Sea-breeze wind shift and low-level shear at Port Harcourt
At Port Harcourt (DNPO, elevation 60 ft) at 1600 local, the wind has veered from 080/6 kt at noon to 230/14 gust 22 kt. Temperature is 33°C, dewpoint 26°C, QNH 1008 hPa. Runway 03/21 is in use; you are on 10 nm final for runway 03 in a Boeing 737. The tower now reports wind 210/18 gust 28 kt, and a preceding arrival reported a 15 kt loss of headwind at 300 ft. The sea breeze is well developed. Your landing mass is near maximum, autobrake 3, and the runway is dry. The crosswind limit is 15 kt; the tailwind limit is 10 kt. The captain asks whether to continue, change runway, or go around. There is 10 minutes of holding fuel.
1. Explain the wind shift and gustiness in terms of local circulation and boundary-layer mixing.
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- At noon the light 080/6 kt wind is the synoptic/land-breeze regime. By 1600 the land has heated strongly to 33°C while the Gulf of Guinea remains cooler. Pressure falls over the heated land, and the denser marine air moves inland as a sea breeze.
- Port Harcourt is close to the coast, so the sea-breeze front can reach the field in the afternoon. The wind veers to a south-westerly direction, here 230°C at 14 kt, and later 210/18 gust 28 kt as the front and turbulent mixing strengthen.
- Gusts are not just the mean sea breeze. Strong surface heating produces thermals and a well-mixed boundary layer, which brings higher-momentum air down to the surface. The result is a gusty, veering wind and a low-level shear layer, as shown by the 15 kt headwind loss at 300 ft.
- The shear is the operational hazard: the mean wind change alone would be manageable, but the reported loss at 300 ft means airspeed and sink rate can change abruptly close to the ground.
2. Compute headwind/tailwind and crosswind for runway 03 and runway 21 with wind 210/18 gust 28. Which runway should be used, and does the tailwind limit decide it?
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- Runway 03 heading is 030. Wind 210 is 180° away, so it is a pure tailwind of 18 kt, gusting 28 kt. Crosswind component is zero.
- Runway 21 heading is 210. The same wind is a pure headwind of 18 kt, gusting 28 kt. Crosswind component is again zero.
- The tailwind limit is 10 kt. On runway 03 the steady tailwind alone is 18 kt, and the gust is 28 kt. That exceeds the limit and also increases ground speed, landing distance, and the risk of a hard or long landing.
- Runway 21 gives a headwind and is the correct choice. The reported 230/14 gust 22 kt from ATIS would give a small crosswind on runway 21, but the tower report of 210/18 gust 28 kt aligns almost exactly with runway 21.
- Decision: go around from runway 03 and request runway 21. Continuing on runway 03 would be a clear tailwind-limit exceedance, not a judgement call.
3. How should the 15 kt loss at 300 ft change your approach? What would you do if you had to continue?
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- A 15 kt loss at 300 ft is low-level wind shear in the most critical phase of flight. On a normal approach speed, that loss can put the aircraft close to the stick-shaker or trigger a hard sink rate.
- The first action is to change runway to 21, which removes the tailwind and gives a headwind. That reduces the shear effect and improves landing performance.
- If continuing were unavoidable, use the wind shear warning, add a speed increment according to company procedure (typically half the reported loss or gust increment, within limits), keep autothrust engaged if approved, and brief a go-around before 500 ft. Do not chase the glideslope with large pitch changes; accept a deviation and go around at the first sign of airspeed loss or sink.
- With 10 minutes holding fuel and a near-maximum landing mass, there is no commercial pressure to accept a known shear. Go around, change runway, and let the sea breeze settle if necessary.