Every airline flight is planned with more than a straight line from departure to destination. Dispatchers and pilots study weather, winds, fuel needs, airport conditions, airspace limits, and possible alternate airports before takeoff. These Plan B airports matter because conditions can change while the aircraft is already in the air.
A safe flight plan always includes options if the original destination becomes unsafe or unavailable.
A diversion happens when the crew decides to land somewhere other than the planned destination. Common triggers include thunderstorms, low visibility, strong crosswinds, medical emergencies, mechanical warnings, runway closures, or fuel concerns. Aircraft carry fuel for the planned trip, required reserves, missed approaches, holding, and sometimes reaching an alternate airport.
The decision combines regulations, aircraft performance, weather reports, fuel calculations, and real-time judgment from the flight crew and dispatch.
Key Facts
- Trip fuel is the fuel needed to fly from departure to destination under planned conditions.
- Total fuel often includes taxi fuel, trip fuel, contingency fuel, alternate fuel, final reserve fuel, and extra fuel.
- Fuel remaining after diversion = fuel on board - fuel needed to reach the alternate.
- If destination weather is below required landing minimums, an alternate airport may be required before departure.
- A diversion is usually chosen when continuing creates more risk than landing at a suitable nearby airport.
- Basic fuel time relation: endurance = usable fuel / fuel flow rate.
Vocabulary
- Alternate airport
- An alternate airport is a preplanned or available airport where an aircraft can land if the destination cannot be used safely.
- Diversion
- A diversion is the decision to fly to an airport other than the original destination.
- Reserve fuel
- Reserve fuel is fuel kept for unexpected delays, holding, missed approaches, or reaching another airport safely.
- Holding
- Holding is a controlled pattern flown near a fix or airport while an aircraft waits for clearance, weather improvement, or traffic spacing.
- Landing minimums
- Landing minimums are the lowest visibility and cloud ceiling conditions allowed for a specific approach and aircraft operation.
Common Mistakes to Avoid
- Assuming the nearest airport is always the best alternate is wrong because runway length, weather, services, terrain, and aircraft performance may make a farther airport safer.
- Counting all fuel on board as usable for planning is wrong because regulations and safety procedures require reserve fuel that should not be planned for normal use.
- Ignoring wind when estimating diversion time is wrong because headwinds can greatly increase time, fuel burn, and the distance needed to reach a safe airport.
- Treating a diversion as a failure is wrong because diverting is often the safest and most professional choice when conditions change.
Practice Questions
- 1 An aircraft has 9,000 kg of usable fuel remaining and burns 2,500 kg per hour. What is its approximate endurance in hours?
- 2 A diversion airport is 180 nautical miles away. The aircraft groundspeed is 360 knots and fuel flow is 3,000 kg per hour. How long will the diversion take, and how much fuel will be used?
- 3 A flight is approaching its destination, but thunderstorms have formed over the airport, visibility is below landing minimums, and a suitable alternate has clear weather. Explain why diverting may be safer than holding near the destination.