Unclassified

Executive summary

Natlonaal Lucht- en Rulmtevaartlaboratorlum

National Aerospace Laboratory NLR

Running out of runway

Analysis of 35 years of landing overrun accidents

Probleem area

Landing overruns belong to the

group of most frequently reported

accident types in the world.

Fortunately, landing overruns do

not often result in causalities

amongst passengers and crew.

Despite this fact landing overruns

can still be considered a major

threat to aviation safety. It is

therefore interesting to have an

overview of factors that increase the

landing overrun risk, the trends in

statistics and in the influence of

safety initiatives. A safety study on

landing overruns of commercial

transport aircraft was conducted

which addressed these issues.

Unclassified

Description

This paper presents an analysis of

landing overrun accidents of

commercial transport aircraft that

took place during the period 1970-

2004. A total of 400 accidents were

identified and analysed. The

accident data were obtained from

the NLR Air Safety Database. A

data taxonomy was developed

based on factors that influence

landing performance. The data were

evaluated through a straightforward

single-variable analysis. This

included developing frequency

distributions of each risk factor

considered. It also included an

exploratory analysis that provided a

general understanding of the

landing overrun accident data. A

central objective of this study was

to estimate the risk associated with

the various landing factors (such as

excess speed, tailwind, runway

condition etc.). It was therefore

Report no.

NLR-TP-2005-498

Author(s)

G.W.H. van Es

Classification report

Unclassified

Date

September 2005

Knowledge area(s)

Flight Safety

Aircraft Operations

Descriptor(s)

Overruns, unstabilised approach,

braking, landing, flare, floating,

wet runways, contaminated

runways, runway safety areas,

ground arrestor
Unclassified

essential to understand the

prevalence of these individual

factors during landings which did

not end up in a landing overrun. For

instance to estimate the risk

associated with long landings it

should be known how many long

landings took place without

resulting in an overrun. The risk

associated with the presence of a

number of factors was estimated.

Finally the data were analysed for

trends.

Conclusions

The following conclusions are

drawn from the landing overrun

accident data studied in this paper:

• The Africa region demonstrated

the highest landing overrun accident

rate, followed by Central/South

America, and Asia. All these

regions had rates of more than one

accident per million landings. The

rest of the world demonstrated rates

below one accident per two million

landings which was less than half of

the rate of the previous mentioned

regions. North America had the

lowest rate of all regions.

• No statistically significant

difference in the estimated landing

overrun accident rate between

commercial transport jet and

turboprop aircraft was found.

• On a worldwide basis, there

appears to be a significant increase

Running out of runway runway

Analysis of 35 years of landing overrun accidents

in landing overrun risk when one of

the following factors is present

during a landing: Non-precision

approach, touching down far

beyond the threshold (long landing),

excess approach speed, visual

approach, significant tailwind

present, high on approach,

wet/flooded runway, and/or

snow/ice/slush covered runway.

The highest risk increase occurred

when the aircraft touched down far

beyond the threshold (long landing),

followed by excess approach speed.

• On a worldwide basis, the

landing overrun accident rate has

reduced by a factor of three over a

period of thirty-five years. This

reduction is most likely the result of

a number of factors including

improvement in braking devices

(antiskid, autobrakes etc.), better

understanding of runway friction

issues, and safety awareness

campaigns.

• Late or no application of

available stopping devices was

often found to be a factor in the

landing overrun accident. These

overrun accidents were all

avoidable if the crew had used the

available stopping devices, without

any delay.

Nationaal Lucht- en Rulmtevaartlaboratorium, National Aerospace Laboratory NLR

Anthony Fokkerweg 2, 1059 eM Amsterdam,

P.O. Box 90502, 1006 BM Amsterdam, The Netherlands

Telephone +3120 5113113, Fax +3120 511 32 10, Web site: www.nlr.nl
Natlonaal Lucht- en Rulmtevaartlaboratorlum

National Aerospace Laboratory NLR

NLR-TP-2005-498

Running out of runway

Analysis of 35 years of landing overrun accidents

G.W.H. van Es

This report has been based on a paper presented at 58th annual International Air

Safety Seminar (lASS), Moscow, Russia, 7-10 November, 2005.

This report may be cited on condition that full credit is given to NLR and the author.

Customer: National Aerospace Laboratory NLR

Working Plan number: AT.1.A

Owner: National Aerospace Laboratory NLR

Division: Air Transport

Distribution: Unlimited

Classification title: Unclassified

August 2005

Reviewer 21/0~/~ ~

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NLR- TP-2005-498

Summary

Landing overruns belong to the group of most frequently reported accident types in the world.

Fortunately, landing overruns do not often result in causalities amongst passengers and crew.

Despite this fact landing overruns can still be considered a major threat to aviation safety. It is

therefore interesting to have an overview of factors that increase the landing overrun risk, the

trends in statistics and in the influence of safety initiatives. A safety study on landing overruns

of commercial transport aircraft was conducted which addressed these issues.

Landing overrun accidents of commercial transport aircraft that took place during the last

35 years were analysed. A total of 400 accidents were identified and analysed.

It was found that on a worldwide basis, there appears to be a significant increase in landing

overrun risk when one of the following factors is present during a landing: Non-precision

approach, touching down far beyond the threshold (long landing), excess approach speed, visual

approach, significant tailwind present, high on approach, wet/flooded runway, and/or

snow/ice/slush covered runway. The highest risk increase occurred when the aircraft touched

down far beyond the threshold (long landing), followed by excess approach speed.

Furthermore, it was found that on a worldwide basis, the landing overrun accident rate has

reduced by a factor of three over a period of thirty-five years. This reduction is most likely the

result of a numbers of factors including improvement in braking devices (antiskid, autobrakes

etc.), better understanding of runway friction issues, and safety awareness campaigns.

Late or no application of available stopping devices was often found to be a factor in the landing

overrun accident. These overrun accidents were all avoidable if the crew had used the available

stopping devices, without any delay.
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NLR- TP-2005-498

Contents

1 Introduction 7

1.1 Background 7

1.2 Objective and scope 7

1.3 Organisation of the paper 8

2 Factors influencing landing performance 8

2.1 What is a 'good' landing? 8

2.2 Approach speed 8

2.3 Approach path 9

2.4 Flare and touchdown 10

2.5 Rollout 10

2.6 Automatic versus manual landing 13

3 Data analysis methodology 15

3.1 Approach 15

3.2 Data inclusion criteria 15

3.3 Data sources 15

3.4 Taxonomy 16

3.5 Analytical process employed 17

4 Findings 18

4.1 Univariate analysis 18

4.2 Bivariate analysis 20

4.3 Trend analysis 21

5 Discussion 23

5.1 Aircraft accident distribution by region 23

5.2 Long, fast and high landings 23

5.3 Approach type 24

5.4 Runway condition 24

5.5 Tailwind landings 24

5.6 Application of available stopping devices 25

5.7 Autolands 25

5.8 Trend analysis 25
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NLR- TP-2005-498

6 Final remarks 28

7 Conclusions and Recommendations

7.1 Conclusions

7.2 Recommendations

29

29

29

8 References 30

(32 pages in total)
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NLR- TP-2005-498

This page is intentionally left blank.
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NLR- TP-2005-498

1 Introduction

1.1 Background

'On February 28, 1984 the first officer flying a DC-1O was making a manual CAT 11ILS

approach to Runway 04R at New York JFK airport. The captain noted that the airspeed was

high and informed the first officer. The approach bug speed was 168 knots. However when the

aircraft crossed the threshold the speed was 204 knots. The aircraft touched down about 4,700

ft. beyond the threshold of the 8,400 ft. runway and could not be stopped on the runway. The

captain steered the aircraft to the right to avoid an approach light pier as it overran and it

came to rest on the waters of Thurston Basin some 600ft. beyond the end of the runway. The

accident happened on a wet runway. The National Transport Safety Board NTSB determined

that the probable cause of the accident was the crew's disregardfor prescribed procedures for

monitoring and controlling airspeed during the final stages of the approach, their decision to

continue the landing rather than execute a missed approach and their over-reliance on the

autothrottle speed control system, which had a history of recent malfunctions. The 163

passengers and 14 crewmembers evacuated the aircraft safely, but a few received minor

injuries. The nose and lower forwardfuselage sections, wing engines, flaps, and leading edge

devices were substantially damaged at impact. (source: NTSB accident investigation report

AAR-84/15).' This is a typical example of an accident in which the pilot was not able to stop the

aircraft before the end of the runway. This is event is called an 'overrun '. Overruns can occur

during both takeoffs and landings. However the vast majority took place during landing.

Takeoff overruns normally occur after high-speed rejected takeoffs. Although rejected takeoffs

are not uncommon the majority happen at relatively low speeds explaining the lower number of

takeoff overruns. Most aircraft land on runways that are longer than the minimum required

distance. Still each year landing overruns are reported worldwide. Landing overruns belong to

the group of most frequently reported accident types in the world. Fortunately, landing overruns

do not often result in causalities amongst passengers and crew. The landing overrun accident

with an Airbus A340 that occurred recently at Toronto - Lester B. Pearson International airport

clearly illustrates this. Despite this fact landing overruns can still be considered a major threat to

aviation safety. It is therefore interesting to have an overview of factors that increase the landing

overrun risk, the trends in statistics and in the influence of safety initiatives. This paper presents

a safety study on landing overruns of commercial transport aircraft. For this purpose landing

overrun accidents that took place during the last 35 years were analysed.

1.2 Objective and scope

The objectives of the study are to identify and quantify the most important risk factors

associated with landing overruns; to see if there are any trends in landing overruns during the
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NLR- TP-2005-498

last 35 years of flying; and to try to see what influence safety initiatives possibly have had on

landing overruns. This study was limited to commercial transport aircraft.

1.3 Organisation of the paper

Section 2 of this paper presents an overview of the factors that influence the landing

performance. Section 3 discusses the methodology applied in this study. The findings are

presented in section 4 and are discussed in section 5. Section 6 gives some final remarks. The

conclusions and recommendations are presented in section 7.

2 Factors influencing landing performance

There are a number of factors that influence the landing performance. For the present study it is

important to have a basic understanding of these factors without going into much detail. This

section presents a brief overview of those landing performance factors

2.1 What is a 'good' landing?

In short a 'good' landing has the following characteristics. It starts with a stabilised approach on

speed, in trim and on glide path. During the approach the aircraft is positioned to land in the

touchdown zone. When the aircraft crosses the threshold it is at the correct height and speed.

The approach is ended by a flare without any rapid control column movements which is

followed by a positive touchdown without floating. Immediately after touchdown of the main

gear the spoilers (if available) are raised (manually or automatically), the brakes are applied

(manually or automatically), (if available) the reverse thrust or propeller reverse is selected and

the nose is lowered. These actions are all conducted without delay and according to the standard

operating procedures. This is the landing as it can be found in flight crew training manuals.

However, not many landings are conducted exactly like this every day. Deviations from this

good practice occur often without any serious consequences. However, when there are large

deviations from the 'good' practice it can become more difficult to stop the aircraft on the

runway. These deviations are discussed in the next sections.

A good landing is one that you can walk awcryfrom.

A great landing is one where you can use the aircraft again.

2.2 Approach speed

The approach speed is determined by a number of factors such as flap setting, weight of the

aircraft, the headwind, turbulence, and the handling of the pilots. Based on a number of these

factors the pilot calculates a target approach speed (bug speed) which the pilot tries to fly during
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NLR- TP-2005-498

the approach. In the example presented in the introduction of this paper, the DCl 0 was flying

36 kts too fast when crossing the threshold. Excess approach speed increases the tendency that

the aircraft floats during the flare. Some aircraft have a higher tendency to float than others.

This is mainly affected by the aerodynamic ground effect which varies amongst different

aircraft types. In case of floating the pilot often tries to bleed off the excess speed. This action

takes a significant part of the amount of runway remaining to stop the aircraft. The effect of the

excess speed on the ground rolI distance is usualIy less than the increase of the flare distance

due to floating. This is explained by the fact that the declaration of the aircraft during the flare is

only a fraction of what can be achieved during braking on the ground even on slippery runways.

Therefore putting down the aircraft with an excess in speed is important instead of bleeding off

the excess speed in the air. Excess approach speed landings are more often associated with nonprecision and visual approaches than with precision approaches. Precision approaches are

inherently related with a procedure in which a constant descent gradient from the final approach

altitude to touchdown is defined. The descent gradient can be verified during the flight. Nonprecision approaches can be designed to be a stabilised approach procedure. However this is not

always the case which makes such approaches more vulnerable to excess speed.

2.3 Approach path

Atmospheric turbulence, guidance errors and inaccurate control by the pilot can result in

deviations from the nominal glide path. It is important that the aircraft crosses the threshold at

the correct height and with the intended glideslope. Excess height at the threshold can increase

the landing distance. The same applies when the glideslope is shalIower. For example the

increase in landing distance for an aircraft on a 3 degree glides lope approach with excess height

of 30 ft. at the threshold is approximately 700 ft. In combination with a one degree shalIower

glideslope this increases to approximately 1,000 ft. Some pilots tend to make a so-calIed duck

under manoeuvre when crossing the runway threshold. In this situation the pilot is flying the

aircraft below the nominal path with a shalIower glides lope. The tendency to do so varies

amongst the pilots, aircraft type flown and visual conditions. Such a flying technique can also

result in longer landings.

Excess height landings are more often associated with non-precision and visual approaches than

with precision approaches. Precision approaches are inherently related with a procedure in

which a constant descent gradient from the final approach altitude to touchdown is defined. This

descent gradient can be verified during the flight. Non-precision approaches can be designed to

be a stabilised approach procedure. However this is not always the case which makes such

approaches more vulnerable to excess height.
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2.4 Flare and touchdown

During the flare manoeuvre the pilot reduces the rate of descent so that an excessively hard

touchdown is avoided. In the execution of the flare the pilot relies on hislher experience and

judgement. The pilot decides on the moment to initiate the flare and on the amount of elevator

input during the flare. The touchdown should follow immediately upon the completion of the

flare. However, often the aircraft floats for some time before touchdown. This can take a

considerable amount of runway. In the example presented in the introduction of this paper, the

DeIO landed some 4,700 ft. beyond the threshold. In the example the aircraft floated for some

distance after the initial landing flare. The 20ft. callout was made three times. Thereafter, the

captain (PNF) told the First Officer (PF) to put the aircraft down. The tendency to float depends

on a number of factors which are difficult to generalise. For instance, ground effect appears to

play an important role. Ground effect is the aerodynamic influence of the ground on the flow

around an aircraft. It increases the lift, reduces the aerodynamic drag, and generates a nose

down pitching moment as the ground is approached. The nature of and magnitude of ground

effect are strongly affected by the aircraft configuration. Ground effect provides a landing

cushion that feels very comfortable to the pilot. This could explain to some extent the influence

of ground effect on the tendency to float. As explained already excess approach speed can also

result in floating of the aircraft after the flare as the pilot tries to bleed off the excess speed.

The touchdown should be done positive without being excessively hard. When the touchdown is

too smooth spin up of the tires could be delayed when the runway is slippery. As explained later

this can affect the deployment of ground spoilers and the proper functioning of the antiskid

system.

After touchdown of the main wheels the nose should be lowered without delay in order to

maximise the load on the tires. On some fighter jets the pilots tend to keep the nose up as long

as possible in order to increase drag and shorten the needed runway length. This technique is

called 'aerodynamic braking' and is an acceptable technique on some fighter jets. However for

commercial transport aircraft it is not a recommended technique. The stopping forces associated

with this technique are only a fraction of those forces when the aircraft is braked with the nose

down. The 'aerodynamic braking' technique has resulted in landing overruns with commercial

transport jets in the past. Therefore it should never be used during landings with commercial

transport aircraft.

2.5 Rollout

The prompt use of all available stopping systems helps to minimise the rollout distance. As soon

as the aircraft has touched down these devices should be utilised without any delay. There are a

number of stopping devices used: ground spoilers, reverse thrust, and tire brakes. Ground
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spoilers are installed on a large number of commercial transport aircraft. In particular jet

transport aircraft are equipped with ground spoilers. Reverse thrust is available on a number of

jet and propeller aircraft. This device provides effective means of stopping the aircraft. Tire

brakes are the stopping device that every aircraft has installed. Another stopping force that

comes for free during the ground roll with any aircraft is the airframe aerodynamic drag.

Problems with the stopping devices and or any delay in using them can make it difficult for the

pilot to stop the aircraft on the runway. Some of the issues with the mentioned stopping devices

will be briefly discussed next.

Tire braking is one of the primary means of generating stopping forces on an aircraft. The tire

has to slip to generate a braking force. Maximum braking force is achieved at a tire slip in the

order of 10-15%. The braking force on a tire is proportional with the vertical load on the tire.

Runway conditions also influence the amount of braking force a tire can generate. The highest

braking forces are obtained on dry surfaces. Whenever the runway is wet, flooded or covered

with snow, ice or slush, lower braking forces are obtained than on a dry runway. In case of wet

runways the texture of the surface is also important. On a wet, rough surface higher braking

forces are achievable than on a wet, smooth surface. Most commercial transport aircraft are

equipped with an antiskid system. This system prevents tires from lockups and automatically

optimises tire slip for maximum braking forces by controlling the braking pressure. The pilot

can therefore apply maximum brake pedal input without being concerned of possible tire

lockups and optimum braking. The antiskid needs a reference wheel speed to function. This

speed is initially generated by the wheel itself just after touchdown. However wheel spin-up

can be delayed when landing on flooded runways. On such runways the aircraft tires can

hydroplane. The footprint of the tire is then separated from the surface by a film of water.

Frictional forces between the tire and the ground are then very low as water cannot develop

significant friction forces. Friction forces are needed to get the tire spinning. The speed at which

a tire starts to hydroplane depends on a number of factors such as tire inflation pressure, forward

speed of the tire, tire design (radial or cross-ply), etc (see Van Es, 2001 for more information on

hydroplaning). The tires can become locked if the pilot applies braking before the tires are

spinning. As a result the braking forces are significantly lower.

Jet transports can be equipped with an automatic braking system. The autobrake system was

introduced in the early and mid seventies. The autobrake system automatically controls the

braking of the aircraft after touchdown. An autobrake selector switch allows the pilot to select

from several deceleration levels for landing. During the landing roll pressure is automatically

applied to the brakes after touchdown. The system regulates brake pressure to compensate for

the effects of aircraft drag, thrust reversers, and spoilers to maintain the selected deceleration

level. The auto brakes system disarms immediately when the pilot applies manual braking. The
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auto brake system is a very efficient system which is not always recognised as such by the pilots.

Compared to manual braking the deceleration generated by the auto brake system is usually

more consistent. Furthermore pilots tend to limit their brake input. In case of the need to stop

the aircraft when only limited runway is available this behaviour can be critical. Flight

simulators do a great job in simulating the flight characteristics of an aircraft. However they are

not good in simulating ground forces. The sensation of a truly maximum braking effort cannot

be simulated correctly. The noises, the vibrations, the deceleration associated with a maximum

braking effort are not similar to the real situation. Therefore simulator training to familiarise

pilots with the maximum manual braking situation is in general not fully effective. So whenever

the pilot applies maximum manual braking, the pilot's reaction will often be to reduce the brake

pedal input. The use of autobrakes for landing on slippery runways instead of manual braking

has been recommended in the past by accident investigation agencies. For instance the National

Transportation Safety Board (NTSB) and FAA gave the following recommendation after

examining the MD82 overrun accident at Little Rock (June 1999): "Autobrake systems, when

available and operative, should be armed and confirmed armed by both pilots, in accordance

with manufacturers' recommended procedures for the airplane and autobrake system regarding

landing on a wet or slippery runway, or landing in a high crosswind, or in accordance with

equivalent approved company procedures. Those procedures should be reflected in the

respective flight manual, checklists, and training program used by the pilot, or when

recommended procedures are not specified by the applicable manufacturers regarding landing

on a wet or slippery runway, or landing in a high crosswind, autobrake systems, when available

and operative, should be armed and confirmed armed by both pilots when preparing to land in

any of those conditions. Those procedures should be reflected in the respective flight manual,

checklist, and training program used by the pilot. "

Ground spoilers (also known as lift dumpers) are located on the top of the wing. When deployed

they increase the aerodynamic drag. They also decrease the aerodynamic lift significantly,

resulting in a higher load on the tires. Ground spoilers are most effective at high speeds. Aircraft

can be equipped with wing mounted ground spoilers that can raise automatically right after

main gear touchdown. For this the ground spoilers need to be armed prior to touchdown.

Ground contact sensors are installed on the aircraft in order to prevent ground spoilers to deploy

automatically in the air. There are different types of contact sensors in use. Wheel spin-up of the

main gear tires can be used as an indication of ground contact. Main landing gear oleo

compression can also be used (often in combination with wheel spin-up). On aircraft equipped

with bogie main landing gears, the tilt angle of can be used as an indication of ground contact.

As discussed earlier in this section wheel spin-up can be delayed when landing on flooded

runways. As the friction force on a tire is proportional with the load on the tire it is important to

get as much load on the tires right after touchdown. Ground spoilers are designed to do just that.
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However if the ground spoilers are waiting for the tires to spin-up a major problem has raised.

The ground spoilers need then to be deployed manually. On many aircraft the ground spoilers

can also deploy upon activation of thrust reversers. For this the spoilers do not need to be armed

before touchdown. However, it is always better to arm the ground spoilers before touchdown in

the event of inoperative reversers or no use of the reversers. It can also take some time to select

the reversers which delays the deployment of the spoilers.

Thrust reversers are stopping devices which do not depend on runway condition. They are very

effective in generating stopping forces especially on slippery runways. Thrust reversers on jet

transports generate the highest stopping forces at high speeds. Below a certain speed maximum

reverse thrust is often not allowed. The reverse thrust is modulated to idle reverse between 80-

60 knots lAS on ajet transport in order to avoid foreign objected damage to the engine and to

avoid the ingestion of turbulent air from the reverse thrust into the main engine inlet, possibly

leading to an engine surge or stall. On turboprop aircraft the propellers are normally moved out

of reverse at lower speeds than on jet transports. On some turboprop aircraft full reverse cannot

be selected at high speeds due to the possibility of asymmetrical reserve thrust. Another issue is

that the reversers on jet transports can produce a lot of noise. This sometimes restricts their use

on airports to idle thrust only. If thrust reversers are available and the conditions are marginal

(e.g. wet/contaminated runway, wind conditions, short runway etc.) they should always be used

regardless of environmental restrictions. Thrust reversers can also give directional

controllability problems in some cases. For instance, tail mounted engine can affect the flow

around the vertical tail reducing rudder effectiveness. Also the use of thrust reversers in heavy

crosswind conditions can give controllability problems. These controllability problems can be

solved by reducing the reverse thrust. However, the pilot then looses a valuable stopping force.

2.6 Automatic versus manual landing

Aircraft that can land during low visibility and/or cloud ceilings (CAT III conditions) are

equipped with a system that allows the aircraft to make a fully automatic landing. The majority

of aircraft that have these systems installed can only conduct a fully automatic landing up to

touchdown (autoland with no roll-out guidance). After touchdown the crew must disengage the

autopilot and take control of the aircraft. Although the auto land system is very accurate, it is not

able to the get the aircraft to touchdown on the exact same spot on the runway every time.

However compared to manual instrument landings the touchdown scatter of an automatic

landing is much less. Unpublished flight data showed that the mean distance from the threshold

to the touchdown point is about 30% higher during a manual instrument landing. The scatter in

this distance (in terms of standard deviation) is about 130% higher during a manual landing.

These facts are not a big surprise as the manual instrument landing is strongly influenced by
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NLR- TP-2005-498

pilot flight handling. Touching down far on the runway, flying fast and/or flying high above the

flight path are things that are less likely to occur during automatic landings.

Normally auto lands are conducted when the visibility condition or cloud ceiling is too low to

make a safe manual landing. However this does not rule out the use of auto land systems during

better weather conditions. Indeed auto lands are conducted during fine weather conditions with

excellent visibility (although not many). Full protection of the ILS is not required for that case.

It is also expected that the crew will have sufficient visual references to detect and correct any

deviations from the expected flight path. However there are some risks of performing auto land

operations on runways not meeting CAT WIll standards. Protection of the ILS sensitive area is

not assured, and other aircraft and vehicles may cause disturbance to the localiser signal.

Unexpected flight control movements may occur at a very low altitude when the autopilot

attempts to follow the disturbed beam bends. The crews should therefore be alert to the

possibility of abnormal autopilot behaviour and guard the flight controls throughout the

automatic landing. The crew should also be prepared to disconnect the autopilot and manually

land or go-around. However during significant crosswind landings disconnecting the autopilot

at low altitudes can be risky. The operator should always include the appropriate instructions in

the flight operations manual for auto land landings under good visibility conditions. The crew

should also inform ATC about the intention to conduct an auto land under the above mentioned

scenario. In that case ATC can inform the flight crew of any known or anticipated disturbance

of the ILS beam due to other aircraft and vehicles.

On February 21, 1986 a DC9 landed on runway 24 of Erie international airport. The aircraft

touched down some 2,OOOft beyond the displaced threshold. Although the pilots armed the

spoilers they did not automatically deploy so that the captain armed them manually. Reverse

thrust was selected and the brakes activated. The brakes were not effective. Subsequently the

aircraft could not be brought to a halt before the end of the runway. The aircraft overran

through a fence eventually coming to rest partly across a road. The runway was covered in

snow with a reported braking action of fair-to-poor. The approach was flown with a tail wind

and approximately 10kt above reference speed. Tailwind landings on Runway 24 were not

authorised in wet or slippery conditions. Source: NTSB report DCA86AA018
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3 Data analysis methodology

3.1 Approach

The overall data analysis approach employed in this study was to:

• Develop a taxonomy for the collation and analysis of the data;

• Identify a sample of landing overrun accidents; and,

• Analyse the data to determine what factors and to what degree they were associated with

landing overrun accidents.

3.2 Data inclusion criteria

The following criteria were used to establish the data sample:

• Only occurrences that were classified as 'accidents' according to ICAO Annex 13

definition were included.

• Both fatal and non-fatal accidents were included.

• The accidents involved a landing overrun. An overrun is an event in which the aircraft

departed the end of the runway. Also included are those events where the pilots noticed

that the aircraft could not be stopped on the remaining runway and decided to deliberately

steer the aircraft off the runway to avoid a collision with objects placed near the runway

end. Not included are those events in which the pilots lost directional control of the aircraft

on the ground resulting in a veer-off.

• Accidents related to unlawful or military action were excluded.

• The accidents involved fixed wing aircraft with a maximum takeoff mass of 5,500kg or

higher that were used in a commercial operation (passenger or cargo) excluding training

and ferry flights. There was no restriction to the geographical location.

• The accidents occurred during 1970 through 2004.

3.3 Data sources

The primary data source used in this study was the NLR Air Safety database. For many years

National Aerospace Laboratory NLR maintains a large database with aviation safety related data

called the NLR Air Safety Database. The NLR Air Safety Database is a collection of databases

containing different types of data. The NLR Air Safety Database contains detailed information
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NLR- TP-2005-498

on accidents and incidents of fixed wing aircraft from 1960 and onwards. Currently the NLR

Air Safety Database contains detailed information on more than 40,000 accidents and serious

incidents that occurred world-wide. For each occurrence a wide variety of factual information is

available. For a large number of occurrences the causal and contributing factors are also

available. Besides data on accidents and incidents the NLR Air Safety Database also contains a

large collection of non-accident related data. These data include the following: airport data,

flight exposure data (hours & flights at the level of airlines, aircraft type, and airports), weather

data, fleet data, and more. The NLR Air Safety Database is updated frequently using reliable

sources including data from official reporting systems, insurance claims, accident investigation

boards, aircraft manufacturers, civil aviation authorities and more. Queries were conducted in

the NLR Air Safety Database using the data inclusion criteria. The level of detail of the

information available for each individual accident varied. For a large number of accidents

detailed reports were available. However for some accidents there was only limited information.

3.4 Taxonomy

The accident data were analysed using a taxonomy that was developed for this study. The

taxonomy was based on the factors that influence landing performance as discussed in section 2

extended with some additional elements such as aircraft type and location. The taxonomy is

listed in Table 1.

Table 1: Taxonomy.

Aircraft type

Approach type (precision, non-precision, visual)

Autoland

Date

Excess approach speed

Failure of stopping device

High on approach

Hydroplaning of the tires

Late or no application of available stopping devices (reversers, brakes, spoilers)

Location

Long landing (touching down far beyond the threshold)

Propulsion type

Runway condition (dry, wet, flooded, icy, snow covered)

Tailwind
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3.5 Analytical process employed

The major steps included in the analysis of the study are listed below:

1. The data were evaluated through a straightforward single-variable analysis. This included

developing frequency distributions of each risk factor considered. It also included an

exploratory analysis that provided a general understanding of the landing overrun accident

data.

2. A central objective of this study was to estimate the risk associated with the various

landing factors (excess speed, tailwind, runway condition etc.). It was therefore essential to

understand the prevalence of these individual factors during landings which did not end up

in a landing overrun. For instance to estimate the risk associated with long landings it

should be known how many long landings took place without resulting in an overrun.

These data were obtained in various ways. First of all the NLR Air Safety Database

contains data which allows making fairly accurate estimations of the prevalence of a

number of risk factors in non-accident landings. Examples are the number of landings

conducted on the different runway surface conditions. For other risk factors data obtained

from Flight Data Monitoring systems from a limited number of operators were used. These

data were used to estimate prevalence of a number of risk factors in non-accident landings.

Examples are excess approach speed, long landings, and high approaches. It is realised that

this only gives a rough order of magnitude of the prevalence of those risk factors for

operations worldwide. This should be considered when analysing the results. An estimate

of the risk of having a landing overrun accident with a particular risk factor present was

accomplished by calculating a risk ratio. This risk ratio provides insight on the association

of a factor on the risk in a landing overrun accident. The risk ratio is the rate of the accident

probability with the factor present over the accident probability without the factor present.

The risk ratio is given by the following formula:

(

accidents with presence of a risk factor )

. k Rati normal landings with presence of a risk factor Rzs RatIO = -,-''---------=-----=-----------'-,--

(

accidents without presence of a risk factor )

normal landings without presence of a risk factor

Risk ratio values greater than 1 indicate an increase level of risk due to the presence of a

particular factor. A risk ratio of 4 means that the probability of accident with the risk factor

present is 4 time higher than without its presence. Positive associations between a risk

factor and landing overruns accidents show that a demonstrated association exists.

However it does not prove causation.
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3. Finally trends in the accident data were analysed. In particular changes over time were

considered.

4 Findings

4.1 Univariate analysis

A total of 400 landing overrun accidents were found that met the data inclusion criteria. During

the study period (1970-2004) it was estimated that approximately 796 million landings were

conducted worldwide with passenger and cargo aircraft with a takeoff mass of 5,500kg or

higher. The estimated landing overrun accident rate for the study period was 0.5 per million

landings worldwide. Table 2 presents the accident distribution by region. The landing accident

overrun rate per million landings is also given. Table 2 clearly shows the differences in landing

overrun rates between the world regions.

Table 2: Aircraft accident distribution by region

Region Landings Accidents Rate

millions per million landings

Africa 31.84 86 2.70

Asia 71.64 74 1.03

Australasia 31.84 8 0.25

Central/South America 55.72 75 1.35

Europe 191.04 91 048

North America 397.99 61 0.15

Middle East 15.92 5 0.31

All 795.99 400 0.50

The distribution of accidents by aircraft category is shown in Table 3. The difference in landing

accident overrun rate between jets and turboprop aircraft was not statistically significant at the

5% level. This means that the probability of a landing overrun accident of a jet aircraft is not

different from a turboprop aircraft.

Table 3: Landing overrun accident distribution by aircraft category.

Aircraft type Landings

millions Accidents Rate

per million landings

Transport jet

Transport turboprop

527.22

268.76

250

150

0.47

0.56

Table 4 shows the distributions of the landing overrun risk factors for the complete data sample.

The values shown in Table 4 are raw values only. They are not corrected for the number of

landings conducted which is done in the next section of the paper.
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Table 4: Landing overrun risk factors distribution.

Factor Number of accidents Percent

Non-precision approach

Long landing

Excess approach speed

Hydroplaning of the tires

Late or no application of available stopping devices

Visual approach

Tailwind present

High on approach

Brakes inoperative

Reverser inoperative

Ground spoilers inoperative

72.3%

52.8%

27.8%

15.0%

15.0%

14.0%

12.3%

7.3%

5.3%

2.5%

0.5%

289

211

111

60

60

56

49

29

21

10

2

The different types of runway surface conditions in the landing overrun accidents are shown in

Figure 1. Often the surface condition varied along the runway. For instance part of the runway

can be icy and another part covered with snow. Also in the case of flooded runways it was often

only a part of the runway that had pools of standing water with the remaining part of the runway

being wet. For this reason the different surface conditions that can exist are grouped in Figure 1.

The values shown in Figure 1 are raw values only. They are not corrected for the number of

landings conducted on under such runway conditions which is done in the next section of the

paper.

Ice/Snow /Slush Wet/Flooded

5.5% 47.8%

Dry

46.8%

Figure 1: Runway condition distribution.
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4.2 Bivariate analysis

In order to estimate risk ratios as defined in section 3.5, the number oflandings with or without

a factor absent should be known. Different approaches were followed to obtain these data. For

instance, data from airline flight data monitoring programs were used to estimate the number of

long, fast and high landings for the complete data set. The approach type flown was estimated

from the NLR Air Safety Database which contains information regarding precision, nonprecision and visual approaches by airport (see also Khatwa et. aI., 1996). The actual runway

conditions at airports (e.g. wet, snow covered etc.) are not well recorded in databases. Therefore

the number of landings conducted on the different runway conditions were estimated from

historical hourly precipitation observations at airports. The fact that it, for instance, rains does

not automatically mean that the runway is wet. This depends on the drainage characteristics of

the runway, the wind, the amount of rain that is falling and some other factors. With a

precipitation like snow the runway can be made clear of it when large amounts accumulate on

the surface. Therefore adjustments were made on the calculated number of landings on

wet/contaminated runways based on hourly precipitation observations. These adjustments were

done by using engineering judgement. Although it is realised that this approach can introduce

errors in the results it is believed that the errors are small enough just to fulfil the basic

objectives of this study.

The calculation of risk ratios could not be accomplished for all variables that were considered.

Denominator data for the late or no use of stopping devices and the failure of stopping devices

were not available. There were data available on the failure of stopping devices for a number of

countries with a high safety standard. However it was felt that these data were not applicable to

the overall sample.

Table 5 presents the association of landing overrun related risk factors, adjusted for the number

of landings involved in each factor. A value greater than 1 indicates a greater risk. The larger

the risk ratio value the stronger the association between the factor and the landing overrun

accident risk. All risk ratios presented in Table 5 are statistically significant at the 5% level. The

landing overrun accident risk while flying a non-precision approach was twenty-five times

greater than that associated with precision approach. The risk ratio was twenty-seven when

flying a visual approach compared to a precision approach. If the landing was long, the landing

overrun accident risk was fifty-five times greater than when it was not long. The landing

overrun risk is thirty-eight times greater when there was excess approach speed. A tailwind of 5

knots or more increases the landing overrun risk by a factor of five times. Finally being high on

approach increases the risk with factor of twenty-six. The results presented in Table 5 treat the

long landing (touching down far beyond the threshold), excess approach speed, high approach
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and approach type variables as independent. However, in some cases these variables were

related. For instance high and fast landings often resulted in long landings.

Table 6 shows the risk ratios associated with runway condition. All risk ratios presented in

Table 6 are statistically significant at the 5% level. The landing overrun accident risk increases

with factor often when the landing was conducted on a wet or flooded runway. If the runway

was covered with snow, ice or slush the landing overrun accident risk is fourteen times greater

than when landing on a dry surface.

Table 5: Risk ratio for landing overrun related risk factors

Risk-factor Risk factor Risk factor

Landing overrun related Risk-factor absent landings absent landings

risk factor Risk Ratio accidents accidents million million

Non-precision approach' 25 289 55 135.32 636.79

Long landing 55 211 189 15.92 78007

Excess approach speed 38 111 289 7.96 788.03

Visual approach' 27 56 55 23.88 636.79

Significant tailwind present 5 49 351 23.88 772.11

High on approach 26 29 371 2.35 793.63

* Comparedto a precisionapproach.

Table 6: Risk ratio for runway surface conditions.

Risk-factor Risk factor Risk factor

Risk·factor absent landings absent landings'

Runway condition Risk Ratio accidents accidents' million million

wet/flooded 10 191 187 73.71 716.42

snow/icy/slush 14 22 187 5.86 716.42

* Dry runway condition

4.3 Trend analysis

Figure 2 shows the variation in the landing overrun accident rate for the period 1970 through

2004. The data were grouped in 5-year blocks in order to increase the statistical robustness of

the data. Figure 3 shows the share of landing overrun accidents in the overall number of

approach and landing accidents that occurred worldwide. Again the data were grouped in 5-year

blocks.
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Figure 3: Trend in share of landing overrun accidents in approach & landing accidents.
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5 Discussion

In this study 400 landing overrun accidents were analysed that occurred worldwide in the period

1970-2004. Based on the findings of the analysis of these accidents a discussion of the results is

presented in this section.

5.1 Aircraft accident distribution by region

It was found that the landing overrun risk varies for the different world regions (see Table 2).

There are several explanations for this finding. There exists a difference in the level of aviation

safety between the different regions in general. This could also affect the landing overrun risk.

Note that an almost similar regional distribution in accident rates was found for landing

accidents in general, e.g. not limited to overruns (see Khatwa et. aI., 1996).

The highest landing overrun rate was found for Africa. The lowest rate was for North America.

However when comparing the rates for the different regions it should be realised that not all

differences in accident rates are statistically significant (at the 5% level). Although North

America seems to have the lowest rate it was not found to be statistically different from the rates

estimated for the Middle East and Australasia regions. The low rate for North America was

statistically different from the rate for the Europe and remaining regions.

5.2 Long, fast and high landings

In more than half of all accidents the landing was long meaning that the aircraft contacted the

runway far beyond the threshold. Landing far beyond the threshold showed the highest landing

overrun risk increase. A long landing itself is not always hazardous. For instance, when a small

turboprop aircraft lands on a very long runway, landing long will not automatically result in

difficulties stopping the aircraft on the remaining runway. However, long landings can become

more hazardous when the available runway to stop the aircraft becomes shorter and/or the

runway is slippery. The estimated number oflong landings used to derive the risk ratio,

contained landings on all kinds of runways with different lengths. In that respect the derived

risk ratio for long landings represents an average risk value. Landing fast and/or high also

increased the landing overrun risk significantly. Long landings are often associated with fast,

high landings and/or tailwind landings. Excess approach speed is often a reason for a pilot to

float the aircraft after the landing flare during which the pilot tries to get rid of the excess speed.

Excess approach speed was mentioned in 37.4% (79 out of 211) of all long landings. Being high

on approach can also lead to longer landings. High on approach was mentioned in 12.8% (27

out of 211) of all long landings. In only 2 high approach cases there was no long landing

reported. Pilots clearly need to follow their procedures for monitoring and controlling airspeed

and height during the final stages of the approach. Tailwind can also increase the tendency to
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float. A tailwind condition existed in 15.2% (32 out of211) of all long landings. Long landing

cannot be explained by excess speed, high approaches etc. only. Clearly pilot flying technique

plays a significant role in the occurrence of a long landing. More study is required to get a better

understanding of this.

5.3 Approach type

The landing overrun risk is much higher when a non-precision or visual approach is flown.

These approach types are more likely to become unstabilised (e.g. flying too fast and too high)

than precision approaches. Indeed the vast majority of overruns in which there was an excess

approach speed occurred during a non-precision or visual approach (81%). In 80% of all landing

overrun accidents that were high over the threshold the approach type was non-precision or

visual. Similar in 82% of all overruns in which a long landing was reported the approach type

was a non-precision or visual approach.

5.4 Runway condition

Slippery runway conditions were associated with higher risk of a landing overrun accident (see

Table 6). This finding is not a surprise and is well known in the aviation community. However

the quantitative increase in risk was not known. Runway condition affects the braking forces the

aircraft tires can generate. Furthermore wheel spin-up can be delayed on slippery runways,

which affects the proper functioning of the antiskid system and the deployment of ground

spoilers. On wet/flooded or slush covered runways the tire may hydroplane which reduces the

braking forces between the tire and runway significantly. On snow and ice covered runways the

braking friction levels are very low making it difficult to stop the aircraft. During the last 35

years there have been many initiatives to get a better understanding into runway traction.

Numerous studies have been conducted for instance in the United States by NASA, USAF and

FAA and in the United Kingdom to understand the impact of runway condition on the stopping

capabilities of an aircraft. These studies examined the influence of runway texture on braking

friction, analysed the hydroplaning of tires, and showed what impact snow and ice had on

braking friction. Several studies also looked at measuring runway friction using ground vehicles

and the correlation of the outcome of these vehicles with the friction of an aircraft. Such

correlations could be valuable for the pilot when making an assessment of the landing

performance. Unfortunately, despite the great effort made so far, an acceptable solution to this

problem of measuring runway friction and correlating it to aircraft landing performance is still

to be found.

5.5 Tailwind landings

Tailwind landing are associated with higher risk of landing overruns (see Table 5). Tailwind

increases the ground speed and therefore the landing distance (see Van Es & Karwal, 2001).
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Typically aircraft are certified to make landings with a maximum tailwind component. For most

commercial aircraft this is 10 knots on a dry runway. Some aircraft are certified for higher

tailwinds. However, this is usually not more than 15 knots. On slippery runways lower tailwinds

are allowed during the landing varying from 5 knots to no tailwind at all. A more detailed

discussion on tailwind operations is provided by Van Es & Karwal, 2001.

5.6 Application of available stopping devices

In 8.3% of the landing overrun accidents one or more stopping devices did not function (see

Table 4). This was mainly due to problems with the hydraulic systems. This sometimes also

prevented the use of flaps which resulted automatically in excess approach speed landings.

More worrying is the fact the in 15% of the accidents there was a late or no application of the

available stopping devices (see Table 4). In many of these accidents an overrun was avoidable if

the available stopping devices would have been properly used. The problems were mainly

caused by the fact that the ground spoilers were not armed (52% of all cases with a late or no

application of the available stopping device). In these cases the pilots often failed to notice that

the spoilers did not deploy. Also late or no application of thrust reversers was often found in the

accidents (67% of all cases with a late or no application of the available stopping device). In

some cases reverse thrust was selected initially. However shortly afterwards it was deselected

again. It could be not derived from the analysed data that insufficient manual braking was often

a factor. However, to identify that fact detailed flight data recordings need to be analysed.

Unfortunately, in many of the analysed accidents such information was not available to the

present author.

5.7 Autolands

None of the analysed landing overrun accidents was reported to be attributable to

malfunctioning or improper functioning of the auto land system. In one accident from the data

sample the crew initially conducted an autoland, however, took manual control over the aircraft

again just after passing the threshold. In only a very few number of other cases it was suspected

that an auto land was most likely conducted due to the visibility conditions at the time of

landing. However, not enough details were reported to be absolutely sure about these facts. This

made it difficult to estimate a reliable risk ratio for manual landings. Still it can be argued that

auto lands can reduce the landing overrun probability as it reduces the likelihood of flying too

high, too fast, and making long landings. As shown in this study these factors increase the risk

of a landing overrun accident.

5.8 Trend analysis

Figure 2 shows the trend in the landing overrun accident rate worldwide. It is shown that in the

seventies the rate was the highest for the period considered in this study (1970-2004). During
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the eighties the rate significantly improved. However this improvement did not continue in

nineties. The first five years of the twenty first century finally showed a reduction in the landing

overrun accident rate again. It is difficult to say what exactly caused the reduction in the

accident rate during the period 1970-2004. However there are a number of initiatives that could

have contributed to the safety improvement. Some of the more important ones will be discussed

now.

The efficiency of the antiskid systems has improved significantly over the years. The early

antiskid systems were simple on-off systems that produced braking efficiencies of 60% and

were introduced in the fifties. Later (sixties) modulated antiskid systems were introduced that

had braking efficiencies in the 70-85% range. During the seventies braking efficiencies of

consistently over 90% were achieved for the first time with the newer antiskid systems. The

commercial aircraft that were operated in the analysed period in this study were equipped with

one of the antiskid systems described here. As time progresses older aircraft equipped with less

sophisticated antiskid systems were replaced with newer models having more efficient antiskid

systems.

Autobrake systems were introduced during the seventies. They are found on many jet transport

aircraft today. It was estimated that autobrakes were used in 30% of all landings in the study

period. In 2004 this share was estimated to be nearly 50% of all landings.

Since the sixties research on tire braking friction is conducted. These studies provided insight

into runway friction and how it could be improved. This has led to the introduction of for

instance grooved and porous friction course runways. Although these surfaces often gave an

improvement in runway friction on wet runways they do not rule out the possibility to overrun

such a runway. Indeed there were a number of landing overrun accidents that took place on

grooved runways. Also many studies were conducted to measure runway friction using ground

vehicles. The objective was often to correlate the braking friction of these ground vehicles with

those of an aircraft. Unfortunately, despite the enormous effort a lot of work is still to be done in

this area to arrive at a useful way to correlate ground vehicles with full scale aircraft.

During the late nineties different safety studies were initiated with the aim to improve the level

of flight safety. Special attention was given to accidents that occurred during the approach and

landing including landing overruns. Studies include those conducted by the commercial

aviation safety team (CAST) on approach & landing accidents, the Flight Safety Foundation

task force on approach & landing accidents (FSF, 2001), and the joint study into landing aids

(Khatwa, 1996). These studies provided the aviation community with a set of mitigating

measures. Especially the FSF Approach-and-Landing Accident Reduction Briefing Notes are of

great importance. Several briefing notes are devoted to issues that affect the possibility of

landing overruns. However, it is too early to conclude that these initiatives had a major
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influence on the reduction of the landing overrun accident rate during the first five years of the

twenty-first century.

Another interesting technology that is worthwhile to mention here is the application of a ground

arrestor system which is located beyond the end of the runway and centred on the extended

runway centreline. A ground arrestor system is designed to stop an overrunning aircraft by

exerting deceleration forces on its landing gear Although this technology (as explained later)

cannot prevent overruns from happening its application can mean the difference between an

accident and a minor incident. Different types of ground arrestor systems were studied in the

UK in the seventies and later in the United States. An example of a soft ground arrestor system

is Engineered Material Arresting Systems (EMAS). A soft ground arrestor system like EMAS

deforms under the weight of an aircraft tire that runs over it. As the tires crush the material, the

drag forces decelerate the aircraft, bringing it to a safe stop. In recent years EMAS became

popular in the United States at airports that have difficulties to comply with the rules on runway

safety areas defined by the FAA. There have been at least three reported overruns in which

EMAS stopped the aircraft. These occurrences took place in the United States with a Saab 340

(May 1999, see Figure 4), a MD11 (May 2003), and most recently in January 2005 with a B747.

Clearly no soft ground arrestor system can prevent overruns. However, it seems evident that

such a system can reduce the consequences. Other arrestor systems were also studied the past.

Examples are loose gravel, water ponds, and arrestor cables. Application of these systems to

commercial airports has been limited.

Figure 4: Overrun with a SAAB 340 that ended in a soft arrestor bed.
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6 Final remarks

The variables that increase the risk of a landing overrun were discussed in the previous sections.

Each of the investigated variables played an important role in the chain of events leading to an

overrun. Typically a landing overrun was not characterised by the presence of only one variable.

It is often the combination of factors that finally made the aircraft to overrun the runway. The

quantified risk ratios in this study demonstrate that associations exist between a number of

landing related factors and the risk of a landing overrun accident. Such associations do not

prove any causation and only suggest that an increase in risk for a landing overrun accident

appears when the factor is present. The present study did not try to identify the underlying

causal factors related to landing overruns. There have been many studies conducted in the past

in which these underlying causal factors have been identified (see e.g. FSF, 2001).

On September 19, 1972 a Fokker F28 made an NDB approach to Runway 22 in conditions of

heavy rains and poor Visibility at Port Harcourt, Nigeria. The final approach to touchdown was

steep. Finally the aircraft touched down smoothly with a speed 20 kts in excess of the

recommended touchdown speed at 3,300ft. beyond the threshold. During flare the pilot added

power. The remaining runway length after touchdown was some 3,700ft .. After touchdown there

was no appreciable deceleration of the aircraft. The ground spoilers did not deploy due to the

lack of wheel spin up. This was caused by hydroplaning of the main gear tires. The pilot did not

select ground spoilers manually. The aircraft was not stopped on the runway and it overran

across an area of soft ground before impacting an embankment, breaking off the left wing. The

aircraft eventually came to rest some 750ft beyond the end of the runway. In the final part of

the approach the controller informed the crew that the runway was wet. However in actual fact

the runway was flooded. This was due to the heavy rains in combination with the fact that the

runway contained undulations in the surface which favoured the flooding of the runway.

Source: Accident Investigation Report published by the Dutch Civil Aviation Authorities and

Nigerian Government, 1973.
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7 Conclusions and Recommendations

7.1 Conclusions

The following conclusions can be drawn from the landing overrun accident data studied in this

paper:

• The Africa region demonstrated the highest landing overrun accident rate, followed by

Central/South America, and Asia. All these regions had rates of more than 1 accident per

million landings. The rest of the world demonstrated rates below 1 accident per two million

landings which was less than half of the rate of the previous mentioned regions. North

America had the lowest rate of all regions.

• No statistically significant difference in the estimated landing overrun accident rate

between commercial transport jet and turboprop aircraft was found.

• On a worldwide basis, there appears to be a significant increase in landing overrun risk

when one of the following factors is present during a landing: Non-precision approach,

touching down far beyond the threshold (long landing), excess approach speed, visual

approach, significant tailwind present, high on approach, wet/flooded runway, and/or

snow/ice/slush covered runway. The highest risk increase occurred when the aircraft

touched down far beyond the threshold (long landing), followed by excess approach speed.

• On a worldwide basis, the landing overrun accident rate has reduced by a factor of three

over a period of thirty-five years. This reduction is most likely the result of a number of

factors including improvement in braking devices (antiskid, autobrakes etc.), better

understanding of runway friction issues, and safety awareness campaigns.

• Late or no application of available stopping devices was often found to be a factor in the

landing overrun accident. These overrun accidents were all avoidable if the crew had used

the available stopping devices, without any delay.

7.2 Recommendations

• It is recommended to disseminate the results of this study to all interested parties including

airlines, regulators, and pilot unions.

• It is recommended to analyse in detail the characteristics associated with long landings

using recorded flight data of normal day-to-day landings.
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8 References

• Khatwa, R., Roelen, A., Karwal, A., Enders, I.H., Dodd, R., Tarrel, R. An evaluation of

approach and landing factors influencing airport safety. National Aerospace Laboratory

NLR, Technical Paper TP-96221, 1996.

• Van Es, G.W.H. and Karwal, A.K. Safety aspects of tailwind operations. National

Aerospace Laboratory NLR, Technical Paper TP-200 1-003, 2001.

• Van Es, G.W.H. Hydroplaning of modern aircraft tires. National Aerospace Laboratory

NLR, Technical Paper TP-200 1-242, 2001.

• Flight Safety Foundation FSF, Approach-and-Landing Accident Reduction-ALAR tool kit.

2001.