Kármán line
The altitude at which the atmosphere becomes too thin to support aerodynamic flight.
Kármán line: where air runs out for wings
The Kármán line is the altitude boundary, conventionally set at 100 kilometers (328,000 feet), above which the atmosphere is too thin to generate enough aerodynamic lift for conventional aircraft to maintain flight. Below this line, wings work because air molecules are dense enough to create pressure differences; above it, even at maximum speed, there is not enough air to push against a control surface. This is not a hard physical wall but rather a threshold where the physics of aircraft operation fundamentally changes.
The 100-kilometer figure comes from work by aerospace engineer Theodore von Kármán in the 1950s. He calculated that at this altitude, an aircraft would need to travel faster than orbital velocity to generate lift equal to its weight. In practice, most crewed aircraft reach absolute ceiling around 12 to 15 kilometers; military jets top out near 25 kilometers; and high-altitude research aircraft have touched 37 kilometers. The Kármán line is therefore a theoretical rather than operational limit for aviation maintenance crews.
For maintenance personnel, the line matters mainly in regulatory and jurisdictional contexts. The Federal Aviation Administration and most national aviation authorities define airspace and aircraft certification within the troposphere and lower stratosphere, well below Kármán altitude. Military and space agencies reference it when distinguishing between aircraft, spacecraft, and spaceplane operations. Insurance, liability, and pilot licensing all stop where aerodynamic lift becomes meaningless.
Atmospheric density at Kármán altitude is about one millionth of sea-level density, yet it is not zero. Small satellites and the International Space Station experience measurable drag even in this rarefied environment. For maintenance work, the practical takeaway is that conventional aircraft maintenance procedures, performance calculations, and safety margins assume operation well below this line, and any system designed to work higher must be treated as space hardware, not aviation hardware.