Updated: Jan 20
This pic was taken by James ball that flies a Q400 in frigid temperatures.
January's enRoute magazine is running my article on cold temperatures.
Below are some facts I conjured up:
Cold temperatures mean denser air - welcomed by any aviator. Frigid air at - 40° C (-40° F) is about 33% denser than hot air at + 40° C (104° F). Cold air produces more lift over the wings and flight controls and more thrust from the engines and propellers. Pilots liken the airplane’s improved climb performance to a home sick angel.
But to start a jet engine requires oil temperatures above - 40° C (- 40° F) so the engines must be preheated. An airplane itself is built for cold temperatures as it hovers at - 57°C (- 71° F) at cruising altitude.
It is the ground personnel that are challenged during extreme cold. They must retreat inside frequently for safety reasons. Machinery is reluctant to start (which includes employee’s cars), cabin heaters are less effective, and getting potable water to the airplane can be an issue as well as cabin doors freezing shut. If an aircraft remains at the gate overnight, ground power must remain on to prevent the water lines from freezing, and if it’s parked off the gate with no power, the water is drained. The shipping of livestock is also challenging. Hairless cats and dogs are forbidden to travel during the winter.
During one winter’s extreme cold snap, I’ve seen the wheels to the jetway freeze requiring the ramp attendants taking 20 minutes to thaw out the frozen wheels. Aircraft parking brakes may freeze so they may be released when the aircraft is safely chocked.
Winter operations are a challenge, but when the mercury plummets, our goal remains to get you to your destination safely and expeditiously.
A flight departing the Edmonton International airport in bone-chilling air infiltrating from the disputable Polar Vortex will encounter 33% denser air than a mid-summer departure in Dubai, UAE.
When the temperature is zero degrees or below, a pilot must adjust their decision height to land by consulting a cold temperature correction table. For example, if the minimums for an approach is 750 feet ASL (Above Sea Level), but the outside temperature is -20° C, then twenty feet is added so the new height is 770 feet ASL.
For those pondering about learning to fly, don’t rule out winter. Flight during a cold, crisp, clear winter’s day is a pleasant adventure.
Procedures state flights will not be planned to operate for periods longer than 90 minutes in areas where temperatures are -65° C (-85°F) or colder. To help mitigate this, an aircraft can change altitude, avoid the area or speed up.
Mercury thermometers freeze at -39° C thus an alcohol filled thermometer is used thereafter.
The magic temperature at which snow starts to squeak is -10° C or around 14° F. You may encounter this while walking to an airplane parked out on the ramp.
Water can exist as a liquid to temperatures as low as -40° C. Thus, an airplane can pick up airframe icing when in cloud when these supercooled water droplets lose their heat as they impinge on the airplane. We have deicing equipment to rid the ice build-up.
Below -40° C, air no longer holds liquid moisture. We meteorologists call this homogeneous nucleation. Basically, the air freezes. It’s also the threshold where aircraft deice equipment is no longer required. There is an exception to this called ICI (Ice Crystal Icing) and the B787 Doug flies was susceptible to ICI, but they modified the engines. Ice crystals do not adhere to cold airframe surfaces as ice crystals bounce off. However, the crystals can partially melt and stick to relatively warm engine surfaces. New software sensors sense the ice particles and activate a VBV (Variable Bypass Valve) ejecting ice into the bypass duct. No more ICI.
At what temperature does Celsius and Fahrenheit become the same value? -40° C/F.
High cloud, with bases starting above 20,000 feet, are composed entirely of ice crystals because of the frigid temperatures aloft.
One such place aircraft manufactures take their airplane for cold temperature testing is Iqaluit, Nunavut.
The Airbus 350 getting a cold weather work out in Iqaluit. Photo compliments of Dr. Sandy
Captain D (Yes, I look better with my hat on).
The freezing point of Jet A1 (mostly used by AC) is -47° C. Fuel cools at a rate of 3° C/hour. According to Boeing, an increase of .01 Mach number, i.e. increasing from Mach .84 to Mach .85, increases the airplane’s skin temperature by .5° C to .7° C.
Square tires? Sometimes when an aircraft sits in prolonged cold temperatures, the aircraft tires are known to take a while to warm up so taxiing may be a bit bumpier.
One recent fast freeze at Toronto Pearson caused the covers to the fuel hydrants to freeze shut. Delays incurred until applied heat thawed things.
Two types of fog that develop during frigid temperatures: steam fog emanating from open water and ice fog from car and jet exhaust.
How does a pilot know frost is reported at the airport’s weather office? When FROIN (Frost On Indicator) is observed.