Runway excursion-related accidents and incidents are more common than we usually think. The 2021 ICAO safety report shows that in the year 2020, nine accidents occurred due to runway excursions accounting for 24 fatalities, 77 serious injuries, six cases of substantial damage to the aircraft, including a total of 3 hull losses. The recent Korean air incident adds to this.

What is a runway excursion?

A runway excursion involves an aircraft departing the end or the side of the runway surface. They can occur during both takeoffs and landings.

There are two main types of runway excursions. They are:

  • Veer-Off: A runway excursion in which an aircraft departs the side of the runway.
  • Overrun: A runway excursion in which an aircraft departs the end of the runway.
Tower Air
Photo: Getty Images

What factors lead to runway excursions?

During takeoffs

Several factors lead to runway excursions during takeoffs. One of the most common factors that are found in many takeoff-related excursions is the use of incorrect takeoff performance.

When pilots underestimate the weight of the aircraft at takeoff, it gives pilots the option to take off from a runway intersection point without using the whole runway (the lighter the aircraft, the less runway that is required for a takeoff). This saves time as the pilots are not required to enter and backtrack the runway for the departure lineup.

As taking off from an intersection point reduces the total runway length, when weight is underestimated, the aircraft may run out of runway during the takeoff. This was allegedly what happened to Globus Airlines Boeing 737, which suffered from a near-runway excursion event in Moscow back in 2019.

The other factor involves pilots trying to stop the aircraft after the decision speed. Beyond this speed, the aircraft may fail to stop even with full braking. This happens most of the time due to poor decision-making, whereby pilots try to stop the aircraft when a failure occurs after reaching V1 speed.

Ryanair
Photo: Getty Images

The final factor is the most important, and this happens to very experienced pilots well. It involves an aircraft suffering from an engine failure right at the start of the takeoff where the rudder control is not effective enough to control the aircraft. The result is the thrust produced by the live engine causing the aircraft to veer off the runway. Practice and proper technique could prevent this from happening.

During landings

Runway excursions during landings occur not only due to pilot error. Environmental factors, runway conditions, etc., play a major role as well.

A lot of runway excursion-related accidents and incidents during landing are a result of pilots making unstabilized approaches. The inability to maintain a stable approach where the aircraft is at the correct speed, correct glide, correct heading, vertical path, etc., could lead to a runway overrun. Being too fast on the approach puts the aircraft in a high-energy state, which requires the pilots to use heavy braking. This braking might not be enough, causing the aircraft to depart the runway after touching down.

Excessive floatation over the runway can also cause a runway excursion. This often happens in an otherwise stable approach. The pilot maintains the aircraft perfectly stable during the approach but, in the end, due to his or her poor technique and, at times, due to poor judgment, the aircraft is inadvertently put in a float where it fails to touch down within the proper touch-down zone of the runway. When the touchdown eventually occurs, it may occur so far beyond the threshold that there simply is not enough room to decelerate the aircraft, leading to a runway excursion.

The common pilot errors found in such incidents and accidents include holding off the aircraft for a smoother touch down and late idling of the engine thrust.

United Airlines Boeing 757-300 landing
 Photo: Denver International Airport

Landing the aircraft in strong tailwinds can also cause a runway overrun. Airplanes are generally certified to a maximum landing tailwind component. When this limitation is exceeded, there is an increased chance of a runway excursion.

A lot of runway excursions also occur when pilots use the wrong runway conditions to calculate the landing performance. For instance, if the pilots calculate landing speeds and distance for a dry runway when it is wet, there is a chance of the aircraft not being able to stop in time.

Emirates Airline A360
Photo: Getty Images

In crosswind conditions, improper pilot actions could veer the aircraft off the runway. When in crosswinds, the aircraft nose is pointed to the direction of the wind while it tracks the runway center line. This is called a crab condition. Before the touchdown, the pilots kick out the crab by applying the rudder to align the aircraft to the runway centerline and, at the same time, bank the aircraft into the wind to prevent drift.

If the crab is kicked out too quickly, the aircraft may drift, and the aircraft may veer off the runway.

Research shows that the majority of the excursions are not caused by one single factor. It is usually a combination of many factors. For example, making an unstabilized approach to a wet runway in strong crosswinds puts the aircraft at a higher risk of a possible runway overrun or veer-off event.

How to prevent runway excursions

For both takeoffs and landings, nothing beats following proper procedures.

To prevent incorrect takeoff performance from being entered into the flight management system, the pilots should independently calculate the performance and do a comparison of each others' data. This prevents human error.

The pilots should never try to stop the aircraft after the decision speed V1, as this could easily lead to a runway excursion. The decision speed, V1, is to be always respected. If a failure occurs beyond V1, the pilots should get in the air and try to solve the problem in flight.

If an engine failure were to occur at a low speed, the pilots should idle the engine thrust immediately and use differential braking and small tiller movements to keep the aircraft on the runway. This should prevent a runway veer-off.

For landings, the pilots should always aim to make stable approaches. Trying to go for extra smooth touchdowns should be avoided, as this wastes the available runway distance. Any time, the approach gets unstable, or if the safety of the landing is jeopardized, a go-around must be initiated.

There is also nothing wrong with being a little conservative when calculating runway performance. If there are any doubts over the conditions of the runway (such as the braking action), the worst possible conditions should be used. This way, even if the runway conditions are better than the calculated ones, there would be no issues as this would only reduce the actual distances required.

What is the industry doing to prevent runway excursions?

Training is a key part of preventing runway excursions. Thus, pilot training has improved over the years to train the pilots to follow the standard operating procedures and teach them the importance of those procedures.

The training syllabuses have improved to include simulator takeoff and landing scenarios in the wet and contaminated runway to show the pilot the behavior of the aircraft in such conditions and how to react to them.

British Airways flight simulator
Photo: British Airways

The Runway Overrun and Protection System (ROPS) by Airbus is an initiative to improve pilot awareness during landings. The system is a part of the aircraft avionics that uses the airport database in the aircraft Terrain Awareness Warning System (TAWS) to find the landing runway. This data is then used by the system to calculate an estimated landing distance that is required based on aircraft weight and prevailing weather conditions.

If the system finds that the runway is too short, it gives an aural and visual warning to the pilot to go around. Once the aircraft touches down, it transitions to the ground phase and again calculates the remaining runway distance. If the system feels that the runway is coming to an end, it can give callouts such as “MAX BRAKING” and “MAX REVERSE” if they are not already in use.

Airbus ROPS

Ever been on board during a runway excursion? Let us know about your experience in the comments.