ATR: Take-off flight path segments

The one engine out take-off flight path is divided in four different segments: first, second, third and final segment. Each segment begins when change is made either in the aircraft configuration, power or speed.

For each segment, specific requirements apply, and must be fulfilled during the whole flight of the segment, i.e. at the most critical point –due to weight, configuration, power...– prevailing on the segment.

NOTE: The flight path must be based on the performance of the aircraft without ground effect. As a general rule, the aircraft is considered out of the ground effect, when it reaches a height equal to its wing span.

IMPORTANT: Remember that these requirements must always be met so that a minimum level of climb gradient is available, whatever the obstacle clearance problem may be (generally more restrictive).

After an engine failure at VEF, the aircraft must fulfill minimum climb gradients, on 1st, 2nd and final segment as required by the regulation.

First segment
CS / FAR 25.121 Climb: one-engine-inoperative
(a) In the critical take-off configuration existing along the flight path (between the points at which the aeroplane reaches VLOF and
at which the landing gear is fully retracted) (…) the steady gradient of climb must be positive.

Second segment
CS / FAR 25.121 Climb: one-engine-inoperative
(b) In the take-off configuration existing at the point of the flight path at which the landing gear is fully retracted (…) the steady
gradient of climb may not be less than 2.4%.
The 2nd segment requirement is generally the most limiting of the climb requirements at take-off and leads to Take-Off
Weight limitation especially in hot and high altitudes runways.

The acceleration performed during the 3rd segment must be done in a regulated height range.

Minimum Acceleration Height
CS / FAR 25.111 Take-off path
(c)(2) The aeroplane must reach V2 before it is 35 ft above the take-off surface and must continue at a speed not less than V2 until it is 400 ft above the take-off surface.
(3) At each point along the take-off flight path, starting at the point at which the aeroplane reaches 400 ft above the take-off surface, the available gradient of climb may not be less than 1.2%.
Below 400 feet, the speed must be maintained constant to a minimum of V2, with a 2.4% minimum climb gradient, and above 400 feet, a 1.2% minimum climb gradient is required. The regulatory minimum acceleration height is 400 feet above the take-off surface. The aircraft can accelerate in level flight at 400ft.

Maximum Acceleration Height
The Reserve Take-Off (RTO) power is certified for use for a maximum of 10 minutes in EASA regulation, and 5 minutes in FAA. The Maximum Continuous Thrust (MCT), which is not time-limited, can only be selected once the en-route configuration is achieved. As a result, the en-route configuration (end of the 3rd segment) must be achieved within a maximum of 10 / 5 minutes after take-off, thus restricting the maximum acceleration height.

Final segment
CS / FAR 25.121 Climb: one-engine-inoperative
(c) Final take-off. In the en-route configuration at the end of the take-off path (…) the steady gradient of climb may not be
less than 1.2%.