Definition
A situation in the air traffic system where the number of aircraft wanting to use a piece of airspace, an airport, or a runway exceeds what that resource can safely handle at that time. Air traffic management uses traffic flow programs, reroutes, and ground delays to resolve these imbalances.
Plain English
More airplanes want to use a place than that place can handle right now. Controllers have to slow some down, send them a different way, or hold them on the ground until things even out.
Context Anchor
Seen in NextGen and air traffic management discussions, especially when explaining delays, reroutes, airport congestion, or flow programs.
Derivation
Demand comes from a root meaning to ask for or require. Capacity comes from a root meaning able to hold. Imbalance means the two sides are not even. In aviation, the phrase compares what aircraft are asking the system to handle with what the system can actually handle safely.
Why Pilots Care
These imbalances produce ground delays, airborne holding, and longer flight times, increasing fuel use and disrupting schedules.
Analogy
Like a busy highway off-ramp at rush hour: more cars want off than the ramp can flow, so traffic backs up. The fix is either spreading arrivals over time or sending some cars to a different exit.
Grounding Statement
If more airplanes are trying to arrive at an airport than the runways and controllers can handle safely, there is a demand and capacity imbalance.
Intuition Check
Do not read demand as a personal request from one pilot. Here, demand means the total traffic trying to use a resource, and capacity means how much traffic that resource can safely handle.
Example Sentence 1
Thunderstorms over the arrival corridor created demand and capacity imbalances at the airport, so ATC issued a ground delay program for inbound flights.
Example Sentence 2
NextGen tools reduce demand and capacity imbalances by allowing more direct routing and better spacing of arrivals.