DOT/FAA/AM-01/2

Office of Aviation Medicine 

Washington, D.C. 20591 

Access-to-Egress: A Meta-Analysis 

Of the Factors That Control 

Emergency Evacuation Through 

The Transport Airplane Type-III 

Overwing Exit 

Garnet A. McLean 

Civil Aeromedical Institute 

Federal Aviation Administration 

Oklahoma City, Oklahoma 73125 

January 2001 

Final Report 

This document is available to the public 

through the National Technical Information 

Service, Springfield, Virginia 22161. 

U.S. Department 

of Transportation 

Federal Aviation 

Administration 
NOTICE

This document is disseminated under the sponsorship of 

the U.S. Department of Transportation in the interest of 

information exchange. The United States Government 

assumes no liability for the contents thereof. 
Technical Report Documentation Page 

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 

DOT/FAA/AM-01/2 

4. Title and Subtitle 5. Report Date 

January 2001 

6. Performing Organization Code 

Access-To-Egress: A Meta-Analysis of the Factors That Control 

Emergency Evacuation Through the Transport Airplane Type-III 

Overwing Exit 

7. Author(s) 8. Performing Organization Report No. 

McLean, Garnet A. 

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) 

11. Contract or Grant No. 

FAA Civil Aeromedical Institute 

P.O. Box 25082 

Oklahoma City, Oklahoma 73125 

12. Sponsoring Agency name and Address 13. Type of Report and Period Covered 

Office of Aviation Medicine 

Federal Aviation Administration 

800 Independence Ave., S.W. 

Washington, D.C. 20591 14. Sponsoring Agency Code 

15. Supplemental Notes 

This work was performed under task AM-B-00-PRS-93. 

16. Abstract 

The factors that control emergency evacuation from transport aircraft are many. The physical factors include the 

aircraft structure and the configuration of aircraft interior components such as aisles, seating arrangements, 

monument placements, and crewmember assist spaces. Information factors related to emergency evacuation 

include safety briefing cards and videos, signs, placards, emergency lighting and marking systems, and verbal 

briefings by the crew. Trained crewmembers perform the functions necessary to initiate and conduct emergency 

evacuations, providing passenger management functions intended to produce fast and effective evacuations. 

Individual passengers have a large, typically negative, impact on the conduct of emergency evacuations, 

resulting from their general naivete regarding aircraft emergencies and the proper procedures needed to cope 

with such circumstances. Egress through the Type-III overwing exit is particularly susceptible to this deficiency, 

since passengers typically must operate the exit as well as use it. 

Research efforts conducted to define the relative contributions of these factors have been focused to a large 

degree on the interior configuration of transport aircraft, attempting to establish the appropriate access-to-egress 

required. These studies have employed an array of techniques and posited an assortment of experimental 

questions designed to address the issue, resulting in a comprehensive body of evidence related to access-toegress, particularly for the Type-III exit. Additional information has been provided about many of the other 

factors that also exert control of evacuations, allowing assessments to be made regarding the relative importance 

of individual factors, and their various combination(s), on the outcome of emergency evacuations. 

This analytical review of the studies conducted to address access to the Type-III exit has confirmed that human 

factors effects related to passengers present the biggest challenge to the execution of successful evacuations. 

Deficiencies that may exist regarding configural and informational egress factors are expressed through their 

interactions with these human factors effects, which have often made determination of specific deficiencies more 

difficult. Solutions to overcoming deficiencies must address both the specific deficiency and its interactiveness. 

17. Key Words 18. Distribution Statement 

Document is available to the public through the 

National Technical Information Service 

Aircraft Evacuation, Passageway Configuration, Human 

Factors, Hatch Operation, Competitive Behavior 

Springfield, Virginia 22161 

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price 

Unclassified Unclassified 31 

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized 

i

fi

1 

ACCESS-TO-EGRESS: A META-ANALYSIS OF THE FACTORS THAT CONTROL

EMERGENCY EVACUATION THROUGH THE TRANSPORT

AIRPLANE TYPE-III OVERWING EXIT

Theoretical Foundations

It is well noted that accidents are generally the result 

of situations that a given system is not able to handle. 

Such is often the case for transport airplanes, where 

emergency situations can easily result in the need to 

hastily evacuate the airplane. Even with intact cabin 

interior configurations, these emergency situations can 

create interactive conditions that have not been fully 

predicted nor modeled. 

Airplane configuration factors that have an effect on 

evacuations include exit size and availability, aisle width, 

seating arrangements, monument placement, and fl ight 

attendant assist space, as do such considerations as 

the number, ages, weights, gender, agility, health, and 

distribution of passengers and crew within the airplane. 

Loose carry-on baggage and galley carts, overhead bin 

displacements, and hull damage can provide additional 

impediments to egress. Problems increase dramatically 

when the environment becomes toxic from fi re and 

smoke. Survival after some evacuations is also an issue 

that impacts the evacuation proper, as emergency

provisions that may be needed in some environments 

must be transported as well. In sum, there is potentially 

no end to the complexity that an airplane accident 

might embody, and consequently, no end to the number 

or quality of interactions that can be imagined to 

exist in these scenarios. 

Combined, the effects of potential interactions can 

appear unfailingly intertwined, unable to be teased apart 

successfully, and thus unable to be clearly understood 

in regard to the contributions of independent factors. 

These factors may also appear not to be testable or 

independently measurable without sacrificing the

essence of the evacuation contingencies to be described. 

As a consequence, little validity may be attributed to 

the results obtained with the experimental tools and 

techniques used to date. Thus, the lack of absolute 

delity when experimentally simulating an emergency 

evacuation, in all its potential manifestations, may 

become an excuse to disregard data that do not conform 

to expectations. 

The problem with such an ideological approach is 

that it is built on belief and assumption, not data, 

confounding science and technology with undefi ned 

contingencies and constraints. To quote Perrow (1999, 

pg. 63), “What is needed is an explanation based 

upon system characteristics.” Without knowing or

explaining the factors and the effects of those factors 

on an evacuation, the number or quality of possible 

interactions that those factors can effect is indeterminate 

(and perhaps greatly overestimated). Further, emergent 

(nested) factors that result from those interactions

cannot be considered. Defining the system and its 

function(s), then, is a key concern. 

In regard to interactions, it is again useful to turn 

to Perrow (1999, Ch. 3), who distinguishes between 

linear and complex interactions that result from the 

structure and function of linear and complex systems. 

Interestingly, Perrow (pg. 72) states, “Interactiveness 

per se, though, is not a useful concept.” He makes this 

claim because “Almost any organization [system] of 

any size... will have many parts that interact... [which]

is no great trouble for either system designers or

system operators if their interactions are expected and 

obvious... These are linear interactions: production is 

carried out through a series or sequence of steps laid 

out in a line... It doesn’t matter much whether there 

are 1,000 or 1,000,000 parts... There will be product 

accumulating upstream and incomplete product going 

out downstream of the failure point.” He also states, 

“Linear interactions overwhelmingly predominate in 

all systems” (pg. 75).

In contrast, complex interactions result from

situations in which a single component is used to 

perform a common-mode function, resulting in

“branching paths, feedback loops, jumps from one 

linear sequence to another... The connections are not 

only adjacent, serial ones, but can multiply as other 

parts or units or subsystems are reached... But even 

the most complex systems of any size will be primarily 

made up of linear, planned, visible interactions (pg 

75)... Complex interactions are those of unfamiliar 
sequences, or unplanned or unexpected sequences, 

and [are] either not visible or not immediately 

comprehensible (pg. 78).” 

However, “As we gain more experience with systems, 

and design them more effectively, the high degree of 

interactiveness may be reduced... It is also true that a 

poorly trained or inexperienced operator [observer] may 

see a system as replete with unsuspected interactions or 

‘traps’, but after gaining more experience may find it 

to be more linear (pg. 84)... Limited knowledge, 

then, allows unsuspected interactions, and requires 

many control parameters and indirect sources of 

information (pg.85).” A corollary to this statement is 

the understanding that anyone who is unfamiliar with 

the intricacies of any system will find it more complex 

and less explainable. The number of factors will appear 

larger and more unmanageable, and their interactions 

can seem much more complicated. 

From a research perspective, studying each factor in 

isolation would not clarify its effects on the function of 

the system as a whole, nor would it allow elucidation of 

its interaction(s) with other factors. However, studying 

as many contributing factors as possible, interwoven 

without regard for their individual contributions to 

the functioning of the system, would also provide little 

insight as to the importance of each factor and its 

interactive potential on total system function. 

Instead, factorial studies implemented to illuminate 

the contributions to system function of an individual 

factor(s) and the interactions it produces with another 

factor(s) provide a basis for understanding the total 

system and its functions. “Factorial experimentation 

is highly efficient, because every observation supplies 

information about all the factors included in the 

experiment... [and] is a workmanlike method of 

investigating the relationships between the effects of 

different factors” (Snedecor & Cochran, 1967, pg. 

339). Further, “The factorial experiment allows the 

effects of each and every factor to be estimated and 

tested independently through the usual analysis of 

variance. In addition, the interaction effects are easily 

assessed. The disadvantage, of course, with the factorial 

experiment is the excessive amount of experimentation 

that is required” (Walpole & Myers, 1972, pg.426). 

Combining the same factor with disparate factors in a 

series of small factorial experiments can overcome some 

of this need for excessive experimentation that a 

full factorial design requires, not to mention the positive 

benefits achieved regarding statistical analysis of 

smaller factorial datasets as compared with a large, 

multi-factorial database. Selection of appropriate factors 

to be addressed becomes the issue. 

Thus, defining the experiment is the main consideration. First, the research design must be constructed to 

provide sufficient explanatory power (in terms of the 

research question being addressed). Toward this end, 

employing appropriate numbers of subjects/groups is 

important, as is designing the experiment to accurately 

reflect the levels of the factors being examined. 

Techniques of proper research design would include 

randomizing, matching, or blocking (so long as a 

replication of the experimental observations of the 

second factor(s) is accomplished for each block of the 

first) subjects assigned to experimental groups. 

Typically, this technique results in either complete 

between-subject research designs in which each 

subject/group receives only one level of each treatment, 

or randomized/counterbalanced within-subject research designs in which subjects are presented multiple 

treatment levels. 

Secondly, measurement error must be minimized. 

Control of extraneous factors that could induce error 

is one such method for minimizing error. Factors to 

be controlled include those that have been shown to 

increase measurement error of a second factor, e.g., 

by being unstable during the course of an experiment. 

The effects of research subject experience and fatigue 

are examples of such instability. Randomizing or 

counterbalancing treatments to achieve unbiased 

presentation of factor levels is also necessary; both 

between-subject and within-subject research designs are 

treated thusly to mitigate against such effects, although 

each has its limitations. Germane to the issue at 

hand, purely between-subject research designs are 

extremely large and costly, while within-subject research 

designs are not appropriate for examining the effects 

of procedural treatments on subject performance. 

Thus, factorial experiments that can provide useful 

information must be constructed and controlled 

within a defined range of design constraints to yield 

maximal fidelity with regard to a limited number of 

identified factors. 

In response, and as is typical of much research 

involving human subjects, targeted research questions 

are derived to address a subset of the total range of 

factors at work. Extraneous factors are controlled, 

where possible, to allow better discrimination of the 

other factors being studied. These factorial research 

designs are married with statistical techniques, such as 

analysis-of-variance, that provide the targeted answers 

2
being sought, including examination of the interactions 

that are obtained via the research design. This approach 

is theoretically opposed to more complex (uncontrolled) 

research that might be imagined to provide absolute 

fidelity regarding the entire range of (potential) 

contingencies evidenced in evacuations, but which 

would be very disorganized in practice, be extremely 

difficult to interpret regarding the responsibility of 

individual factors for specific effects seen, and not 

be certain to model the entire range of factors to 

be understood. 

The final consideration, of course, is the degree to 

which the findings model reality. Failing the ability 

to make such comparisons, which is generally the 

case with regard to actual emergency evacuations, the 

findings must be compared with those from evacuation 

simulations employing similar techniques, as well as 

with results obtained using different methodologies. 

Should the effects of a studied factor not compare 

well with those from similar studies and techniques, 

then the measurement of the factor being addressed is 

suspect for one study or the other. However, should 

the effects compare well within one methodological 

approach but not with those from another, then the 

results may be technique-dependent, or perhaps an 

interaction is at work, and interpretation of the findings 

becomes potentially more problematic. There may be 

problems with both the validity and reliability of the 

results. If the results compare well both within and 

between methodological approaches, then they may 

be seen as more generalizable to the entire domain 

under study. This is an important consideration for the 

Type-III exit evacuation issues at hand. 

The Evacuation Problem 

The transport airplane, as an evacuation system, 

is generally designed to be linear. As such, when an 

incident/accident occurs, the crew assess external 

conditions; the crew open the exits to initiate the 

evacuation; the escape assist means are deployed 

(where provided); the crew direct the passengers to the 

emergency exits; the passengers and crew egress through 

the exits and onto the assist means; and the evacuation 

terminates in either a rescue or survival mode. While 

many airplane system elements participate to effect this 

process, each has been designed to perform dedicated 

functions that combine to produce the evacuation. A

theoretical model of this process has been developed and 

described by the ARACPerformance Standards Working 

Group within its Performance-Based Rulemaking for 

Transport Category Airplanes: A Systems Approach 

(1998). 

Each element of the system and each step in the 

process may be thought of as a factor to be addressed 

in understanding the evacuation process. As a linear 

system, these factors are expected to exhibit linear 

interactions, if any, although the potential for complex 

interactions exists where common-mode functions are 

necessary. One such potential for interactions concerns 

the actions of the crew, who may be faced with the need 

to perform more than one (essentially simultaneous) 

activity. Where behavioral requirements overlap, the 

potential for either linear or complex interactions is 

evident, especially where passengers are also involved. 

Another potential common-mode function may be 

required of certain passengers, i.e., those who become 

responsible for operation of the (Type-III) exits. To 

the extent that the requirements for opening the exit 

influence the evacuation through that exit, additional 

interactions are possible. Generally, however, the 

potential for such interactions, whether linear or 

complex, is physically circumscribed to the area of 

the exit opening. 

Within this context, airplane system elements 

contributing to an evacuation through the Type-III 

exit include physical, information, operator, and user 

factors. The seat assembly type; exit position and 

dimensions; exit plug weight; number, width, and 

arrangement of passageways; overhead bin configuration; and descent assisting means form the physical 

elements comprising the exit subsystem. Signs, placards, 

emergency lighting and marking systems, safety cards, 

and briefings (pre-flight and emergency-related) form 

the information subsystem elements. The crew (and 

some passengers) form the exit operator subsystem 

elements, and the passengers form the user subsystem of 

airplane system elements. Each airplane system element, 

outside of the passengers, is theoretically designed to 

achieve a specific effect with regard to producing a fast, 

effective evacuation. None of the elements is intended 

to rely on the functioning of other system elements, 

with the exception of the general need to have the 

Type-III exit operated by a passenger. This is the single 

potential interaction included by design, except for the 

necessary human factors effects related to passengers and 

crew navigating the passageway/exit/descent route. 

The effects of other potentially interactive factors on 

the evacuation, especially those that exist at a distance 

from the exit, will be seen to be negligible, as long as 

3 
the number of passengers prepared to egress through 

the Type-III exit is greater than the number that can be 

continuously accommodated, or unless the exit cannot 

accommodate the passengers available. For example, 

baggage in the aisle, overhead bin displacements, hull 

damage, etc., may affect the total airplane evacuation, 

but not necessarily egress through the (Type-III) exit. 

Similarly, toxic smoke and fire may impair the success 

of the evacuation, including egress through the Type-III 

exit, although the effects produced by the smoke and 

fire would not be seen to result from interactions with 

the physical airplane system elements, but by linear 

interactions with the passengers, and perhaps through 

derivative (complex) interactions mediated by effects 

on passenger perceptibility of information elements. 

Human factors effects, related to individual passenger 

differences in age, weight, agility, health, or psychological 

factors, may or may not be found to be interactive with 

the physical or information airplane system elements 

in an evacuation, depending on the degree to which 

any individual passenger impedes, or is impeded 

by, the egress of fellow passengers. Determining the 

degree to which any or all of these factors impact 

evacuations has been a main thrust of the empirical 

research to date. 

Evacuation Research 

The first FAA Office of Aviation Medicine Report 

on contingencies of evacuations was Evacuation Pattern 

Analysis of a Survivable Commercial Aircraft Crash 

(Hasbrook, Garner & Snow, 1962). Subsequent to 

that report, Mohler, Swearingen, McFadden and 

Garner (1965) published Human Factors of Emergency 

Evacuations, which analyzed 49 incidents/accidents 

and 66 aircraft evacuation demonstrations to provide 

recommendations on 1) seating density, 2) aisle width, 

3) exit number, size, and location, 4) exit markings, 

and 5) exit-opening strength requirements, as well as 

a number of human factors issues related to post-crash 

survival. The first published experimental investigation 

of factors related to evacuation of a crashed airplane 

occurred in 1964 (Garner and Blethrow, 1966). The 

factors of interest in that study were some of the same 

factors studied today: emergency lighting, exit signs, 

debris in the aisles, smoke effects on exit location, 

rescue of injured passengers, and egress with infants. 

Since that time dozens of additional investigations have 

been conducted on the importance of the physical, 

information, operational, and user factors related to 

egress in both incidents/accidents and simulations 

thereof – the result being that many data, especially 

human factors data, have been accumulated on the 

factors that influence evacuations. Knowledge derived 

from these studies, as well as information gained by 

airframe manufacturers and industry from their own 

studies, has been applied to the design of airplane 

(evacuation) systems, and much of this knowledge has 

been codified in the Code of Federal Regulations. 

Building on the general state of knowledge about 

evacuation contingencies, more recent research has 

focused on the factors that impact evacuations through 

specific effects on passenger egress at floor-level and 

overwing exits. Included have been use of emergency 

lighting, exit size, type of descent assisting means, 

aircraft interior configuration, crewmember actions 

relative to egress, motivational state of passengers, 

and individual passenger attributes. Importantly, 

these studies have employed human research subjects, 

generating a comprehensive body of evidence about 

human performance in evacuations. Typically, these 

studies have also investigated the interactions of 

individual passenger attributes with the other factors 

being studied. In sum, much is known about human 

performance, its control, and its disruption, during 

both actual and simulated airplane emergencies and 

ensuing evacuations. 

Evacuations through the Type-III exit have, within 

the last ten years or so, been particularly well-studied. 

Rasmussen and Chittum (1989) first described the 

effects of seating configuration adjacent to the Type-III 

exit on exit plug removal and egress, and that same 

year McLean, Higgins, Lyne, and Vant (1989) reported 

the effects of wearing protective breathing headgear 

(smokehoods) on evacuations through the Type-III and 

Type-IV exits in clear air and smoke. This work was 

complimented by that of Muir, Marrison, and Evans 

(1989), who evaluated passenger motivation on egress 

through different bulkhead apertures and different 

passageway configurations leading to a Type-III exit. 

Muir, Marrison, and Evans (1990) continued their 

studies, next assessing passageway-width effects in their 

“low” motivation condition and in smoke in a manner 

analogous to their 1989 work. Muir, Bottomley, and 

Hall (1992) again studied motivation effects on egress 

through bulkhead apertures and the Type-III exit in 

smoke, describing effects relative to different passageway 

widths. In parallel, McLean, Chittum, Funkhouser, 

Fairlie, and Folk (1992) reported the effects of dual or 

triple seat assembly placement next to either one or two 

Type-III exits on exit operation and speed of egress. 

4
Fennell and Muir (1993) next described the effects of 

exit plug weight and seat configuration on operation 

of the Type-III exit. McLean, George, Chittum, and 

Funkhouser (1995, Part I) conducted another study 

of seat placement effects on evacuations through the 

Type-III exit, designed specifically to compare a range 

of single passageway widths and aft seat assembly 

encroachment distances on egress. The data from this 

study were further examined by McLean and George 

(1995, Part II), highlighting the effects of individual 

passenger attributes and their interactions with the 

physical layout adjacent to the Type-III exit. Muir 

(1996) reported on another study of passageway 

configuration, looking specifically at narrow passageway 

widths. McLean, Corbett, and George (1999) later 

presented the results of an evacuation study examining 

the effects of passenger management (presence of a 

flight attendant at the Type-III exit) and passenger 

density in the cabin, and McLean and Corbett (2000) 

evaluated the effects of individual subject attributes 

in that study. 

Combined, these studies enhance our general 

understanding of the human factors of egress from 

transport airplanes and identify the effects of many 

other specific factors and their interactions regarding 

egress through the Type-III exit. While the data are 

generally not amenable to direct statistical comparison 

because of differences in apparatus, methodologies, 

and possible cultural influences, there is an ability 

to determine whether the findings are mutually 

supportive and generally reliable and, by exclusion 

therefrom, whether any of the findings deserve not 

to be recognized. 

FINDINGS AND INTERPRETATIONS 

Rasmussen and Chittum (1989). The first study 

to address Type-III exit configuration issues was that of 

Rasmussen and Chittum (1989). They compared four 

passageway configurations leading from the center aisle 

to the Type-III exit between triple seat assemblies: a) the 

then-current FAA minimum standard single passageway 

(6”- 8” with maximum aft seat encroachment into the 

exit opening), b) the CAA minimum single-passageway 

standard (10” with exit midline aft seat encroachment), 

c) the current FAA standard single passageway standard 

(20” with a 5” aft seat encroachment), and d) the 

current FAA standard dual passageway configuration 

with the outboard seat removed (OBR) and two 6”

passageways (one fore and one aft of the exit). Four 

subject groups, ranging in age from 17 to 70 years, 

were employed. Presentation of the four passageway 

configurations was counterbalanced across the four 

groups, with exit plug removal times and egress 

flowrates through the Type-III exit being the dependent 

variables of interest. 

Table 1 shows the flowrate results in a trial-by-trial 

format. One-way analysis of variance (ANOVA) found 

a significant main effect of passageway width on mean 

egress times; simple effects of individual passageway 

configurations were gauged by independent t-tests. The 

t-tests found that the dual 6” passageway configuration 

was significantly faster than both the 6” (p<.005), and 

10” (p<.01) single passageway configurations, and the 20”

single passageway configuration was significantly faster 

than the 6” single passageway configuration (p<.025), 

but not the 10” single passageway configuration. 

These were mean egress time data, obtained across 

a series of four trials, during which a significant degree 

of experience was being acquired by the subjects. 

For example, on the first egress trial when subjects 

were naïve, the 6” single passageway configuration 

produced essentially identical egress times to the 

20” single-passageway. ANOVA showed no effects 

of passageway width on the first egress trial times;

however, independent t-tests were then used to compare 

TABLE 1

Individual Egress Times Through The Type-III Exit

(Rasmussen and Chittum, 1989).

Configuration

Evacuation Trials

1 2 3 4 mean

6” single 1.65 / 0.56 1.81 / 1.03 1.49 / 0.48 1.53 / 0.64 1.62 / 0.71

10” single 1.75 / 0.56 1.41 / 0.39 1.47 / 0.48 1.44 / 0.56 1.52 / 0.51

20” single 1.67 / 0.71 1.50 / 0.45 1.29 / 0.33 1.31 / 0.36 1.44 / 0.50

6” dual OBR 1.46 / 0.41 1.38 / 0.32 1.37 / 0.63 1.28 / 0.37 1.37 / 0.45

Times in seconds = mean / std. dev. n = 33 per group

5
configurations. (Note that without a significant main 

effect in the ANOVA, this statistical approach is 

unwarranted.) Even so, the analysis showed that the 

6” dual passageway configuration provided faster 

evacuations than the 10” single passage-way (p<.01); 

no other differences were found on the first trial. 

Subsequent to that first trial, as can be seen in the 

table above, performance at each configuration varied 

significantly, eventually “sorting itself out” by the fourth 

trial, which mirrored the mean egress performance. 

Thus, as subjects acquired egress experience, eliminating 

the variability in their own individual performances, 

the effects on egress produced by passageway width, 

per se, were revealed. 

A second phase of the study examined hatch (exit 

plug) removal times in a separate single-side cabin 

mockup, using three rows of seats configured identically 

to the passageway configurations employed in the 

flowrate trials. Forty active (exit opening) subjects, 

ranging in age from 19 to 58 years, were employed to 

prepare the Type-III exit for use. Additional passive 

subjects sat in the remaining seats. Each trial ended 

when the exit was available for egress. Note that in this 

phase of the study two different exit opening strategies 

were examined with the OBR (outboard seat removed) 

configuration. In the first case, the active subject 

sat in the middle seat adjacent to the exit; in the 

second case, the subject sat in the outboard seat 

aft of the exit. 

The results from the exit preparation phase of the 

study can be found in Table 2. The total exit preparation 

times were dissected to reveal the time to unlatch, 

and the time to dispose of, the exit plug. ANOVA 

failed to yield significant differences among the five 

configurations examined; nonetheless, independent 

t-tests were again employed to compare configurations. 

This analysis showed that the 6” single passageway 

configuration allowed the exit plug to be unlatched 

faster that either the 20” single passageway or the 6” 

OBR configuration with the subject seated adjacent to 

the exit, and the 10” single passageway configuration 

also allowed the plug to be unlatched faster than the 6” 

OBR configuration with the subject seated adjacent to 

the exit. No differences were found among any of the 

configurations for either exit plug disposal time or total 

exit preparation time. These results indicate that, while 

small effects on exit plug removal may be produced 

by passageway configuration, these differences are 

embedded within a larger exit preparation process 

that is largely robust to perturbation by differences in 

passageway configuration. 

In their discussion of the results, Rasmussen 

and Chittum (1989) noted that subjects with prior 

experience with the Type-III exit produced flowrate data 

of reduced variability, leading to increased statistical 

significance of the results obtained. As an example, 

they cited the egress time of a single subject using the 

6” single passageway configuration on trial 2 as being 

responsible for an 8.4% increase in mean egress time 

for that trial. The implication was that, as subjects 

learned to egress more effectively during the study, 

such deviant egress times were eliminated, illuminating 

specific effects of the passageway configurations. While 

generally true, removal of this particular outlying 

data point would have eliminated some of the average 

difference between the6” single passageway configuration 

and the faster 20” single and 6” OBR passageway 

configurations, conceivably eliminating the statistical 

significance of the passageway configuration effect. 

Perhaps more importantly, their notation points to 

the fact that errant individual subject performance can 

skew results to suggest greater treatment effects than 

otherwise exist. Without specific knowledge about the 

particular reason for this data outlier, it is difficult 

TABLE 2

Type-III Exit Preparation Times

(Rasmussen and Chittum, 1989).

Exit

Opening

Activity

Passageway Configuration

6”

Single

10”

Single

20”

Single

6” OBR

(Adjacent)

6” OBR

(Aft)

Unlatch Plug 1.78 / 0.47 2.08 / 0.41 2.28 / 0.34 2.54 / 0.60 2.39 / 1.36

Plug Disposal 3.79 / 1.58 3.55 / 1.75 3.33 / 1.78 3.68 / 1.36 2.61 / 1.42

Total Time 5.56 / 1.95 5.63 / 1.93 5.60 / 1.74 6.21 / 1.79 5.00 / 2.33

Times in seconds = mean / std. dev. n = 40

6
7 

to ascribe some systematic effect, human factors or 

otherwise, on egress performance. Further, without 

similar egress performance for this individual subject 

with the comparable 6” OBR configuration, it is unlikely 

that some unique personal interaction was at work. 

More globally, without similar egress performances 

by other (similar) subjects at all of the 6” passageway 

configurations, it is unlikely that a generalized human 

factors effect was responsible. Rather, the subject is 

apt to have made some misstep, such as slipping or 

getting a foot wedged between the outboard seat and 

the inside of the fuselage, that impaired his performance 

excessively on this single trial. Such instances happen 

often during evacuations and can obscure useful

information relative to such questions as, “What is an 

appropriate passageway configuration?” 

The authors also cited the uncontrolled placement 

of the exit plug as a factor relevant to their findings. 

Lacking specific instructions on exit plug disposal, 

subjects using the 6” dual passageway configuration 

evidenced more instances of leaning the plug against the 

inside of the fuselage beneath the exit opening, whereas 

trials at the narrower 6” and 10” single-passageway 

configurations resulted in the subjects placing the plug 

vertically in the seat they had previously occupied or 

on the passageway floor. (No mention was made of 

what was done with the plug at the 20” passageway 

configuration.) Inthe first case, Rasmussen and Chittum 

(1989) concluded that the placement appeared not 

to offer the potential for significant impediments to 

egress, although they judged placement vertically in 

the unoccupied seat or placement on the passageway 

floor to have the potential for adverse effects. Lacking 

data to support their speculations, they suggested

that additional studies would have to be conducted 

to assess the interaction effects of these potential exit 

plug placements and specific passageway configurations 

on evacuations. 

Thus, the Rasmussen and Chittum (1989) study 

was able to determine the effects of several factors. 

First, the human factors effects, related to naïve

subject performance, clearly outweighed the effects 

of passageway configuration and produced variable 

placement of the exit plug subsequent to its removal. 

Second, the passageway configuration, per se, was

shown to produce systematic effects on evacuation 

times, these being evidenced as the human factors 

effects waned with increasing subject experience. Third, 

passageway configuration had little effect on time for 

preparation of the Type-III exit, although the lack of 

appropriate experimental controls, regarding placement 

of the exit plug after its removal, confounded the ability 

to accurately describe any systematic potential for an 

interaction between passageway configuration and exit 

plug placement. Together, these findings support an 

initial understanding that while the factors involved 

in evacuations through the Type-III exit may seem 

exceedingly complex and inestimably intermingled, 

careful examination through wellcontrolled factorial 

research studies has the potential to illuminate the 

individual and combined contributions that specific 

egress factors provide. 

McLean, Chittum, Funkhouser, Fairlie, and 

Folk (1989). Another study relevant to these issues was 

that of McLean et al. (1989), in which the effects of 

wearing smokehoods on evacuations through Type-III 

(20” x 36”) and Type-IV (19” x 26”) exits in clear air and 

smoke were examined. Access to the exits conformed to 

the then-typical minimum single-passageway width of 

6 inches. The theatrical smoke was maintained during 

egress trials at an optical density of approximately 0.5

per foot, i.e., the density at which human survival in a 

transport airplane fire is possible for approximately 90 

to 120 seconds (cf. Crane, 1978). 

Subjects ranged in age from 18-63 years. Each

subject group performed two egress trials, which were

counterbalanced regarding the wearing of smokehoods 

versus not. The hoods were of two sizes. The first was 

small and hugged the subjects’ heads rather closely, 

while the second was much larger and “ballooned” when 

activated. Both total evacuation times and individual 

“hatch-crossing times” were examined. 

In Phase 1 of the study, the evacuations without 

smokehoods in clear air through the Type-III exit were

faster than those through the Type-IV exit (p<.005), 

and wearing smokehoods increased egress times through 

both exit types (p<.05). The effects of smoke were found 

to depend on the obscuration of visual information in 

the area of the exit opening, as opposed to delaying 

approach to the exit. As can be seen in Table 3, the exit 

size effect was much larger than the effect of wearing 

smokehoods. As is typical, smoke in the cabin slowed 

evacuations through the Type-III exit significantly when 

compared with clear air. However, egress through the 

Type-IV exit did not conform to this effect, probably 

because exit size was a much more powerful factor. 

Individual hatch crossing times accounted for the

significant main effects of both exit opening size and 

wearing of smokehoods; the larger smokehood also 

produced longer hatch crossing times than did the 
TABLE 3

Individual Hatch Crossing Times

(McLean et al., 1989)

Clear Air Smoke

Type III Type IV Type III Type IV

PPBE 1.70 / 0.12 3.30 /0.15 2.00 / 0.09 3.30 / 0.16

No PPBE 1.40 / 0.08 2.90 / 0.16 1.70 / 0.08 2.60 / 0.12

Times in seconds = mean / std err. n = 20 per group in clear air / 80 per group in smoke

smaller one. The counterbalanced presentation of egress 

with/without a smokehood revealed an interaction 

effect whereby the increase in hatch crossing times 

produced by wearing smokehoods could be overcome 

by prior experience, but only in the clear air condition, 

affirming that obscuration of visual cues was the 

mechanism responsible for the increase in egress 

times seen. 

In their discussion of the results, McLean et al. (1989) 

invoked the term “personal ergonomic workspace” 

to interpret the findings regarding slower egress 

performance at the smaller exit opening size and while 

using the larger smokehood. In both cases, as personal 

ergonomic workspace requirements increased, egress 

times increased as well. However, the finding that 

subject egress experience only eliminated smokehood 

effects in clear air indicates that visual psychomotor 

learning, not “skill practice” effects, was responsible 

for the effects of experience. This finding comports 

well with the findings of McLean and George (1995, 

Part II), in which older subjects were found to improve 

egress performance on a second egress trial at narrow 

passageway widths after many other egress trials at larger 

passageway widths, and after generalized egress skill 

through a Type-III exit opening was well established. 

Those authors (1995, Part II) concluded that a 

change in an individual subject’s egress “strategy” 

was responsible. This 1989 finding was, therefore, 

another early indication that human factors effects 

predominate in the control of naïve subject performance 

in evacuations through the Type-III exit. 

Muir, Marrison, and Evans (1989). The third 

relevant study was that of Muir et al. (1989), who 

studied subject flowrates between bulkheads and the 

effects of passageway width on egress through a Type-III 

exit. Focusing here on the Type-III exit phase of the 

study, the passageway configurations employed were 

3”, 13”, 18”, 25”, and 34” single passageways between 

triple-seat assemblies and a 6” OBR dual-passageway 

configuration. Differences in the single-passageway 

configurations were achieved by locating the seat 

assembly forward of the exit as far rearward as possible 

for all of the passageway widths employed and moving 

only the seat assembly aft of the exit to get the 

desired passageway width. The 6” OBR configuration 

conformed to CAA Airworthiness Notice No. 79. For 

the 3”(a) single passageway configuration the outboard 

seat in the exit row had its recline and breakover 

restricted; in all other trials, all three of the exit row 

seatbacks were restricted in their ability to recline 

and breakover, assuring that the configuration was 

maintained along the entire length of the passageway. 

A total of 2262 subjects (60 per group), ranging in age 

from 20-50 years, was employed. Subject motivation 

level was a second factor of interest; a monetary bonus 

was offered to half of the subject groups, using a payoff 

strategy in which the first 50% of the subjects to 

evacuate in each group would receive a 5-pound bonus 

(half the participation fee) immediately upon exiting 

the airplane. Two competitive trials were conducted 

at each configuration, and subjects in the competitive 

groups performed four evacuations (two through the 

bulkhead and two through the Type-III exit), whereas 

non-competitive subjects performed two evacuations 

(one through the bulkhead and one through theType-III 

exit). Trials were run in clear air. 

The mean cumulative times for the first 30 subjects 

to evacuate through the Type-III exit in both the 

competitive and non-competitive evacuation trials can 

be found in Table 4. Also shown are the cumulative 

times for the 30 subjects to evacuate in the first and 

second trials in the competitive condition alone. Note 

the rather large, but statistically insignificant, variability 

between the times for the first and second egress trials 

at the various passageway configurations. ANOVA

found a significant main effect of motivation condition 

(p<.001) on egress times, resulting from congestion at 

the exit associated with the competitive evacuations, 

8
9 

TABLE 4

Total Cumulative Evacuation Times For the First 30 Subjects to Evacuate

(Muir et al., 1989)

Passageway

Configuration

Competitive Trials Non-Competitive Trials

1st trial 2nd trial Mean Mean

3”a 83.8 / 11.2 84.0 / 0.0 83.9* / 9.7

3”b 61.9 / 4.6 81.0 / 17.0 71.4*/ 15.0 53.2 / 1.8

6” OBR 55.1 / 11.6 48.6 / 1.4 53.2 / 10.0 39.6 / 2.5

13” 54.6 / 13.4 57.5 / 6.3 55.9 / 10.3 39.9 / 3.3

18” 49.1 / 6.5 58.5 / 7.7 53.7 / 8.20 37.2 / 0.2

25” 54.9 / 14.3 54.9 / 10.0 54.9 / 11.5 40.8 / 2.7

34” 57.2 / 5.7 67.3 / 7.2 62.3 / 8.10 35.3 / 0.6

Times in seconds = mean / std. dev.

which increased evacuation times. In fact, five of the 

competitive evacuation trials (two with the 3”(a) single 

passageway, two with the 6” single passageway, and 

one with the 18” single passageway) had to be aborted 

because of blockages at the exit proper. Significant 

differences in mean egress times were also shown to 

result from the different passageway configurations in 

both the competitive (p<.001) and non-competitive 

(p<.01) conditions. However, no interaction effect 

of motivation condition with specific passageway 

configuration was reported, although mean times for 

the 3”, 13”, and 34” single passageway configurations 

were significantly different between competitive and 

non-competitive evacuations, while those for the 18” 

and 25” passageways were not. 

The reason for the significant motivation-related 

differences at the 13” single-passageway configuration 

is unclear, given the smaller differences in its mean 

evacuation times, and the larger standard deviations 

associated with those times, when compared with times 

for the 18” single passageway configuration, which 

failed to achieve statistical significance. One likely 

explanation would be the aborted trial for the 18” 

* = significant (p<.05)

passageway, which would reduce the amount of data 

and the degrees of freedom in the analysis, thereby 

reducing its power. 

A significant main effect of age (p<.0001) was shown 

in the competitive evacuation trials, as subjects over 

35 years of age were generally in the latter positions 

in the evacuation stream. Gender effects were also 

highly significant in the competitive evacuation trials 

(p<.0001), males being much faster to egress. Finally, 

subjects who reported having an evacuation plan were 

more likely to receive a bonus in the competitive 

evacuation trials (p<.0001), and subjects who were 

able to use the aisle/passageway, instead of climbing over 

seatbacks to get to the Type-III exit, also had shorter 

evacuation times (p<.001). These effects were not found 

in the non-competitive condition. 

Various competitive group subjects also were said to 

have walked over each other, searched for family and 

friends before attempting to egress, and had difficulty 

opening their seat belts; some subjects were even unable 

to move from their seats. A qualitative analysis 

of the videos from the evacuation trials led the 

authors to suggest that non-competitive evacuations 
were particularly useful in simulating precautionary 

evacuations and other evacuation events in which the 

physical conditions in the cabin have not deteriorated, 

whereas the use of monetary incentives has the potential 

to provide data more relevant to emergencies perceived 

as life-threatening. This interpretation was supported 

by accounts of survivors of an actual accident, which 

became progressively more involved with smoke and fire, 

and which had begun with orderly egress that evolved 

to resemble the competitive egress trials. 

Citing the relative youth and good health of their 

subjects, Muir et al. (1989) suggested that evacuation 

times should be longer and [ergonomic] problems 

should be greater in the aftermath of an actual accident. 

They also suggested that exploration of a possible 

interaction between passageway configuration and exit 

plug removal/disposal would require crowding and 

pushing by subjects at the exit during the time the exit 

plug was being manipulated. 

Thus, Muir et al. (1989) again confirmed large 

human factors effects on egress, including effects 

of subject motivation, strategic planning, age, and 

gender, as well as an array of behaviors both related 

and unrelated to egress. However, the positive effects 

of egress experience were not seen for the competitive 

evacuations, as the second trial was generally slower 

than the first trial. Comparisons of the effects of 

egress experience could not be made within the noncompetitive group results, or between the competitive 

and non-competitive group results, because of the 

lack of repeated egress trials for the non-competitive 

subjects. Given the strategy of paying the monetary 

bonus to, and reporting on, only the first 50% of 

subjects to egress in the competitive evacuations, the 

effects of the behavioral aberrations (searching for 

family, difficulties with seatbelt buckles, not moving 

from seats, etc.) in producing the competitive results 

are likely to be minimal. What is clear is that the high 

degree of subject motivation, especially at very narrow 

passageway widths, led to the exit blockages. 

An effect of passageway configuration on speed of 

non-competitive egress was also replicated for the 3” 

and 34” single-passageway configurations. ((Recall 

that these configurations were different from those of 

Rasmussen and Chittum (1989), who only compared 

6”, 10”, and 20” passageway configurations)). The 

failure to find differences in flowrates for the 13”, 

18”, and 25” single-passageway configurations in both 

competitive and non-competitive evacuations suggested 

that these configurations were not ergonomically 

different from each other, although the authors 

surmised that the 18” passageway configuration could 

be optimum (in spite of the blockage at that passageway 

configuration in one competitive evacuation). These 

findings added weight to the interpretation that 

passageway configuration has a systematic influence on 

speed of egress, although the human factors aspects of 

evacuations were again shown to be a more important 

factor to be understood. 

Muir, Marrison, and Evans (1990). The preceding 

(non-competitive) methodological approach was 

continued by Muir et al. (1990), who investigated the 

effects of theatrical smoke in the cabin on evacuations 

using four passageway configurations identical to those 

employed in their 1989 study. The configurations again 

included the 13”, 18”, and the 34” single passageways, 

as well as the 6” OBR dual passageway configuration. 

A total of 254 subjects, ranging in age from 20 to 

50 years, and grouped 30 to 35 subjects per group, 

was employed. The optical density of the theatrical 

smoke was again maintained at approximately 0.5 

per foot. 

Table 5 presents the results of this study in comparison 

with the results from the Muir et al. (1989) study. 

ANOVA revealed no significant differences among 

configuration-based egress times in theatrical smoke, 

although comparison of the evacuations in smoke 

with the competitive and non-competitive evacuations 

conducted in 1989 showed a significant (p<.01) 

difference between the non-competitive evacuation 

times in clear air (1989) and those in smoke (1990), 

which were not significantly different from the (1989) 

competitive evacuation times. Interestingly, the 6” 

OBR configuration produced evacuations in smoke 

about six seconds slower than those in the competitive 

condition, whereas the evacuations in smoke with the 

13”, 18”, and 34” single- passageway configurations 

were about four seconds faster than were competitive 

evacuations in clear air for the same passageway 

configurations. The statistical significance of this 

apparent interaction effect was not reported, nor were 

any other interactions apparent in the reported results. 

The differences in research design between the two 

studies (number of evacuations per subject and number 

of subjects per group) makes clear-cut interpretation 

difficult. 

Muir et al. (1990) suggested that removal of the 

outboard seat may have eliminated tactile cues that 

subjects would have used to aid their egress and 

recommended that additional evacuation studies be 

10 
11 

TABLE 5

Total Cumulative Mean Evacuation Times For The First 30 Subjects To Evacuate

(Muir et al., 1990)

Passageway

Configuration

Competitive

Trials

Non-Competitive

Trials

Smoke

Trials

6” OBR 53.2 / 10.0 39.6 / 2.5 59.6 / 9.9

13” 55.9 / 10.3 39.9 / 3.3 51.6 / 14.9

18” 53.7 / 8.20 37.2 / 0.2 49.6 / 7.0

34” 62.3 / 8.10 35.3 / 0.6 57.9 / 3.2

Times in seconds = mean / std. dev.

conducted to confirm the effect and its cause(s). They 

also recommended additional studies to determine

the influence of seating configuration on ease of exit 

opening and placement of the exit plug in a smoke-fi lled 

cabin situation, as well as the interaction of theatrical 

smoke and egress competition.

Thus, this study extended our understanding of the 

effects of smoke on egress, as well as its relationship 

to the effects of passenger motivation and passageway 

configuration. However, because of the preliminary 

nature of the study, little information was made available 

regarding human factors effects and their potential 

for interactions with the effects of the independent 

treatments. Nonetheless, the lack of visual information, 

in general, was assuredly responsible for the generalized slowing of the evacuations in smoke, and the 

combination of minimal tactile cues and higher subject 

density at the exit, proper, was likely responsible for the 

additional slowing seen in the 6” OBR confi guration. 

These effects were again relatively consistent with regard 

to the 13” and 18” single passageway confi gurations, 

indicating that no specific interaction of passageway 

configuration and smoke was producing discriminative 

differences in egress for these intermediate passageway 

widths. 

McLean, Chittum, Funkhouser, Fairlie, and 

Folk (1992). The next study to address these issues was 

that of McLean et al. (1992), which investigated four 

different exit/seat assembly/passageway confi gurations. 

The four exit configurations were presented in a

counterbalanced repeated-measures design. The singlepassageway configurations included: a) triple- seat

assemblies with a single 20” passageway and a 5” aft seat 

encroachment; b) triple-seat assemblies with the seats 

forward of the exit broken over 15o

 and having a single 

10” passageway with midline aft seat encroachment;

and c) dual-seat assemblies with a single 10” passageway 

with midline aft seat encroachment. A dual Type-III

exit configuration (d) was also examined: triple-seat 

assemblies formed three 6” passageways in which the 

outboard seat of both seat assemblies centered on the 

Type-III exits and bounding the center passageway was 

removed. Four groups of 39 subjects, ranging in age 

from 19 to 61 years, were employed. The intent of 

the study was to compare the relative flowrates of the 

various configurations, as well as the time required to 

remove the hatch (exit plug), with the results of the 

Rasmussen and Chittum (1989) study.

Table 6 shows the total group evacuation times and 

mean individual subject egress times for trials 1 through 

4 at each configuration. Total group times include both 

the time to remove the exit plug and the time for all 39

subjects to exit completely. 

Mean individual subject egress times were derived 

by subtracting the time at which the last body part of 

a preceding subject emerged from the exit from the 

time at which the last body part of the next subject 

emerged from the exit, specifically assuring a measure 

of flowrate, and not just hatch crossing time, as had 

been shown previously by McLean et al. (1989).

The average flowrates also included only the times 

for the third through 37th subject, as potential

confounding effects of both exit plug removal and 

potential “stragglers” at the end of the egress stream 

were removed to reveal as pure a measure of fl owrate 

as possible. 
TABLE 6

Total Group Evacuation Times And Mean Subject Flowrates

(McLean et al., 1992)

Trial

Passageway Configuration / Seat Assemblies

20” Single

Triples

10” Single

Triples w/Breakover

10” Single

Duals

6” Triple OBR

Triples

1 91.67 / 2.21 74.03 / 1.78 81.86 / 1.92 72.36 / 3.00

2 74.90 / 1.80 82.50 / 1.96 87.37 / 2.13 39.00 / 1.50

3 64.20 / 1.53 89.83 / 2.14 80.93 / 1.92 46.60 / 1.96

4 77.16 / 1.86 82.54 / 2.04 62.36 / 1.48 43.90 / 1.99

Mean Time 76.98 / 1.85 82.23 / 1.98 78.13 / 1.86 50.47 / 2.11

Times in seconds = Total group time / flowrate in seconds per subject n = 39 per group

The ANOVA found a significant effect of passageway 

configuration (p<.007), as the double exit/triple 

passageway configuration produced 36% shorter total 

evacuation times, compared with the single passageway 

configurations. This effect occurred in spite of an 

11% reduction in average flowrate through the dual 

exit/triple passageway configuration, as well as a 32% 

increase in the average time required to remove the exit 

plug (see Table 7). There were no significant differences 

in flowrate among single-passageway configurations, nor 

were there significant differences in exit plug removal 

times among the single passageways. 

In spite of the absolute differences in flowratesbetween 

the two studies and the lack of statistical significance 

among single passageway flowrate differences, McLean 

et al. (1992) concluded that the findings had supported 

and extended those of Rasmussen and Chittum (1989), 

specifically by providing corroboration that the 20” 

single passageway configuration appeared to allow 

the most efficient egress of the single passageways 

studied. Reduced ergonomic restrictions of the 20” 

passageway, as compared with the narrower passageway 

configurations, was the main rationale for that 

conclusion, although the 10” single passageway between 

dual seat assemblies had provided an essentially identical 

flowrate to that of the 20” single passageway between 

triple seats. This seat-assembly effect was seen to rely 

on the reduced distance that subjects had to travel from 

the center aisle to the exit opening, leading the authors 

to suggest that providing both dual seat assemblies and 

a 20” passageway configuration could produce even 

lower egress times. McLean et al. (1992) continued, in 

contrast, adding that the 6” dual exit/triple passageway 

configuration increased the ergonomic restrictions 

and provided additional behavioral latitude relative to 

egress, decreasing flowrates, but also decreasing total 

evacuation times. These effects suggest an apparently 

complex interaction of the number of exits, number of 

passageways, passageway width, distance-to-be-traveled, 

and seat assembly type, that can again be reduced to 

the single construct of “personal ergonomic workspace” 

that passengers require (have imposed) in relation to 

TABLE 7

Time To Remove The Exit Plug

(McLean et al., 1992)

Trial

Passageway Configuration / Seat Assemblies

20” Single

Triple Seats

10” Single

Triples w/Breakover

10” Single

Dual Seats

6” Triple OBR

Triple Seats

1 6.83 5.37 6.43 10.84

2 4.47 8.86 4.14 5.77

3 5.13 3.70 7.23 6.14

4 4.14 4.87 4.03 5.84

Mean Times 5.15 5.70 5.46 7.18

Times in seconds n = 39 per group

12 
13 

egress. In this vein, while many physical elements

may participate in what appears to be a complex

interaction, designing these elements to achieve the 

single construct of good personal ergonomic workspace 

appears sufficient to render potentially undesirable

features of the interaction ineffective.

Thus, it appeared from another early Type-III exit 

study that passageway width, per se, has a relatively 

small effect on egress flowrate, with single passageways 

of intermediate width being similar in their ability to 

support evacuations. Narrower seat assemblies were

also found to be better at supporting egress, although 

the gains obtained with dual-seat assemblies (relative 

to triple-seat assemblies) were offset somewhat in the 

case of OBR configurations, where removal of the 

outboard seat presented behavioral options that may 

have consumed additional decision time. An increase in 

the number of exits and passageways further promoted 

egress by distributing both the workspace and the 

evacuation across a greater number of egress routes, 

although flowrates through the single passageways

were reduced. The positive effects of increasing the 

distribution may have been moderated by the presumed 

increase in decision-making requirements imposed. 

Again, similar to Rasmussen and Chittum (1989), 

none of the single passageway configurations was shown 

to provide superior (statistically different) exit plug 

removal time, although the 6” OBR confi gurations 

produced arguably slower exit plug removal, depending 

on the specifi c configuration. This study also reinforced 

the Rasmussen and Chittum finding that exit plug 

removal is a relatively robust activity with regard to 

effects of passageway width, with the exception that 

subjects who are seated adjacent to the exit(s) in a 6” 

OBR configuration require a little more time and effort 

to remove the exit plug. This finding, coupled with the 

potential for added behavioral variability in the dual 

exit/triple passageway confi guration, led McLean et al. 

(1992) to suggest that a reconfiguration of that entire 

exit scheme to employ single passageways, each leading 

to one of the Type-III exits, could produce a net gain 

in efficacy of egress. It should be noted that without 

such a reconfiguration, however, the ability of the dual 

exit/triple passageway configuration to support egress 

was still far superior to the single-exit/single-passageway 

confi gurations studied.

Muir, Bottomley, and Hall (1992). In 1992, Muir 

et al. revisited the approach of Muir et al. (1990), 

studying the effects of different apertures between

bulkheads and different Type-III exit passageway

widths on competitive evacuations conducted in cabin 

conditions of non-toxic theatrical smoke maintained 

at an optical density of 0.5 per foot. The studied 

passageways leading to the Type-III exit included

configurations of 6” dual OBR and 13”, 18”, and 

34” single passageways, which were again achieved by

holding the seat assembly forward of the exit as far aft 

as possible and moving the seat assembly aft of the exit 

to achieve the desired passageway width. Thirty-two 

evacuations, (8 at each of the 4 confi gurations) were

conducted, employing 669 subjects (79.2% male ) in 

groups of approximately 40. Subjects ranged in age 

from 20 to 50 years. The competition payoff strategy 

allowed the fi rst 75% (30) of the subjects to receive a 

5-pound bonus (half the participation fee) immediately 

upon exiting the airplane. 

ANOVA conducted on the evacuation times (screened

to remove outliers) for each confi guration revealed a 

significant effect of passageway confi guration (p<.01) 

caused by an increase in evacuation time at the 6” 

OBR configuration, relative to the single passageway 

configurations (see Table 8). One outlying trial at the 

18” passageway width was removed from the analysis 

because it “was delayed from the outset... [and] also 

TABLE 8

Evacuation Times From Competitive Evacuations In Non-toxic Smoke

(Muir et al., 1992)

Configuration All Evacuations

Evacuations Without

Outliers

6” OBR 70.7 / 16.2 70.7 / 16.2

13” 55.3 / 9.2 55.3 / 9.2

18” 64.1 / 20.5 57.2 / 6.7

34” 58.2 / 19.7 51.5 / 6.2

Times in seconds = mean / std dev. n = 30 per cell
hampered by several blockages in the exit aperture, 

although none were considered serious enough to 

warrant cancellation of the evacuation.” Another case 

at the 34” passageway width was removed because 

the “evacuation began to display an abnormal pattern 

somewhere between the fifth and tenth volunteers 

to evacuate... undoubtedly primarily caused by an 

exit blockage in which two males attempted to exit 

simultaneously and, as one of them was extremely 

heavily built, became stuck in the aperture. This will 

have been compounded by an additional couple of 

minor blockages, none of which were considered serious 

enough to necessitate abandonment.” One evacuation 

at the 13” passageway width was also aborted, as “four 

people were jammed in the exit aperture, unable to 

move. These volunteers were continually pushed by 

the mass of people still in the aircraft cabin and, 

immediately prior to the [alarm] signal, this group fell 

facedown onto the ramp.” Combined, these outliers 

and the aborted trial indicate an extreme level of subject 

motivation, making evaluation of passageway effects 

more difficult, since data were lost at all three of the 

single passageway configurations. Again, human factors 

effects were responsible. 

A significant effect of gender on time to egress was 

shown (p<.05), as males were faster than females, but 

there were no systematic differences in egress time 

resulting from age, weight, and height. Subjects who 

climbed over seats were faster than subjects who used 

the aisles, although questionnaires given to subjects 

after the evacuations failed to reveal an effect of escape 

strategy (p<.95). Except for the gender effect, these 

results are in direct contrast to the previous findings by 

Muir et al. (1989). Subjects more often reported that 

touch was their single most useful sense, followed next 

by vision, although 95% of the subjects reported not 

relying on the escape path marking system. 

In addition, Muir et al. (1992) compared the 

competitive evacuation times with the non-competitive 

evacuation times obtained by Muir et al. (1990), which 

were obtained with a methodology identical to the Muir 

et al. (1989) non-competitive methodology, except for 

the greater number of subjects per group in the 1992

study. The mean egress times and standard deviations 

may be found in Table 9. A 2-way (passageway 

configuration x motivation level) ANOVA found a 

significant main effect of passageway configuration 

(p<.01), without a main effect of motivation level. Nor 

was there an interaction of passageway configuration 

with motivation level. 

In the discussion of the results, the authors noted 

that the mean total evacuation time was slowest with 

the (narrowest) 6” OBR configuration, and noted that 

Muir et al. (1989) found faster evacuations with this 

configuration in clear air. They suggested that this 

effect could have been produced by a combination of 

the two competing streams of subjects and the lack of 

visual cues produced by the smoke, which eliminated 

subjects’ ability to conform to the “neat streammerging behavior pattern as previously found.” This 

interpretation agrees with that of McLean et al. (1989), 

who concluded that subjects’ inability to profit from 

prior egress experience in clear air, while wearing 

smokehoods during evacuations in smoke, resulted 

from an inability to use previously-helpful visual 

information. 

Muir et al. (1992) also addressed the apparent 

inconsistency seen with respect to the somewhat faster 

TABLE 9

Comparison of Evacuation Times From Competitive And

Non-Competitive Evacuations In Non-toxic Smoke

(Muir et al., 1992)

Configuration Non-Competitive

Evacuations

Competitive

Evacuations

6” OBR 59.6 / 9.9 70.7 / 16.2

13” 51.6 / 14.9 55.3 / 9.2

18” 49.6 / 7.0 57.2 / 6.7

34” 57.9 / 3.2 51.5 / 6.2

Times in seconds = mean / std dev. n = 30 per cell

14
fi

15 

evacuation at the 13” passageway confi guration, as 

compared with the 18” passageway, citing a possible 

perception by subjects that the 18” passageway might 

be wide enough to allow more than a single person 

to egress simultaneously (thereby producing more

competition for available egress workspace). They

further suggested that the 13” passageway may have 

been perceived by subjects as only large enough to allow 

one person to egress at a time, and that other subjects 

may have “held back” to allow single subjects to egress 

individually, creating a faster evacuation. Either or 

both of these suggestions could be true, and the fact 

that the study by Muir et al. (1989) also obtained 

a blockage at the 18” passageway might support the 

rst interpretation, although the blockage at the 13” 

passageway in the present study suggests that subjects 

were controlled more by the motivation factor than by

apperception. The authors tacitly acknowledged this 

probability in their discussion of outlying cases, where 

they noted that “ the escape times for 30 [subjects] in 

the outlying trials were excessive for all confi gurations 

in [a] class of evacuations... and suggests that it is not 

the specifi c configuration that led to extreme escape 

times... Instead, it is hypothesized that other factors 

were in evidence... [it] is more likely due to the nature 

of the people who arrive at the exit at the same moment, 

and it is suggested that changes in seat confi guration can 

only minimize the probability of such circumstances 

appearing. If they do appear, it is likely that the

evacuation will be delayed regardless of the particular 

seat configuration... Ideally, evacuations in which this 

behavior occurred would be subject to separate analysis.” 

This discussion again attests to the powerful forces that 

human factors effects can exert on evacuations and the 

degree to which answers to the experimental question 

can be obscured by such uncontrolled factors. 

Importantly, the caveat to the authors’ discussion, 

regarding subjects’ prospective perceptions of available 

egress workspace and the “probability” that this “effect 

may disappear if a larger number of evacuations using 

these configurations were performed” (see paragraph 

4.3), is the lack of a significant difference found between 

the evacuation times at the 13” and 18” passageway 

configurations. Their explanation for the apparent

“effect” is based on a perceived inconsistency with 

the results of Muir et al. (1989), for which a similar 

over-attribution of significance to the 18” passageway 

configuration (relative to the13” and 25” confi gurations)

had led to a suggestion of its optimality. Had the 

authors not tried to “coax” significance from either of 

these two sets of findings, no apparent inconsistency (or 

need to explain) would have existed, since there were no 

significant differences to attribute in either case.

However, other actual inconsistencies were displayed, 

such as the lack of an evacuation strategy effect and 

faster egress produced by crawling over seats instead 

of using the aisle, both of which were in contradiction 

to the findings of Muir et al. (1989). Again, the 1989 

effects were produced in cabin conditions of clear air, 

which would have allowed the use of visual information 

to aid egress. Given the relative consistency in the 

pattern of passageway configuration effects in the two 

studies, egress strategy and crawling over seats appear 

to have interacted minimally with the differences in 

egress workspace, instead supporting an interaction 

with information factors as responsible.

Fennell and Muir (1993). In 1993, Fennell and 

Muir reported another study of egress and passageway 

configuration, although the research question of interest 

focused on hatch (exit plug) removal and disposal. 

Two passageway configurations were employed, a 6” 

single passageway with maximum aft seat-assembly 

encroachment and a 13” single passageway with a 10” 

encroachment, both between triple seat assemblies. 

Three different exit plug weights were also employed:

12.5kg, 15kg, and 25kg. Subjects ranged from 19 to 54 

years of age, and were restricted in height and weight 

to no more than the 50th percentile value for the 

US population. In half the trials a 50th percentile 

male anthropomorphic dummy was placed in the

outboard seat adjacent to the Type-III exit, simulating 

an incapacitated passenger. The study was divided

into two phases. The first employed the 6” and 13” 

passageway configurations and 96 subjects (1/2 male 

and 1/2 female) distributed evenly among the three 

exit plug and two dummy conditions. Each subject 

performed one trial, using only one of the exit plug 

weights, either with or without the dummy. Phase 

2 of the study was a replication of Phase 1, except 

that subjects performed three trials, all either with or 

without the dummy, and all using the same exit plug 

weight for all trials for a single subject. Trials were

complete when the subject(s) first stepped onto the 

“wing” outside the fuselage. Subjects also completed 

questionnaires regarding their personal air-travel

histories and their perceptions about different aspects 

of the study.

The effects of passageway confi guration were assessed 

by t-test, using data from the Phase 1 and Phase 2 

(test 1) trials, which showed that exit plug removal 
and disposal were significantly faster with the 13” 

single passageway configuration than with the 6” single 

passageway confi guration (p<.001). No effects were

reported for the simple presence or absence of the dummy,

although the mean times for all conditions suggest a 

large effect (equally large variances notwithstanding), 

especially for female subjects. In fact, 18% of the 

subjects using the 6” configuration and 2% of the 

subjects using the 13” configuration (all female) were

unable to complete the task. As a result, those subjects 

were assigned a time, as if they had completed the 

task, equal to the longest exhibited task time, to allow 

analysis of the data. Also, two of the males operating 

the 15kg exit without the dummy present jammed the 

exit plug between the outboard seat and the exit frame, 

and a third opened the exit without unlatching his seat 

belt. These exit plug removal miscues caused the 15kg 

exit plug times for males to be longer than the removal 

times for the 25 kg exit plug. 

The authors reported that the mean time for all 

subjects to complete the task in the 6” passageway 

configuration was 38.0 seconds (38.6 sec. std. dev.); the 

13” passageway configuration produced mean times 

of 17.2 seconds (11.4 sec. std. dev.). Whether this 

included the adjustment for those who failed to fi nish 

the task is unclear. The mean times for the trials from 

Phase 1 may be found in Table 10. 

ANOVA was used to evaluate treatment effects in the 

data from both phases of the study for trials in which 

the dummy was absent. Main effects of passageway 

confi guration (p<.001), exit plug weight (p<.001), and 

gender (p<.001) were found, as the 13” confi guration 

and lower exit plug weights allowed faster exit plug 

removal/disposal and evacuation, with females being 

significantly slower than males. These effects were

sufficiently robust to establish a 3-way (passageway 

configuration x exit plug weight x gender) interaction 

effect (p<.01), based on the fact that, when compared 

with the 12.5 kg and 15 kg exit plug weights, the 25 kg 

exit plug was operated more slowly by females (only) in 

the 6”, but not the 13”, passageway confi guration. 

A separate ANOVA was employed to evaluate

treatment effects in the data from both phases of the 

study for trials in which the dummy was employed. This 

analysis revealed a significant main effect of passageway 

confi guration (p<.001), resulting from the faster times 

in the 13” confi guration. The authors reported that 

this effect held true for all three exit plug weights. The 

effect was greater for females, who were also shown to 

be generally slower at the task (p<.001). Combined, 

these effects were again strong enough to establish a 

2-way (passageway confi guration x gender) interaction 

effect (p<.001), indicating that, in the presence of the 

dummy, males were able to remove/dispose of the 

exit plug and egress relatively faster than females

at the 6” confi guration. However, only females had 

relatively improved egress times at the 13” passageway 

configuration. A significant difference was also observed 

in the time taken to remove/dispose of the 12.5 kg exit 

plug, when compared with the 25 kg exit plug, in the 

13” passageway confi guration (p<.05).

TABLE 10

Mean Times To Operate The Exit And Step Onto The Wing

(Fennell & Muir, 1993)

12.5kg Exit Plug 15kg Exit plug 25kg Exit Plug

6” 13” 6” 13” 6” 13”

Male

N 11.35 / 4.03 7.66 / 2.43 13.87 / 8.61 12.88 / 7.72 15.91 / 7.14 9.96 / 2.10

D 20.49 / 12.28 12.86 / 4.52 15.05 / 7.89 13.12 / 4.33 25.60 / 13.64 21.95 / 11.48

Female

N 17.08 / 4.73 11.53 / 3.22 26.56 / 16.18 13.33 / 6.26 80.65 / 48.19 19.63 / 7.12

D 65.29/ 46.30 21.97 / 13.33 87.57 / 42.59 29.61 / 16.85 76.25 / 43.52 31.87 / 14.11

Note that times do not include reaction time to begin the evacuation or time for moving the dummy.

Times in seconds = mean / std. dev. N = No dummy D = Dummy n = 8 per cell

16
The data from Phase 2 of the study (see Table 11), 

using only the 13” passageway configuration, were 

then analyzed for the effects of subject experience. 

A repeated-measures ANOVA on data from trials 

without the dummy present revealed that there was 

no generalized effect of practice on exit operation 

and evacuation times, nor was the improvement in 

evacuation times produced by the reduction in exit 

plug weight (as shown in Phase 1) enhanced by practice 

on the task. However, females were not able to benefit 

to the degree that was shown for males by the third 

trial (p<.025). In contrast to these findings, subject 

experience in the presence of the dummy was shown 

to improve exit operation and evacuation times 

significantly (p<.01), without regard to gender. No 

differences related to practice were found regarding 

exit plug weight. 

Subjects reported a variety of difficulties associated 

with the task, including impediments caused by the 

dummy, awkwardness in removing and disposing of the 

exit plug, lack of workspace, and personal injury while 

attempting to operate the exit. A repeated-measures 

ANOVA found that, by the end of the third trial, 

subjects perceived the size (p<.01) and weight (p<.025) 

of the exit plug to be greater. Fennell and Muir (1993) 

attributed these changed perceptions to possible fatigue. 

Subjects also reported that, when given the opportunity 

to examine the exit plug beforehand, they were often 

able to deduce how to approach the task better, 

how much the exit plug weighed, and that the exit 

plug should be disposed of outside the cabin (which 

was clearly indicated on seatback placards along the 

passageway). Interestingly, 63.5% of subjects employed 

with the 6” passageway configuration (without practice) 

placed the exit plug outside the cabin, whereas subjects 

employed with the 13” configuration placed the exit 

plug outside the cabin 38%, 70%, and 80% of the time 

in Phase 2 tests 1, 2, and 3, respectively. However, 22%, 

30%, and 33% of the subjects also held onto the exit 

plug until after egress in tests 1, 2, and 3, respectively. 

Similarly, 85%, 79%, and 79% of the Test 1, 2, and 3 

subjects placed the exit plug in a location that would 

have partly blocked egress, although instructions about 

exactly what to do with the exit plug after its removal 

had not been provided. 

Except for the facilitative effect of regular exercise 

for some females (p<.025) on the Phase I exit operation 

times at the 6” passageway configuration, there were no 

systematic effects of individual subject differences on 

the results. This is more than likely due to the restricted 

(< 50th percentile) anthropometric population range 

from which the subject sample was drawn. Clearly, 

however, small females had much more difficulty with 

the task, often being unable to handle the exit plug 

effectively. Handedness was shown to have an effect, 

in that the dominant hand was used more often to 

TABLE 11

Repeated Mean Times To Operate The Exit And Step Onto The Wing At The 13” Configuration

(Fennell & Muir, 1993)

Repeated

Evacuations

12.5 kg Exit Plug 15kg Exit Plug 25kg Exit Plug

Male Female Male Female Male Female

Test 1 N 7.66 / 2.43 11.53 / 3.22 12.88 / 7.72 13.33 / 6.26 9.96 / 2.10 19.63 / 7.12

D 12.86 / 4.52 21.97 / 13.33 13.12 / 4.33 29.61 / 16.85 21.95 / 11.48 31.87 / 14.11

Test 2 N 6.17 / 3.14 8.88 / 5.12 7.52 / 3.08 14.11 / 13.41 7.36 / 4.19 18.32 / 9.87

D 9.11 / 5.44 20.61 / 13.63 14.49 / 15.15 23.85 / 11.43 19.76 / 16.63 25.69 / 17.20

Test 3 N 6.23 / 1.95 14.85 / 19.29 5.96 / 2.19 11.81 / 9.03 7.30 / 1.49 19.02 / 17.89

D 7.98 / 5.03 14.35 / 11.56 13.10 / 14.46 18.35 / 12.54 13.96 / 7.74 21.99 / 17.51

Note that times do not include reaction time to begin the evacuation or time for moving the dummy.

Times in seconds = mean / std. dev. N = No dummy D = Dummy n = 8 per cell

17
grasp the exit handle for operation (p<.001), although 

this circumstance did not predict the time required 

to operate the exit.

In their discussion of the results, Fennell and Muir 

(1993) concluded that exit plug weight, passageway 

configuration, and gender all had effects on exit

operation and evacuation time, although the decrease 

in task time produced by the larger 13” passageway 

configuration was not achievable without also reducing 

the exit plug weight (pg. 20). This interpretation is 

somewhat puzzling, given the significant main effect 

of passageway configuration, which is not dependent 

in any way on the main effects for exit plug weight 

and subject gender, or the significant 3-way interaction 

effect, found for Phase 1 with the dummy absent. Each 

factor had its own specific effects, which were altered by

particular combinations with the other factors.

The effect of the dummy (incapacitated passenger) 

on exit operation and evacuation time was also seen 

to be important, as the indecision by subjects about 

whether or not to move the dummy before or during 

operation of the exit produced greater variability in 

the results. Recall that the presence of the dummy also 

made exit plug removal and disposal more diffi cult 

ergonomically, especially for females. Together, these 

two effects accounted for much of the treatment

variability found in the results of this study, and again 

point to the importance of subject characteristics and 

behavior in understanding the intricacies of aircraft 

evacuations. Neither passageway confi guration, exit 

plug weight, nor subject gender were shown to interact 

with egress experience, probably because a simple

behavior such as lifting (the plug) has more to do with 

innate strength than strategy (especially for females), 

and the increase in egress workspace provided by the 

increased passageway width was probably offset, at a 

minimum, by the added physical impediment produced 

by the presence of the dummy. This interpretation is 

supported by the subjects’ perceptions of the benefi ts 

of egress experience, as they reported practice-based 

improvements in knowledge about an appropriate

technique to use for operating the exit, knowledge 

that apparently failed to help them behaviorally. It is 

unclear whether the cumulative fatigue attributed to 

subjects mitigated against facilitative effects of practice 

on exit operation.

In addition to the (physical) effects of passageway 

confi guration and exit plug weight, negative (information) effects were produced by the quality of the safety 

cards and briefi ng materials, which failed to effectively 

explain the proper exit plug removal technique and 

disposal location. The authors suggested that this

problem was responsible for the large number of

subjects placing the exit plug on the passageway fl oor, 

an interpretation supported by the increased incidence 

of placing the exit plug outside the cabin (instead) 

as Phase 2 progressed. They also cited an apparent 

miscommunication about the degree of difficulty

subjects should expect in lifting the exit plug, which 

may have accounted for the large number of subjects 

who dropped or otherwise mishandled it, resulting in 

delayed egress. Some subjects indicated that the exit 

plug depicted on the safety card appeared to be hinged, 

perhaps explaining why 35% of the subjects in Phase 

I were hit on the head by the plug as they released it from 

the exit frame. Together, these results indicate the strong 

role that information factors played in the outcome of 

the egress trials, workspace considerations aside.

The results obtained by Fennell and Muir (1993) are 

noteworthy with regard to the number and importance 

of factors affecting egress, both in terms of the specifi c 

effects that each factor produced and the interactions 

that resulted from their combination(s). The physical 

evacuation system elements again combined to delimit 

the amount of egress workspace, and the human factors 

effects were once again shown to be larger than could 

be overcome by establishing what appeared to be an 

adequate amount of workspace. These effects were

exacerbated by provision of the incapacitated passenger, 

which produced an ergonomic impediment, especially 

for females. The human factors aspects of egress were

shown to interact significantly with the quality of

information provided to assist egress. The lack of specifi c 

instructions that could have eliminated improper exit 

plug removal and disposal, for example, revealed an 

inattention to experimental detail that allowed the loss 

of a large degree of external control of subject behavior. 

Combined, these factors and their interactions further 

depict a situation, in which each particular egress factor 

has a particular function in establishing an effective 

aircraft evacuation, and indicate that there should not 

be a reliance on one class of evacuation system features 

to overcome deficiencies in another. 

McLean, George, Chittum, and Funkhouser 

(1995, Part I). Building on lessons learned from

the studies described above, McLean et al. (1995, 

Part I) studied the specific effects of differences in 

single-passageway confi guration on evacuations through 

the Type-III exit. Five different passageway widths, 

6”, 10”, 13”, 15”, and 20”, and three different aft 

18
seat-assembly encroachment distances, a 5” minimum, 

a 10” midline, and a 15” maximum, were investigated. 

Two groups of 37 subjects were employed in a 

counterbalanced research design; the first subject 

group ranged from 18 to 40 years of age and subjects 

comprising Group 2 were from 40 to 62 years old. 

Each group of subjects was required to perform 30 

experimental trials (ten on each of three successive 

mornings) after a short learning exercise which consisted 

of two egress trials in which the aft seat assembly had 

been completely removed to allow subjects to “step 

through” the exit opening unimpeded. This exercise was 

allowed in order to reduce the overwhelming human 

factors effects related to egress through the Type-III 

exit shown in all of the previous studies and to provide 

superior identification of the effects of passageway 

configuration, per se. 

Further, a “competitive cooperation” was created 

among subjects to serve as a motivational mechanism 

designed to encourage optimum individual performance. 

This technique was intended to reduce the variability 

associated with individual subject performance and 

improve discrimination of passageway configuration 

effects, and was based on offering a (unspecified) 

monetary bonus to the fastest 3 performers in each 

group. Seating arrangement was counterbalanced to 

provide all subjects an equal opportunity to obtain the 

bonus. One airline flight attendant was stationed at the 

rear of the cabin to urge subjects forward during trials, 

and another was initially seated in the outboard seat 

of the row immediately forward of the exit row. At the 

start of the trial, the forward flight attendant stood up 

and turned around (as if coming to the Type-III exit 

from a primary duty location), and instructed subjects 

(in the manner dictated by her emergency evacuation 

training) to egress quickly. Again, this technique was 

intended to minimize performance variability related to 

subjects’ potential inattention to the task. 

Finally, as the research question was directed toward 

the effects of passageway configuration on exit flowrates 

(and because neither Rasmussen and Chittum (1989) 

nor McLean et al. (1992) had found evidence of 

passageway effects on exit plug removal), a research 

confederate removed the Type-III exit cover from 

outside the aircraft simulator to preclude the possibility 

of that activity confounding the flowrate results. Given 

these experimental controls, and the minimally-variant 

data that resulted, the authors concluded that the results 

should be viewed as a “benchmark” of passageway 

configuration effects. 

Total evacuation times included the first through the 

35th subjects, as the times for the last two subjects in 

each trial were deleted to control for potential changes 

in performance related to their rearward (straggler) 

positions in the evacuation stream. The results obtained 

from each group were remarkably consistent across trials; 

repeated measurement at the end of each experimental 

day, using the 20” passageway with a 5” aft seat 

assembly encroachment as a control, confirmed the 

consistency with which subjects were performing. A 

3-way ANOVA revealed significant main effects of 

subject group (p<.001), passageway width (p<.001), 

and seat encroachment distance (p<.001), with no 

significant interactions between any of the factors. The 

effects were indicative of slowed egress produced by 

advanced age, narrower passageways, and the greatest 

aft seat encroachment distance, and resulted from the 

reduced agility and athleticism of the older subjects, as 

well as the reduction in egress workspace produced by 

the more restrictive passageway configurations. 

Simple effects ANOVA on group evacuation times 

found a significant effect of passageway width for both 

the younger (p<.001) and older (p<.025) groups. Post 

hoc analyses indicated that the 6” and 10” passageway 

widths produced longer evacuation times for the 

younger group, but only the 6” passageway width 

slowed the older group significantly (p<.05). This lack 

of effect at the 10” passageway width for the older 

subject group resulted from an inadvertent change 

in instruction set produced when the forward flight 

attendant unexpectedly began instructing subjects to 

crawl over the seats to egress, eliminating the effects 

of passageway configuration and reducing the time 

required for the group to evacuate. This change in older 

group egress instructions affected the reported results 

for only the 10” passageway configuration. A simple 

effect of encroachment distance was also significant 

for the younger group alone (p<.03), resulting from 

slowed egress at the maximum encroachment distance, 

relative to the other two seat encroachment distances. 

The older group results were essentially identical to 

those of the younger group, except for an approximate 

15-second increase in egress times at all three seat 

encroachment distances. However, the older group 

times were not statistically different, probably because 

of increased variability at the maximum encroachment 

distance. 

The essentially interchangeable character of the results 

from both subject groups suggested that combining the 

raw data from both groups into a single data set could 

19 
fl

provide a more generalizable answer to the research 

question (cf. Loftus, 1993), without violating the

assumptions of the statistical model (see Table 12). This 

approach was then supported by a 2-way repeatedmeasures ANOVA, which revealed a lack of interactions 

between subject group (age) and either passageway 

width (p<.14) or seat encroachment distance (p<.96), 

and which further suggested that any effects of age on 

mean egress performance, as embodied in the data from 

the two broadly-based age groups being studied, were

confined to the main effects. 

This lack of interactivity was reconfirmed by a 2-way 

ANOVA on the combined group data, which showed 

a main effect of passageway width (p<.05), without an 

effect of seat encroachment distance. Post hoc analyses 

indicated that only the 6” passageway width produced 

significantly slowed evacuation times; the slowing

produced by the 10” passageway for the younger subject 

group was rendered non-significant by combining both 

groups’ data, which resulted in a reduced mean egress 

time and an increase in the variability associated with 

the 10” passageway. A similar fate befell the times 

related to seat encroachment distance, which also were

not significantly different. Thus, the combined group 

results had come to resemble the results from other 

studies of passageway configuration effects, where 6” 

single passageway widths were clearly outside the range 

that could support effective egress through the Type-III 

exit, although the exact answer as to whether a 10” 

passageway is acceptable remained in doubt. 

In their discussion of the results, McLean et al. 

(1995, Part I) were careful not to suggest that the 10” 

passageway width might provide appropriate egress 

workspace, given the results from the younger subject 

group alone, which had shown that egress through 10” 

passageways was significantly slower than through the 

wider configurations employed. Citing this latter effect, 

and the change in instruction set for the older subject 

group, the authors concluded that only the 13”, 15”, 

and 20” passageway widths could truly be seen as 

equivalent, since the 10” passageway width data for the 

older group were incomplete. 

Although the experimental design had been

constructed to eliminate many of the human factors 

issues previously associated with studies of egress

through the Type-III exit, another interactive human 

factor was displayed. That factor was one related to the 

“operator” of the system, i.e., the ight attendant who 

was in charge of the evacuation process. The fact that 

the change in egress instructions occurred at only the 10” 

passageway width produced an unexpected interaction, 

the outcome of which was to partially eliminate egress 

slowing produced by a single passageway 10" in width, 

thereby obscuring the actual egress flowrate that would 

otherwise have occurred. Thus, a human factors aspect 

of the evacuation was shown once again to confound the 

ability to discriminate effects of changes to the physical 

evacuation system elements, substantiating a need to 

explore the data further for as much understanding 

as could be achieved. 

McLean and George (1995, Part II). Toward that 

end, McLean and George reexamined the McLean et al. 

(1995, Part I) data, looking specifically at the human 

factors aspects. The unified dataset that resulted from 

the combination of the two Part I subject groups’ data 

contained over 2,000 individual observations, allowing 

recombinations of the data to form more discrete

categories within the general domains of age, weight, 

waist size, and height. These individual subject variables 

were then evaluated for their ability, individually and in 

combination, to affect egress fl owrates. 

A multivariate ANOVA was conducted on these new 

groups of individual subject data, using the individual 

subject egress times for each passageway confi guration 

as the dependent variable. Main effects were found for 

subject age (p<.0001), weight (p<.0004), waist size 

TABLE 12

Group Egress Times At Each Passageway Width

(McLean et al., 1995, Part I)

Subject

Group

Passageway Width

6” 10” 13” 15” 20”

Younger 43.78 / 2.2 42.77 / 2.4 38.03 / 1.8 35.85 / 2.8 36.39 / 2.5

Older 61.65 / 5.6 51.72 / 1.9 49.68 / 1.6 51.06 / 2.0 49.82 / 4.0

Combined 52.72 / 3.9 47.24 / 2.2 43.86 / 1.7 43.46 / 2.4 43.11 / 3.3

Times in seconds = mean / std. dev. n = 37 per age group

20
(p<.00125) and gender (p<.001); older, heavier, and 

larger subjects were found to be significantly slower to 

egress, as were females. There was no effect of subject 

height (p<.3), nor were there any interactions found 

between any of the subject variables and passageway 

configuration. Importantly, the effects of age (pooled in 

10-year subgroups across the entire subject sample age 

range) appeared to be essentially linear (see Table

13), further substantiating that the combining of

Groups 1 and 2 data by McLean et al. (1995, Part I) 

was methodologically appropriate, i.e., there was no 

masking of an interaction that would render younger 

subject egress differentially more or less efficient by the 

circumstance of being in an aircraft evacuation with 

older cohorts. (This point will be revisited below, where 

part of the discussion regarding the effects of egress 

experience will provide a fi nal clarifi cation vis-à-vis 

the ability of the mere presence of older subjects in 

an evacuation to synergistically impede, or facilitate, 

younger subject egress.) A stepwise multiple regression 

analysis revealed that, of the individual subject attributes 

evaluated, age accounted for the largest amount (43%) 

of experimental variance; residual effects were also

shown (in decreasing order of infl uence) for weight/waist 

size (girth), gender, and height. 

As described above, these subject characteristics

produced effects on mean egress effi ciency, without 

interactions with passageway confi guration, although 

mitigation of potential interaction effects could have 

resulted from differential effects of the learning

exercise provided subjects at the beginning of their 

participation. 

Two hypotheses had been advanced with regard

to that possibility. McLean et al. (1995, Part I) had 

suggested that first, the lack of an interaction of

(advanced) age and (narrow) passageway confi guration 

might result from the “skill practice” that egress

experience provided, or second, that enhanced

knowledge about egress contingencies would allow

older subjects to develop better strategies that could 

overcome age-related decrements in agility. The answer 

to which, if either, of these hypotheses would be correct 

was found in the confi guration-specifi c evacuation

results, after egress time difference scores were derived 

from successive egress trials at a particular passageway 

configuration. These difference scores were subjected to 

a 2-way (age x passageway width) ANOVA that showed 

an age x passageway width x egress trial interaction 

effect (p<.002) on egress, resulting from slowed egress 

at narrow passageway widths on the fi rst trial for older 

subjects. This was the first indication that there was 

a synergistic effect on egress efficiency produced by

combining advanced age (50-62 years old) with narrow

passageway widths. Simple effects analysis on data

from Trial 1 for subjects in each decade of age found 

main effects of age (p<.001) and passageway width 

(p<.001), and an age x passageway width interaction 

effect (p<.02); a main effect of age (p<.001) was the only 

significant effect found for Trial 2 scores. 

The mean scores for each decade of subject age 

showed that, many trials after generalized skill at using 

the Type-III exit was well established, older subjects 

were still relatively slower on the first trial using the 

6” and 10” passageways (see Table 14). This reduction 

in egress efficiency was eliminated on the very next 

(second) egress trial (conducted in all instances with 

the same passageway configuration as on the fi rst trial), 

indicating that older subjects had discovered some 

evacuation contingency on the first trial by which they 

were able to guide their egress performance on the 

second trial, eliminating the age-related increase in 

egress time. This ability of older subjects to “correct” 

their performances on the second trial allowed them to 

appear no more differentially compromised, on average, 

than their younger counterparts, whose superior agility 

provided equivalent egress efficacy on both the fi rst and 

second trials for all passageway confi gurations. Thus, 

older subjects were displaying strategic learning effects 

related to specific egress experience, not just ongoing 

improvements in motor skill. 

TABLE 13

Mean Individual Egress Times For Each Age Group

McLean and George (1995, Part II)

Age Groups

18-29 30-39 40-49 50-59 60-62

Egress Times 0.98 / 0.34 1.15 / 0.39 1.37 / 0.54 1.58 / 0.72 1.98 / 0.88

Times in seconds = mean / std. dev. n = 37 per age group

21 
fi

TABLE 14

Individual Mean Times By Trial And Difference Scores

For Each Age Group At Each Passageway Width

McLean and George (1995, Part II)

Pooled

Ages

6” Trials 10” Trials 13” Trials 15” Trials 20” Trials

1 2 D 1 2 D 1 2 D 1 2 D 1 2 D

18-29 0.99 0.96 0.03 1.03 0.95 0.08 0.88 0.87 0.01 0.94 0.97 -0.03 1.15 1.09 0.06

30-39 1.39 1.07 0.32 1.30 1.27 0.03 1.04 1.04 0.00 0.97 0.95 0.02 1.11 1.11 0.00

40-49 1.33 1.42 -0.09 1.37 1.37 0.00 1.46 1.32 0.14 1.46 1.48 -0.02 1.56 1.46 0.10

50-59 2.66 1.33 1.33 2.62 1.60 1.02 1.22 1.08 0.14 1.36 1.54 -0.18 1.35 1.35 0.00

60-62 2.59 1.71 0.88 2.48 1.86 0.62 1.82 1.72 0.10 2.03 2.07 -0.04 1.91 2.13 -0.22

Mean 1.79 1.30 0.49 1.76 1.41 0.35 1.28 1.21 0.07 1.35 1.40 -0.05 1.42 1.43 -0.01

Times in seconds D = Difference between trial 1 and trial 2 egress times.

These difference score effects were replicated for seat 

encroachment distance, with the age x encroachment 

distance x egress trial interaction effect again being 

signifi cant (p<.002), as were the simple effects of

age (p<.001) and an interaction effect of age and

encroachment distance (p<.002) on trial 1 scores, with 

only a main effect of age (p<.001) found for trial 2

scores. The mean scores for each decade of age showed 

that performance for the older subjects was again

significantly slower at the midline and maximum seat 

encroachment distances, relative to the minimum

encroachment distance, although the times for the 

midline seat encroachment distance were heavily

confounded by the 10” passageway width (midline 

seat encroachment) condition. Combined, the results 

indicate that there are definite limits to the range of 

passageway widths and seat encroachment distances 

that can support fast, effective egress; these limits were

shown more clearly to exclude the 10” single passageway 

configuration between triple-seat assemblies, as well as 

seat encroachment distances beyond the Type-III exit 

midline, even for larger passageway widths.

Similar analyses were conducted on all of the other 

subject attributes in combination with passageway

width and seat encroachment distance. No other

systematic effects were found. 

Returning to the question of mixing the data from 

the 2 subject groups, it is instructive that the age 

x passageway confi guration interaction effects were

limited to subjects 50 years of age and older, i.e., those 

in Group 2, which also contained 40- to 49- year old 

subjects, who performed like their 18- to 40- year old 

counterparts in Group 1. This lack of a synergistic 

effect among these Group 2 age subgroups is the

nal component in the rationalization of combining 

data from Groups 1 and 2, as any interaction effects 

produced by including subjects of mixed (older) age 

should have been seen on the 40 to 49 year old Group 

2 subjects, but were not. Thus, the original decision 

to combine the data has been fully justified by three 

coalescing lines of evidence, and has allowed the

discovery of both the age by passageway confi guration 

interaction effect and the manner by which the older 

subjects were able to benefit from egress experience to 

overcome the effects of this interaction. As a result, the 

ability of experience to overcome the human factors 

influences on evacuation performance can be seen

both as allowing illumination of the pure effects of 

passageway configuration and providing a treatment 

that holds promise for studying other egress factors that 

are affected by the instability in performance associated 

with multiple egress trials (experience). 

Muir (1996). In 1996, Muir reported the results 

of another follow-on study to the Muir et al. (1989) 

work. Recall that in the earlier 1989 study, the authors 

had investigated the effects on egress of fi ve different 

single-passageway widths: 3”, 13”, 18”, 25”, and 34”, 

as well as the 6” OBR dual passageway confi guration, 

conducting trials in both competitive and noncompetitive subject motivation conditions. Subjects 

ranged in age from 20 to 50 years. In 1989, competitive 

subjects had completed four evacuations each, two 

through one of several aperture sizes between bulkheads 

and two through one of the passageway widths leading 

to a Type-III exit. In the Muir (1996) study, similar 

subjects performed four evacuations in the competitive 

22
motivation condition. However, one of the evacuations 

was performed through a single bulkhead aperture of 

28” and the other three evacuations were performed 

through 6” or 10” single passageway confi gurations 

(either one or two at each width, depending on the 

specific subject group). The results were compared with 

those of the 1989 study.

Cumulative egress times for the fi rst 30 subjects were

compared. ANOVA revealed a significant main effect 

of passageway configuration (p<.0001), resulting from 

reduced flowrates at narrower passageway widths. Not 

including the trials with blockages at 6” and 10”

passageways, comparison of individual means showed 

that the 3” and 6” single passageway confi gurations 

were responsible for the overall main effect; the 10” 

passageway produced egress times not signifi cantly

different from the 13”, 18”, 25”, and 34” singlepassageway widths, or the 6” OBR passageway. If

anything, the 10” passageway configuration appeared to 

give slightly faster egress (see Table 15), notwithstanding 

the trial at 10” that resulted in a blockage. 

These results again appear to suggest that 10”

passageways provide egress equivalent to that resulting 

from 13” through 25” passageways. However, differences 

in the research design between the Muir et al. (1989) 

and Muir (1996) studies, as well as the difference in 

subject age range between the Muir et al. (1989, 1996) 

studies and the study of McLean et al. (1995, Parts I & 

II), indicate that this is likely not the case. The design 

differences relate to the variably-practiced nature of 

the subjects employed by Muir et al. (1989) and Muir 

(1996), as subjects completed two Type-III exit egress 

trials in the competitive phase of the 1989 study and 

three total (one or two at each width) Type-III exit 

egress trials in the 1996 study. As demonstrated above, 

naïve subjects do not perform as effi ciently as do

well-practiced subjects, and subjects do not gain nearly 

as much benefit from only one (practice) egress trial, 

e.g., Muir et al. (1989), as they do from two (practice) 

trials, e.g., McLean et al. (1995, Parts I & II). This 

situation skews the results from trials after practice 

progressively to the left, i.e., mean results that include 

three or more trials will show faster egress, as a rule, than 

mean results from one or two trials. This subtle learning 

effect could otherwise be misconstrued (as in the 1996 

study) as indicating that 10” single passageways are 

just as effective in supporting evacuations as are larger 

passageway confi gurations. When taken together with 

the findings by McLean and George (1995, Part II), 

regarding evacuation performance of subjects over 50 

years of age (considering the more restricted subject 

age range in the Muir et al. 1989, 1990, 1992, & 1996 

studies) this confounded finding provides little reason 

to conclude that the 10” passageway confi guration 

provides adequate egress.

McLean, Corbett, and George (1999). A 1999 

presentation by McLean et al. described the effects on 

aircraft evacuations of passenger density in the aircraft 

cabin and passenger management strategy, vis-à-vis 

initial flight attendant duty station relative to moving to 

TABLE 15

Cumulative Evacuation Times For the

First 30 Competitive Subjects to Evacuate

(Muir, 1996)

Passageway

Configuration

Trial

Means

Standard

Deviations

3” 71.48* 15.04

6” 70.10* 16.18

10” 52.22 11.09

13” 55.92 10.38

18” 53.75 8.27

25” 54.90 11.54

34” 62.32 8.14

6” OBR 53.29 10.06

Times in seconds * = significant (p<.05)

23 
the Type-III exit and conducting evacuations. For this 

study, a single-passageway configuration was established 

by positioning the seat assembly forward of the exit row 

as far rearward as possible, with the aft seat assembly 

positioned to create a 13” passageway width. Passenger 

density was set at either 30 or 50 subjects per group, 

and the flight attendant was positioned at one of three 

initial duty locations, either outboard in the seat row 

forward of the exit row, seated outboard in the exit 

row, or in the aft of the cabin. Two of the three duty 

locations were essentially identical for both lowand high-density conditions; the third location was 

different for each density condition and allowed a 

within-subjects examination of particular passenger 

management strategies. An additional passenger 

management condition was established by the absence 

of an active flight attendant. Five egress trials were 

conducted for each of six groups in each density 

condition; trials one and five were pre/post flight 

attendant-absent trials, with the counterbalanced 

flight attendant (present) duty locations nested in 

Trials 2, 3, and 4. 

Cumulative group evacuation times were calculated 

on the fifth through thirtieth subject for the flight 

attendant duty locations common to both density 

conditions. The low-density trials averaged 5.08 seconds 

for five subjects to egress, accumulating to 37.04 seconds 

for thirty subjects. The high-density trials averaged 9.14

to 46.09 seconds for five to thirty subjects, respectively, 

confirming the expected hyper-additive increase in 

egress times associated with higher passenger density. 

A 2-way repeated-measures ANOVA was employed 

to evaluate the effects on individual egress times 

of passenger management and passenger density. 

Significant main effects were shown for both passenger 

management (p<.001) and passenger density (p<.002), 

and a management by density interaction effect 

(p<.001). These effects resulted from the increase 

in evacuation efficiency produced by the presence 

of a flight attendant, especially in the high-density 

condition, which otherwise produced significantly 

slower evacuations (see Table 16). 

Each passenger density condition was then examined 

individually for the effects on egress of specific flight 

attendant duty location, none of which was shown 

as superior in either the low- (p<.9) or high- (p<.15) 

density condition. Similarly, comparison of the two 

flight attendant duty locations common to both 

density conditions showed that passenger density and 

flight attendant duty location produced no significant 

interactions (p<.2). 

These results bear directly on the question of whether 

the 13” passageway configuration provides adequate 

access-to-egress, and address the issue of flight attendant 

(operator) effects on evacuations through a Type-III 

exit. The mean times per subject to egress in the low 

passenger density condition, both with and without a 

flight attendant present, were in the average range of 

egress times found in previous non-competitive studies, 

i.e., within the range of mean individual egress times 

seen with intermediate passageway configurations. 

The high-density egress times attained with a flight 

attendant present were also in this range, although the 

high-density egress times without a flight attendant 

present resembled those from competitive evacuation 

trials, as well as trials conducted with smoke in the 

cabin. This combination of effects suggests that subject 

(in)attention to performing the task, particularly with 

regard to the organizing function provided by the 

flight attendant, was the responsible mechanism for 

the passenger management effects seen. It also suggests 

that the passenger density effects can be explained 

by variable inattention to the task, with less-involved 

passengers producing relative increases in egress 

time above that required to merely traverse the exit 

opening. This single construct is the most parsimonious 

explanation for the effects of both passenger management 

and passenger density, as well as the interaction between 

them. As such, the degree to which flight attendants 

facilitated evacuations in the other studies reviewed 

TABLE 16 

Passenger Management (Flight Attendant)

Effects on Mean Egress Times

(McLean et al., 1999)

Density Present Absent

Low 1.44 1.53

High 1.52 1.80

Times in seconds

24
herein should be a partial predictor of the reliability of the 

results obtained in those studies, especially where other 

treatments, such as changes to passageway confi guration, 

rely on comparisons of subject performance to

discriminate among alternatives. 

McLean and Corbett (2000). McLean and Corbett 

evaluated the data from the McLean et al. (1999) study 

for effects on egress of individual subject attributes. 

Main effects of age (p<.001), weight (p<.001), and 

gender (p<.001) were found for both the low- and 

high-density conditions, but there were no interactions 

between any of the subject variables and either passenger 

density or passenger management (the presence or 

absence of a flight attendant at the Type-III exit). These 

effects generally replicate those found by McLean 

and George (1995, Part II), regarding the impact of 

passengers’ physical attributes on evacuations; i.e., 

older and heavier passengers generally egress more 

slowly, as do females. The lack of interactions

attests again to the generally linear character of the 

evacuation system. 

DISCUSSION 

The central theme evidenced throughout the

experimental Type-III exit evacuation literature to

date is the overwhelming domination of evacuation 

performance by human factors and ergonomics effects. 

Differences in individual subject attributes and behavior, 

especially errant behavior unrelated to the research 

questions at hand, have often influenced the fi ndings 

to obscure identification of the intricacies related to the 

issue being addressed. This circumstance is particularly 

acute in relation to the passageway confi guration issue, 

where the large variability in the available data from 

almost all the studies previously conducted has resulted 

in a variety of suggested effects, many of which remain 

unsubstantiated. Beginning with Rasmussen and

Chittum (1989), naïve subjects performed equivalently 

using both the 6” and 20” single-passageway widths 

between triple seat assemblies; specific effects of

passageway configuration became more evident as

subjects became more experienced. Similarly, the 10”

single-passageway width between triple seat assemblies 

has been found almost universally to provide evacuation performance statistically comparable to larger

single-passageway configurations, although the small 

differences in flowrates between the 10” passageway 

width and larger dimensions in those studies have

spawned a array of negative assessments and attendant 

rationalizations designed to deny its acceptability. For 

example, Rasmussen and Chittum (1989) reported 

potentially negative effects on exit plug placement, and 

McLean et al. (1992) described reduced ergonomic 

workspace relative to larger passageway confi gurations. 

Importantly, actual differences in egress performance 

related to the 10” single passageway confi guration

were found to be significant in the study by McLean 

et al. (1995, Parts I & II). This ability to delimit 

the 10” single passageway effects resulted from better 

experimental controls that reduced the variability

in individual subject performance, allowing further 

clarification of passageway configuration effects, per se. 

Without gaining that degree of experimental control, 

the human factors effects would likely have continued 

to obscure the fact that a 10” single passageway

between triple seat assemblies is actually too narrow to 

provide egress capability equivalent to the intermediate 

passageway widths (13” through 25”) studied to date. 

In addition to highly-variable behavior by research 

subjects, the reason that such human factors effects have 

influenced the results so much is that no matter what 

the experimental question, the general rule has been 

to use minimal latin square (type) research designs, 

comprised of only a few egress trials per group and/or 

only a few groups per treatment level, resulting in 

data that are largely confounded by individual subject 

variability and the effects of practice. Problems related to 

these incomplete designs have often been compounded 

further by comparisons of the data thusly obtained 

with other data acquired using similar methodologies, 

which have, unfortunately, also generally suffered

from the same types of defi ciencies. An example is 

the comparison of data acquired using different egress 

practice regimes, which led to a misinterpretation

with respect to the acceptability of the 10” passageway 

confi guration. Fortunately, however, the general trend 

in these studies has been to advance the position that 

only larger intermediate passageway widths provide 

essentially equivalent egress capability. 

The design of McLean et al. (1995, Parts I &

II) was able to discriminate more clearly between

passageway confi gurations, identifying the appropriate 

range of physical limits that, combined, would

provide appropriate ergonomic workspace. This design 

employed well-practiced subjects to reduce individual 

performance variability, use of a minimal motivation 

technique intended to keep the subjects “involved” in 

the task at hand, and employment of a fl ight attendant 

to encourage subjects and further keep them on task. 

25
This study was the first to “benchmark” the effects 

of passageway confi guration, per se, substantiating

only the intermediate range of single-passageway

configurations as equivalent for a broader, more general 

passenger population. 

The problems with using minimal research designs 

have also been compounded by the tendency in some 

studies to introduce extraneous egress factors into the 

experimental process and then address the obtained 

results to the issue of passageway confi guration. For 

example, much has been made of the inability of

subjects to appropriately remove and dispose of the 

Type-III exit plug, as if the passageway confi guration 

was responsible. The data acquired to date generally 

show that this is not the case, although in the one 

instance where a small, differential effect on exit plug 

operation was found, information and user factors were

more responsible for the effects seen. The safety briefi ng 

card and seatback placards were available to aid subject 

performance, but they were apparently not used to gain 

the relevant information. Nor were verbal briefi ngs 

given. Nonetheless, the results related to the exit plug 

removal and disposal in that study were addressed to 

the passageway configuration issue, leading to a general 

expectation that increasing the passageway width would 

alleviate the lack of applied information. 

In fact, none of the studies has made sure that 

subjects who were responsible for performing exit plug 

removal and disposal were demonstrably aware of the 

proper procedure before the egress trials began. Where 

problems arose and the passageway confi guration was 

implicated by the study authors, there was no indication 

provided as to how wider passageways would improve 

the situation. Similarly, the negative impact on exit 

plug removal and disposal produced by placing an 

incapacitated passenger (dummy) in the seat next

to the exit has been seen as indicating a need for 

wider passageways, but more importantly, the size and 

strength of the subjects who operated the exit were

largely responsible for the results, as very small females 

were unable to perform the task. While the inclusion 

of such factors in the research designs provided

important information relative to egress and the

possible interactions of such factors in evacuations, 

ameliorative actions other than maximizing passageway 

width could reasonably be expected to provide much 

better outcomes regarding the effects of these negative 

factors. It cannot be that maximizing passageway

configuration is the solution for every potential

evacuation-related problem. 

The effects of passageway configuration have been 

shown to relate specifically to the construct of “personal 

ergonomic workspace” needed to egress effectively and 

efficiently. Passageway width and aft seat-assembly

encroachment into the area of the exit opening are generally 

responsible for delimiting this workspace, although the 

use of multiple exits and passageways can distribute the 

workspace to facilitate egress. This holds true even though 

multiple passageways may be narrower and less effi cient, 

individually, than would be the case for a larger single 

exit/passageway configuration. This occurs because the 

rate at which the exit is being fed evacuees is cumulatively 

higher, allowing more passengers to egress per unit of time. 

Other interactive factors, such as smoke in the cabin and 

high passenger motivation, have been shown to offset this 

facilitation, somewhat, but the positive effects of multiple 

passageways remain, as long as the exit continues to

be available and the number of passengers ready to

egress exceeds that which a single passageway would

accommodate.

In sum, the factors that control evacuations through a 

Type-III overwing exit are many. Passageway confi guration 

provides only one of the important contributions, its 

effects as a physical subsystem element being to delimit 

the egress workspace. As long as the egress workspace is 

adequate, passageway configuration may be said to be 

acceptable as well. Information subsystem elements such 

as safety briefing cards, placards, and personal passenger 

briefings are also important contributors, since “knowing 

what to do” has been shown to be more important than 

having an optimum space in which to do it. Without 

knowledge about the airplane evacuation system and its 

function, fast effective evacuations rarely seem to be the 

rule. This outcome is readily apparent in the positive 

effects produced by egress experience, the lack of which 

institutes variable, often errant, passenger behavior as the 

norm. The Type-III exit operator subsystem includes both 

the fl ight attendants, where available, and (especially) the 

passengers, who have been shown to open the exit and 

dispose of the exit plug in a variety of ways, both intended 

and not. This propensity for exit operation to exemplify 

idiosyncratic functional approaches further indicates the 

degree to which knowledge about the evacuation system is 

crucial. The evacuation user subsystem is also comprised 

of the passengers who, through virtue of their personal 

attributes, knowledge, and behavior, contribute the largest 

amount to the success or failure in an evacuation, especially 

through the Type-III exit. As has been recognized,

performance effects related to the passengers can obscure 

identification of the contributions of the other evacuation 

26 
system elements, in essence rendering insignificant the 

exact nature and specification of those elements. Such is the 

situation regarding passageway configuration. 

Interactions among these subsystems and elements, 

where found, have been shown to be generally linear, once 

again being more related to the degree to which human 

factors effects are evidenced. Without the need to account 

for such effects, an evacuation system could be designed to 

function flawlessly. However, the fact that humans must 

use the system engenders the need to fine tune each and 

every evacuation subsystem and element to maximize total 

system proficiency and linearity. This is the reason that 

multiple FARs have been established, addressing the range 

of evacuation system elements, rather than legislating a 

single class of evacuation system elements/functions to 

address the spectrum of contingencies that passengers 

and crewmembers will encounter in evacuations. Where 

deficiencies are identified with regard to specific evacuation 

subsystems and elements, these need to be addressed. 

However, they need to be addressed in a way that will 

solve the specific deficiency identified, not just strive to 

compensate for it with supplementary performance 

by another subsystem or element. Thus, if physical 

subsystem elements provide inappropriate egress workspace, 

modify them; if information subsystem elements are 

not informative and useful, perfect them; and if the 

operator/user subsystem elements are not effective or 

efficient, instruct them. Only through this type of balanced 

approach will the success of airplane emergency evacuations 

be better guaranteed. 

CONCLUSIONS AND REGULATORY 

APPLICATIONS 

• Human factors effects predominate in controlling 

evacuation performance and obscure the effects of other 

evacuation factors. Controlling human factors (and other 

confounding) effects is necessary to clarify the effects of 

other factors, such as passageway configuration. 

• Forward encroachment of the exit row aft seat 

assembly to the midline of the exit gives better egress 

flowrates, although lesser seat encroachment distances 

are acceptable. 

•Passageways between 13” and 25” provide essentially 

equivalent egress flowrates, whereas those with greater 

or narrower (especially for older passengers) widths 

are less effective. 

• Blockages of the Type-III exit by subjects during 

competitive evacuation trials is related more to the 

attitudes and motivation levels of individual subjects, 

not passageway configuration, as blockages or extremely 

delayed evacuations have occurred at almost all studied 

passageway widths. 

• Exit plug removal and disposal is affected little by 

passageway configuration, although the placement of the 

plug after removal has been shown to be variable, resulting 

from poor instruction about what to do with it. Exit 

designs that include automatic disposal, and/or better 

instructions for passengers who must open exits, could 

alleviate this problem. 

• Information materials, such as safety briefing cards, 

related to emergency evacuation activities have been 

poorly rendered, as passengers either cannot understand 

the intent of the materials or do not seem obliged to read 

and follow the instructions. 

• Provision of a flight attendant can organize passenger 

behavior during both actual and experimental evacuations, 

without producing idiosyncratic effects or interactions 

that necessarily render the results of evacuation studies 

inapplicable to rulemaking. 

• Interactions between evacuation system elements 

(physical, information, operator, and user) are generally 

linear and physically circumscribed to the area of the 

exit opening. 

•There should be no reliance on one class of evacuation 

system elements (physical, information, etc.) to overcome 

deficiencies in another. Regulatory strategies adhere to this 

principle by having multiple rules related to both single 

and multiple evacuation factors. These include rules on 

exit size and passenger ratings, exit distribution, descent 

assisting means, emergency lighting, safety briefing cards, 

signs, placards, emergency procedures, and crew emergency 

training, to name a few. 

REFERENCES 

ARAC Performance Standards Working Group, 

Performance-Based Rulemaking for Transport 

Category Airplanes : A Systems Approach, 

Washington, DC, July 1998. 

Code of Federal Regulations, Title 14, Aeronautics 

and Space, Vol. 1, US Govt Printing Office, 

Washington, DC, January 1, 2000. 

Crane, CR, Human Tolerance Limit To Elevated 

Temperature : An Empirical Approach To 

The Dynamics Of Acute Thermal Collapse, 

Memorandum Report No. AAC-114-78-2, FAA 

Civil Aeromedical Institute, Oklahoma City, 

OK, May 1978. 

27
Fennell, PJ and HC Muir, The Influence Of Hatch 

Weight And Seating Configuration On The 

Operation Of A Type III Hatch, CAA Paper 

93015, Civil Aviation Authority, UK (1993). 

Garner, JD and JG Blethrow, Emergency Evacuation 

Tests Of A Crashed L-1649, Office of Aviation 

Medicine Report, AM 66-42, Washington, DC, 

August 1966. 

Hasbrook, AH, JD Garner, & CC Snow, Evacuation 

Pattern Analysis Of A Survivable Commercial 

Aircraft Crash, Office of Aviation Medicine 

Report, AM 62-7, Washington, DC, 1962. 

Loftus, GR, A Picture Is Worth A Thousand p Values: 

On The Irrelevance Of Hypothesis Testing In 

The Microcomputer Age, Behavior Research 

Methods, Instruments, and Computers, 25 (2), 

250-256, 1993. 

McLean, GA, EA Higgins, PJ Lyne and JHB Vant, 

The Effects Of Wearing Passenger Protective 

Breathing Equipment On Evacuation Times 

Through Type-III and Type-IV Emergency 

Exits in Clear Air and Smoke, Office of Aviation Medicine Report, DOT/FAA/AM-89/12, 

Washington, DC, November 1989. 

McLean, GA, CB Chittum, GE Funkhouser, GW 

Fairlie, and EW Folk, Effects of Seating 

Configuration And Number Of Type III Exits 

On Emergency Aircraft Evacuation, Office of 

Aviation Medicine Report, DOT/ FAA/AM92/27, Washington, DC, August 1992. 

McLean, GA, MH George, CB Chittum & GE 

Funkhouser, Aircraft Evacuations Through 

Type-III Exits I: Effects of Seat Placement At 

The Exit, Office of Aviation Medicine Report, 

DOT/FAA/AM-95/22, Washington, DC, July 

1995. 

McLean, GA and MH George, Aircraft Evacuations 

Through Type-III Exits II: Effects Of Individual 

Subject Differences, Office of Aviation Medicine 

Report, DOT/FAA/AM-95/25, Washington, 

DC, August 1995. 

McLean, GA, CL Corbett and MH George, Passenger 

Management Strategies For Emergency Egress 

Through Airliner Overwing Exits, Presented 

at the Aerospace Medical Association Annual 

Scientific Meeting, Detroit, MI, May 1999. 

McLean, GA and CL Corbett, Effects Of Individual 

Subject Differences On Egress In Simulated 

Aircraft Emergency Evacuations, Presented at the 

Aerospace Medical Association Annual Scientific 

Meeting, Houston, TX, May 2000. 

Mohler, SR, JJ Swearingen, EB McFadden, & JD 

Garner, Human Factors Of Emergency Evacuations, Office of Aviation Medicine Report, AM 

65-7, Washington, DC, 1965. 

Muir, H, The Effect On Aircraft Evacuations Of 

Changes To The Vertical Projections Between 

The Seat Rows Adjacent To The Overwing Exit 

From 3” to 6”, 10” and 13”, Cranfield University, 

CoA Report No. 9408, 1996. 

Muir, H, C Marrison, & A Evans, Aircraft Evacuations: 

The Effect Of Passenger Motivation And Cabin 

Configuration Adjacent To The Exit, Civil 

Aviation Authority UK, CAA Paper 89019, 

November 1989. 

Muir, H, C Marrison, & A Evans, Aircraft Evacuations: 

Preliminary Investigations Of The Effect Of 

Non-Toxic Smoke And Cabin Configuration 

Adjacent To The Exit, Civil Aviation Authority 

UK, CAA Paper 90013, 1990. 

Muir, H, D Bottomley , & J Hall, Aircraft Evacuations: 

Competitive Evacuations In Conditions Of 

Non-Toxic Smoke, Civil Aviation Authority UK, 

CAA Paper 92005, March 1992. 

Perrow, C, Normal Accidents: Living With HighRisk Technologies, Basic Books, New York, 

NY, 1999. 

Rasmussen, PG and CB Chittum, The Influence 

Of Adjacent Seating Configurations On Egress 

Through A Type III Emergency Exit, Office of 

Aviation Medicine Report, DOT/FAA/AM-89/14, 

Washington, DC, (1989). 

Snedecor, G.W. and WG Cochran, Statistical Methods, 

The Iowa State University Press, Ames, Iowa, 

1967. 

Walpole, R.E. and RH Myers, Probability And Statistics 

For Engineers And Scientists, The MacMillan 

Company, New York, 1972. 

282