Definition
The point along a flight path at which an aircraft transitions from cruise flight and begins its planned descent toward the destination or a lower altitude. It is calculated based on cruise altitude, target altitude, planned descent rate, and groundspeed, and is typically displayed on the navigation display of aircraft equipped with flight management systems.
Plain English
The spot in the sky where you stop cruising and start coming down.
Context Anchor
Seen during flight planning, cruise flight, instrument procedures, and in cockpit navigation displays that show when to begin descending.
Derivation
Top indicates the starting point of the downward phase, while descent derives from the Latin descendere meaning to climb down. This anchors the term as the precise transition from level cruise to downward flight.
Why Pilots Care
Correct TOD timing keeps the aircraft at the right altitude for restrictions, saves fuel, and prevents rushed or steep descents.
Intuition Check
TOD does not mean the highest point the aircraft will ever reach. It means the planned point where the descent should begin from the cruise portion of the flight.
Example Sentence 1
The flight management system showed the Top of Descent two miles ahead, so the crew briefed the arrival before reaching it.
Example Sentence 2
At TOD the crew reduced power and began a 1,800-foot-per-minute descent.