DOT/FAA/AM-95/4

Office of Aviation Medicine

Washington, D.C. 20591

IDhe Role of Flight Pf

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r©gires§ straps

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Accesion For

NTIS CRA&I

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Unannounced

Justification

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Availability Codes

Oist

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Avail and /or

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Mark B. Edwards

Dana K. Fuller

O.U. Vortac

University of Oklahoma

Cognitive Processes Laboratory

Norman, Oklahoma 73019

Carol A. Manning

Civil Aeromedical Institute

Federal Aviation Administration

Oklahoma City, Oklahoma 73125

January 1995

DTIC

,ELECTE

MAR 0 3 1995

G

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 19950227 09
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 or use thereof.
1. Report No.

DOT/FAA/AM-95/4

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

4. Title and Subtitle

The Role of Flight Progress Strips in En Route Air Traffic

Control: A Time-Series Analysis

5. Report Date

January 1995

6. Performing Organization Code

7. Author(s)

M.B. Edwards1, D.K. Fuller, O.U. Vortac2; and CA. Manning^

8. Performing Organization Report No.

9. Performing Organization Name and Address

Cognitive Processes Laboratory

University of Oklahoma

Norman, Oklahoma 73019

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

12. Sponsoring Agency name and Address

Office of Aviation Medicine

Federal Aviation Administration

800 Independence Ave., S.W.

Washington, DC 20591

13. Type of Report and Period Covered

14. Sponsoring Agency Code

15. Supplemental Notes

*Now a member of U.S. WEST Technologies' Common Applications Development/Human Factors

Engineering Groups, 1475 Lawrence, Suite 304, Denver, CO 80202. ^O.U. Vortac represents the

collaborative research efforts of F.T. Durso, S.D. Gronlund, and S. Lewandowsky, University of Oklahom

Department of Psychology, 455 W. Lindsey, Norman, OK 73019. ^Human Resources Research Division,

FAA Civil Aeromedical Institute.

16. Abstract

Paper flight progress strips (FPSs) are currently used in the United States en route air traffic control

system to document flight information. Impending automation will replace these paper strips with

electronic flight data entries. In this observational study, control actions, communication events, and

computer interactions were recorded and analyzed using time-series regression models. Regression mode

were developed to predict FPS activities (Writing, Manipulating, Looking) at different levels of traffic

complexity, for individuals and teams of air traffic controllers. Results indicated that writing was well

predicted by a common, simple time-series equation. The ability to predict FPS manipulations was

modest, but prediction of looking at FPSs was poor. Overall, these data indicate that (1) flight strip

activities were similar for individuals and for the data-side controllers in the team (whose primary

responsibility is the strips), and (2) flight strip activity for teams was predictable from the radar-side

controller's actions, but not the data-side controller's actions.

17. Keywords

Air Traffic Control

Flight Progress Strips

ATC Automation

Human Factors

Training

18. Distribution Statement

Document is available to the public

through the National Technical

Information Service, Springfield,

Virginia, 22161

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

14

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
THE ROLE OF FLIGHT PROGRESS STRIPS IN EN ROUTE AIR TRAFFIC CONTROL:

A TIME-SERIES ANALYSIS

In the United States, there are 21 en route air traffic

control centers operated by the Federal Aviation Administration, primarily responsible for the safe and

efficient flight of high-speed, high-altitude aircraft

between takeoffand landing. The airspace assigned to

an en route center is divided into multiple sectors,

each handled my an individual controller or by a team

oftwo controllers1: The radar-side (R-side) controller

is primarily responsible for observing the radar screen

and communicating with pilots; the data-side (Dside) controller, seated next to the R-side, assumes

primary responsibility for preplanning and updating

of flight information. Although this general rule is

true for most facilities, there are situations in which

the responsibilities ofthe D-side controller are changed

due to R-side requests.

Anticipated automation, to be implemented in the

1990s, will drastically affect D-side responsibilities.

The first stage ofthe automation is the Initial Sector

Suite System (ISSS). The implementation ofISSS will

significantly change the display of, and interaction

The FPS is a rectangular piece of paper that contains detailed flight information based on the projected altitudes, routes, and arrivaltimes submitted by

the pilot (see Figure 1). The FPSs are mounted in a bay

of plastic holders next to the radar display. As an

aircraft enters a controller's sector, its corresponding

FPS is moved from the "suspense" bay into the "active" bay, which contains the FPSs ofall aircraft in the

sector. As the flight moves through the sector, the FPS

is continually updated by writing on it, sequencing it

among the other strips, or it is used as a memory aid

by offsetting ("cocking") it from the other strips.

Besides providing a legal record of the flight, the

updated flight strip may also supply information and

decision support for the controller.

Because of the important role of FPSs, several

investigators have voiced concern regarding their conversion to an electronic format. For example, the

active manipulation ofthe strip or deciding where to

insert a strip when moving it from the active to

suspense bay may force the integration of the strip

SNL 1440 240 TUL PHX ./. SNL SHAWN1 TUL

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B727/A

T410 G495

030

1427

1

Figure 1. Example of a flight progress strip.

with, flightinformation (Ammerman & Jones, 1988).

Flight information is currently displayed on paper

flight progress strips (FPSs) that enable controllers to

update and manipulate flight information manually;

under ISSS, flight information will be displayed on a

computerscreen as electronic flight data entries (FDEs)

that will require controllers to interact with flight

information using a keyboard and trackball.

into the existing situation, thereby serving as a memory

aid (Hopkin, 1988). The organization ofstrips within

the bay may also be informative about the scheduling

of work tasks (Shapiro, Hughes, Randall, & Harper,

1991), thus providing an indication of impending

traffic loads. Once the strips have been moved into the

active bay, they may be manipulated and sequenced

among the other strips. Attention can be drawn to a

1

In high traffic areas it is possible that more than two controllers will be responsible for a single sector.
The Role ofFlight Progress Strips

strip by offsetting it from the others by lifting it

slightly offthe board and shirting itto the left or right.

This activitymayhighlight an aircraftso that a planned

control action will not be forgotten, thereby serving as

extensions ofthe controller's memory (Jackson, 1989).

In addition, repeated marking on the strips provides

a historical record ofthe flight that may be beneficial

(Hopkin, 1991; Weston, 1983) and this information

will likely not be preserved in ISSS.

On the other hand, because flight strip management is clearly a time-consuming activity, the time

spent maintaining the strips may be accompanied by

costs as well as benefits. Casual reports from several

controllers indicate that they do not need FPSs to

safely control air traffic. They feel that the only tool

necessary for air traffic control is the radar, and that

any time spent away from the radar is time spent away

from their primary task.

With the implementation ofISSS, the FPS bay will

be replaced by a colored flight data display that allows

computer-controlled manipulation ofFDEs. ISSS has

the capability to place FDEs into the suspense and

active areas automatically, based on computer controlled hand-offs between sectors, and to automatically update flight information. Furthermore, unlike

the current strip bay, the flight data display is not

likely to display all pending flights and may not

provide a visible history of aircraft data (e.g., speed

and altitude). Only the most recent value may be

stored, leaving previous values to be accessed by keyboard and/or trackball. Either of these changes may

interfere with the controllers' memory for the airspace. As these changes imply, the flight data display

provides a smaller workspace for the FDEs. If the

number of FDEs exceeds screen capacity, constant

scrolling may be required to examine the remaining

FDEs. In sum, automation will force the controller to

interact less directly and, perhaps less often, with the

flight data.

Should interaction with FPSs be automated?

The goal ofthe current paper is to provide empirical data addressing the implications of FPS automation before it takes place. The logic of the current

approach can be found in Vortac (1993) and Vortac,

Edwards, Fuller, and Manning (1993). They recommended that automation oftask components is likely

to be successful ifthe task components can be segregated, that is, if they can be conducted in isolation

from the rest ofthe system. Specifying which activities

follow from others may reveal activities that controllers tend to segregate. If flight strip activity can be

segregated, itis possible that automation will facilitate

task and cognitive performance. On the other hand, if

flight strip activity is inextricably intertwined with

other controller functions, automation will probably

not enhance performance.

This article reports a time-series analysis based on

an observational study (Vortac, Edwards,Jones, Manning & Rotter, 1993) in which the behaviors of

individuals and teams of controllers were categorized

"on-line" while controlling simulated air traffic of

high and low complexity2. The behavioral categories

covered the range ofactivities that controllers perform

on the strips: looking at them, writing on them, and

manipulating them. Communication events and computer entries likely to be related to flight strip activity

were also recorded. Time-series models were developed to predict flight strip activity from communication events, and computer interactions. Using

time-series, rather than multiple regression, allows for

the prediction of an action from an earlier action of

the same type, while accounting for the autodependency of errors inherent in any model involving time

(Ostrom, 1991).

Controller teams are assumed to perform an integrated set of activities. Each team member performs

control actions at time t that are contingent upon the

control action that occurred at time t-\. Ifthis is true,

2 Subjects also completed scenarios ofmedium complexity. However, because Vortac, Edwards, Jones, Manning, and Rotter (1993) found

that medium-complexity scenarios have characteristics of both high- and low-complexity scenarios, only the results for high- and lowcomplexity are presented here.
The Role ofFlight Progress Strips

and flight data activities are integrated among other

control activity, the time-series models should show

communication events and computer entries of each

controller in the team predicting flight data activities

of the other (R-side interactions with flight data are

predicted by D-side activity, as well as other R-side

activity; D-side interactions with flight data are predicted by R-side activity, as well as other D-side

activity). If this is the case, the set of FPS activities

performed by each controller should not be automated

because each one forms an integral part ofthe whole.

On the other hand, if flight data activities are

segregated then the time-series models should show

that flight data activities of each controller are predictable by previous flight data activities performed

by a single team member. For example, if D-side

activity is primarily predicted by R-side activity then

the D-side could be viewed as a task component

controlled by the R-side. In this case, it is likely that

the activities performed9 by the D-side controller can

be automated without any decrement in performance

for the R-side controller. This should be the case even

when the controller is working singly.

In summary, the automatic management of FDEs

will be the main characteristic changed by the implementation of ISSS. This change should have one of

two consequences: (1) automation may relieve controllers of time-consuming activities that do not enhance job performance, or (2) automation of strip

activity may deconstruct the integrated nature ofthe

system, perhaps by interfering with the incidental

cognitive benefits accrued by physically interacting

with the strips (Hopkin, 1991).

METHOD

TESTING SITE AND SUBJECTS

The study was conducted at the Radar Training

Facility (RTF) atthe FederalAviation Administration's

(FAA's) Mike Monroney Aeronautical Center in

Oklahoma City, Oklahoma. Ten full-performancelevel, FAAAcademy instructors in the nonradarscreen

program served as subjects. They had worked operationally as en route controllers within the last two

years (M = 7.0 months). The subjects were familiar

with the airspace, but were not familiar with the

particular scenarios used.

SCENARIOS

Five scenarios from each oftwo levels ofcomplexity

were selected from the FAA Academy Scenario Guide.

Complexity is based on the number of departures,

arrivals, en route aircraft control actions, equipment

emergencies, special flights, and other coordination

activities, in each scenario3. The low-complexity scenario lasted 30 minutes, with complexity rating ranging from 50-55%; the high-complexity scenario ranged

from 90-95% complex and lasted one hour. The

average number of FPSs used were 10.2 and 31.4 in

low- and high-complexity, respectively. The highcomplexity scenario was comparable to a situation in

the field where a second controller (D-side) would

likely provide assistance.

In each scenario, the strip bay was located to the

right ofthe radar scope. The two observers sat behind

and to the right and left of the controllers with

computers on their laps. Two "ghost" pilots controlled the simulated aircraft and another assumed the

communication functions of adjacent Centers and

other air traffic control facilities.

APPARATUS

Verbal communication was recorded using a multitrack cassette recorder. One input channel included

the pilots, adjacent Centers, and the controller (or the

R-side member of a team, with the D-side communications recorded on a separate channel). In addition,

each observer was recorded on their own input channel, allowing them to annotate their event recordings.

3 Complexity was measured using the complexity worksheet found in the FAA's Instructional Program Guide (Appendix B, Section 3, Phase

8A for nonradar). Complexity was computed in the following way: departures got 5 points; arrivals, en route aircraft needing a control action,

emergencies and radio failures each received 4 points; special flights got 3 points; en route aircraft not needing a control action got 2 points;

and 1 point for each additional coordination action (e.g., point-to-point flight). More points indicates greater complexity. We selected

scenarios from low and high complexity, corresponding to series 8 and 9, and 24 to 29, respectively, in the Guide.
The Role ofFlight Progress Strips

A video camera was focused on the strip bays to

record when writing and manipulating took place.

Two notebook computers were used for the on-line

data collection by the two observers. The time-lines

generated by the observers were corrected off-line,

due to an occasional misclassification, using the audio

and video tapes.

PROCEDURE

Each subject participated twice; once as an individual and again as the R- or D-side member ofa team.

Teams participated approximately one month after

the individuals were completed. On the lastthree days

of individual controller participation, inter-rater

reliabilities were calculated (Low = .83, High = .75).

Because ofthe high reliability, the teams were coded

using only two observers: one for the R-side and one

for the D-side.

Each individual and team completed a counterbalanced sequence of scenarios. To ensure the same

experimental history, each team member had completed the same sequence ofscenarios when run individually. Subjects never controlled the same scenario

twice.

Upon entering the RTF, subjects first completed a

brief background sketch. They were then given the

opportunity to organize the strip bay in preparation

for the scenario. Subjects were provided with all the

strips for the problem at this time and were instructed

to control traffic as they would in the field.

Each experimental session lasted approximately 3

hours. Break periods between scenarios were approximately 20 minutes.

BEHAVIORAL CATEGORIES

For each scenario, the communication, FPS, and

computer-related events listed in Table 1 were recorded, yielding a time-indexed behavioral record. As

shown in Table 1, each main event listed in the lefthand column represents a composite ofthe individual

actions listed in the right-hand column.

Communication events were categorized into Controller Commands (CCOM), Controller Queries

(CQUERY), Pilot Requests (PREQ), Sector Transitions

(SECTOR), and Team Communication (TEAM). FPS

activities were categorized into Looking at an FPS

(LOOK), Writing on an FPS (WRITE), and Manipulating an FPS (MANIP). Computer-related activities were

categorized into Updating the Computer Database

(UPDATE), Obtaining Information From the Computer

Database (INFO), using the computer to aid in Conflict

Detection (CONFLICT), and using the keyboard or

trackball to initiate the Hand-off(How) of an aircraft

to an adjacent sector or facility.

Communication Events. A CCOM was a command

issued by the controller to a pilot, whereas a CQUERY

was a controller-initiated request for information from

the pilot ("What is your altitude?"). A PREQ was a

pilot-initiated request to the controller ("Can I fly

direct to Tulsa?"). SECTOR involved interactions between the controller and adjacent sectors as well as

other air traffic control facilities, primarily when

aircraft were entering or exiting the sector. When a

team participated, verbal communications between

team members were also recorded (TEAM).

FPS Activities. The LOOK category included looks

at both the active and suspense bays. Because a look

obviously precedes other FPS activities, this category

included only those looks that were not immediately

followed by writing or manipulating. When coding

teams, a look recorded on the D-side indicated a look

at the radar scope, whereas a look on the R-side

indicated a look at the strips. Multiple looks indicate

that the controller looked away and then returned to

look at the strips or the radar. The WRITE category

included both verifications (e.g., a check mark placed

by the altitude entry upon initial contact), and a

change (e.g., crossing out and updating strip information). The MANIP category included any physical

movement of the strip.

Computer-Related Activities. The computer that

controlled the traffic simulation generated a summary

of all computer-related control actions. From this

summary, four additional computer-entry control

actions were added to the data. The UPDATE category

indicated that the controller updated flight information in the computer database, whereas the INFO

category indicated that flight information was retrieved from the database. The CONFLICT category

indicated the placing of a circle around an aircraft's

location on the radar, visually representing a "bubble"

of airspace surrounding that aircraft. The most important job in en route air traffic control is to main4
The Role ofFlight Progress Strips

Table 1

Behavioral Categories and theirIndividualActions

Main Event Individual Actions

Controller Command (CCOM) route change, speed change, altitude change, providing

information (e.g., altimeters, VFR traffic), issuing

clearance, other

Controller Query (CQUERY) aircraft speed, altitude, route, other

Pilot Request (PREQ) route change, speed change, altitude change, providing

information (e.g., altimeters, VFR traffic), other

Sector Transitions (SECTOR) turnover of control to adjacent sector, departure

clearance, initial contact within sector

Team Communication (TEAM) verbal and nonverbal communication between team

members

Look (LOOK) at active bay, at suspense bay

Write (WRITE) verification of FPS information, change of FPS

information

Manipulate (MANIP) move FPS from suspense to active bay, sequence FPSs,

offset FPS, flatten (undo offset) FPS, remove FPS from

bay

Update Computer (UPDATE) input assigned altitude, input interim altitude, change

route

Obtain Computer Info. (INFO) examine an aircraft's flight plan, display an aircraft's

projected route on the radar scope

Conflict Detection (CONFLICT) display a circle with a radius of five miles of airspace

around a specified aircraft

Computer Hand-off (HOFF) receive control from adjacent sector or facility
The Role ofFlight Progress Strips

tain appropriate separation between all aircraft; the

circle represented the boundary for minimum separation. Hand-offs (HOFF'S) are initiated verbally and by

computer. When an aircraft approaches the sector

boundary or is to be transferred to another facility

(e.g., approach control), the pilot is notified verbally

and a sequence ofkeys is pressed to notify the adjacent

facility of the HOFF.

Each ofthe above categories were used as predictors

offlight strip activities. For controller teams, some of

the abbreviated categories were preceded by an 'R' or

'D' indicating the controller responsible for the activity. For example, RwRiTE represented the R-side controller writing on the strips and DwRlTE represented

the D-side controller writing on the strips. Categories

that were not preceded by an 'R' or 'D' indicated that

one controller was responsible for that activity. For

example SECTOR was done by only the R-side controller.

RESULTS AND DISCUSSION

Autoregressive time-series models were used to

predict flight strip activities (i.e., LOOK, WRITE, and

MANIP). With these types of models, complications

arise when pooling across subjects to estimate the

overalltime-series regression model. Various methods

of estimating the pooled regression model exist. The

Seemingly Unrelated Regression (SUR) was chosen

because it can be used when pooling across subjects or

when lagged dependent measures exist in the timeseries model (seeAppendix for additional details). For

pragmatic reasons, the forward selection procedure

recommended by Gallant and Jorgenson (1979) was

used with the restriction that individual variables not

explaining at least four percent of the total variance

were eliminated from the models.

First, the low- and high-complexity scenarios were

divided into 90-second time intervals. The number of

responses for an FPS activity during interval t(F^)was

predicted from the number ofresponses for the other

/»variables from thatinterval (X' ), and the number of

responses from the previous interval (F y). That is, 7

= f(Xh, X2f,..., X (, Ytl). SUR was used to develop

separate models for each ofthe single and team conditions. Residuals were examined for each model and

indicated that the data were well-fit by the model.

Predictors are listed in order of contribution to the

model. The models are divided into the categories,

LOOK, MANIP, and WRITE. Each category will be

discussed in turn.

The adjusted R

2

represents the proportion ofvariance accounted for by the model, corrected for the

number ofpredictors included in the model. For each

model, the degrees of freedom, adjusted Ä

2

, %

2

, and

corresponding /»-value are reported. No reliable predictors were found for those models containing only

an intercept.

LOOK. AS shown in Table 2, looking was not predictable in either the single or team situations. Although three out ofthe four/»-values were significant,

indicating above chance predictability, only the highTaWe 2

Time-series JModels: LOOK

Model df /^adj x

2

P<

SINGLES

LOW: LooKt = 2.07 - .30 SECTOR 1 .03 8.06 .0045

HIGH: LooKt = 1.34 + .20 LOOKM 1 .04 16.59 .0001

TEAMS

LOW: RLOOKt = .75 + .17 TEAMt 1 .03 3.53 .0603

HIGH: RLOOKt = .38 + .26 Ri.ooKt-1 + .1 2 TEAMt 2 .11 21.27 .0001
Table 3

Time-series Models: MANIP

The Role ofFlight Progress Strips

SINGLES

LOW: MANiPt = .44 + .46 SECTORt 1

HIGH: MANiPt = .39 + .28 WRiTEt + .25 SECTORt 2

.15

.16

35.27

75.16

.0001

.0001

TEAMS

LOW:

HIGH:

RMANIPt = .18 + .37 RMANIPt-1

DMANIPt =1.11

RMANIPt = .1 6 + .54 RMANIPt-1

DMANIPt = 1.44 + .46 SECTORt

0

.12

.29

.05

11.58

65.30

9.51

.0007

.0001

.0020

complexity RLOOK model accounted for over 4% of

the variance. This model indicates that when the

traffic situation is complex, the R-side controller is

likely to look at the strips when communicating with

the D-side controller. Also, ifthe R-side has looked at

the strips once, he or she is likely to look again. This

is the only LOOK model that accounts for over ten

percent of the variance. Because no general conclusions can be reached by imposing meaning on one

model, the LOOK models will not be discussed further.

As indicated previously, DLOOK is not included in the

table because it indicated a look to the radar scope and

is therefore not considered a flight strip activity.

MANIP. The MANIP models are shown in Table 3.

Although MANIP is predicted better than LOOK, the

proportion of variance accounted for by each MANIP

model is limited. Of these models, RMANIP in the

teams-high condition accounts for the largest proportion ofvariability. The inclusion ofRMANIP as the only

predictor in the teams-high and -low conditions indicates thatthe best predictor ofan R-side manipulation

is another R-side manipulation. It would appear that

when the R-side leftthe radar to manipulate the strips,

he or she took one or more actions with them. In the

teams-high condition, there is no agreement about

what other activity is a predictor, other than RMANIP j.

Apparently a myriad of other activities covary with

RMANIP, but none sufficiently often enough to be

included as a predictor.

SECTOR is the only predictor in the singles-low and

D-side high-team models, and SECTOR is accompanied by WRITE in the singles-high model. However,

neither SECTOR norWRITE is included in either RMANIP

model, suggesting that the FPS activities performed

by the R-side controller are qualitatively different

than those performed by the D-side or by the controller working singly. Rather than being responsive to

the actions of the R-side controller, which was seen

above for RMANIP, D-side controllers are more responsive to the characteristics ofthe traffic situations, that

is, aircraft entering and leaving the sector.

WRITE. In contrast to other FPS activities, Writing

on FPSs is highly predictable. The average adjusted

R

2

, shown in Table 4, is much higher for these models

than for either the LOOK or MANIP models (.34 vs. .05

and . 15, respectively).

Inspection ofthese models suggests that there may

be a common subset ofpredictors that can account for

writing on the strips. WRITE (performed by an individual or R-side team member) is in five ofthe models
The RoU ofFlight Progress Strips

and SECTOR is in four. However, there are several

other predictors, which when accompanied by SECTOR and/or WRITE may significantly contribute to the

models' predictability (e.g., CCOM, UPDATE, MANIP,

etc.).

In addition to SECTOR and WRITE, CCOM is included in two of the teams models. Futhermore, the

combination of these three predictors represents a

subset ofall ofthe predictors in the teams models with

only RINFO remaining. Note that CCOM does notshow

up as a predictor in either of the single controller

models, perhaps because CCOM does not contribute to

the predictability of writing on flight progress strips.

However, this seems unlikely given its presence in the

teams models. Another possibility is that CCOM

covaried with other predictors and was selected out of

by the forward selection procedure.

With these possibilities in mind we examined the

singles data more closely to determine whether CCOM

was closely competing for inclusion in the models.

This inspection indicated that CCOM covaried with

many ofthe predictors that are included in the single

controller models. Specifically, CCOM was excluded

by the forward selection procedure in favor ofanother

predictor by an average i^of.02. Thus, when predicting writing on flight strips for individuals and teams

of controllers, the most practical and parsimonious

solution may be the following common subset of

predictors:

WRITE = SECTOR + WRITE , + CCOM .

t t t-i t

This model was compared to each of the WRITE

models in Table 4, without respect to predictor order,

and found to account for as much variability as all but

one of the original time-series models. Thus, the

subset model does provide a parsimonious solution,

sacrificing little predictability, and will therefore be

the focus ofthe following discussion.

Beginning with D-side writing, for both high and

low complexity, the common subset model is identical to the original DWRITE models. Thus, D-side

writing can be predicted from the subset model's two

R-side activities and sector transitions.

Substituting the subset model in the singles-low

condition replaces UPDATE with a combination of

CCOM and WRITE but does not significantly change

the adjusted R

2

. Similarly, the subset model did just as

well as the original model at predicting RWRITE in the

teams-low condition, in this case by replacing RINFO

with a combination of SECTOR and CCOM: the .04

change in R

2

is not significant. In addition, substituting the subset model did not change the adjusted R

2

for the teams-high R-side condition (the .01 change is

not significant). Thus, in singles-low, teams-low and -

high R-side conditions, the common subset model predicted writing as well as either ofthe original models.

In the three models mentioned above (singles-low;

teams-low R-side; teams-high R-side) the subset model

adds one or two predictors notincluded in the original

model. Although models with fewer predictors (like

the original models) are generally preferred to multiple-predictor models, especially when they account

for the same proportion of variability, the multiplepredictor subset model is preferred because it is has

the most practical value. Moreover, the RWRITE singlepredictor model, in the teams-high R-side condition,

lacks predictive value because it does not indicate

whatled the R-side controller to begin the sequence of

writing activity. For this reason, the subset model

provides more information and is more useful than

the original model, although the latter could be used

without loss in predictability.

The final WRITE model is the singles-high condition. The subset model replaces MANIP with CCOM

but again does notimpact the adjusted R

2

. Thus, in no

case does the substitution of the subset model significantly reduce the predictability ofwriting on the FPSs.

Segregation. The inclusion of MANIP as a predictor

ofWRITE in the original singles-high model supports

the idea that once controllers switch to the radar, they

tend to perform FPS activities in clusters. This is also

shown by comparing the singles-low and singles-high

models in the MANIP category (see Table 3). WRITE is

not included in the singles-low model, but is the best

predictor in the singles-high model. This clustering of

FPS activities as complexity increases supports the

idea thatindividual controllers tend to segregate flight

strip activities from radar activities, and to perform

those activities in clusters (see also Vortac, Edwards,

Jones, Manning, & Rotter, 1993; Vortac, Edwards,

Fuller, & Manning, 1993). Perhaps this is why many

of the individual controllers in the high-complexity
The Role ofFlight Progress Strips

Table 4

Time-series Models: WRITE

Model df /^adj x

2

P<

SINGLES

LOW: WRiTEt = 1.49 + .68 SECTORt + .58 UPDATEt

SUBSET: WRiTEt = .91 + .57 SECTORt + .19 CcoMt +.19 WRITER

HIGH: WRiTEt = 1 -23 + .29 MANiPt + .28 WRITER 1 + .27 SECTORt

SUBSET: WRiTEt =1.11 +.12 CcoMt + .29 WRiTEt-l + .40 SECTORt

TEAMS

LOW:

SUBSET:

LOW:

SUBSET:

RwRITEt = .26 + .55 RwRITEt-1 + .94 RlNFOt

RwRITEt = .03 + .62 RwRITEt-1 + .20 SECTORt + .04 RccoMt

DWRITEt = .92 + .56 RcCOMt - .67 RWRITEt + .56 SECTORt

DWRITEt = .92 + .56 RcCOMt - .67 RWRITEt + .56 SECTORt

HIGH: RwRITEt = .24 + .60 RwRiTEt-1

SUBSET: RwRITEt = .12 + .60 RWRITEH + .08 SECTORt -.002 CcoMt

HIGH: DwRiTEt = 1.49 + .41 RccoMt - .50 RwRITEt + .48 SECTORt

SUBSET: DwRiTEt = 1.49 + .41 RccoMt - .50 RwRITEt + .48 SECTORt

2 .18 46.36 .0001

3 .19 50.86 .0001

3 .23 118.86 .0001

3 .19 90.96 .0001

2 .38 48.30 .0001

3 .34 42.11 .0001

3 .48 75.21 .0001

3 .48 75.21 .0001

1 .36 89.21 .0001

3 .35 90.29 .0001

3 .38 99.22 .0001

3 .38 99.22 .0001

scenario requested D-side assistance: They felt that

they did not have time to perform the strip activities

and when they took the time they tried to catch up.

For these controllers it became increasingly difficult

to switch roles between the FPSs and the radar,

whereas within a team these roles are naturally separated.

Computer interactions also appear to change as a

function of complexity. Although these predictors

only entered into three ofthe models (MANIP: teamslow R-side; WRITE: singles-low, teams-low R-side),

they always appeared in low-complexity situations.

Controllers may segregate, or severely restrict, unnecessary computer interactions when the traffic situation gets complex. It is possible that performing any

control activity not directly associated with observing the radar might reduce performance in complex

situations.

Another indicator that controllers tend to segregate

flight strip activities is that D-side activites are neve

included as a predictor. In all situations, R-side activi

ties or computer interactions predicted both R- and

D-side activities. This suggests that D-side activitie

truly support actions performed by the R-side.

Single versus Team activities. Once again, the single

controller models and the D-side controller model

share several predictors. For a given level of complex

ity, the D-side models use the same set ofpredictors a

the single models. (Recall that RCCOM and RWRITE in

the DWRITE low model replaces UPDATE in the singles

high model without any loss of predictability.)

The subset model can also be applied to the singles

high, singles-low, and D-side high MANIP models. In

each case, MANIP is triggered by some configuration o

the subset model predictors. R-side manipulations

on the other hand, were not predicted by any of th

subset model predictors.
fggp

CONCLUSIONS

The aim of this study was to examine the current

role ofFPSs in en route air traffic control by determining which control actions reliably lead to FPS activity.

The most predictable flight strip activity was writing,

however, manipulating flight strips was also modestly

predictable. There were generally three things thatled

to writing on a flight strip: (1) a sector transition, (2)

a controller command, and (3) prior writing on the

strips.

Flight strip activities are not as integrated into the

overall control ofair traffic as one might suspect. The

activities performed by the R-side controller predicted the strip activities of both the R- and D-side

controllers. When a team was responsible for a sector,

a D-side activity never entered into any models. Rside control actions influence flight strip activities of

both the R- and D-side, but D-side control actions

rarely influence flight strip activities performed by the

R-side. Thus, with regard to flight strip activities,

when two controllers are responsible for a single

sector, their relationship is not one of mutual exchange as "team" implies. Consequently, it is possible

that flight strip activities performed by the D-side

controller can be automated without any decrement

to R-side performance (Vortac, 1992). On the other

hand, ifthe team performed a more integrated set of

flight strip activities, this would not be the case.

Togetherwith the cognitive and performance analysis ofVortac, Edwards, Fuller, and Manning (1993),

the above conclusions imply that automation of the

FPS activities may enable an individual controller to

control the same amount of aircraft with less effort,

and therefore be better prepared to manage the increase in air traffic expected in the coming decades.

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10
The Role ofFlight Progress Strips

Appendix A

Autoregressive time-series regression models differ from basic regression models in two

A A

fundamental ways: 1) time is included in the model (i.e., Yt= a + bXt + et), and 2) the error terms

need not be independent, as they are assumed to be in the basic regression model.

A

According to Ostrom (1991), the dependence in the error terms does not bias the estimates a

A A A

and b, but does bias the variance estimates of a and b, thereby affecting any test of significance.

Further, Ostrom (1991, p.22) states that the variances of the estimates are typically underestimated

when an autoregressive process is present. Thus, test statistics on the estimates are usually liberal

and overrepresent the fit of the model when non-autoregressive time-series models are used. This

2

means that when the autoregressive process is not taken into account, the R values produced by

the models are typically too high and the probability of rejecting the model is greater than the

predetermined by the experimenter.

Additional complications arise when pooling across subjects to estimate the time-series

regression model. Various methods of estimating the pooled regression model exist and the

selected model of estimation must take into account the random nature of subjects (Sayrs, 1989).

Seemingly Unrelated Regression (SUR) is a random coefficient regression model that allows the

relationship between the criterion and predictors to differ across subjects while remaining constant

for a given subject (Zellner, 1962). SUR accommodates individual subjects by allowing a separate

A

a for each subject. We used SUR in our analyses for this reason.

Finally, because the time-series models also include lagged values of the dependent variable

A A A A A

(i.e., Yt = a + blXt + b2Yf-l + et ), the parameter estimates, a and b, may be inconsistent

estimators of the population regression weights (Ostrom, 1991). Fortunately, SUR adjusts for

lagged dependent variables, thereby avoiding the inconsistent estimator problem (Sayrs, 1989).

A forward selection procedure was used to determine the best predictor models for each of the

dependent variables. However, the standard forward selection procedure cannot be used because it

does not take into account the correlation in the errors. To account for this potential problem, the

forward selection procedure used here is based on Gallant and Jorgenson (1979). They found that

the least squares difference between the full and restricted model, adjusted for the correlation

2

among the errors, is asymptotically a % with degrees of freedom equal to the difference in the

number of parameters estimated in the full and restricted models (SAS, 1988).

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