One relationship, three arrangements
Every question uses the same relationship: distance equals speed multiplied by time. Rearranged, speed is distance divided by time, and time is distance divided by speed.
Before calculating, write down which two values you have and which one you need. Most errors come from choosing the wrong arrangement, not from the arithmetic.
- Distance = speed × time
- Speed = distance ÷ time
- Time = distance ÷ speed
Keep the units consistent
Aviation questions usually use knots, which are nautical miles per hour, and times in minutes. Convert minutes to hours before multiplying a speed in knots, or convert the speed to nautical miles per minute.
A useful shortcut: divide a speed in knots by 60 to get nautical miles per minute. At 240 knots, an aircraft covers 4 nautical miles every minute.
- 1 nautical mile = 1.852 kilometres
- 45 minutes = 0.75 hours; 20 minutes = one third of an hour
- Knots ÷ 60 = nautical miles per minute
Worked examples
Work through each one before reading the solution. The method matters more than the answer.
Distance: 240 knots for 45 minutes
45 minutes is 0.75 hours, so distance = 240 × 0.75 = 180 nautical miles. Using the per-minute shortcut: 240 ÷ 60 = 4 nautical miles per minute, and 4 × 45 = 180.
Time: 150 nautical miles at 300 knots
Time = 150 ÷ 300 = 0.5 hours, which is 30 minutes.
Speed: 420 nautical miles in 1 hour 45 minutes
1 hour 45 minutes is 1.75 hours, so speed = 420 ÷ 1.75 = 240 knots.
Wind: 200 knots airspeed into a 30-knot headwind
A direct headwind reduces groundspeed: 200 − 30 = 170 knots. To cover 85 nautical miles takes 85 ÷ 170 = 0.5 hours, or 30 minutes. With the same wind behind you, groundspeed would be 230 knots.
Fuel: 600 kg per hour for 40 minutes
40 minutes is two thirds of an hour, so fuel used = 600 × 2 ÷ 3 = 400 kg. Fuel questions are the same relationship with fuel flow in place of speed.
Mistakes that cost marks
Most lost marks come from unit slips rather than hard arithmetic, so build a habit of checking units before you answer.
- Multiplying knots by minutes without converting to hours
- Treating 1 hour 30 minutes as 1.3 hours instead of 1.5
- Adding a headwind instead of subtracting it
- Not sense-checking: a faster aircraft should always need less time
How to practise
Start untimed until the method is automatic, then add a timer. Mix the three arrangements so you practise choosing the right one, which is the skill timed tests reward.
- Take the free test to see where speed, distance and time sits among your skills
- Practise the speed-distance-time drills until you rarely need to write the formula
- Add wind and fuel questions once basic problems feel routine