The runway requirements for takeoff are affected by:
- Pressure altitude
- Headwind component
- Runway gradient or slope
- Aircraft weight
The runway required for takeoff must be based upon the possible loss of an engine at the most critical point, which is at V1 (decision speed). By regulation, the aircraft’s takeoff weight has to accommodate the longest of three distances:
- Accelerate-go distance—the distance required to accelerate to V1 with all engines at takeoff power, experience an engine failure at V1 and continue the takeoff on the remaining engine(s). The runway required includes the distance required to climb to 35 feet by which time V2 speed must be attained.
- Accelerate-stop distance—the distance required to accelerate to V1 with all engines at takeoff power, experience an engine failure at V1, and abort the takeoff and bring the aircraft to a stop using braking action only (use of thrust reversing is not considered).
- Takeoff distance—the distance required to complete an all-engines operative takeoff to the 35-foot height. It must be at least 15 percent less than the distance required for a one-engine inoperative engine takeoff. This distance is not normally a limiting factor as it is usually less than the one-engine inoperative takeoff distance.
These three required takeoff runway considerations are shown in Figure 10-34.
Balanced Field Length
In most cases, the pilot will be working with a performance chart for takeoff runway required, which will give “balanced field length” information. This means that the distance shown for the takeoff will include both the accelerate-go and accelerate-stop distances. One effective means of presenting the normal takeoff data is shown in the tabulated chart in Figure 10-35.
The chart in Figure 10-35 shows the runway distance required under normal conditions and is useful as a quick reference chart for the standard takeoff. The V speeds for the various weights and conditions are also shown.
For other than normal takeoff conditions, such as with engine anti-ice, anti-skid brakes inoperative, or extremes in temperature or runway slope, the pilot should consult the appropriate takeoff performance charts in the performance section of the AFM.
There are other occasions of very high weight and temperature where the runway requirement may be dictated by the maximum brake kinetic energy limits that affect the aircraft’s ability to stop. Under these conditions, the accelerate-stop distance may be greater than the accelerate-go. The procedure to bring performance back to a balanced field takeoff condition is to limit the V1 speed so that it does not exceed the maximum brake kinetic energy speed (sometimes called VBE). This procedure also results in a reduction in allowable takeoff weight.