EASA / CAR Part-66 · Module 1 · 1.1 Arithmetic · Cat A

Weights, Measures & Conversion

Objective: aircraft work mixes metric and imperial constantly. Convert a quantity and see the same amount on two scales at once, so the size of the answer is a check on whether you multiplied or divided.

The same quantity on two scales

Quantity

Value 100

Input

Converted

Factor

Back again

to convert, multiply by the factor · to reverse it, divide by the same factor

Decide first whether the answer should be bigger or smaller. A metre is longer than a foot, so a length in feet must be a larger number than the same length in metres. Checking the direction before you calculate catches multiply-instead-of-divide errors instantly.

Carry the units through the sum. Writing 100 m × 3.281 ft/m shows the metres cancelling and leaves feet, which is a reliable way to prove you have the factor the right way up.

Learn a few anchors rather than every factor. One inch is 25.4 mm exactly, one kilogram is about 2.205 pounds, one litre is about 0.264 US gallons, and one bar is 14.5 psi. Most exam conversions are built from these.

Try this: Convert 100 metres to feet. Is the answer bigger or smaller, and does that match your expectation?
Try this: Switch to pressure and set 1 bar. What is it in psi, and is that near the tyre pressure you would expect?
Try this: Convert a value, then use the back-again readout. Do you land on exactly what you started with?