Obstacle Clearance and Takeoff Flight Path

Takeoff Flight Path Segments

The takeoff flight path is divided into segments, each defined by changes in aircraft configuration, speed, or thrust. For Performance Class A aeroplanes, the path begins at the point where the aircraft reaches 35 ft above the runway (the screen height) and continues through several segments:

• First Segment: From liftoff to gear retraction, typically up to 35 ft.
• Second Segment: Gear up, takeoff power set, climbing at V2 speed, usually up to the acceleration altitude (often 400 ft AGL).
• Third Segment: Level-off at acceleration altitude to retract flaps/slats and accelerate.
• Final Segment: Climb out to 1500 ft AGL or higher if required by distant obstacles.

Net Takeoff Flight Path (NTOFP) and Obstacle Clearance

The NTOFP is a conservative, regulatory flight path assuming one engine inoperative (OEI) from the critical point (usually VEF). It is constructed to ensure a minimum clearance of 35 ft above obstacles in straight flight, or 50 ft when turning. The actual aircraft performance is typically better, but planning must use the net path for compliance.

Obstacle clearance requirements apply only to obstacles within a defined obstacle domain, which expands laterally with distance from the runway. Turns are restricted: no turns below 50 ft, and bank angles are limited to 15° between 50 ft and 400 ft. Above 400 ft, higher bank angles may be permitted if procedures require.

Effects of Configuration, Weather, and Clearway

Aeroplane configuration (flap setting, gear position), weight, and meteorological conditions (wind, temperature, pressure) all affect climb performance and thus obstacle clearance. Wet or contaminated runways can degrade actual performance, reducing the margin below the net path by up to 20 ft. Use of a clearway allows a longer takeoff run, potentially increasing the field-length-limited takeoff mass, but does not affect the NTOFP or obstacle clearance requirements.

Calculating Obstacle Clearance

To determine clearance, calculate the aircraft's height at the obstacle's distance along the NTOFP, then subtract the obstacle's height. For multi-engine piston (MEP) aircraft, similar principles apply, but specific gradients and speeds may differ. Always apply regulatory wind adjustments: use only 50% of headwind or 150% of tailwind components in planning.

Operational Procedures

Operators must have contingency procedures ensuring the aircraft can either continue safely en-route or return to land if an engine fails. These must account for all obstacles in the domain and comply with regulatory clearance margins throughout the takeoff flight path.