Crabwise · Library
How do you keep trip fuel, taxi fuel and a chosen reserve separate?
With 210 NM at 120 kt and 8 units per hour, trip fuel is 14 units; a 45-minute reserve adds 6 and 1.5 taxi makes 21.5 units in total.
Three lines that the app keeps apart
The required-fuel mode computes trip time t = D ÷ GS × 60, trip fuel = FF × t ÷ 60, reserve fuel = FF × reserve minutes ÷ 60, and then the total = trip + reserve + taxi. The reserve is entered by you in minutes and burned at the same flow; taxi and run-up fuel is a quantity you enter directly. Each appears as its own result line before the total.
The app's note states that the legal reserve depends on the rules you fly under. It does not choose one; the 45 minutes in the example are an input.
Worked example
An educational 180 NM leg at 120 kt takes 1.5 hours. At 8 units per hour it uses 12 units; a user-entered 45 minutes adds 6, and taxi adds 1. The result is 19 in the same chosen fuel unit.
- Trip time (min)
- 90
- Trip fuel (chosen units)
- 12
- User reserve fuel (chosen units)
- 6
- Total including taxi (chosen units)
- 19
Fill in the required-fuel mode
- Enter distance in NM and ground speed in kt from the wind triangle.
- Enter the hourly flow in the same unit you want the answer in.
- Enter the reserve minutes you have decided on, and the taxi fuel.
- Read flight time, trip fuel, reserve fuel and the total, and keep all four in the record.
The Library worksheet's default case
210 NM at 120 kt takes 210 ÷ 120 × 60 = 105 minutes. At 8 units per hour the trip uses 14 units. A 45-minute reserve is 8 × 45 ÷ 60 = 6 units, and 1.5 units of taxi fuel bring the total to 21.5.
- Flight time (min)
- 105
- Trip fuel
- 14
- Reserve fuel for 45 min
- 6
- Total with taxi
- 21.5
Entering 30 reserve minutes instead changes only the reserve line, to 4 units, and the total to 19.5.
Common mistakes
- Typing the reserve as fuel quantity in the minutes field.
- Using a taxi figure in pounds while the flow is in gallons.
- Reading the total as tank capacity or as usable fuel.
Scope
The total is an arithmetic sum of your inputs. It does not check tank capacity, contingency needs or the reserve rule that applies. The FAA navigation chapter below covers the time and fuel relations.
Educational calculation only. Check current aircraft limits, weather, performance and reserve requirements with approved information.