ForeFlight calculates the time and fuel needed to reach an alternate airport based on the following:
Routing and Cruise Profile
Time and fuel are based on the following factors:
- Routing: A direct route from the destination airport to the alternate is used.
- Performance Profile: The same performance profile used for the initial en route flight portion is applied.
- Cruise Altitude: An appropriate altitude is automatically selected based on aircraft performance and the distance to the alternate.
Fuel Buffer
To account for a missed approach, potential holding, and another instrument approach, a fuel buffer is added to the calculation. The buffer varies by aircraft type:
- Jet and Turboprop Aircraft: Adds 5 minutes of holding fuel and fuel to fly an additional 30 NM.
- Piston Aircraft: Adds 5 minutes of holding fuel and fuel to fly an additional 15 NM.
- Helicopters: No additional fuel buffer is added.
This calculation ensures adequate fuel planning to fly to an alternate airport.
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