What is the V1 Speed for a Commercial Aircraft?
V1 has two different meanings. Firstly, it is the speed by which the first action must have been taken to reject the take-off if the aircraft is to safely stop on the remaining runway. Secondly, V1 is also the minimum speed at which the aircraft is ‘guaranteed’ to get airborne and reach the screen height (35ft dry and 15ft wet) in the remaining take-off distance available if an engine fails.
The FAA state taking the first action to stop the aircraft can be:
- Reducing thrust
- Applying the brakes
- Deploying the speedbrake
In summary, if an engine fails below V1 and the take-off is continued, the aircraft may not get airborne in the remaining take-off distance available. If a take-off is rejected above V1, the aircraft may not be able to stop on the remaining runway available (technically accelerate-stop distance available or ASDA) and leave the paved surface.
The Decision Speed on Take-off?
V1 has previously been called the ‘Go / No-go’ or a ‘decision’ speed, but these are no longer considered to be the most appropriate phrases. This is because the first action to reject the take-off must have been taken by V1 and therefore the decision as to whether to go or stop should have been made prior to V1. Whilst it should not be considered, there is a 2 second buffer built into the calculations which would allow the pilots to reject the take-off 2-seconds after V1 and still be able to stop on the remaining runway. This is an additional safety margin.
V1 must always be greater than VMCG and less than VR.
What affects V1?
V1 is calculated by the pilots prior to every flight. V1 is affected by:
- Take-off Distance Available
- Flap Setting
- Pressure Altitude (Temperature, Pressure, Field Elevation)
- Aircraft Weight
- Runway Surface State (i.e. dry, wet, contaminated)
- Runway Slope
- Wind Speed and Direction
Since V1 must be more than VMCG and less than VR, these speeds can also affect the V1 speed (and therefore the variables which affect these speeds such as engine thrust).
What is the normal V1 speed for a commercial jet?
What happens at V1 on the flight deck?
The pilot monitoring (i.e. the pilot who is not flying the aircraft but is monitoring the instruments) usually calls out V1. On some jets this is automatically called out by the flight computers. When V1 is called out, the pilot flying, or at some airlines the Captain, removes their hands from the thrust levers to stop them reducing the thrust and rejecting the take-off if a malfunction occurs.