John Cox| Special for USA TODAY
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 — about90,000 feet.
The highest airliner flying today reaches45,000 feet.
The highest business jet flying today reaches51,000 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 the cabin pressure vs. altitude?
— Cary, Honolulu
A:The cabin pressure is maintained at 8,000 feet when the 767 operatesat its service ceiling of 43,000 feet.
Q: Great to see the 757 questions in your recent column, it’s my favorite commercial airplane. What makes it cost-prohibitive for Boeing to restart production? Also, what’s the service ceiling, and is it limited by onboard oxygen capacity?
— Buzz, Delray Beach, Fla.
A:The fuel burn of the 757 is the largest consideration. Modern jetliners are more fuel-efficient. The performance of the 757 was unmatched, but the fuel consumption was higher.
The service ceiling of the 757 is 42,000 feet; it is limited by the pressurization and the ability to descend to a low altitude should it be necessary.
Q: Is there a maximum operating height for helicopters?
— Pete, Washington
A:Yes, and it depends on the helicopter. Every manufacturer provides a service ceiling for each model.
John Cox is a retired airline captain with US Airways and runs his own aviation safety consulting company, Safety Operating Systems.
