approach path is not stable.
- If a microburst is encountered, recognise the airspeed loss and sink immediately. Apply maximum takeoff/go-around thrust, pitch to the stick-shaker or company pitch limit, and do not lower the nose to chase airspeed. Maintain wings level and accept altitude loss while flying out of the shear.
- Keep the landing gear and takeoff configuration until a positive climb is established and terrain/obstacle clearance is assured, then clean up. Report the encounter to ATC as soon as workload permits.
3. What reports and warnings should be issued or requested after landing?
Read the worked answer
- File a pilot report with time, location, altitude, wind shear, airspeed loss, turbulence, hail, and the go-around. If the operator uses AIREP special format, include the wind shear and severe turbulence descriptors.
- Ask ATC to issue a wind shear warning and update the ATIS. A special observation (SPECI) is warranted if the gust front or visibility/ceiling change is not in the routine METAR.
- Request the current SIGMET and any AIRMET/GAMET for the area. The thunderstorm, severe turbulence, hail, and low-level wind shear all fall within SIGMET-relevant hazards. Check that the warning is passed to following aircraft.
- After landing, report to operations and the meteorological office so the event can be documented. The key operational point is that the go-around was based on a known shear report and a crosswind/gust exceedance, not on guesswork.