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Question: What is the highest altitude an airplane can fly?

— Churachandpur Manipur

Answer: The highest commercial airliner altitude was 60,000 feet by Concorde.

The highest military air-breathing engine airplane was the SR-71 — about 90,000 feet.

The highest airliner flying today reaches 45,000 feet.

The highest business jet flying today reaches 51,000 feet.

Q: At what altitude would the wings of an aircraft lose effectiveness?

— Kevin T.

A: It depends on the wing and how much air can be kept flowing over it. The SR-71 routinely flew over 80,000 feet, but it was a very special wing. The space shuttle began encountering “usable” air around 100,000 feet during descent; it, too, was a very special wing and vehicle.

Q: If a plane went past 100,000 feet, what would happen to it?

— Bob, Georgia State

A: No commercial or business airplane flying today can exceed 100,000 feet. Special rocket-powered airplanes can fly over 100,000 feet to gather data, but they are specially designed for it.

Q: Much beyond the certified ceiling, can an aircraft maintain altitude?     

— Stealth, Canada

A: During certification testing, airplanes are flown above the certified ceiling, but the performance is limited. The answer is that aircraft may be able to maintain altitude above service ceiling, depending on the weight and temperature, but not very much above it.

Q: What is the highest possible elevation a commercial jetliner can fly? Are there any routes in the world that require a jetliner to fly at its highest elevation?

— CTY, Emeryville, Calif.

A: The highest commercial airliner ceilings are 45,000 feet. It is not uncommon to fly at the certified ceiling of the airplane.

Q: At cruising altitude for a 767, what is…