IFR Approach into a Thunderstorm-Affected Airport
You are flying a twin-engine turboprop on an IFR flight plan into an airport at 1,800 m elevation. The weather report 20 minutes before arrival shows a thunderstorm 15 km west of the airport, moving east at 20 km/h. The airport has a single ILS runway with a decision altitude of 200 ft above ground level and a published missed-approach procedure. The aircraft has weather radar, but it is showing a large red cell directly over the final approach path. The fuel remaining is 1 hour 10 minutes. The alternate airport is 25 minutes away and has good weather. The controller offers vectors for the ILS. The crew has been on duty for 9 hours.
1. Evaluate the risk of continuing the approach and decide whether to attempt the ILS or divert.
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The thunderstorm is 15 km west and moving east at 20 km/h, so it will reach the airport in about 45 minutes. The red cell on radar over the final approach path indicates heavy precipitation, likely severe turbulence, possible hail, and wind shear. Attempting the ILS would place the aircraft in or near the cell during a critical phase of flight, with a decision altitude of only 200 ft AGL, leaving almost no margin for a go-around if wind shear is encountered. The crew has been on duty 9 hours, which increases fatigue and slows reaction time. The fuel remaining is 1 hour 10 minutes, which is sufficient to divert to the alternate 25 minutes away and still land with reserve. The safest decision is to divert to the alternate, inform the controller, and avoid the storm. Continuing would be a violation of good judgement and possibly of the operator's weather minimums for convective activity. The crew should not attempt to 'beat' the storm.
2. If the crew decides to attempt the approach, what precautions and escape options must be briefed?
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If the crew attempts the approach, they must brief the wind shear escape procedure before descent: go-around power, pitch attitude, and the decision to abandon the approach at the first sign of airspeed or vertical-speed deviation. They should request the latest weather and pilot reports, and ask the controller for the storm's position relative to the final approach course. They should set the missed-approach altitude and brief the missed-approach procedure, including the turning direction away from the cell. They should use the weather radar in turbulence mode and avoid painting the cell. They should plan to break off the approach no later than the outer marker if the cell is still over the path, and they should keep the alternate airport in the flight management system. The pilot monitoring should call out airspeed and sink rate continuously. Even with these precautions, the approach remains high risk, and the crew must be prepared to divert.
3. What human-factors and regulatory issues arise from the 9-hour duty day and the decision to divert?
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A 9-hour duty day with a demanding approach and a diversion increases fatigue, which degrades situational awareness, decision-making, and communication. The crew should recognize the fatigue and use explicit callouts, cross-checking, and a sterile cockpit during the approach and diversion. Regulatorily, the crew must comply with flight-time and duty-time limits; if the diversion would exceed those limits, the crew must declare that to the operator and follow the approved fatigue-management procedure. The pilot-in-command has authority to deviate from the flight plan for safety, and the diversion is justified by the convective weather. The crew should document the decision, the weather, and the diversion in the flight report. The operator should review the scheduling that produced a 9-hour duty day before a convective-weather arrival.