Embedded Convective Weather on Arrival into Plaisance
You are inbound to Plaisance (FIMP) at FL180, 40 nm southeast, cleared to descend via the STAR for ILS runway 14. It is 2015 local, dark. FIMP ATIS: wind 120/18 gust 32 kt, visibility 4,000 m in thunderstorm rain, few CB 1,200 ft, broken 3,000 ft, QNH 1005 hPa, runway 14 wet. The aircraft weather radar shows a large red cell over the airport and a narrow green gap on the final approach; the radar return is attenuated beyond the cell. Fuel is 3,200 kg; final reserve 1,100 kg; alternate FMEE is 120 nm away with PROB30 TSRA. ATC reports the ILS is serviceable but the tower has just observed a 25 kt gain followed by a 20 kt loss on the anemometer. You are the pilot flying; the first officer is monitoring.
1. Interpret the weather and identify the main threats.
Read the worked answer
The main threats are convective, not merely low visibility. The ATIS reports thunderstorm rain, CB at 1,200 ft, a gusty wind and a wet runway. The tower anemometer has recorded a 25 kt gain followed by a 20 kt loss, which is direct evidence of wind shear, possibly a microburst or gust front. The radar shows a red cell over the airport and a green gap on final, but the return beyond the cell is attenuated. That means the green gap may be a radar shadow, not a safe corridor, and the red cell may be larger or more intense than displayed.
At night, visual avoidance of embedded cells is unreliable. The wet runway reduces braking action and the gusts increase the required landing distance. The alternate, FMEE, has PROB30 TSRA, so it is not guaranteed clear. The crew should treat the approach as high-risk and avoid the convective core and the known shear area.
2. Decide whether to continue the approach, hold, or divert; justify.
Read the worked answer
The approach should not be continued into the cell or the known wind shear. The aircraft should remain clear of the convective area, request a hold or deviation, and ask ATC for the latest airport weather and any pilot reports. The crew should use radar tilt and gain carefully, but should not attempt to pick through a green gap that is likely an attenuation shadow.
Fuel gives some margin: 3,200 kg total, 1,100 kg final reserve, so about 2,100 kg is available above reserve. That is sufficient for a short hold or a diversion to FMEE, but not for repeated approaches. If the cell is moving away and the tower reports the shear has ended, one carefully briefed approach may be acceptable. If the cell remains over the airport or the shear continues, the correct decision is diversion to FMEE while fuel is sufficient, with a recheck of FMEE weather and landing performance.
The decision should be made before entering the final approach area, not at 500 ft. Continuing because the ILS is serviceable would confuse equipment status with weather suitability.
3. If you do approach and encounter wind shear, state your actions.
Read the worked answer
At the first indication of wind shear, the crew should go around. The pilot flying should:
- Apply maximum take-off/go-around thrust and disconnect autothrust if it does not respond.
- Pitch to the go-around attitude and accept a lower speed if necessary to maintain the flight path; do not chase the speed indicator.
- Maintain configuration until a positive climb is established, then retract gear and flaps as required.
- Follow the published missed approach and ATC instructions; do not turn before the published missed approach point or minimum altitude.
- Report the wind shear to ATC with the altitude and reported gain/loss.
The first officer should call the airspeed and vertical speed trends, confirm positive climb, and monitor the engine parameters. The crew should not attempt to salvage the landing after a significant shear encounter. A wet runway and gusts leave little margin, and a go-around is the safer outcome.