Runway Overrun on Take off
Runway Overrun on Take off
Definition
Overrun. An event when an aircraft passes beyond the end of the runway during an aborted takeoff or landing operation. The overrun distance is described by the longitudinal distance traveled beyond the departure end of the runway.
Source: ACRP Report 3: Analysis of Aircraft Overruns and Undershoots for Runway Safety Areas
Decription
A runway overrun on take off is type of runway excursion that happens when a aircraft that has commenced its take off roll departs the end of a runway. There are two basic scenarios:
- the aircraft cannot generate enough lift to take of by the end of the runway.
- the crew attempts to reject the take off but the remaining distance is less than required.
The minimum allowable runway length required for an aeroplane to accelerate and stop safely is called the Accelerate-Stop Distance Required (ASDR). It depends on the aircraft weight, speed, prevailing weather and runway conditions. In order to reduce the risk of a runway overrun on take off, the ASDR must be smaller than the Accelerate-Stop Distance Available (ASDA) for the runway where the operation is taking place.
Effects
The outcome of a runway overrun on take off is mostly a consequence of the speed at the time of the overrun and the surface after the end of the runway. Depending on the circumstances, the event can result in:
- Casualties or injuries. These are more likely in the extreme scenarios (e.g. collision with a structure, steep slope or a body of water after the runway end, RTO not attempted and the aircraft leaving the runway at high speed with power levers at TOGA, etc.).
- Aircraft damage. This can range from none or minor (e.g. deflated tyre) to a hull loss.
- Aerodrome damage. This includes damage to elements of the lighting system, antennas (e.g. ILS localizer), perimeter fence, etc.
- Impact on aerodrome operations. Depending on the damage to the aircraft and the aerodrome it is possible that a runway is rendered out of service for a prolonged period of time.
Causal Factors
The following is a (non-exclusive) list of causal factors for runway overrun on take off events:
- Incorrect computation of take off parameters (required take off run, thrust settings, speeds, etc.)
- Rejected take-off. Depending on the current speed and the moment the decision is made, there may not be enough runway available to stop the aircraft.
- Aircraft system malfunction. This is the primary reason for the decision to reject a take-off. In addition, some failures/degradations, e.g. those related to the hydraulic system, brakes and flight control surfaces (e.g. spoilers) normally result in reduced decelleration capacity.
- Ineffective use of retardation methods increases the required distance for decelleration.
- Taking off from a wrong (shorter) runway. If this remains undetected, the pilots could have a false impression that they have longer distance available than they actually do.
Contributory Factors
The following factors, while not normally being the leading cause, could aggravate the situation depending on the circumstances:
- For the RTO scenario, the speed at which the decision is made is crucial. High speed RTOs require longer distances, therefore the risk of an overrun is greater in such situations.
- Reduced thrust take off. While this technique reduces engine wear and thus increases its life, it also reduces the safety margins.
- Tailwind increases the distance, required to accelerate the aircraft and results in higher thrust setting. This ultimately necessitates longer distance to decellerate the aircraft in case of a rejected take off.
- Runway surface contaminated by water, snow, slush, ice, etc. reduces braking effectivenes and results in longer runway distance required.
- Runway slope.
- Increased pilot workload. Take off is one of the busiest phases for the flight crew. Any (unexpected) increase of the workload could distract them and contribute to a runway excursion.
- Reduced situational awareness. Oftentimes a take off can be safely completed even though one or more of the causal factors listed above are present. For example, incorrectly computed take off trust could be compensated by applying full engine power. However, if the situation is not properly recognized, the necessary remedial action would probably not be performed.
- Pressures (either real or perceived) could influence flight crew's decision making into continuing the approach and landing.
- Bird strike.
- Long taxi route. This could cause the brakes to overheat and be less effective in case of an RTO. Note that this applies to steel brakes but not carbon brakes.
- Controller intervention:
- Instruction to stop immediately (due to e.g. a runway incursion). The controller would issue such an istruction regardless of the aircraft speed and its ability to stop before the end of the runway if they consider it is unsafe to continue the take off.
- Requesting the crew to start the take off roll before the aircraft is ready. While the controller cannot force the crew to start the take off, and the final responsibility lies with the pilots, it is possible that a controller request is acted upon thus increasing the risk of a rejected take off (and consequently, an overrun).
Defences
The following measures could either reduce the risk or mitigate the consequences of a runway overrun on landing:
- Following SOPs regarding the calculation of take off parameters reduces the risk of using erroneous data.
- Pilot training in decision making and CRM is a crucial factor for making prompt and appropriate decisions as well as their execution.
- Installing an EMAS, while not being able to prevent it, could mitigate the consequences of an overrun.
- In case EMAS is not installed, correct maintenance of the RESA would similarly mitigate the effects of an overrun. A soft surface would have reduced bearing capacity which, in turn, would increase drag and improve decelleration. It should be nothed however, that if the ground is too soft, this could result in landing gear damage.
- Making the aerodrome lights frangible is a standard defined in ICAO Annex 14 and reduces the damage to aircraft.
Accidents and Incidents
On 23 July 2021, the takeoff roll of a Boeing 737-800 making an intersection departure from Yerevan on a non revenue positioning flight using reduced thrust in daylight exceeded the length of runway available by 81 metres but was undamaged and completed its intended flight. The Investigation found that the Onboard Performance Tool when preparing for departure had been wrongly configured but that when the crew realised there was insufficient runway length left to reject the takeoff, the thrust had not been increased and the response had been the commencement of a slow rotation 20 knots before the appropriate speed.
On 18 September 2018, an Airbus A320 crewed by a Training Captain and a trainee Second Officer departing Sharjah was cleared for an intersection takeoff on runway 30 but turned onto the 12 direction and commenced takeoff with less than 1000 metres of runway ahead. On eventually recognising the error the Training Captain took control, set maximum thrust and the aircraft became airborne beyond the end of the runway and completed its international flight. The Investigation attributed the event to the pilots’ absence of situational awareness and noted that after issuing takeoff clearance, the controller did not monitor the aircraft.
On 16 May 2013, a DHC6-300 on a domestic passenger flight made a tailwind touchdown at excessive speed in the opposite direction of the of 740 metre-long runway to the notified direction in use and, after departing the runway to one side during deceleration, re-entered the runway and attempted to take off. This failed and the aircraft breached the perimeter fence and fell into a river. The Investigation identified inappropriate actions of the aircraft commander in respect of both the initial landing and his response to the subsequent runway excursion and also cited the absence of effective CRM.
On 3 March 2021, a Boeing 737-800 departing Lisbon only just became airborne before the end of runway 21 and was likely to have overrun the runway in the event of a high speed rejected takeoff. After a significant reporting delay, the Investigation established that both pilots had calculated takeoff performance using the full runway length and then performed takeoff from an intersection after failing to identify their error before FMS entry or increase thrust to TOGA as the runway end was evidently about to be reached.
On 19 January 2010, PSA Airlines CRJ 200 began take off from Charleston with an incorrect flap setting. After late crew recognition, a rejected take off was commenced at V1+13KIAS and an overrun into the EMAS bed at approximately 50knots followed. It was noted that had the overrun occurred prior to installation of the EMAS bed, the aircraft would probably have run down the steep slope immediately after the then-available RESA. The flap setting error was attributed non-adherence to a sterile flight deck. The late reject decision to an initial attempt to correct the flap error during the take off.
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