Subscriber question:
"I'm a new pilot and took a thermos of coffee up with me for the first time. I opened it at altitude and — you guessed it — sprayed hot coffee all over myself. Is there a trick to this or am I stuck drinking cold coffee in cruise." — Wiley P.
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Jeff:
“A pilot friend of mine also liked to sip coffee in cruise. His solution was a child’s ‘sippie cup.’ This let the pressure out the valve as the airplane climbed—and couldn’t spill on his upholstery.
Personally, I can’t bring myself to do the toddler act. But I also like a cup of hot coffee just before I descend to my destination. Here’s my secret and suggestion for you.
When you fill your thermos before flight, fill it all the way to the top so that liquid spills out when you screw the cap on. This prevents trapped air that pressurizes the contents when you reach cruising altitude. The liquid itself is barely compressible, so it won’t expand and spray out later. This works for any non-carbonated drinks in a thermos, hot or cold.
The other side of this equation is opening the thermos after you land. If you close it tightly at altitude, it may trap low pressure inside such that you need vice-grips to get the top off. Avoid that by leaving the top loose during the descent. Or off entirely if the container is empty.
Of course, drinking too much coffee in cruise can create its own problems, but that’s a different discussion.”
Have you learned something about inflight refreshment in light airplanes … the hard way?
(If so, please share below.)