Ask the Captain: Can it be too hot or cold to fly?

Question: Is there any temperature that is too cold or too hot for planes to fly? Also, can it be too windy to fly a commercial airplane?

— submitted by reader Carolyn, Herndon, Va.

Answer: There are limits on the minimum temperature for fuel, oil or hydraulic fluid. If the airplane can be kept in a hangar prior to flight, it can operate in very, very cold conditions. Airplanes fly in minus 56 celsius (-69 degrees Fahrenheit) or colder conditions at altitude, therefore if the fluids can be kept warm, the airplane can usually operate.

Very hot conditions usually result in performance problems more than mechanical ones. Warm or hot air is less dense; consequently, airplanes produce less lift than if the air is colder. The acceleration and climb temperature limitations are major considerations when the temperature is above 40C (104F).

Airplanes have crosswind and tailwind limitations published in the flight manual. If the conditions result in a crosswind or tailwind component that exceeds the limitation, the landing or takeoff is prohibited.

Q: What is the air temperature at typical cruising altitudes of 30,000 feet? How is the material that aircraft are made from able to constantly withstand the extreme variations in temperatures (since metal expands when hotter and contracts in the cold)?

— Joel, Oklahoma City

A: The standard temperature for 30,000 feet is -44.5C or -48F (Source: meteorologytraining.tpub.com/14269/css/14269_75.htm).

All materials used in airplanes are designed and tested to withstand temperature extremes.

Q: Why not tell the people it is minus 43 degrees outside their window?

— Steve, Indiana

A: The outside temperature varies, therefore a providing a specific number might not be accurate. For the passengers that are interested, many inflight entertainment systems provide the outside temperature. Some pilots will announce the temperature at the cruise altitude.

John Cox is a retired airline captain with US Airways and runs his own aviation safety consulting company, Safety Operating Systems.