Definition
To hold the aircraft at an assigned or selected altitude within acceptable tolerances, making continuous small adjustments to pitch and power as needed to prevent climbing or descending away from that altitude.
Plain English
Keep the aircraft at the height you were told to fly at, and don't let it drift up or down.
Context Anchor
Used during flight instruction, air traffic control instructions, maneuver practice, and any situation where the pilot is expected to hold a selected height.
Derivation
Maintain' comes from Old French maintenir, meaning 'to hold in the hand,' from Latin manu tenere. In aviation it carries that same sense: actively hold the altitude — it doesn't stay there on its own.
Why Pilots Care
Failing to maintain altitude can result in airspace violations, loss of separation from other traffic, or controlled flight into terrain.
Intuition Check
Do not read maintain altitude as simply “try to stay about the same height.” In flying, it means actively hold the specified altitude and correct promptly if the airplane starts to climb or descend.
Example Sentence 1
ATC instructed the student to maintain 3,500 feet until reaching the practice area.
Example Sentence 2
After leveling off from the climb, the instructor directed the student to maintain altitude during the next series of clearing turns.