Aborted start
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Rejected takeoff - English : Rejected Takeoff (short: RTO ) or Aborted Takeoff is the completion of an already initiated startup of an aircraft. After the aborted take-off has been completed, the aircraft is still or is on the ground again. The term is mainly used in commercial aviation or in connection with commercial aircraft.
Reasons for an aborted start
There are various reasons for a start abort:
- On the aircraft side: loss of control, engine fire , flame stall , bird strike , serious system errors, etc. as well
- Airport side: Instructions from the controller, suddenly blocked runway, etc.
The catalog of malfunctions that make aborting a start advisable has changed over time. For example, some manufacturers today advise against aborting take- off if a tire bursts (without any consequences for the rest of the aircraft structure) , because the subsequent massive braking maneuver will cause the tire to fail for the maneuver and thus put additional strain on the remaining components, which makes their failure all the more makes more likely.
Decision parameters
In the case of two-engine or multi-engine aircraft that can still climb with the remaining engines, the question of aborting take-off arises depending on the energy already built up or the movement impulse. This momentum is the product of speed and mass. The faster and heavier an aircraft, the longer its braking distance with the same deceleration. With increasing speed, the chance of coming to a standstill on a given route (namely the remainder of the runway) decreases.
Since the pilots only have a very small time window of a few fractions of a second available for the decision to abort take-off when an aircraft takes off, all known parameters that are relevant for the decision must be calculated before each individual flight. This includes the exact weight of the aircraft including load, condition and age of the tires and brakes, length and condition of the runway as well as weather conditions such as precipitation and icing, which can influence the braking effect of the aircraft on the runway. The reverse thrust of the engines is not taken into account, since their failure can be the reason for the aborted take-off.
The current decision speed " V1 ", which must not be exceeded before or when the start is aborted, is calculated from these variables . It is also important at which point on the runway the decision speed is reached. Usually this should be the case before a previously calculated critical point. In this case, after an aborted take-off, there would still be sufficient runway length available for the subsequent deceleration to a standstill.
If the decision-making speed is exceeded, the risk of being damaged on the ground by the aircraft's high movement impulse outweighs the potential dangers of taking off e.g. B. with reduced performance or limited tax options.
execution
After the decision to abort take-off, the take- off process is aborted before the decision speed is reached and the aircraft is brought to a standstill again with the aid of the hydraulic brakes , the aerodynamic air brakes and (if still functional) the thrust reverser . However, if a decision is made against an aborted start, it is imperative to take off. Multi-engine aircraft are certified in such a way that they can reach the safe take-off speed V2 in the event of a single engine failure after exceeding the decision speed .
After taking off and analyzing the damage in the air, appropriate measures are taken, which can range from an immediate return to the field, to deflating the fuel in the air and continuing the flight normally.
Automation as a support
"Autobrake" , if installed, refers to a setting option for the automatic braking system of an aircraft. In this setting, when a certain rolling speed is exceeded and the thrust lever is withdrawn immediately, the automatic braking system applies full braking. This is used to support the pilots, who, in addition to activating the speed brake and reverse thrust, have to keep the aircraft on the track with any aircraft-side error (e.g. asymmetrical reverse thrust after engine failure).