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 ofmost frequently reported accident types inthe world. Fortunately, landing overruns do not often result incausalities amongst passengers and crew. Despite this fact landing overruns can still be considered amajor threat to aviation safety. It is therefore interesting to have an overview offactors that increase the landing overrun risk, the trends in statistics and inthe influence of safety initiatives. A safety study on landing overruns ofcommercial 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. Atotal of400 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 astraightforward single-variable analysis. This included developing frequency distributions ofeach risk factor considered. Italso included an exploratory analysis that provided a general understanding ofthe landing overrun accident data. A central objective ofthis study was to estimate the risk associated with the various landing factors (such as excess speed, tailwind, runway condition etc.). Itwas 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 arrestorUnclassified

essential to understand the prevalence ofthese individual factors during landings which did not end up inalanding 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 ofa number offactors was estimated. Finally the data were analysed for trends. Conclusions The following conclusions are drawn from the landing overrun accident data studied inthis paper:

• The Africa region demonstrated the highest landing overrun accident rate, followed by Central/South America, and Asia. All these regions had rates ofmore than one accident per million landings. The rest ofthe world demonstrated rates below one accident per two million landings which was less than half of the rate ofthe previous mentioned regions. North America had the lowest rate ofall regions.

• No statistically significant difference inthe estimated landing overrun accident rate between commercial transport jet and turboprop aircraft was found.

• On aworldwide basis, there appears to be asignificant increase Running out of runway runway Analysis of 35 years of landing overrun accidents

in landing overrun risk when one of the following factors ispresent during alanding: 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 aworldwide basis, the landing overrun accident rate has reduced by afactor ofthree over a period ofthirty-five years. This reduction ismost likely the result of anumber offactors including improvement inbraking devices (antiskid, autobrakes etc.), better understanding ofrunway friction issues, and safety awareness campaigns.

• Late orno application of available stopping devices was often found to be afactor inthe landing overrun accident. These overrun accidents were all avoidable ifthe 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 outof runway Analysisof35 years of landing overrun accidents

G.W.H. van Es

This report has been based on apaper 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~/~ ~-3- NLR-TP-2005-498



### Summary Landing overruns belong to the group ofmost frequently reported accident types inthe world. Fortunately, landing overruns do not often result incausalities amongst passengers and crew. Despite this fact landing overruns can still be considered amajor threat to aviation safety. It is therefore interesting to have an overview offactors that increase the landing overrun risk, the trends in statistics and inthe influence of safety initiatives. A safety study on landing overruns ofcommercial transport aircraft was conducted which addressed these issues. Landing overrun accidents ofcommercial transport aircraft that took place during the last 35 years were analysed. A total of400 accidents were identified and analysed.
Itwas found that on aworldwide basis, there appears to be a significant increase in landing
overrun risk when one ofthe following factors ispresent during alanding: Non-precision approach, touching down farbeyond 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, itwas found that on aworldwide basis, the landing overrun accident rate has reduced by afactor ofthree over aperiod ofthirty-five years. This reduction ismost likely the result ofanumbers offactors including improvement inbraking devices (antiskid, autobrakes etc.), better understanding ofrunway friction issues, and safety awareness campaigns. Late orno application ofavailable stopping devices was often found to be afactor inthe landing overrun accident. These overrun accidents were all avoidable ifthe crew had used the available stopping devices, without any delay.-4- NLR-TP-2005-498



### Contents

1 Introduction 7 1.1 Background 7 1.2 Objective and scope 7 1.3 Organisation ofthe 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 ofavailable stopping devices 25 5.7 Autolands 25 5.8 Trend analysis 25-5- NLR-TP-2005-498

6 28 Final remarks

7 Conclusions and Recommendations 7.1 Conclusions 7.2 Recommendations 29 29 29

8 30 References

(32 pages intotal)-6- NLR-TP-2005-498

This page is intentionally leftblank.-7- NLR-TP-2005-498



### 1 Introduction

1.1 Background 'On February 28, 1984 thefirst officerflying aDC-1O was making amanual CAT 11ILS approach toRunway 04R atNew YorkJFK airport. The captain noted that the airspeed was high and informed thefirst 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 ofthe 8,400ft. runway and could not be stopped on the runway. The captain steered the aircraft to the right to avoid an approach lightpier as itoverran and it
came to rest on the waters ofThurston Basin some 600ft. beyond the end ofthe runway. The accident happened on awet runway. TheNational Transport Safety Board NTSB determined that theprobable cause ofthe accident was the crew's disregardfor prescribed procedures for monitoring and controlling airspeed during thefinal stages ofthe 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 ahistory ofrecent malfunctions. The 163 passengers and 14crewmembers evacuated the aircraft safely, but afew received minor injuries. The nose and lowerforwardfuselage sections, wing engines, flaps, and leading edge devices were substantially damaged at impact. (source: NTSB accident investigation report AAR-84/15).' This is atypical example ofan accident inwhich the pilot was not able to stop the aircraft before the end ofthe runway. This isevent iscalled 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 atrelatively low speeds explaining the lower number of takeoff overruns. Most aircraft land onrunways that are longer than the minimum required distance. Still each year landing overruns are reported worldwide. Landing overruns belong to the group ofmost frequently reported accident types inthe world. Fortunately, landing overruns do not often result incausalities amongst passengers and crew. The landing overrun accident with an Airbus A340 that occurred recently atToronto

-Lester B. Pearson International airport clearly illustrates this. Despite this fact landing overruns can still be considered amajor threat to aviation safety. It istherefore interesting to have an overview offactors that increase the landing
overrun risk, the trends in statistics and inthe influence of safety initiatives. This paper presents asafety study on landing overruns ofcommercial 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 ofthe study are to identify and quantify the most important risk factors associated with landing overruns; to see ifthere are any trends in landing overruns during the-8- NLR-TP-2005-498

last 35 years offlying; 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 ofthe paper Section 2 ofthis paper presents an overview ofthe factors that influence the landing performance. Section 3 discusses the methodology applied inthis study. The findings are presented in section 4 and are discussed insection 5. Section 6gives some final remarks. The conclusions and recommendations are presented in section 7.



### 2 Factors influencing landing performance

There are anumber offactors 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 abrief overview ofthose landing performance factors

2.1 What is a 'good' landing? In short a 'good' landing has the following characteristics. It starts with astabilised approach on speed, intrim and on glide path. During the approach the aircraft ispositioned to land inthe touchdown zone. When the aircraft crosses the threshold itis atthe correct height and speed. The approach isended by aflare without any rapid control column movements which is followed by apositive touchdown without floating. Immediately after touchdown ofthe main gear the spoilers (ifavailable) are raised (manually or automatically), the brakes are applied (manually or automatically), (ifavailable) the reverse thrust orpropeller reverse is selected and the nose is lowered. These actions are all conducted without delay and according to the standard operating procedures. This isthe landing as itcan be found inflight 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 itcan become more difficult to stop the aircraft onthe runway. These deviations are discussed inthe next sections.

A good landing is one thatyou can walk awcry from. A great landing isone where you can use the aircraft again.
2.2 Approach speed The approach speed is determined by anumber offactors such as flap setting, weight ofthe aircraft, the headwind, turbulence, and the handling ofthe pilots. Based on anumber ofthese factors the pilot calculates atarget approach speed (bug speed) which the pilot tries to fly during-9- NLR-TP-2005-498

the approach. Inthe example presented inthe introduction ofthis paper, the DCl 0was 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 ahigher tendency to float than others. This ismainly affected by the aerodynamic ground effect which varies amongst different aircraft types. In case offloating the pilot often tries to bleed offthe excess speed. This action takes asignificant part ofthe amount ofrunway remaining to stop the aircraft. The effect ofthe
excess speed onthe ground rolI distance isusualIy less than the increase ofthe flare distance due to floating. This isexplained by the fact that the declaration ofthe aircraft during the flare is only afraction ofwhat 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 ofbleeding off the excess speed inthe air. Excess approach speed landings are more often associated with nonprecision and visual approaches than with precision approaches. Precision approaches are inherently related with aprocedure inwhich aconstant descent gradient from the final approach altitude to touchdown isdefined. The descent gradient can be verified during the flight. Nonprecision approaches can be designed to be a stabilised approach procedure. However this isnot 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. Itis important that the aircraft crosses the threshold at the correct height and with the intended glideslope. Excess height atthe 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 of30 ft. atthe threshold is approximately 700 ft. In combination with aone degree shalIower glideslope this increases to approximately 1,000 ft. Some pilots tend to make aso-calIed duck under manoeuvre when crossing the runway threshold. Inthis situation the pilot isflying the aircraft below the nominal path with ashalIower glideslope. The tendency to do so varies amongst the pilots, aircraft type flown and visual conditions. Such aflying 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 aprocedure in which aconstant descent gradient from the final approach altitude to touchdown isdefined. This descent gradient can be verified during the flight. Non-precision approaches can be designed to be astabilised approach procedure. However this isnot always the case which makes such approaches more vulnerable to excess height.-10- NLR-TP-2005-498



### 2.4 Flare and touchdown During the flare manoeuvre the pilot reduces the rate ofdescent sothat an excessively hard touchdown is avoided. Inthe execution ofthe flare the pilot relies on hislher experience and judgement. The pilot decides onthe moment to initiate the flare and on the amount ofelevator input during the flare. The touchdown should follow immediately upon the completion ofthe flare. However, often the aircraft floats for some time before touchdown. This can take a considerable amount ofrunway. Inthe example presented inthe introduction ofthis paper, the DeIO landed some 4,700 ft. beyond the threshold. Inthe 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 putthe aircraft down. The tendency to float depends
on anumber offactors which are difficult to generalise. For instance, ground effect appears to play an important role. Ground effect isthe aerodynamic influence ofthe ground onthe flow around an aircraft. It increases the lift, reduces the aerodynamic drag, and generates anose down pitching moment as the ground isapproached. The nature ofand magnitude ofground effect are strongly affected by the aircraft configuration. Ground effect provides alanding cushion that feels very comfortable to the pilot. This could explain to some extent the influence ofground effect onthe tendency to float. As explained already excess approach speed can also result infloating ofthe aircraft after the flare as the pilot tries to bleed offthe excess speed.
The touchdown should be done positive without being excessively hard. When the touchdown is too smooth spin up ofthe tires could be delayed when the runway is slippery. As explained later this can affect the deployment ofground spoilers and the proper functioning ofthe antiskid system.
After touchdown ofthe main wheels the nose should be lowered without delay inorder to maximise the load onthe tires. On some fighterjets the pilots tend to keep the nose up as long
as possible inorder to increase drag and shorten the needed runway length. This technique is called 'aerodynamic braking' and is an acceptable technique on some fighterjets. However for commercial transport aircraft itisnot arecommended technique. The stopping forces associated with this technique are only afraction ofthose forces when the aircraft isbraked with the nose down. The 'aerodynamic braking' technique has resulted in landing overruns with commercial transport jets inthe past. Therefore itshould never be used during landings with commercial transport aircraft.


### 2.5 Rollout The prompt use ofall 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 ofstopping devices used: ground spoilers, reverse thrust, and tire brakes. Ground-11- NLR-TP-2005-498

spoilers are installed on a large number ofcommercial transport aircraft. Inparticular jet transport aircraft are equipped with ground spoilers. Reverse thrust is available on anumber of jet and propeller aircraft. This device provides effective means ofstopping 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 isthe airframe aerodynamic drag. Problems with the stopping devices and or any delay inusing them can make itdifficult for the pilot to stop the aircraft onthe runway. Some ofthe issues with the mentioned stopping devices will be briefly discussed next.
Tire braking is one ofthe primary means ofgenerating stopping forces on an aircraft. The tire has to slip to generate abraking force. Maximum braking force is achieved at atire slip inthe order of 10-15%. The braking force on atire isproportional with the vertical load onthe tire. Runway conditions also influence the amount ofbraking force atire can generate. The highest braking forces are obtained on dry surfaces. Whenever the runway iswet, flooded or covered with snow, ice or slush, lower braking forces are obtained than on adry runway. In case ofwet runways the texture ofthe surface is also important. On awet, rough surface higher braking forces are achievable than on awet, 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 ofpossible tire lockups and optimum braking. The antiskid needs areference wheel speed to function. This speed is initially generated by the wheel itselfjust after touchdown. However wheel spin-up
can be delayed when landing on flooded runways. On such runways the aircraft tires can hydroplane. The footprint ofthe tire isthen separated from the surface by afilm ofwater. 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 atwhich
atire starts to hydroplane depends on anumber offactors such as tire inflation pressure, forward speed ofthe tire, tire design (radial or cross-ply), etc (see Van Es, 2001 for more information on hydroplaning). The tires can become locked ifthe pilot applies braking before the tires are spinning. As aresult the braking forces are significantly lower.

Jet transports can be equipped with an automatic braking system. The autobrake system was introduced inthe early and mid seventies. The autobrake system automatically controls the braking ofthe 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 ofaircraft drag, thrust reversers, and spoilers to maintain the selected deceleration level. The autobrakes system disarms immediately when the pilot applies manual braking. The-12- NLR-TP-2005-498

autobrake system is avery efficient system which isnot always recognised as such by the pilots. Compared to manual braking the deceleration generated by the autobrake system isusually
more consistent. Furthermore pilots tend to limit their brake input. In case ofthe need to stop the aircraft when only limited runway is available this behaviour can be critical. Flight simulators do agreatjob in simulating the flight characteristics ofan aircraft. However they are not good in simulating ground forces. The sensation ofatruly maximum braking effort cannot be simulated correctly. The noises, the vibrations, the deceleration associated with amaximum braking effort are not similar to the real situation. Therefore simulator training to familiarise pilots with the maximum manual braking situation is ingeneral not fully effective. Sowhenever the pilot applies maximum manual braking, the pilot's reaction will often be to reduce the brake pedal input. The use ofautobrakes for landing on slippery runways instead ofmanual braking has been recommended inthe 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 atLittle Rock (June 1999): "Autobrake systems, when available and operative, should be armed and confirmed armed by bothpilots, inaccordance with manufacturers' recommended procedures for the airplane and autobrake system regarding landing on awet orslippery runway, orlanding inahigh crosswind, or inaccordance with equivalent approved company procedures. Thoseprocedures should be reflected in the respective flight manual, checklists, and training program used by thepilot, orwhen recommended procedures are not specified by the applicable manufacturers regarding landing
on awet orslippery runway, orlanding inahigh crosswind, autobrake systems, when available and operative, should be armed and confirmed armed by bothpilots when preparing to land in any ofthose conditions. Thoseprocedures should be reflected in the respective flight manual, checklist, and training program used by thepilot. "
Ground spoilers (also known as lift dumpers) are located onthe top ofthe wing. When deployed they increase the aerodynamic drag. They also decrease the aerodynamic lift significantly, resulting in ahigher load onthe tires. Ground spoilers are most effective athigh 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 onthe aircraft inorder to prevent ground spoilers to deploy automatically inthe air. There are different types ofcontact sensors inuse. Wheel spin-up ofthe main gear tires can be used as an indication ofground contact. Main landing gear oleo compression can also be used (often incombination with wheel spin-up). On aircraft equipped with bogie main landing gears, the tilt angle ofcan be used as an indication ofground contact. As discussed earlier inthis section wheel spin-up can be delayed when landing on flooded runways. As the friction force on atire isproportional with the load onthe tire itis important to get as much load onthe tires right after touchdown. Ground spoilers are designed to dojust that.-13- NLR-TP-2005-498

However ifthe ground spoilers are waiting for the tires to spin-up amajor problem has raised. The ground spoilers need then to be deployed manually. On many aircraft the ground spoilers
can also deploy upon activation ofthrust reversers. For this the spoilers do not need to be armed before touchdown. However, itis always better to arm the ground spoilers before touchdown in the event ofinoperative reversers orno use ofthe reversers. Itcan also take some time to select the reversers which delays the deployment ofthe spoilers.

Thrust reversers are stopping devices which do not depend on runway condition. They are very effective ingenerating stopping forces especially on slippery runways. Thrust reversers onjet transports generate the highest stopping forces athigh speeds. Below acertain speed maximum
reverse thrust is often not allowed. The reverse thrust ismodulated to idle reverse between 80- 60 knots lAS on ajet transport inorder to avoid foreign objected damage to the engine and to avoid the ingestion ofturbulent 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 ofreverse at lower speeds than onjet transports. On some turboprop aircraft full reverse cannot be selected athigh speeds due to the possibility ofasymmetrical reserve thrust. Another issue is that the reversers onjet transports can produce alotofnoise. This sometimes restricts their use on airports to idle thrust only. Ifthrust reversers are available and the conditions are marginal (e.g. wet/contaminated runway, wind conditions, short runway etc.) they should always be used regardless ofenvironmental 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 ofthrust reversers inheavy crosswind conditions can give controllability problems. These controllability problems can be solved by reducing the reverse thrust. However, the pilot then looses avaluable 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 asystem that allows the aircraft to make afully automatic landing. The majority ofaircraft that have these systems installed can only conduct afully automatic landing up to touchdown (autoland with no roll-out guidance). After touchdown the crew must disengage the autopilot and take control ofthe aircraft. Although the autoland system is very accurate, itisnot able to the get the aircraft to touchdown onthe exact same spot on the runway every time. However compared to manual instrument landings the touchdown scatter ofan automatic landing ismuch less. Unpublished flight data showed that the mean distance from the threshold to the touchdown point is about 30% higher during amanual instrument landing. The scatter in this distance (in terms of standard deviation) is about 130% higher during amanual landing. These facts are not abig surprise as the manual instrument landing is strongly influenced by

### -14- NLR-TP-2005-498

pilot flight handling. Touching down faronthe runway, flying fast and/or flying high above the flight path are things that are less likely to occur during automatic landings. Normally autolands are conducted when the visibility condition or cloud ceiling istoo low to make asafe manual landing. However this does not rule outthe use ofautoland systems during better weather conditions. Indeed autolands are conducted during fine weather conditions with excellent visibility (although not many). Full protection ofthe ILS isnot 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 ofperforming autoland operations on runways not meeting CAT WIll standards. Protection ofthe ILS sensitive area is not assured, and other aircraft and vehicles may cause disturbance to the localiser signal. Unexpected flight control movements may occur atavery low altitude when the autopilot attempts to follow the disturbed beam bends. The crews should therefore be alert to the possibility ofabnormal autopilot behaviour and guard the flight controls throughout the automatic landing. The crew should also beprepared to disconnect the autopilot and manually land or go-around. However during significant crosswind landings disconnecting the autopilot at low altitudes can berisky. The operator should always include the appropriate instructions in the flight operations manual for autoland landings under good visibility conditions. The crew should also inform ATC about the intention to conduct an autoland under the above mentioned scenario. Inthat case ATC can inform the flight crew ofany known or anticipated disturbance ofthe ILS beam due to other aircraft and vehicles.

On February 21, 1986 a DC9 landed on runway 24 ofErie international airport. The aircraft touched down some 2,OOOftbeyond 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 afence 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 wasflown with a tail wind and approximately 10kt above reference speed. Tailwind landings on Runway 24 were not authorised inwet orslippery conditions. Source: NTSB report DCA86AA018-15- NLR-TP-2005-498



### 3 Data analysis methodology

3.1 Approach The overall data analysis approach employed inthis study was to:

• Develop ataxonomy forthe collation and analysis ofthe 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 alanding overrun. An overrun is an event inwhich the aircraft departed the end ofthe runway. Also included are those events where the pilots noticed that the aircraft could not be stopped onthe remaining runway and decided to deliberately steer the aircraft offthe runway to avoid acollision with objects placed near the runway end. Not included are those events inwhich the pilots lost directional control ofthe aircraft onthe ground resulting in aveer-off.

• Accidents related to unlawful ormilitary action were excluded.

• The accidents involved fixed wing aircraft with amaximum takeoff mass of5,500kg or higher that were used in acommercial operation (passenger or cargo) excluding training and ferry flights. There was no restriction tothe geographical location.

• The accidents occurred during 1970 through 2004.

3.3 Data sources The primary data source used inthis study was the NLR Air Safety database. For many years National Aerospace Laboratory NLR maintains alarge database with aviation safety related data called the NLR Air Safety Database. The NLR Air Safety Database is acollection ofdatabases containing different types ofdata. The NLR Air Safety Database contains detailed information-16- NLR-TP-2005-498

on accidents and incidents offixed 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 awide variety offactual information is available. For alarge number ofoccurrences the causal and contributing factors are also available. Besides data on accidents and incidents the NLR Air Safety Database also contains a large collection ofnon-accident related data. These data include the following: airport data, flight exposure data (hours &flights atthe level ofairlines, aircraft type, and airports), weather data, fleet data, and more. The NLR Air Safety Database isupdated 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 ofdetail ofthe information available for each individual accident varied. For alarge number ofaccidents detailed reports were available. However for some accidents there was only limited information.
3.4 Taxonomy The accident data were analysed using ataxonomy that was developed for this study. The taxonomy was based onthe 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 inTable 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-17- NLR-TP-2005-498



### 3.5 Analytical process employed The major steps included inthe analysis ofthe study are listed below:
1. The data were evaluated through astraightforward single-variable analysis. This included developing frequency distributions ofeach risk factor considered. Italso included an exploratory analysis that provided ageneral understanding ofthe landing overrun accident data.
2. A central objective ofthis study was to estimate the risk associated with the various landing factors (excess speed, tailwind, runway condition etc.). Itwas therefore essential to understand the prevalence ofthese individual factors during landings which did not end up in alanding 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 invarious ways. First ofallthe NLR Air Safety Database contains data which allows making fairly accurate estimations ofthe prevalence ofa number ofrisk factors innon-accident landings. Examples are the number of landings conducted onthe different runway surface conditions. For other risk factors data obtained from Flight Data Monitoring systems from alimited number ofoperators were used. These data were used to estimate prevalence ofanumber ofrisk factors innon-accident landings. Examples are excess approach speed, long landings, and high approaches. It isrealised that this only gives arough order ofmagnitude ofthe prevalence ofthose risk factors for operations worldwide. This should be considered when analysing the results. An estimate ofthe risk ofhaving alanding overrun accident with aparticular risk factor present was accomplished by calculating arisk ratio. This risk ratio provides insight onthe association ofafactor onthe risk in alanding overrun accident. The risk ratio isthe rate ofthe 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 )



### . kRati 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 ofrisk due to the presence ofa particular factor. A risk ratio of4 means that the probability ofaccident with the risk factor present is4 time higher than without itspresence. Positive associations between arisk factor and landing overruns accidents show that ademonstrated association exists. However itdoes not prove causation.-18- NLR-TP-2005-498

3. Finally trends inthe accident data were analysed. Inparticular changes over time were considered.



### 4 Findings

4.1 Univariate analysis Atotal of400 landing overrun accidents were found that met the data inclusion criteria. During the study period (1970-2004) itwas estimated that approximately 796 million landings were conducted worldwide with passenger and cargo aircraft with atakeoff mass of5,500kg or higher. The estimated landing overrun accident rate for the study period was 0.5 per million landings worldwide. Table 2presents 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 NorthAmerica 397.99 61 0.15 Middle East 15.92 5 0.31 All 795.99 400 0.50

The distribution ofaccidents by aircraft category is shown inTable 3. The difference in landing accident overrun rate between jets and turboprop aircraft was not statistically significant atthe 5% level. This means that the probability ofalanding overrun accident ofajet aircraft is not different from aturboprop 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 ofthe landing overrun risk factors for the complete data sample. The values shown inTable 4 are raw values only. They are not corrected forthe number of landings conducted which is done inthe next section ofthe paper.-19- NLR-TP-2005-498

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 ofrunway surface conditions inthe landing overrun accidents are shown in Figure 1. Often the surface condition varied along the runway. For instance part ofthe runway can be icy and another part covered with snow. Also inthe case offlooded runways itwas often only apart ofthe runway that had pools ofstanding water with the remaining part ofthe runway being wet. For this reason the different surface conditions that can exist are grouped inFigure 1. The values shown inFigure 1 are raw values only. They are not corrected for the number of landings conducted onunder such runway conditions which isdone inthe next section ofthe paper.


## Ice/Snow /Slush Wet/Flooded 47.8% 5.5%

Dry

46.8% Figure 1: Runway condition distribution.-20- NLR-TP-2005-498

4.2 Bivariate analysis In order to estimate risk ratios as defined in section 3.5, the number oflandings with orwithout
afactor 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 indatabases. Therefore the number oflandings conducted onthe 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 iswet. This depends onthe drainage characteristics of the runway, the wind, the amount ofrain that isfalling and some other factors. With a precipitation like snow the runway can be made clear ofitwhen large amounts accumulate on the surface. Therefore adjustments were made onthe calculated number oflandings on wet/contaminated runways based on hourly precipitation observations. These adjustments were done by using engineering judgement. Although itisrealised that this approach can introduce
errors inthe results itisbelieved that the errors are small enough just to fulfil the basic objectives ofthis study.
The calculation ofrisk ratios could not be accomplished for all variables that were considered. Denominator data for the late orno use ofstopping devices and the failure of stopping devices
were not available. There were data available onthe failure of stopping devices for anumber of countries with ahigh safety standard. However itwas feltthat these data were not applicable to the overall sample.
Table 5presents the association of landing overrun related risk factors, adjusted for the number oflandings involved ineach factor. Avalue greater than 1 indicates agreater risk. The larger the risk ratio value the stronger the association between the factor and the landing overrun accident risk. All risk ratios presented inTable 5 are statistically significant atthe 5% level. The landing overrun accident risk while flying anon-precision approach was twenty-five times greater than that associated with precision approach. The risk ratio was twenty-seven when flying avisual approach compared to aprecision approach. Ifthe landing was long, the landing
overrun accident risk was fifty-five times greater than when itwas not long. The landing
overrun risk isthirty-eight times greater when there was excess approach speed. Atailwind of5 knots ormore increases the landing overrun risk by afactor offive times. Finally being high on approach increases the risk with factor oftwenty-six. The results presented inTable 5treat the long landing (touching down farbeyond the threshold), excess approach speed, high approach-21- NLR-TP-2005-498

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 atthe 5% level. The landing overrun accident risk increases with factor often when the landing was conducted on awet or flooded runway. Ifthe runway was covered with snow, ice or slush the landing overrun accident risk isfourteen times greater than when landing on adry 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 

## *Compared

toaprecisionapproach.
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 runwaycondition
4.3 Trend analysis Figure 2 shows the variation inthe landing overrun accident rate for the period 1970 through 2004. The data were grouped in 5-year blocks inorder to increase the statistical robustness of the data. Figure 3 shows the share oflanding overrun accidents inthe overall number of approach and landing accidents that occurred worldwide. Again the data were grouped in 5-year blocks.-22- NLR-TP-2005-498

Figure 3: Trend in share oflanding overrun accidents in approach & landing accidents.-23- NLR-TP-2005-498



### 5 Discussion Inthis study 400 landing overrun accidents were analysed that occurred worldwide inthe period 1970-2004. Based on the findings ofthe analysis ofthese accidents adiscussion ofthe results is presented inthis section.


### 5.1 Aircraft accident distribution byregion Itwas found that the landing overrun risk varies for the different world regions (see Table 2). There are several explanations forthis finding. There exists adifference inthe level ofaviation safety between the different regions ingeneral. This could also affect the landing overrun risk. Note that an almost similar regional distribution in accident rates was found for landing accidents ingeneral, 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 (atthe 5% level). Although North America seems to have the lowest rate itwas not found to be statistically different from the rates estimated for the Middle East and Australasia regions. The low rate forNorth America was statistically different from the rate for the Europe and remaining regions.


### 5.2 Long, fast and high landings In more than half ofall accidents the landing was long meaning that the aircraft contacted the runway farbeyond the threshold. Landing farbeyond the threshold showed the highest landing
overrun risk increase. A long landing itself isnot always hazardous. For instance, when asmall turboprop aircraft lands on avery long runway, landing long will not automatically result in difficulties stopping the aircraft onthe 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 allkinds ofrunways with different lengths. Inthat 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 areason for apilot to float the aircraft after the landing flare during which the pilot tries to get rid ofthe excess speed. Excess approach speed was mentioned in 37.4% (79 out of211) ofall long landings. Being high
on approach can also lead to longer landings. High on approach was mentioned in 12.8% (27 out of211) ofall long landings. In only 2high 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 ofthe approach. Tailwind can also increase the tendency to-24- NLR-TP-2005-498

float. Atailwind condition existed in 15.2% (32 out of211) ofall long landings. Long landing cannot be explained by excess speed, high approaches etc. only. Clearly pilot flying technique plays asignificant role inthe occurrence ofalong landing. More study isrequired to get abetter understanding ofthis.
5.3 Approach type The landing overrun risk ismuch higher when anon-precision orvisual 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 ofoverruns inwhich there was an excess approach speed occurred during anon-precision orvisual approach (81%). In 80% ofall landing
overrun accidents that were high over the threshold the approach type was non-precision or visual. Similar in 82% ofall overruns inwhich along landing was reported the approach type was anon-precision orvisual approach.
5.4 Runway condition Slippery runway conditions were associated with higher risk ofalanding overrun accident (see Table 6). This finding isnot asurprise and iswell known inthe aviation community. However the quantitative increase inrisk 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 ofthe antiskid system and the deployment ofground 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 itdifficult to stop the aircraft. During the last 35 years there have been many initiatives to get abetter understanding into runway traction. Numerous studies have been conducted for instance inthe United States by NASA, USAF and FAA and inthe United Kingdom to understand the impact ofrunway condition onthe stopping capabilities ofan aircraft. These studies examined the influence ofrunway texture on braking friction, analysed the hydroplaning oftires, and showed what impact snow and icehad on braking friction. Several studies also looked atmeasuring runway friction using ground vehicles and the correlation ofthe outcome ofthese vehicles with the friction ofan aircraft. Such correlations could be valuable for the pilot when making an assessment ofthe landing performance. Unfortunately, despite the great effort made so far, an acceptable solution to this problem ofmeasuring runway friction and correlating itto aircraft landing performance is still to be found.
5.5 Tailwind landings Tailwind landing are associated with higher risk oflanding overruns (see Table 5). Tailwind increases the ground speed and therefore the landing distance (see Van Es &Karwal, 2001).-25- NLR-TP-2005-498

Typically aircraft are certified to make landings with amaximum tailwind component. For most commercial aircraft this is 10knots on adry runway. Some aircraft are certified for higher tailwinds. However, this isusually not more than 15knots. On slippery runways lower tailwinds
are allowed during the landing varying from 5knots to no tailwind at all. A more detailed discussion ontailwind operations isprovided by Van Es & Karwal, 2001.

5.6 Application ofavailable stopping devices In 8.3% ofthe landing overrun accidents one ormore stopping devices did not function (see Table 4). This was mainly due to problems with the hydraulic systems. This sometimes also prevented the use offlaps which resulted automatically inexcess approach speed landings. More worrying isthe fact the in 15% ofthe accidents there was alate or no application ofthe available stopping devices (see Table 4). In many ofthese 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% ofall cases with alate orno application ofthe available stopping device). Inthese cases the pilots often failed to notice that the spoilers did not deploy. Also late orno application ofthrust reversers was often found inthe accidents (67% ofall cases with alate orno application ofthe available stopping device). In
some cases reverse thrust was selected initially. However shortly afterwards itwas deselected again. Itcould be not derived from the analysed data that insufficient manual braking was often
afactor. However, to identify that fact detailed flight data recordings need to be analysed. Unfortunately, inmany ofthe analysed accidents such information was not available to the present author.
5.7 Autolands None ofthe analysed landing overrun accidents was reported to be attributable to malfunctioning or improper functioning ofthe autoland system. In one accident from the data sample the crew initially conducted an autoland, however, took manual control over the aircraft againjust after passing the threshold. In only avery few number ofother cases itwas suspected that an autoland was most likely conducted due to the visibility conditions atthe time of landing. However, not enough details were reported to be absolutely sure about these facts. This made itdifficult to estimate areliable risk ratio for manual landings. Still itcan be argued that autolands can reduce the landing overrun probability as itreduces the likelihood offlying too high, too fast, and making long landings. As shown inthis study these factors increase the risk ofalanding overrun accident.
5.8 Trend analysis Figure 2 shows the trend inthe landing overrun accident rate worldwide. It is shown that inthe seventies the rate was the highest for the period considered inthis study (1970-2004). During-26- NLR-TP-2005-498

the eighties the rate significantly improved. However this improvement did not continue in nineties. The first five years ofthe twenty first century finally showed areduction inthe landing overrun accident rate again. It isdifficult to say what exactly caused the reduction inthe accident rate during the period 1970-2004. However there are anumber ofinitiatives that could have contributed tothe safety improvement. Some ofthe more important ones will be discussed
now.
The efficiency ofthe antiskid systems has improved significantly over the years. The early antiskid systems were simple on-off systems that produced braking efficiencies of60% and were introduced inthe fifties. Later (sixties) modulated antiskid systems were introduced that had braking efficiencies inthe 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 inthe analysed period inthis study were equipped with one ofthe 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 manyjet transport aircraft today. Itwas estimated that autobrakes were used in 30% ofall landings inthe study period. In2004 this share was estimated to be nearly 50% ofall landings.
Since the sixties research on tire braking friction is conducted. These studies provided insight into runway friction and how itcould be improved. This has ledto the introduction offor instance grooved and porous friction course runways. Although these surfaces often gave an improvement inrunway friction on wet runways they do not rule outthe possibility to overrun such arunway. Indeed there were anumber oflanding 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 ofthese ground vehicles with those ofan aircraft. Unfortunately, despite the enormous effort alotofwork is still to be done in this area to arrive atauseful 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 offlight 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 thejoint study into landing aids (Khatwa, 1996). These studies provided the aviation community with a set ofmitigating 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, itistoo early to conclude that these initiatives had amajor-27- NLR-TP-2005-498

influence on the reduction ofthe landing overrun accident rate during the first five years ofthe twenty-first century.
Another interesting technology that isworthwhile to mention here isthe application ofaground arrestor system which is located beyond the end ofthe runway and centred onthe extended runway centreline. A ground arrestor system isdesigned 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 aminor incident. Different types ofground arrestor systems were studied inthe UK inthe seventies and later inthe United States. An example ofa soft ground arrestor system is Engineered Material Arresting Systems (EMAS). A soft ground arrestor system like EMAS deforms under the weight ofan aircraft tire that runs over it. As the tires crush the material, the drag forces decelerate the aircraft, bringing itto asafe stop. Inrecent years EMAS became popular inthe United States atairports that have difficulties to comply with the rules on runway safety areas defined by the FAA. There have been at least three reported overruns inwhich EMAS stopped the aircraft. These occurrences took place inthe United States with aSaab 340 (May 1999, see Figure 4), aMD11 (May 2003), and most recently inJanuary 2005 with aB747. Clearly no soft ground arrestor system can prevent overruns. However, it seems evident that such asystem can reduce the consequences. Other arrestor systems were also studied the past. Examples are loose gravel, water ponds, and arrestor cables. Application ofthese systems to commercial airports has been limited.

Figure 4: Overrun with 

### a SAAB 340 that ended in 

### a soft arrestor bed.-28- NLR-TP-2005-498



### 6 Final remarks

The variables that increase the risk ofalanding overrun were discussed inthe previous sections. Each ofthe investigated variables played an important role inthe chain ofevents leading to an overrun. Typically alanding overrun was not characterised by the presence ofonly one variable. It is often the combination offactors that finally made the aircraft to overrun the runway. The quantified risk ratios inthis study demonstrate that associations exist between anumber of landing related factors and the risk ofalanding overrun accident. Such associations do not prove any causation and only suggest that an increase inrisk for alanding overrun accident appears when the factor ispresent. The present study did not try to identify the underlying causal factors related to landing overruns. There have been many studies conducted inthe past inwhich 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 andpoor Visibility atPort Harcourt, Nigeria. Thefinal 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 thepilot added power. The remaining runway length after touchdown was some 3,700ft

..After touchdown there
was no appreciable deceleration ofthe aircraft. The ground spoilers did not deploy due to the lack ofwheel spin up. This was caused by hydroplaning ofthe main gear tires. Thepilot did not select ground spoilers manually. The aircraft was not stopped on the runway and it overran across an area ofsoft ground before impacting an embankment, breaking offthe left wing. The aircraft eventually came to rest some 750ft beyond the end ofthe runway. In thefinal part of the approach the controller informed the crew that the runway was wet. However in actualfact the runway wasflooded. This was due to the heavy rains in combination with thefact 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.-29- NLR-TP-2005-498



### 7 Conclusions and Recommendations

7.1 Conclusions The following conclusions can be drawn from the landing overrun accident data studied inthis paper:

• The Africa region demonstrated the highest landing overrun accident rate, followed by Central/South America, and Asia. All these regions had rates ofmore than 1 accident per million landings. The rest ofthe world demonstrated rates below 1 accident per two million landings which was less than half ofthe rate ofthe previous mentioned regions. North America had the lowest rate ofall regions.

• No statistically significant difference inthe estimated landing overrun accident rate between commercial transport jet and turboprop aircraft was found.

• On aworldwide basis, there appears to be asignificant increase in landing overrun risk when one ofthe following factors ispresent during alanding: Non-precision approach, touching down farbeyond 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 farbeyond the threshold (long landing), followed by excess approach speed.

• On aworldwide basis, the landing overrun accident rate has reduced by afactor ofthree
over aperiod ofthirty-five years. This reduction ismost likely the result ofanumber of factors including improvement inbraking devices (antiskid, autobrakes etc.), better understanding ofrunway friction issues, and safety awareness campaigns.

• Late orno application ofavailable stopping devices was often found to be afactor inthe landing overrun accident. These overrun accidents were all avoidable ifthe crew had used the available stopping devices, without any delay.

7.2 Recommendations

• Itis recommended to disseminate the results ofthis 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 ofnormal day-to-day landings.-30- NLR-TP-2005-498



### 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 oftailwind operations. National Aerospace Laboratory NLR, Technical Paper TP-200 1-003, 2001.



# • Van Es, G.W.H. Hydroplaning ofmodern 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.