As aviators, we are particularly concerned with temperature. We monitor our EGT or ITT, CHT, OAT, TAT, or SAT. Most of the time we deal with this alphabet soup of temperatures in terms of degrees Celsius. Most Americans however, still think in terms of degrees Fahrenheit. We need a simple method to convert degrees Celsius from the ATIS report to degrees Fahrenheit.
Even pilots who deal with Metrics measurements on a regular basis are more “at home” with the Fahrenheit scale. We know that 90º F is hot, and that it might be wise to wear a coat if the temperature was forecast to be 40º F.
Now what if the ATIS reported 15º C at your destination? Do you bundle up? Is 25º C T-shirt weather? Pilots need a quick and simple way to convert degrees Celsius to Fahrenheit.
Recall the unintuitive formula for converting degrees Celsius into degrees Fahrenheit:
F = ( 1.8 * C ) + 32
In words, multiply the temperature Celsius by 1.8, then add 32.
Although this works, this formula poses two problems. First off, it is not easy to remember. Furthermore, the math is difficult to do in your head, especially while flying an airplane!
The Rule of Thumb:
To simplify the math, we can sacrifice a little accuracy for an easier formula:
F = ( 2 * C ) + 30
Simply double the temperature Celsius, then add 30.
So, do you still need your coat on at your destination? ATIS reports 15º C, lets figure it out.
2 * 15 = 30, We double 15 to get 30,
30 + 30 = 60, then add 30 to the result (30) to get a temperature of 60º F.
That’s pretty close to the actual temperature (from the first formula) of 59º F.