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The 1,2,3 of pilot maths

by SFO Barbara McKay BALPA Member

Teachers around the country will no doubt recognise cries of protest from children unhappy at the thought of having to study mathematics:

“I don’t need to learn that… I have a calculator on my phone and most jobs have computers these days.” 

To a certain degree the statement is right… even for pilots. Like everyone these days, aircrew use calculators and computers regularly. Nevertheless, it is too simple to assume there is no longer a need for mental arithmetic and times tables.  

Day to day flights are in fact a potpourri of small calculations, which pilots tend to do without even thinking. Calculating fuel, top of descent point, crosswind, tailwind, endurance, time or simply checking the load sheet is part of the job. Most of these calculations are done by heart since grabbing a calculator is usually not efficient.

Particularly useful to pilots is a good knowledge of the three times table! This is used constantly in descent to work out altitudes versus miles to go.  

To descend 30,000 feet you need approx. 90 miles at normal descent rates. We also have to work out how many miles to reduce speeds to the next desired speed (whilst still keeping the descent 3 times table going). 

This, three times table check, is one all pilots use throughout descent to make sure they are not too high or low. It is a 2 times table if you should lose an engine and have to fly the approach on just the one.

Pilots also have to convert figures from one unit to another regularly. For example, temperatures from celsius to fahrenheit, knots to metres per second for wind speed, thousands of feet to thousands of metres for altitude reporting.

While 90% of airfields use QNH (where the altimeter reads airfield elevation when you land) in feet, some, like Russian and China use QFE (where the altimeter reads zero when you land.) in metres, so that can create lots of mental arithmetic. There are tables to use, but generally these are used to cross check, the brain is going constantly and keeping alert for any misreading of the tables.

Where low temperature or pressure are prevalent, a constant calculation of the difference between what the altimeter is reading and the ACTUAL height above the ground is a must, as low temperature and pressure will mean you are much lower than the altimeter says and needs to be considered when flying on standard altimeter settings. Again, there are tables, but a good working knowledge is essential and is regularly used.

Similarly, for an approach which does not give vertical guidance (non-precision), three times tables are again in constant use and where the approach is visual, the correction for cross wind, whilst maintaining the ever present 3 times table for descent, is going on in parallel in a pilot’s brain.

So, while pilots don’t have to be the next Pythagoras or Albert Einstein when it comes to maths, we do need to be nimble with numbers.