DEFINITION: A take-off that is discontinued after take-off thrust is set and initiation of the take-off roll has begun.
The Rejected Take-Off (RTO) is a maneuver performed during the take-off roll if the flight crew determines that the take-off should not be continued. Most RTOs (approximately 95%) are initiated at speeds below 100 knots and are executed without incidents. However the potential for an accident or incident following a high speed RTO remains high. A review of the available data over the history of western built transportjet operations shows that approximately one in 3.000 take-offs has been rejected.
Of these RTOs about one in 1.000 was unsuccessful, resulting in an overrun accident or incident.
That is an accident/incidentrate of one per 3.000.000 take-off attempts.
From the above statistics one can conclude that:
-An RTO is not a very common event.
-The probability of an RTO incident/accident is remote.
-The infrequency of RTO events may lead to an ease off with regard to maintaining sharp decision-making skills.
In spite of these statistics pilots should be prepared to make the correct go / no go decision on every take-off.
V1 is the maximum speed at which the RTO maneuver can be initiated and the aircraft stopped within the remaining field length under the conditions and procedures defined in the FARs / JARs.
It is the latest point in the take-off roll where a stop can be initiated. If an engine failure is recognized before V1 an abort can be made within the remaining runway. If an engine failure is recognized at or after V1, the take-off can be continued within the remaining take-off distance.
V1 is the end of the go / no go decision process, not the beginning.
2. Factors Influencing Stopping Distance
If available, autobrakes must be set to the RTO mode before the take-off. The proper braking sequence for a RTO at V1 is clearly different from a normal landing.
Braking has top priority and provides the primary stopping forces, followed by spoilers and reverse thrust.
If autobrakes are not available the proper braking technique during an RTO is to apply full brake pedal force and maintain full brake pedal force until the aircraft comes to a complete stop. Autobrakes are not available below a specified aircraft speed value (usually 85-90 knots).The PNF must monitor the autobrake system and advise the PF if a failure occurs.
One some aircraft types dispatch is possible with the antiskid system inoperative. This represents a special case for brake application techniques. In this situation the pilot executing the RTO should apply steady moderate pedal pressure consistent, in his judgement, with runway conditions, aircraft dispatch weight and the available runway length. Full brake pressure should not be applied with the antiskid system inoperative due to the risk of tire failure.
To minimize the possibility of skidding a tire, which can lead to a blowout, the speedbrakes / spoilers should be deployed before brakes are applied. This provides the highest possible wheel loads to keep the wheels rotating with the forward motion of the aircraft.
Correct runway line-up technique should always be applied regardless of whether or not there is excess runway available.
The V1 Call
One important factor in avoiding RTO overrun accidents is to recognize reaching V1 when the aircraft actually does reach V1. The PF cannot react properly to V1 unless the V1 call is made in a timely, crisp and audible manner. When V1 is reached this call out must be finished.
3. Stop and Go Options
When performing a take-off at a field length limit weight, the pilot is assured that the aircraft performance will, at the minimum, conform to the requirements of the FARs /JARs. This means that the take-off can be rejected prior reaching V1 and the aircraft stopped before the end of the runway, or if the take-off is continued, a minimum height of 35 feet will be reached over the end of the runway. This section discusses some effects when deviating from the minimum requirements.
The horizontal axis of figure 1 is the incremental speed in knots above V1 at which a maximum effort stop is initiated. Typically at V1, the aircraft is accelerating at 3 to 6 knots per second. This means that a ‘REJECT’ or ‘STOP’ call made at V1 results in a minimum speed of 80 knots at which the aircraft would cross the end of the runway, assuming the pilot used all of the transition time allowed in the Aircraft Flight Manual (AFM) (approximately three seconds depending on aircraft type) to reconfigure the aircraft to the stop configuration, and that a maximum stopping effort was maintained.
VEF is the speed at which the AFM calculation assumes the engine to fail (a minimum of one second before reaching V1). The horizontal axis of figure 2 shows the number of knots prior to VEF that the engine actually fails, and the vertical axis gives the ’screen height’ achieved at the end of the runway. A typical range of acceleration is 3 to 6 knots per second, so the shaded area shows the range in screen height that might occur if the engine actually failed ’one second early’, or approximately two seconds prior to V1. In other words, a go decision made with the engine failure occurring two seconds prior to V1 will result in a screen height of 15 to 30 feet for a field length limited take-off weight.
4. Decisions and Procedures
The rejection of a take-off should be restricted to:
- Aural warnings (configuration warning siren, caution beeper, fire bell).
- Engine failure.
- Control problems affecting safe aircraft handling.
The rejection of a take-off is initiated by the call ‘REJECT’ or ‘STOP’ (as per company policy). In the above mentioned cases both pilots may the call. In all other cases the decision to initiate the rejection of a take-off is restricted to the captain. Once the rejection is initiated, it must be completed. As the speed approaches V1 a decision to stop is recommended only for an engine failure / fire or a malfunction which impairs the safety of flight.
To reduce decision time, system malfunctions, which do not affect fly ability should be systematically disregarded as the speed approaches V1.
In order not to distract the attention of the cockpit crew during the rejection of a take-off, no information about the reason to reject will be given until the aircraft has come to a complete stop.
An RTO from close to V1 speed encountered at high elevation airports and/or at very high temperatures will require the brakes to absorb a significant amount of energy during the stop. After a high energy stop is made, the first officer or flight engineer must monitor brake temperatures (if possible) in order to recognize the possibility of a brake/tire fire.
If a high speed RTO is performed the tower should immediately be advised that the aircraft is still on the runway, that a high energy stop was made, and that emergency equipment is requested to observe the tires and brakes for possible fires.