Description

The Net Take-off Flight Path (NTOFP) is the vertical profile of an aircraft beyond the take-off point, giving the minimum height that will be attained by an aircraft flown in accordance with the Aircraft Flight Manual (AFM) following failure of the most critical power unit.

Aircraft Performance calculations prior to take-off must establish that the aircraft will clear all significant obstacles in the obstacle domain (see below) by at least 35 ft.

The NTOFP is calculated taking into account possible deviations from the ideal due to circumstances such as weather, wind, and below average engine performance.

Figure 1 is a typical example with four segments in the NTOFP. In the first segment, the landing gear is retracted and the aircraft accelerates to the appropriate speed. During the second segment, the aircraft climbs to the height selected for flap retraction, which may not be less than 400 ft. In the third segment the flap is retracted and the aircraft accelerates to the fourth segment climb speed. In the fourth segment, the aircraft climbs to 1500 ft or until it is clear of significant obstacles.

In this case, the two obstacles must be cleared by at least 35 ft. If this is not possible, the take-off weight must be reduced until it is. Other solutions are sometimes available but discussion of them is beyond the scope of this article.

Figure 2 illustrates the Obstacle Domain. This is calculated so as to ensure that an aircraft operating in accordance with the AFM will not encounter any other significant obstacle. Calculations take into account likely deviations from the runway centre-line due to circumstances such as weather, wind and below average pilot performance.

Further Reading

JAR-OPS 1, especially paragraph 1.430, Appendix 1 and related IEM.

ICAO Annex 6 (Operation of Aircraft) especially Chapter 4 and Appendix 2.