Definition
The speed during the takeoff roll at which, if an engine fails or another serious problem occurs, the pilot must decide whether to abort the takeoff or continue. Below this speed, the takeoff is rejected and the aircraft is brought to a stop on the remaining runway. At or above this speed, the takeoff is continued because there is no longer enough runway to stop safely. This speed is calculated for each takeoff based on aircraft weight, runway length, surface conditions, altitude, and temperature.
Plain English
The speed on the runway where the pilot is committed to flying. Below it, you can still stop on the runway if something goes wrong. Above it, you have to keep going and lift off, because there is not enough runway left to stop.
Context Anchor
You see this term in multiengine and turbine airplane takeoff performance planning, especially during the pre-takeoff briefing and in performance charts.
Derivation
The name describes its function exactly: the speed at which the takeoff decision (go or stop) must already be made.
Why Pilots Care
It marks the point where continuing the takeoff becomes safer than attempting to stop, directly affecting the outcome of an engine failure or other emergency during the takeoff roll.
Analogy
It is like a marked point on a road where, if you have not turned off yet, you no longer have enough room to stop safely before the end. Before the point, stopping is still planned for; after the point, continuing is the safer choice.
Grounding Statement
On the runway, Takeoff Decision Speed is the point where the pilot changes from “I can still stop safely” to “I should continue and fly.”
Intuition Check
Do not read “decision” as meaning the pilot starts thinking about what to do at that moment. The decision is made before takeoff; the speed tells the pilot which preplanned action to take.
Example Sentence 1
The captain briefed that any malfunction before takeoff decision speed would result in a rejected takeoff, and any after would mean continuing into the air.
Example Sentence 2
An engine failure occurred just below takeoff decision speed, so the crew rejected the takeoff and brought the aircraft to a stop.