Definition
The point along a flight route at which an aircraft leaves cruise altitude and begins its planned descent toward the destination or a lower assigned altitude.
Plain English
The spot in the flight where you stop cruising level and start coming down.
Context Anchor
Seen during cross-country planning, instrument arrivals, and in cockpit navigation systems that calculate when to leave cruise altitude.
Derivation
“Descent” comes from Latin words meaning “to climb down” or “go down.” In aviation, the “top” of descent means the upper starting end of that downward path, not the highest point of the whole flight.
Why Pilots Care
Starting descent at the correct point keeps the aircraft on an efficient profile, avoids arriving too high or too low, and reduces fuel use and workload.
Analogy
It is like choosing where to start slowing down before a highway exit. If you wait too long, you have to brake hard; if you start at the right point, the whole change is smooth.
Intuition Check
Do not read “top” as simply the highest altitude reached in the flight. Here it means the starting point at the upper end of the planned descent path.
Example Sentence 1
The pilot calculated Top of Descent about 90 miles from the airport to allow a steady 500-foot-per-minute descent from cruise altitude.
Example Sentence 2
By reaching the top of descent on schedule the crew arrived at the first fix at the planned altitude.