Introduction

This article describes typical reasons for high-speed rejected takeoff events associated with inappropriate ATC instructions and identifies a number of potential mitigation actions to be implemented by ATCOs. It further provides an overview of the factors to be considered before issuing an instruction to reject takeoff and identifies best defensive controlling techniques and practices.

There is no set of ready out-of-the-box rules to be followed universally. The controllers should exercise their best judgment when dealing with rejected takeoffs. The examples and advice provided in this article are not intended to be exhaustive and shall not have prejudice to local ATC procedures.

Description

The takeoff phase of each flight is critical as the error-tolerance margin becomes very slim as the aircraft approaches the calculated takeoff decision speed (V₁). Normally, a rejected takeoff (RTO) will be successful if initiated prior to reaching V₁ and properly executed. Beyond V₁, a RTO should only be considered should there be a strong reason to doubt the aircraft’s ability to fly.

Any ATC instruction to reject takeoff issued after reaching V₁ is likely to be considered as inappropriate. It is impossible for the controllers to assess when the aircraft is at or near that speed, therefore any instructions to reject takeoff are most effective when they are issued during the early stage of the takeoff run.

Typical reasons for issuing an instruction to reject takeoff

Some of the most common reasons that have led controllers to issue a RTO instruction include, but are not limited to:

• Observed runway incursion or an obstacle on the runway;
• Observed fire/smoke from the aircraft;
• Observed burst tyre(s);
• The crew mis-identifies the runway and begins a takeoff roll from wrong runway or taxiway.

Factors for controllers to consider

• Cockpit workload is very high during takeoff. Distracting pilots after issuing a takeoff clearance is generally considered unsafe.
• The controller does not know the value of V₁ for each flight, as it depends on a number of factors (e.g. aircraft type and weight, flap setting, pressure altitude, runway condition, air temperature, etc).
• Usually pilots have better situational awareness of whether or not the aircraft is unsafe to fly. They also might have better situational awareness in case of a runway incursion.
• The crew may choose not to comply with an instruction to abort the takeoff. This should be considered with respect to the safety of other traffic.
• The crew might elect to execute an early rotation during the takeoff roll, risking a tail strike, in order to avoid an obstacle on the runway, e.g.: B742 / B744, Chicago O'Hare IL USA, 1999.
• The speed up to which a takeoff should be rejected for all observed failures, varies between 70-100 kt with a typical value of 80 kt or 100 kt.
• A rejected takeoff (RTO) above 80 kt (100 kt in some aircraft types) is considered high-speed RTO.
• In general, high speed rejected takeoffs should only occur in response to a major malfunction. In the high speed regime prior to V₁, pilots will reject for any engine failure, any fire indication or any other circumstance recommended by the aircraft manufacturer. A system malfunction is, on many types, not sufficient reason for a high-speed reject and the failure warning may even be inhibited from above a specific speed until after the aircraft is safely airborne to avoid unnecessary distraction.
• According to “Rejecting a takeoff after V₁, why does it still happen?” (See Further Reading) about 50% of the pilot decisions for high speed rejected takeoffs have been considered incorrect after investigation completion.
• According to “Rejecting a takeoff after V₁, why does it still happen?” a rejected takeoff initiated after V₁ is very likely to result in a runway excursion. Analysis of such occurences shows that in 90% of these cases, the aircraft could not be stopped on the runway.
• In case of runway incursion the aircraft may collide with the obstacle regardless of whether the takeoff has been aborted or continued.
• Controllers should normally consider continuation of the takeoff run preferable to issuance of instruction for RTO at high speed, even when executed from wrong runway (or from taxiway). In this case, however, an informed certainty must exist that the takeoff will be successful and there are no hazards along the runway/taxiway.

Defences

• There is no strict set of rules - controllers should use their best judgement based on their experience and prevailing circumstances.
• Controllers should maintain high situational awareness and be prepared to use the most appropriate RTF when in doubt that an instruction to cancel the takeoff would be effective.
• In general, an instruction to abort a takeoff should only be issued if circumstances exist such that continuing the takeoff run will result in an accident (e.g. if there is an aircraft or a vehicle on the runway).
• Controllers should communicate the most accurate information regarding the location and nature of a runway obstruction.
• In the case of an observed aircraft malfunction, such as a burst tyre or fire/smoke, it is preferable to inform the crew of the problem and wait for their decision.
• Unnecessary communication should be avoided. If in doubt about pilots’ decision it is better not to harass the crew with information requests. Ensuring the safety of the other traffic considering both cases (rejected and continued takeoff) is preferable.
• Adherence to local SOPs and checklists will allow controllers to react quickly and appropriately.
• Deployment of safety nets to mitigate the risk of runway incursion (such as A-SMGCS) to protect runways and designated areas is recommended.

Further Reading

FAA

• Pilot guide to takeoff safety

Airbus Flight Operations Briefing Notes

• Revisiting the stop or go decision Revisiting the stop or go decision
• Understanding takeoff speeds

Others

• Rejecting a takeoff after V₁, why does it still happen?, NLR Report, March 2010