Nearly every year, we see numerous news reports of airplane runway overruns. From the major DHL 757 overrun in Costa Rica in 2022, to the recent United 737-8 MAX excursion in Houston (and a whole load more in between).
In 2023, the US National Aerospace System recorded more than 54 million takeoffs and landings, with 1756 incursions (when things are on the runway when they shouldn’t be) and 492 excursions (when things go off parts of the runway they shouldn’t go off). The International Air Transport Association (IATA) reported that from 2005 to the start of 2019 (it takes a while for reports to catch up), 23% of some 283 accidents were due to runway excursions.
Now, the vast majority of these were in the General Aviation (GA) arena but just one excursion by a commercial jet aircraft is a major event with the potential to cause millions of dollars in damage and lead to injuries or worse for the passengers and crew, so the issue is treated very seriously.
So, how do runway excursions happen, what methods are in place to stop them and do you need to worry about it as a passenger?
What leads to a runway excursion?
Runway excursions can occur due to a wide number of factors, and there is rarely (if ever) a single root cause. However, we can highlight some factors which are more often the most significant contributing ones in excursion events for commercial aircraft. The majority of these apply to both takeoff and landing.
EASA (the European Aviation Safety Agency) studied excursions in great detail and came up with the a list of common factors which we have organized into three main categories:
- Poor visibility, tailwinds, crosswinds, contamination etc. Basically, weather type stuff, all of which we’ve lumped into ‘EnvironMental!’
- Then there are a whole bunch of factors from incorrect configurations, high energy over the threshold, long flares, deep landings, excessive thrust, too much energy, slow deceleration etc etc which can lead to unstable approaches, abnormal runway contact and that sort of thing. We have wittily titles this section “The horse has bolted”.
- Our third category is “Give me a Break!” which includes broken brains, broken brakes and other things which might result in less braking and things bending and getting banged up.
EnvironMental!
Runway contamination considerably reduces an aircraft’s ability to decelerate by preventing the aircraft tyres from contacting the runway surface, reducing friction and wheel spin-up. It can also result in reduced directional control and this can lead to aircraft going off the side as opposed to the end.
Then there is the wind. Tailwinds do not just increase the landing roll, they can also have a significant effect on aircraft ‘stabilization’ (which we’ll go into more below). Crosswinds reduce directional control, wind shear and turbulence reduce, well, control, and all of these can add to the risk of an excursion.
Low visibility is another one. How does this lead to a possible excursion? Well, if not prepared for low visibility conditions, crew may struggle to maintain visual awareness and when combined with strong crosswinds for example, it may lead to a ‘sideways’ excursion. Autolands conducted when the protected area is not protected (when LVPs are not in force) can lead to disruption of the localiser signal, which can result in an aircraft not landing where it should and tracking incorrectly – again potentially leading to a lateral excursion.
Of course, performance calculations take all the environmental factors into account but a small change – a sudden gust, not having accounted for the actual contamination levels, landing long (floating) can all invalidate performance calculations. Combine these with some other factors and you have a recipe for an overrun.
Southwest Airlines flight 1248 went off the end of Chicago Midway Airport’s runway 31C in 2005, when it attempted to land during a snowstorm. The Boeing 737 had no technical issues, but a combination of the flying pilot failing to select maximum reverse thrust, combined with insufficient surface condition reports from ATC and a tailwind increasing the touchdown speed led to the accident.
The horse has bolted
I don’t get the pun? It is a joke on something being ‘out of the stable’… unstable…
Unstable approaches (that crew continue to land from) are a major factor in many excursion events on landing. ‘Stabilization’ is, in brief, the requirement for an aircraft to be in the correct configuration, at the right speed and thrust setting, and on the correct trajectory, usually by 1000’ (in IMC conditions).
So, why wouldn’t they be?
Well, environmental conditions can make this more challenging. Tailwinds make it hard for aircraft to slow down (and in turn, to configure because flaps have maximum speeds). They mean a higher speed which requires a greater rate of descent, more energy to lose, higher touchdown speeds etc and all this can increase the risk of an aircraft being unstabilised.
ATC can add to the threat as well. Shortcuts, and keeping aircraft high or fast can increase the chances of the approach becoming unstable, while changing runways on short notice can lead to crew being overloaded or unprepared for the approach and more likely to make mistakes.
On takeoff, late runway changes are also a common factor for performance related excursions. Either the performance for the wrong runway is calculated leading to incorrect speed and/or configuration settings, or crew may take an incorrect intersection for departure leading to a shorter takeoff run length being available than expected.
A Honda HA-420 business jet aircraft overran the runway at AGC/Pittsburgh’s Allegheny County in 2022, when it continued to land from an unstable approach. The investigation showed it was 11 knots above its reference speed as it descended through 1000 ft. The speed was still 9 knots high as it passed the threshold. The runway was contaminated with slush and combined with the increased speed, this led to reduced deceleration. The crew attempted to apply maximum braking but hydroplaned, skidded sideways and overran the end of the runway
Give me a break
Things sometimes break. Pilot brains are not immune to the problem, particularly when fatigued or stressed. While a single error or mistake rarely leads to a major event, chains of errors can. In Tibet, 2022, an Airbus 319 “excurted” off to the side of a runway during a rejected takeoff. The aircraft was working fine and there were minimal environmental factors. The main factor was, in fact, the pilot’s foot pressing down on the left rudder – an inadvertent (and not initially noticed) reaction to other distractions. When the pilots did realize what was happening, the subsequent startle effect led to incorrect call-outs and actions to correct the diversion.
Fatigue, stress and limited capacity (too high workload) can all add to something called “get home-itis” (not the technical term). This is, basically, when the pilot focuses on landing and loses the ability to think “it might be better to throw this approach away and try again”.
Of course, aircraft systems can break as well. The DHL excursion was attributed to a failure in the hydraulic system which led to an emergency landing. During the roll out, excessive deceleration on the right side only caused the aircraft to veer to the side and onto uneven terrain, causing failure in the undercarriage.
Degradation or unserviceability of braking systems, or flight control systems which enable slower speeds (ie flaps/slats) can also contribute to potential excursion risks and where multiples failures occur, or failures and degraded conditions add up, crew may opt to land knowing a low speed excursion is a possibility, instead of trying to reach a longer, but riskier to get to, runway elsewhere.
Have we scared you?
Don’t be scared! Remember, the statistical percentage of excursions is tiny and it takes a whole chain of factors to add up before it even becomes a possibility. There are also multiple barriers in place to help prevent excursions, or to mitigate against the severity of them should they happen, and that’s what we’re going to take a look at now.
1. EMAS
EMAS (engineered material arrestor systems) is similar to the gravel traps you see at the end of race circuits, or on truck over-run ramps. These arrestor beds are usually made up of large blocks of frangible material which crush ‘reliably and predictably’ under the weight of an aircraft and the energy transfer (speed energy to crushing energy) slows the aircraft down very effectively.
In the US, (as of 2023) these are installed at some 125 runway ends, across 72 airports. They are mandatory at US airports where there is insufficient over-run space after the runway. You can recognise it on an airport chart by looking for a small rectangle at the end of the runway with an arrow pointing to it, saying ‘EMAS’. A good one to look at is New York’s JFK Airport – they have short runways, limited over-run areas and have installed EMAS on several of the runways for that reason.
While this system is really good at slowing big, fast aircraft down, they are much less efficient for smaller aircraft because they require weight to make them properly effective. During low speed events, pilots have also been known to try and lose speed quicker through ‘steering’ side to side in the hope of losing speed through drag. This tends to either lead to the aircraft going off the side of the runway, missing the EMAS entirely, or entering the arrestor bed at an angle which is far less effective.
So a good system, but not an actual prevention to excursions.
2. Warning systems
Airbus has a system called ROW/ROP (runway over-run warning/protection), and other aircraft types have something similar.
The prevention (ROP) function continuously calculates whether the aircraft is going to be able to stop with the runway length available. Continuously as in it does it even during the roll out, so if an aircraft floats and lands long, it is still monitoring. It uses groundspeed, airspeed, weight, wind and a whole load of other parameters and if it thinks the runway is going to be too short it will give a caution. In flight, this prompts the crew to re-assess and go-around, and during the roll out, commands maximum braking and reversers to help increase deceleration.
The warning (ROW) system kicks in at 500 ft and then reverts back to ROP during the roll out. It calculates the dry and wet distances and offers up an “If wet: RWY too short” type warning or a “RWY too short” aural and visual message if, well, it is just too short.
Many aircraft types also have systems designed to prevent wrong intersection or runway departures (and landings). These work by giving an audio announcement to the crew when they are approaching a particular runway, with the aim of triggering an “Eh? Is that the one we meant to go for?” response in the pilots. Moving maps also assist the crew in identifying the correct runway departure intersections, particularly in low visibility conditions, by increasing situational awareness.
All aircraft run a ‘config check’ when the thrust levers are set to takeoff position. This checks various parameters to ensure things like the flap configuration matches what has been programmed. It checks that speeds match and helps prevent crew from taking off with the wrong figures in. Similar warnings occur on landing if the flap setting physically does not match the setting selected in the performance pages of the FMC.
An Air Serbia Flight overran during takeoff from runway 30L at BEG/Belgrade airport in 2024 when they inadvertently lined up from the wrong intersection. Intersection D5 left them with only 1273 m of runway available. The crew realized accelerating through 100 knots but failed to reject the takeoff, and the Embraer 195 dragged its landing gear through the approach light system for the opposite end approach.
3. Braking systems
Most aircraft nowadays have auto brake systems. These clever systems do two things – they ensure a pre-set level of deceleration occurs, and they take the pressure off the pilot’s feet. Literally. Once the aircraft touches down, they start braking automatically. This is beneficial because pilot feet rarely manage to apply the exact same level of pressure, or manage to apply it at the exact moment they should (we have a bit of a delay between our brain and our feet). This leads to less than optimal braking and potential directional control issues.
So, performance calculations are run and an autobrake setting is selected. Because it works off deceleration rate, if reverse thrust is used (or if it doesn’t work) then the braking system will moderate the braking required to still maintain the deceleration rate required. Airbus take it a step further and have a system called BTV – ‘brake to vacate’ – which combines managing the required deceleration rate with actually knowing which exit the crew are planning on taking, and bringing the aircraft down to the correct speed at that point.
There are other systems on aircraft which help them decelerate – spoilers help “dump” the lift off the wings on touchdown, ensuring firmer contact between the wheels and the runway surface. Reverse thrust we already mentioned – this system re-directs the engine airflow to produce drag. It helps aircraft slow down, but is not a primary braking system as such. In very general terms, the use of max reverse over idle, only results in around 10% reduction of stopping distance, but it does improve brake wear significantly.
Flaps and slats – all those flight controls that enable aircraft to fly at slower speeds for approach – also help reduce the landing distance required by reducing the speed at which the aircraft will touchdown at.
4. A thing called GRF
GRF stands for the Global Reporting Format and it is used (should be used) by every airport in the world to provide reports on the conditions of runway surfaces when contamination is present.
In Ye Olden Days (and frustratingly still in some places) they liked to give friction coefficients. These mean very little to pilots because, well, they don’t mean a huge amount. They can be too subjective, depend on how the measurements were taken, require tables to calculate what that means for this aircraft’s specific braking etc etc. So, someone clever (ICAO) invented GRF.
GRF means reports are standardized and harmonized, and it does so by using something called an RCAM – runway contamination assessment matrix. This considers the type and depth of contamination and removes the subjectivity, and instead provides a code which pilots can use in their performance calculations, and which gives them a “heads-up” on the potential deceleration and directional control they are likely to experience.
5. Procedures, procedures, procedures
We may have been somewhat harsh on pilots and their contribution to runway excursion events. Pilots do receive a huge amount of training to help prevent incidents like these, and the training and procedures they follow are becoming more robust as more understanding of what leads to events increases.
Procedures for ATC, crew, even airport design improvements are all helping reduce the risk of runway excursion events. So, it turns out, there are a lot of things stopping you, and worrying about excursions and overruns should not be one of them.
![An example full flight summary response from the Flightradar24 API: { "data": [ { "fr24_id": "0987654321", "flight": "SK1415", "callsign": "SAS1415", "operated_as": "SAS", "painted_as": "SAS", "type": "A20N", "reg": "SE-DOY", "orig_icao": "ESSA", "orig_iata": "ARN", "datetime_takeoff": "2023-01-27T05:15:22", "runway_takeoff": "12R", "dest_icao": "EKCH", "dest_iata": "CPH", "dest_icao_actual": "EPWA", "dest_iata_actual": "WAW", "datetime_landed": "2023-01-27T06:15:10", "runway_landed": "27L", "flight_time": 3600, "actual_distance": 1007.74, "circle_distance": 6245, "category": "Passenger", "hex": "4A91F9", "first_seen": "2023-01-27T05:06:22", "last_seen": "2023-01-27T06:18:10", "flight_ended": "true" } ] }](https://www.flightradar24.com/blog/wp-content/uploads/2025/04/Flight-summary-API-cover-768x378.jpg)
2 Responses
One of the most informative items I’ve read. Suitable for the layman (person) to understand. Clearly whenever you decide to walk away from the flight deck a career in Aviation Journalism awaits you.
In the meantime more items written by you please and perhaps explain why an a/c would “blow its tyres” when attempting an emergency halt.
great explanation of unknown or understood terms.