Definition
A category of aircraft that achieves flight by using a gas or heated air that is less dense than the surrounding atmosphere, producing buoyancy that lifts the craft. Lighter-than-air aircraft include balloons (free or tethered) and airships (powered, steerable craft such as blimps and dirigibles).
Plain English
An aircraft that floats up into the sky because it is filled with something lighter than normal air, such as hot air, helium, or hydrogen. Balloons and blimps are the main examples.
Context Anchor
Seen when the FAA describes categories of light-sport aircraft, including balloons and airships.
Derivation
The phrase is literal: the aircraft, taken as a whole, weighs less than the volume of air it displaces. This is the same principle that makes a cork float on water -- it is lighter than the water around it.
Why Pilots Care
This classification determines the applicable regulations, pilot certificates, and operating limitations for the aircraft.
Analogy
A boat floats because it pushes aside water and is supported by it. A lighter-than-air aircraft does something similar in the air: it is supported because it pushes aside air that is heavier than the gas inside it.
Grounding Statement
Picture a hot air balloon rising after the air inside the balloon is heated; that is lighter-than-air flight.
Intuition Check
Do not read lighter-than-air as simply meaning a small or low-weight aircraft. In aviation, it means an aircraft supported by buoyancy in the air, such as a balloon or airship.
Example Sentence 1
A hot air balloon is a lighter-than-air aircraft because the heated air inside the envelope is less dense than the cooler air outside.
Example Sentence 2
Unlike airplanes, lighter-than-air vehicles maintain altitude through gas buoyancy instead of engine power or wing lift.