Definition
In a Standard Instrument Departure (SID) clearance, the altitude assigned to a pilot at which to level off after departure unless ATC issues a different altitude. It is the published or assigned ceiling for the climb portion of the departure procedure.
Plain English
The altitude you are cleared to climb to and stop at when flying a published departure procedure, unless the controller tells you to climb higher.
Context Anchor
Seen on instrument departure charts and in air traffic control departure clearances.
Derivation
“Top” means the highest point or upper limit. In this term, it points to the upper altitude limit of the initial departure clearance, not the aircraft’s maximum possible altitude.
Why Pilots Care
It keeps the aircraft from climbing above the authorized altitude, preserving separation from other traffic and terrain.
Intuition Check
“Top” does not mean the highest altitude the airplane can reach or the cruise altitude you filed. Here it means the highest altitude you are cleared to climb to during that departure step.
Example Sentence 1
The SID listed a top altitude of 5,000 feet, so we leveled off there until ATC cleared us higher.
Example Sentence 2
After reaching top altitude the pilot leveled the aircraft and waited for the next instruction.