Time, speed and distance
Every flight-time problem is the same relationship: distance = ground speed × time. Choose what to solve for, fill in the other two and the answer appears in the read-only field. The worked example is the Pilot's Handbook's: 220 nautical miles at a ground speed of 88 knots takes 2 hours 30 minutes. The result also gives minutes per nautical mile, which makes checkpoint timing easy: at 88 knots each mile takes 41 seconds.
Time is entered as hours and minutes. Distances are nautical miles and speeds knots; the unit conversions on the home page convert statute miles and kilometers.
Fuel required
The fuel calculator multiplies flight time by fuel burn and adds a reserve:
- Trip fuel = 2:30 × 8 gal/h = 20.0 gallons.
- Reserve = 30 minutes × 8 gal/h = 4.0 gallons.
- Planned fuel = 24.0 gallons, about 144 pounds of 100LL.
Add the usable fuel on board and it shows endurance and the fuel left at landing. Falling below trip plus reserve shows a red warning. The Pilot's Handbook reminds pilots to allow for taxi, the higher burn during climb and a lower ground speed while climbing. Build those into the burn rate or the time, or plan the climb separately with the climb calculator.
Reserves: what the regulation says
14 CFR 91.151 sets the minimum VFR reserve for airplanes: fuel to the first point of intended landing, then 30 minutes at normal cruising speed by day or 45 minutes at night. It is a legal minimum, not a comfort level. Choose 45 or 60 minutes in the reserve menu to plan more.
On the E6B
The time-speed-distance problem is the E6B's most basic use. Put the RATE index under the ground speed and the whole wheel becomes a lookup table for that speed: every time on the inner scale sits under the distance you cover in it. Fuel works the same way with the burn rate in place of speed. The E6B simulator animates these steps with your own numbers.
Time, speed and distance on a mechanical E6B
- Turn the inner disc until the RATE index (the triangle at 60) is under the ground speed on the outer scale.
- Find the distance on the outer scale and read the time directly below it on the inner scale, in minutes (the hours ring shows h:mm).
- For ground speed from a timed leg, put the time on the inner scale under the distance on the outer scale and read the speed above the RATE index.
Questions pilots ask
How do you calculate ground speed?
Divide the distance by the time. A 32 nautical mile leg flown in 16 minutes is 32 ÷ (16 ÷ 60) = 120 knots. Before the flight, get the expected ground speed from the wind triangle instead.
How much fuel reserve do I need?
For VFR flight in an airplane, 14 CFR 91.151 requires enough fuel to reach the first point of intended landing plus 30 minutes at normal cruise by day, or 45 minutes at night. Many pilots plan more.
How much does avgas weigh?
Planning normally uses 6 pounds per US gallon for 100LL and 6.7 for Jet A. The FAA Aircraft Weight and Balance Handbook lists 6.01 and 6.68 pounds per gallon at 59 °F; fuel is heavier when cold.
Why use ground speed instead of true airspeed for time?
Time over the ground depends on speed over the ground. True airspeed plus a headwind or tailwind is ground speed, so a strong headwind can add a lot of time and fuel to the same trip.