chan lower-rated controllers to ensure accuracy during
high worktoad conditions. t¢Ti suggested that more
experiments be performed to systematically control
and manipulate message composition to verify their
perceptions.

Acoustical Correlates in Radio
Communications

Overview

As shown in Table 12, the research presented in this
section is organized around laboratory studies chat
examined the acoustical-phonetic properties of human
voice under conditions of laboratory-induced stress
and acoustical-phonetic properties of human voice
when environmental catastrophes occurred. Thirty
percent of the literature on acoustical correlates in
tadio communications are resources, such as literature
reviews, conference papers, or reference books; 30%
are accident tapes, and 40% represent laboratory-
based experiments,

Within aviation, analyses of voice transmissions
stem from research data that focused upon pilot com-
munications and workload. Three voice qualities ap-
peared to vary systematically when workload {which
again, is not consistently defined) was examined: pitch,
loudness, and rate of speech. Under emotional stress or
increased task complexity, pitch rose, the person talked
ioudez, and the person talked faster (Griffin, 1987).
Mental workload also appeared to produce similar
effects on language production (Brenner, ez al, 1935).
However, Ruiz, Legros, and Guell (1990) argued that
results obtained from laboratory and simulator envi-
ronments are incomplete and may not be generalizable
to actual real-life situations.

Differences also appeared in the variables selected
by researchers for investigation. The measurement of
voice qualities varies, depending on the acoustical
property investigated and on the measurement scale
used. For example, intensity can be measured in refer-
ence to power decibel levels when using watts or in
decibels sound pressure level when using pressure as
the reference (Borden & Harris, 1984). Notably inves-
tigated were male voice versus female voice, preferred
rate of presentation, preferred frequency, voice to
noise ratios, and inteffigibifity. Recently, quafieacive

ié

and quantitative analyses on rate of speech were exatn-
ined within the air craffic control environment. For
example, Cazdosi (in preparation), as part of a larger,
preliminary study, used a general, subjective approach
to speed of transmission (sounds slow, fast) and prosody
(distinct accent present or absent) whereas Morrow, et
al. (1991) reported the number of syllables spoken per
second,

Laboratory Studies: Emotions, Stress, and
Workload

Changes in pitch perturbations or “jitter,” along with
changes in fundamental frequency as a function of
workload stress were properties of the human voice
investigated by Brenner, Shipp, Doherty, and Morrissey
(1983). Workload was defined by the number of digits
subjects had ro listen to, hold in working memory, and
repeat following a 2-second pause. The numbers “one”
and “nine” were presented in either a 2-digit number
condition (defined as an easy task) orembedded within
a 7-digit number condition (defined as a difficult
task), The number of digits that subjects repeated
placed different demands upon working memory,
thereby changing anxiety and stress ievels due to the
variability in memory load (Miller, 1956; Beatty, 1982).
The resuits indicated that lower mean jitter scores were
associated with repeating back the numbers “one” or
“nine” embedded in a 7-digit string.

Brenner and Shipp (1987) identified and tested 8
different voice measures, thought to be indicative of
Psychological stress, using an aviation-based tracking
task developed by Jex, McDonnell, and Phatak (1966).
The Jex, etal. wracking task required the subject to keep
acomputer-generated triangle centered on a computer
sczeen, The triangle moved in unpredictable left and
right horizontal patterns. Subjects also counted aloud
from 90 to 100 so that acoustic patterns could be
analyzed in cerms of fundamental frequency, ampli-
tude, speech rate, jitter, and shimmer. Frequency jitter
was defined as minute variability chat occurred in the
spacing of the fundamental frequency periods when
measured on a cycle-by-cycle basis (Brenner & Shipp,
Pp. 365). Amplitude shimmer is the cycle-by-cycle
vatiabiliry in the amplitude pattern (Brenner & Shipp,


Morrsw, D., Clark, H_H., Lee, A., & Rodvold, M.
(Nov., 1990). Collaboration in Controller-Pilot
Communication. Presented at the 1990 Meeting
of the Psychonomics Society, New Orleans, LA.

Morrow, D., & Rodvold, M. (1992). Analysis of Prob-
lems in routine controller-pilot communication.
Paper presented at the Annual Meeting of the
American Psychological Association. Washington,
DC.

Morrow, D., Rodvold, M., & Lee, A. (in press).
Nonroutine transactions in controller-pilot com-
munication. Discourse Processes.

Navarro, C. (1989). A Method of studying errors in
flight crew communications. Perceptual and Mc-
tor Skills, 69, 719-722.

Peterson, L. R., & Peterson, M. (1959). Short-term
retention of individual items. Journal of Experi-

menta! Psychology, 58, 193-198.

Pope, J. A. (Oct., 1986). The “Heasback’ Problem. Acci-
dent Prevention Bulletin, Ve. 43, No 10 (3).

Ruiz, R., Legros, C., & Gueil, A. (1990, March). Voice
analysis to predict the psychological or physical
state of a speaker. Aviation, Space, and Environ-
mental Medicine. pp. 266-271.

Salt Lake City terminal comraunications staff study
(1991). Report to the Federal Aviation Adminis-
tration.

Schweickerr, R., & Boruff, B. (1986). Short-term memory
capacity: Magic number or magic spell? Journal of
Experimental Psychology: Learning, Memory, and
Cognition, 12, 419-425.

Schweicks.-. R., & Hayt, C. (1987). Short term memory

load sid pronunciation rate. NASA Cenference
Paper.

Spence, C. (1992, April 27). Communications recurrent
ASRS problem, seminar attendees told. Air Safety
Week. pp. 1,2.

Tomilin, V. V., & Pikovskiy, B. M . (1974). Foreasic
expert testimony in airplane crashes. Sudebno-
Meditsinskaya Eksperntiza, 17, 7-12.

Wickens, C. D. (1984). Processing resources in atten-
tion. In: Varieties of Attention, pp. 63-102. New
York: Academic Press.

Williams, C. E., & Stevers, K. N. (1972). Emotions and
speech: Some acoustical correlates. The Journal of
the Acoustical Society of America, 52, 1238-1250.

Work Group of Human Factors Relating to Controller
and Pilot Errors, Final Repori. (1992).

33


Table 6

Morrison and Wright (1989}. Taxonomy of ATC erzors.

Controller Errors

Monitoring:
Timeliness:

Coordination:

Comtaunications Errors

Clearance Composition:

Phraseology and
Delivery Technique:
Readback/Hearback:

Workload Performance Factors

Large numbers of aircraft
Frequency congestion
Combined position/sectors
Need io resolve a conflict
Weather conditions
Sector/corridor design
Similar call signs
Giving/receiving training
Scope/daia block clutter
Long work hours

positions, altitudes, flight path

delivery of frequency change, climb/descent clearance, crossing
restriction, traffic advisory, correct pilot navigation error, altitude
deviation, or clearance readback

handoffs, pointouts, approval requests
order/sequence, content of a message (wrong heading or altitude
assignment; faulty instructions)

non-standard clearance terminology; too rapid speaking rate
failure to correct erroneous flight crew readbacks

Table 7
Morrison and Wright (1989). Categories of ATC communication errors.
Communications Type of Error Contributing
Errors Factors
Clearance Composition Sequencing/Content Heavy traffic causing controller
overload
Heading Similar cskt signs
Altitude Coordination difficulties

Phraseology and Delivery

Readback/Hearback

Misleading instructions
inappropriate instructions
instructions to wrong aircraft

Inconsistent instructions
Non-standard vectors given

Non-standard terminology Frequency congestion
Blocked transmissions
Enunciation, speech rate
Poor radio technique

Failure to correct erroneous Frequency congestion
readbacks Blocked transmissions
Controller overload

10


Tabie 13

An overview to the cognitive/psycholinguistic approaches literature.

information Processing Models

Data Source
Shart Term Memory

Interactive Conversations

Bisseret (1971)
-Mental processes in ATC

Navarro (1989)
-Errors in flight crew
communication

McCoy & Funk (1991)
-Taxonomy of ATC errors based
on a madel of information
processing

Adams & Hweschinsky (1991)
-Information transfer limitations
in ATC

Loftus, Dark & Williams (1979)
-Short-term memory in
controller-pilot communication

Schweickert & Hayt (1987)
-Memory load and pronunciation
rate

Salt Lake City Study (1991)
-Miscommunication errors

Morrow & Rodvold (1992)
-Routine controller-pilot
communications

Clark & Schaefer (1987:
-Collaboration in conversation

Clark, Morrow, & Rodvoid (1930)
-Routine communication in ATC

Morrow, Lee & Rodvoid (1991)
-Collaboration in controller-pilot
communication

Table 14

Navarro’s taxcnomy of work sitzations with regaré to types of error in
communication and to types of adjustment.

_ Type of Adjustment _
Type of Error individual interactive
Data Transmission
(Uncertain or Erroneous) Self-Cerrection Exchange: discussion

Detection
(No sign of detection)

Identification
(Data detected but not identified;
message heard but not listened to)

interoretaiion
(Data identified but forgotten,
distorted, or modified)

Action
{Wrong actions being taken or
already done}

Detection curing message
tepetition

Subject asks for a repetition

Subject asks for a verification
of the values of the data

‘Crew member detects or reports
the data

Crew member reports the type of data

Crew member corrects or checks data

Self-correction (verbalized)

20

Crew member halts or changes the
action


ATC/PILOT VOICE COMMUNICATIONS —
A SURVEY OF THE LITERATURE

“When I use a word,” Humpty Dumpty said, “it means just
what I choose it to mean neither more nor less.”

I. INTRODUCTION

Pilots and air traffic control specialists (ATCS)! operate
as teams to ensure the safe and efficient use of the
Nation’s airspace so that passengers and cargo arrive
safely at their destinations. The Airman’s Information
Manual (AJM) states that the pilot in command of an
aircraft is directly sesponsible for and is the final
authority as to the operation of that aircraft. The air
tratfic controller is responsible to 1) give first priority
to the separation of aircraft and to the issuance of radar
safety alerts, 2) second priority to other services that
are required, but do not involve separation of aircraft,
and 3) third priority to additional services to the extent
possible (para 5-71). Efficient, accurate, and timely
information transfer between pilots, their crew, and
controllers is critical for these teams to operate
effectively.

Air traffic control/pilot voice radio communica-
tions illustrate some of the redundancies that are built
into the ATC system to compensate for potential
emergencies and errors. The readback/nearback loop
is a communications procedure developed for actively
listening and confirming messages between pilots and
controllers. A typical ATCS/pilot communication con-
sists of 4 parts: (1) ATCS sends message, (2) Pilot
actively listens to the message, (3) Pilot repeats the
message back to the ATCS, and (4) ATCS actively
listens for a correct readback for confirmation. Al-
though either can initiate a transaction, the exchange
of information between them begins once the control-
ler accepts responsibility for an aircraft requesting
permission to enter his/her assigned airspace. Aircraft
call signs, altitudes, crossings, airspeeds, radio fre-
quencies, and other pertinent information might be
included in a readback by the recipient to ensure that

— Lewis Carol

the transmitted information was received and under-
stood correctly. Unlike Humpty Dumpty, controllers
and pilots do not have the luxury of ig Mean-
ings to words. To do so could have catastrophic results.
Pilots ard controllers use a standard phraseology’ to
minimize the likelihood that a transmission is misin-
terpreted in order to achieve a mutual understanding
of the pilot's intentions.

Problems in information transmission, reception,
or comprehension can occur at any point in this
communication chain, The role of the ATC specialist
within this chain is to issue a correct clearance to the
correct aircraft and then ensure that the pilot correctly
reads back that clearance. If the occurrence of an
incorrect pilot readback goes undetected, then the
controller may be cited witn 2 “systems deviation”
(Monan, 1988, p. 5). If a loss in maintaining mini-
mum separation between aircraft or obstructiens should
result, then the responsible controller could be cited
with an operational error. Although misunderstand-
ings and other forms of miscommunications eccur,
many are corrected through recipient requests for
clarification, additional information, message repeti-
tion, or when faulty readbacks are detected; however,
these extra communications increase radio frequency
congestion and reduce the efficiency of information
transfer.

assi:

Overview of the Information Transfer
Problem

The fiterature presented and summarized in this
document was obtained from survey data, field and
laboratory studies, narrative reports, and reviews. A
total of 43 reports are represented. Table I provides a

* ATCS and controller are interchangeable terms used to refer to an air traffic control specialist.

7 These words and phrases can be found in the AIM or the 7110.65 Air Traffic Control Pilot/Controller Glossary.

1


5. Apply a cognitive/psycholinguistic approach to
identify problems in ATC message composition,
delivery techniques, and memory limitations.
Experimental research and high fidelity simula-
tion studies need to be performed to address
these issues.

. Undertake a coordinated research effort to inves-
tigate how acoustical approaches can be com-
bined with the cognitive/psycholinguistic
approach using communication taxonomies to
improve our understanding of air traffic control-
ler/pilot voice communications.

. Examine current training program approaches
for communications instruction so strengths and
weaknesses can be identified and potential
changes to the curriculum assessed prior to their
implementation in the field. The implementa-
tion of suggested training initiatives should be
evaluated to determine how they would change
communication efficiency ard accuracy. Untested
changes in current practices might reduce some
existing types of miscommunications, but could
increase others and have the potential of creating
new categories of communicatior. problems.

IV. REFERENCES

Adams, R. J., & Hwoschinsky, P. V. (April, 1991).
Information transfer limitations in ATC.In (Ed: R.
S. Jensen) Proceedings of the Fifth International
Symposium of Aviation Psychology, Columbus,
Ohio; Volume 1.

Sirman’s Information Manua!, Officiai Guide to Basic
Flight Information and ATC Procedures. (June,
1992). Washington, DC; U.S. Government Print-
ing Office.

7110.65G Air Traffic Control. (March, 1992). Wash-
ington, DC: Air Traffic Rules and Procedures Ser-

vice.

Alpert, M., & Sclincider, S. J. (1987). Voice-stress mea-
sure of mental workioad. ir. Mental State Estima-
tion. NASA Conference Publication 2504.

ATH Report on September Readback Survey. (1989).
ATH-360, System Improvement Division.

Aviation Safety Reporting System. (1990). FAA Human
Factors Workshop Briefing.

31

Baddeley, A. D., Thomson, N., & Buchanan, M. (1975).
Word-length and the structure of short-term
memory. journal cf Verbal Learning and Verbal
Behavior, 14, 575-589.

Beatty, J. (1982). Task evoked pupillary responses, pro-
cessing load, and the structure of processing re-
sources. Psychological Bulletin, 91, 276-292.

Billings, C. E., & Cheaney, E. S. (Sept., 1981). The
information transfer problem: Summary and com-
ments. In Information Transfer Problems in the
Aviation System, (Eds. Billings, C. E. and Cheaney,
E. S.). NASA Technical Paper 1875.

Bisseret, A. (1971). Analysis of mental processes involved
in air traffic control. Ergonomics, 14, pp. 565-570.

Borden, G. J., & Harris, K. S. (1984). Speech Science
Primer (2nd edition). Baltimore: Williams &
Wilkins.

Brenner, M., & Cash, J. R. (1991). Speech analysis as an
index of alcohol intoxication - The Exxon Valdez
accident. Aviation, Space, and Environmental Medi-
cine, 62, pp. 893-898.

Brenner, M., & Shipp, T. (1987). In: Constuck J. R.
{ed.) Voice stress analysis: mental state estimation.
Washington, DC: NASA Conference Publication,
2504.

Brenner, M., Shipp, T., Doherty, E. T., & Morrisey, P.
(1985). Voice measures of psychological stress -
Laboratory and field data. In I. R. Titze & R. C
Scherer (Eds.), Vocal fold physiology, biomechan-
ics, acoustics, and phonatory control (pp. 239-
248). Denver: The Denver Center for the Perform-
ing Arts.

Brown, J. (1958). Some tests of decay theory of immedi-
ate memory. Quarterly Journal of Experimental
Psychology, 10, 12-21.

Cardosi, K. M., & Boole, P. W. (1991). Analysis of pilot
response time to time-critical air traffic control
calls. Cambridge, MA: National Transportation
Systems Center. (NTIS No. DOT/FAA/RD-91/
20).

Clark, H.,8 Schaefer, E. (1987). Collaborating on con-
tributions to conversations. Language & Cognitive
Processes, 2, 19-41.

Clark, H. HI, Morrow, D., & Rodvold, M. (1990).
Analysis of routine communication in the air traffic
control system: Final Report, Sept 1989-Aug 1990.


Table 12

An overview to the acoustical correlates approach literature.

Data Source

Overview of Acoustical Approaches Accident Audio Tape Analyses

Laboratory Studies

Ruiz, Legros & Guell (1991)
-Voice analysis to predict the
psychological or pirysical state

Tomilin & Pikovskiy (1979)
-Forensic expert testimony in
airpiane crashes

Borden & Harris (1984)
-Speech science primer

Williams & Stevens (1372)
-Acoustical correlates of emotions
and speech

Dornheim (1991)
-LAX tapes show controller unaware
of aircraft holding on runway
- USAir/Skywest Metro accident

Brenner & Cash (1991)
-Speech analysis as an index of
intoxication - The Exxon Valdez

Brenner, Shipp, Doherty, & Morrissey (985)
-Voice measures of psychological stress

Brenner & Shipp (1987)
-Yoice stress analysis; mental
state estimation

Hecker, Stevens, von Bismarck & Williams
(1968)
-Acoustic speech signal and task-induced

accident

stress

Alpert & Schneider (1987)
-Voice-stress measures of mental workload

p. 365). The average fundamental frequency, ampli-
tude, and rate of speech increased when task difficulty
increased from easy to difficult.

Hecker, Stevens, von Bismarch, and Williams (1968)
attempted to determine whether stress was detectable
ina speaker’s voice by examining the respiratory func-
tion, the operation of the larynx, and articulation
under varying levels of experimentally-induced stress.
Subject stress level was measured by changes in facial
expressions, body movement (strain gauges), respira-
tion (strain gauge respirometer), and galvanic skin
response (electrodes placed on the surface of the skin).
Graphic-level tracings were used to measure speech
level (dB) changes and narrow-band spectrograms were
used to measure changes in fundamental frequency
(pitch). Two peaks of each test phrase were selected for
level measurements. Thirty percent of the subjects
spoke lower than average when stressed, and 10%
displayed higher levels than when relaxed. Individual
differences in fundamental frequency, indicated that
for some subjects, stress was associated with increases
in fundamental frequency, whereas for other subjects,
stress was associated with a decrease in fundamental

17

frequency. This study demonstrated that laboratory-
induced stress could be detected by changes in the
acoustical properties of human speech. Although indi-
vidual differences occur, systematic changes within the
individual appeared to be consistent for the individual,
when compared to baseline measures.

Alpert and Schneider (3987) described a method-
ology for identifying some properties of mental
workload by examining hypothesized changes in voice
properties. The microtremor in human voice signals
changes in emphasis, rhythm, ard voice inflection of
the speaker and often can help the listener understand
the intended meaning of 2 communicated message.
Suppression of the 8 - 12 Hertz microtremor has been
used as. a measure for the presence of stress. Alpert and
Schneider argued that emotions (e.g., fear) differ from
mood (e.g., sadness) and affect (e.g., excitement).
Emotions manifested themselves through physiolog:-
cal changes in respiration, muscle tone of the vocal
folds; moods by changes in temporal patterns of
utterances, such as pause length and length of utter-
ance; and affect by changes in voice amplitude and the
number of multipeak utterances.


Figure 1
A functional model of human information processing.

—>
| — —>
Pattern Recogniton

Central Processing | Response
Execution
— _| Responsel > ;
« tention “| Selector | !
=
— Reasoning

Table 16

A comparison between a typical trial in the Brown-Peterson paradigm and the Loftus, Dark, and
Williams controller/pilot analogue.

Brawn-Peterson Paradigm

Controlier/Pilot Analogue

1, Present to-be-remembered information (BKG)

2. Variable iength retention interval in which subject
performs distracting activity to prevent rehearsal
of the to-be-remembered information (counting
backward}

3. Recall signal: subject attempts to recall information

23

1. Transmitto-be-acted-on message (e. g. altimeter 2997)

2. Variable length of time in which pilot must perform
distracting activity that prevents rehearsal or acting
on message

3. Pilot's attention feed and attempts to recall and act
on message (e. g. dial 29.97 into altimeter)


analysis of the phrase “Exxon Valdez” during each time
period indicated a slowing of speech prior to the
accident. Misarticulations (c.g., slurring of speech)
examined through phoretic transcription, plus power
spectra displays of individual sounds, indicated changes
in the sound [iz] to [is] in the word Valdez; {s} to [sh]
in Exxon. Changes in voice quality measured by changes
in fluency (¢.g., speech rate, responsiveness, hesita-
tion, grammar) indicated more word interjections,
broken words, incomplete phrases, corrected errors,
and increases in speaking time and hesitations.

Dornheim (1991) reported that approximately 1
minute before the US Air-Skywest aircraft collision at
Los Angeles, “the local tower controller showed some
surprise in hez voice on the tape...” (p. 61).

These examples indicate that voice quality can be
used to infer the psychological and physiological states
of the speaker. Changes in a controller’s voice qualities
could signal changes in workload or stress levels that
could coniribute to the potential for error. Previously
reviewed studies and reports indicated that workload
was associated with increased incident reports and
strategic changes such as procedural shortcuttings (cf.
Morrison & Wright, 1989; HTI, 1991; Morrow, et
al., 1991). Based on the acoustical correlates approaches
reviewed, changes in fundamental frequency, ampli-
tude, and frequency jitter may be important predictors
of psychological and emotional stress levels. Changes
in delivery technique, such as the presence of more
hesitations, mere misarticulations and dysfluencies,
and rushed speech also may be indicative of heightened
cognitive stress levels. When the literature on commu-
nications taxonomies is combined with the acoustical
correlates literature, it would seem that as workload or
stress increases, air traffic controllers and pilots alter
their communications techniques to compensate for
congested radio frequencies. These changes included
shorter messages, message composition, message trans-
mission speed, and voice properties.

Cognitive/Psycholinguistic Approaches

Overview

There are 3 major components in the cognitive/psycho-
linguistic approaches section. Several information
ptocessing models applied to ATC are presented. Next,

research examining human short-term memory
limitations and their relationship to ATC/pilot message
content and delivery techniques are presented. Lastly,
interactive ATC/pilot conversations are examined using
the collaborative scheme. Thirty percent of the
information in this section was obtained from survey
materials, 40% was obtained from field studies, and
40% of the information was derived from laboratory-
based reports. See Table 13 for a summary.

Early information processing medels proposed that
controllers’ mental! operations and thought processes
centered around the performance of 2 primary func-
tions: surveillance and correction. McCoy and Funk’s
ATC operationai errors taxonomy (1991) is based on
a functional model of human cognition that included:
sensation, perception, working memory. long-term
memory, central processing, and response execution.
Some studies examined short-term memory as a hu-
man factors limitation in air traffic control informa-
tion transfer. Studies on short-term memory mainly
focused on the encoding process in order to identify
strategies that would minimize perceptual errors. More
recent studies are concerned with reducing encoding
errors. “Chunking,” the process of combining several
small units of information into larger units wichout
disrupting their order, may prove to be effective in
reducing some types of encoding errors. Alternative
explanations re-introduce decay theory. Some studies
assessed the time retention of chunks using the decay
theory, while later studies suggested that using shorter
units and allowing more time between those units
would improve short-term memory performance and
lower miscommunication errors. Studies in interactive
conversations reexamined the traditional view of con-
versational speech, and replaced it with acollaborative
scheme of conversational speech. Studies based on the
collaborative scheme approach analyzed ATC-pilot
audio tapes to identify how air traffic controllers and
pilots detect and correct miscommunications. Some
studies looked at routine communications to see what
disruptions occurred, while other studies examined
non-routine communications to identify the types of
misunderstanding: that were present.

19


Dornheim, M. A. (1991, April 8). L.A. tapes show
controller unaware of aircraft holding on runway.
Aviation Week & Space Technology, pp. 61.

Foushee, H. C., Lauber, J. K., Baetge, M. M., & Acomb.
(1986). Crew factors in flight operations: IH. The
operational significance of exposure to short-haul
air transport operations. Moffett Field, CA: NASA
Ames research Centex. (NASA Technical Memo-
randum 88322).

Gellman Research Associates, Inc. (1987). An analysis of
pilot-controlier read back errors. Jenkintown, PA:
Author.

Golaszewski, R. (1989). An analysis of pilot-controller
read-back errors. Journal of ATC, (October-De-
cember), 53-56.

Grayson, R. L., & Billings, C. E. (Sept., 1981). Informa-
tion transfer between air traffic control and aircraft:
Communication problems in flight operations. In
Information transfer problems in the aviation sys-

tem, (Eds, Billings, C. E. and Cheaney, E.S. NASA
Technical Paper 1875.

Griffin, G. R., & Williams, C. E. (1987). The effects of
different levels of task complexity on three vocal
measures. Aviation, Space, and Environmental
Medicine, 58, 1165-70.

Hecker, M. H. L., Stevens, K. N., von Bismarck, G., &
Williams, C. E. (1968). Manifestations of task-
induced stress in the acoustic speech signal. The
Journal of the Acoustical Society of America, 44,
993-1001.

Human Technology, Inc. (1990). Cognitive task analy-
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Human Technology, Inc. (1991). Cognitive task analy-
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Administration. McLean, VA.

Human Technology, Inc. (1991). Analysis of coniroller
communication in en route air traffic control. Re-
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McLean, VA.

Jex, H. R., McDonnell, J. D., & Phatak, A. V. (1966). A
critical tracking task for manual control research.

IEEE Transactions on Human Factors in Electron-
ics, HFE-7, 138-145.

32

Kanki, B. G., & Foushee, H. C. (1989). Communica-
tion as group process mediator of aircrew perfor-
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cine, 60, pp. 402-410.

Loftus, G.R., Dark, V.J., & Williams, D. (1979). Short-
term memory in ground controller/pilot commu-
nication. Human Factors, 21 (2), 169-181.

Mackworth, }. F. (1963). The duration of visual image.
Canadian Journal of Psychology,17, 62-81.

McCoy, W. E., & Funk, K. H. (April, 1991). Taxonomy
of ATC operator errors based on a model of human
information processing. In (Ed: R. S. Jensen) Pro-
ceedings of the Fifth international Symposium of
Aviation Psychology, Columbus, Ohio; Volume 2.

Miller, G. A. (1956). The magical number seven plus or
minus two: Some limits on our capacity for pro-
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The Mitre Corporation. (1990). Study of pilot readback,
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Monan, W. P. (Mar., 1986, Nov., 1988). Human Fac-
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Monan, W. P. (Jan., 1983). Addressee Errors in ATC
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Morrison, R..& Wright, R. H. (April, 1989). ATC
Control and communications problems: An over-
view of recent ASRS data. In (Ed: R. S. Jensen)
Proceedings of the Fifth International Symposium
of Aviation Psychology, Columbus, Ohio; Volume
2.

Morrow, D. G., Lee, A., & Rodvold, M. (April, 1991).
Collaboration in Pilor-Controller Communication.
Presented at the Sixth International Symposium on
Aviation Psychology, Columbus, OH.

Morrow, D. G., Lee, A., & Rodvold, M. (Dec., 1990).
Analysis of Routine Pilot-Controller Communica-
tion. In Managing the Modern Cockpit: Third
Human Error Avoidance Techniques Conference
Proceedings. Warrendale PA: Society of Autemo-
tive Engineers, Inc.



Table 9
Morrow, Rodvold, and Lee (Discourse Processes, in press). Percentage of nonroutine transaction
samples containing understanding and information problems (n = 163 and n = 120).

Type of Communication Problem Percent Contributing Factors Percent Resuit
(in understanding probiems)

Understanding Problems

Addressee signals misunderstanding 60 'Radio-related factors Repeat the message
frequency congestion
Speaker repeats fo get evidence of poor/blocked transmission 15 Query
understanding 36
‘Callsign recognition problems 9 Expand
Controller corrects erroneous pifot 4
readback ‘Other/nondeterminable 76

Information Problems

Self-correction 29 ?Failure to acknowledge 60
Addressee updates speaker message 19 Partial acknowledgment 9
Incomplete message 2Noisy transmission ?
{request for additional information) 19

?Communication stepped on 16
Speaker asks for other information
(request for additionai information) = 11 2Other/nondeterminable 8

Pilot has to ask for command

{timing problem) 14
Pilot challenges appropriateness of 8
a command

‘Addressee problems? Speaker problems

4


into macro categories. Later, studies were conducted
using audiotape analysis that developed better com-
munications taxonomies. A speech act coding scheme
was developed by Kanki and Foushee (1989) and
modified by Morrow, et al. (1990) to catalogue rou-
tine and non-routine pilot-cuntroile: voice radio com-
munications. Most of these audiotapes came from the
TRACON’ environment. Finally, beginning around
1990, simulation, survey, and field studies were per-
formed that examined difference: in communication
patterns and controller task categories. One simulator
study that examined controllers communications indi-
vidually and as team performance, indicated that top-
rated en route controller teams issued more reports
and smaller units of information than lower-rated
teams (Human Technoiogies, Inc., 1991).

(NASA) Aviation Safety Reporting System
(ASRS)

Much of the early air traffic control voice radio
communications research focused on determining the
impact of ATC/pilot miscommunications on air safety.
This was accomplished by tallying the frequency with
which miscommunications were cited in filed reports
to the ASRS. The ASRS is an independent third-party
that receives and analyzes reports, as specified by the
Aviation Safety Reporting Program. This program was
de eloped by the FAA to “stimulate the free and
unrestricted flow of information concerning
deficiencies and discrepancies in the aviation system ...
a program intended to ensure the safest possi>le system
by identifying and correcting unsafe conditions before
they lead to accidents” (P7-81, AIM). “Problems in
the transfer of information within the aviation system
were noted in over 70% of 28,000 reports submitted
by pilots and air traffic controllers ... during 2 5-year
period 1976-1981. These problems are related primarily
tc voice communications ...” (p. 1, Billings and
Cheaney, 1981). Grayson and Billings (1 981} indicated
that 70% of the reports submitted to ASRS between
May 1, 1978 and August 31, 1979, involved some type
of oral communications problem between flightcrews
and air traffic controllers (p. 48). There were 6,527

*TRACON is an acronym for Terminal Radar Approach Controi

6

reports in which 5,402 information transfer probiems
were found. Some of the reports contained more than
1 information transfer celated problem. Using acoding
scheme developed by the research team, these problems
were classified into 10 generic types of communications
problems, as shown in Table 3. From these and simitar
reports (Monan, 1983), it became apparent that
miscommunications occurred with such frequency as
to be considered a problem for air traffic safety. For
example, Monan (1986) noted that out of 763 incidents
reported to the ASRS during a29-month time interval,
417 were due to misunderstandings, misinterpretations,
mis-transmissions or unheard numbers in ground-to-
air communications. From these pilct and controiler-
generated narrative reports, an analyst tabulated the
frequency with which a misheard communication
resulted in a hazardous incident. Four classifications
emerged from the reports. As shown in Table 4,
approximately 90% of the 417 hazardous incidents
reported to the ASRS were classified as the result of
ATC/pilot miscommunications stemming from
misheard altitude/flight levels and headings. As shown
in Table 5, active listening during information transfer
was a major problem for both air traffic controllers and
pilots. One clear pattern was identified as contributing
to the mishearing of numeric content: 1 senten.e
clearance requiring 2 or more separate pilot actions
(e.g., crossing, change in altitude, change in speed).
Pope (1986), citing Monan (1986), states “No
other essential activity in aircraft operations is as
vulnerable to failure through human error and perfor-
mance limitations as spoken communication.”
Morrison and Wright (1989) reviewed the narrative
reports submitted to the ASRS database from January,
1986 to September, 1988. Variabies of interest associ-
ated with ATC communication problems included
controller workload, traffic volume, frequency conges-
don, ATC communications, and facility management
policy. Forty-cwo percent of the 340 incident reports
were filed by cont-ollers. As shown in Table 6, errors
were divided into 3 major groupings: Controller Perfor-
mance Errors, Communication Errors, and Environmen-
tal Factors, Pilot errors were only briefly mentioned in


Audio tapes, like narrative reports, provide retro-
spective accounts of human factors, environmental
factors, and task performance factors that may contrib-
ute to, act as catalysts for, or result in, miscommunica-
tions. These miscommunications may or may not
result in operational errors or deviations. The context
in which these communications occur must be consid-
ered before a complete understanding of the nature of
interactive, dynamic, air traffic control/pilot voice
communications and their involvement in air safety
can be achieved and recommendations for change
determined. An analysis of audio tapes alone is not
sufficient to draw causal conclusions. Also, the amount
of research that has been performed is limited to
examining oniy a few TRACONs and even fewer en
route centers. Thus, it is not appropriate to consider
these limited results to be representative of the com-
munications problems that occur at all ATC facilities
making up the National Airspace System (NAS).

Audio tape recordings also were used to examine the
relationshig between the acoustical properties of the
human voice when individuals directly experienced
increased mental workload or experienced or wit-
nessed emotionally charged events (cf. Brenner, et al.,
1985, 1987, 1991; Williams & Stevens, 1972). Brenner
and co-authors’ laboratory study on mental workload,
their evaluation of the Exxon Valdez audio tape, and
analysis of cockpit recorders recovered from aircraft
accidents revealed that voice quality changed as a
function of cognitive, psychological, physiological or
emotional stressors. Consistent and stable changes
included an increase in pitch and a change in speech
rate. Voice amplitude (speaking louder or softer),
“jitter,” and “shimmer” were less reliable measures.
Overall, acoustical properties of human voice appeared
to change as a function of change in mental workload
or stress in many of the reported 5’ adies (cf. Griffin,
1987; Hecker, et al.,2968). Although the ASRS com-
munications taxonomies and the speech act communi-
cations taxonomies included delivery technique as 2
miscommunications factor associated with operational
errors/deviations, multivariate research invesuigating
the influences of voice quality and speech rate on
miscommurications has not been performed.

29

The major strength of acoustical forensic research is
its methodology. That is, researchers compared the
same syllable, word, or phrase spoken by the same
person under normal conditions and when mental
workload increased, emotional climate changed, or
increased stress was experienced. With the introduc-
tion of technologically-advanced computer systems,
acoustical and speech processing software, and digi
tized recording equipment, researchers have the capa-
bility to examine human voice properties with greater
precision and accuracy. Changes in amplitude, jitter,
or shimmer may be detected because of technological
improvements in equipment. Often, changes in voice
properties can be detected by the computer that are not
detected by the human ear (Brenner, et al., 1987)

The primary weakness of performing an acoustical-
phonetic analysis of voice tapes has been technologi-
cally based. Overused audio tapes with poor signal
quality, unintelligible speech on audio tapes, poor
recording equipment, and gain control settings that
dampened voice amplitude are some of the problems
researchers previously encountered when analyzing
cockpit recordings and VHF audio tapes provided by
air traffic control facilities.

Cognitive/psycholinguistic theories and models of
human information processing have evolved signifi-
cantly over the past 30 years. The cognitive/
psycholinguistic approach views the human as an in-
formation processing system. Within this view, hu-
mans are thought to actively combine in a working
memory environmental information with information
obtained from permanent memory, store the contents,
and perform a response. Human information process-
ing, memory characteristics, and storage limitations
place constraints on how much and how long informa-
tion can be remembered. Established principles de-
rived from research performed in academic settings
have been applied to the aviation industry (cf. Mor-
row, et al.,1990, 1991, 1992; Salt Lake City Terminal
Communications Terminal Staff Study, 1991; Loftus,
etal., 1979). This research suggests that: 1) only a few
speech acts should be presented within an ATC mes-
sage; 2} speech acts embedded in the same message
should be situation and time relevant; and 3) pauses
between messages should be of sufficient duration so
the message car be completely understood before



optional} 1234" or it has a phrasal structure if the
subject and the verb are absent (e.g., [prefix optional]
1234). Installment utterances can be sentential or
phrasal in form. They differ from continuous utter-
ances in that the numbers are spoken in brief packets
and may or may not contain confirmation acknowl-
edgments trailing each of the packets. For example,
“It’s O1 [yes] 234 [yes]” is an example of a sentential
installment utterance with recipient confirmations.
Telephone operators generally use a phrasal structure
(46.2%) over a sentence form (27.6%) when provid-
ing telephone numbers. Operators increased their use
of instaliment utterances only when it became self-
apparent that teiephone users’ displayed severe diffi-
culties in understanding.

The acceptance phase in the collaborative model
states that once an utterance has been received, the
recipient's current state of understanding should be
conveyed back to che speaker. It is at this point that any
failures in understanding should be addressed and
corrected. As shown in Table 17, Clark and Schaefer
define & categories for recipient responses. The 8th
category, side sequences and errors, although included,
was not presented with sufficient explanation. Gener-
ally, presuppositions or assert full hearing occurred as a
function of type of information {i.e., contribution)
requested. Mote presuppositions or assert full hearing
occurred for towns (39% of the time) or for addresses
(33%) than for either names (15%), numbers (14%),
or for combinations of towns, addresses, and names
(19%). The apparent heuristic employed was “the
easier the information was to grasp, or the less impor-
zant it was, the more often the partner [in the conver-
sation] presupposed or asserted full hearing” (p. 39).

Using the Clark and Schafer modei of collaboration
in conversations, Clark, Morrow, and Rodvold (1990)
described the organization of routine communications
berween a single TRACON and air carriers using the
Morrow, Clark, Lee, and Rodvold (1990) coding
scheme. Audiotaped samples of approach and depar-
ture TRACON communications were analyzed to
examine how controllers and pilots indicate and repair
communication problems. Consider this transaction:

Table 17

Clark and Schaefer (1987). Categories of
responses foliowing message transmission.

| Category Example

1 didn’t hear you.
What did you say?

| Assert no hearing
| Presuppose no hearin,

Presuppose incomplete hearing.

Presuppose fallible hearing ..
| Display full hearing.
| Assert full hearing
| presuppose full hearing.

Other side sequences and errors.

Pilot: Caczus 123 sir, request direct Charlotte

Controller: Cactus 123 unable, contact Atlanta Center one-
two-cight-point-seven-five

Pilot: One-rwenty-four-seven-five, switching

Coniroller: That's one-rwo-eight, one-cwenty-cight seventy-
five, Cactus 123

Pilot: ‘Onc-twenty-cight point seventy-five, roger

During the pilot’s firs: turn both phase 1 and phase
2 occurred. During phase 1, the pilot initiates the
conversation and redirects the controller’s attention
to receive a transmission. During phase 2, informa-
tion is presented. In this context, the new information
is presented in the form of a request. Phase 3 is
completed in the conrroller’s first turn. During phase
3, the controller accepts the understanding of that
message and denies the pilot’s request. The controller
presents new information in the form ofacommand to
the pilot. During the pilot’s second turn, the pilot
acceptsthe new radio frequency information and com-
plies by reading back the radio frequency. During
turn 2, the controller indicates that there is a miscom-
munication by noe accepting the pilot’s message. Note
that during the pilot's second turn, the pilot’s readback
of the radio frequency is incorrect, signifying an
understanding problem (see Table 7). During the
controller’s second turn, the controller repaizs the
communication by repeating the radio frequency in-
formation twice. Collaborative effort to maintain a


Table 1 (cont)

An Overview to the ATC/Pifot Voice Radio Coramunications Literature.

Data Source

Approaches Survey Field Laboratory
Acoustical Borden & Harr's (1984) | Brenner & Cash (1991) Hecker, 3tevens, von Bismarck &
Approach — -Textbook -Valdez radio voice Williams (1968)
transmissions -Lab study

Alpert & Schneider (1987)

-Lab study
Cognitive — Navarro (1989) Salt Lake City Study (1991) Bisseret (1971)
Psycho- -Literature survey -Interviews, reports -Lab study
linguistic -ATC tapes
Approach

McCoy & Funk (1991)
-NTIS

Adams & Hwoschinsky

(1991)
-ASRS

Morrow & Rodvold (1992)
-ATC tapes

Clark ¢ Schaefer (1987)
-Telep sone operator tapes

Mitre Corporation (1990)
-Observations

Loftus, Dark & Williams (1879)
-Simulation study

Schweickert & Hayt (1987)
-Lab study

Morrow & Rodvold (1992)

-Simulation study

summary of the reports and their derivation. Bold
faced terms are defined in the Glossary. Italicized
words and phrases reference corresponding terms
presented in cited tables.

Information transfer between air traffic control
specialists and pilots is the most frequently reported
problem cited in the Aviation Safety Reporting System
(ASRS). Controller and pilot communication tech-
niques are qualitatively different. The ASRS data sug-
gest that controilers often deliver information too
rapidly, fail to detect erroneous pilot readbacks, or fail
to verify pilot readbacks. Pilots tend to use non-
standard phraseology, truncate their readbacks, fail to
issue a readback, or do not ask for clarification when
information is unclear. Although the ASRS is valuable
in tracking problems, it fails to explain why such
problems arise (Spence, 1992).

Based on the findings of the Work Greup on Hu-
man Factors Relating to Controller and Pilot Errors,
verbal miscommunications in (ATC) operations have
been identified as a causal factor in operational errors
and pilot deviations (Final Report, in preparation).
For example, some ASRS database studies shed light
on the severity of miscommunication in flight safety
and identify procedural factors associated with mis-
communications (Billings & Channey, 1981; Monan,
1983, 1986). A comprehensive analysis of survey ze-
perts that focused on controllers monitoring pilot
readback procedural deviations led to the development
of 2 readback taxonomy that included frequency of
occurrence by type of readback error (commissions
by the Office of Air Traffic Syseem Effectiveness (ATH),
1989). Cardosi (in process) is currently in the process
of analyzing tapes to identify the frequency of occur-
rence of specific communication practices; whereas,


Tabie 1

An overview to the :. fC/pilot voice radio communications literature.

Approaches Survey

Data Source

Field

Laboratory

Taxonomic Grayson & Billings
Approach (1981)
-ASRS

Monan (1986)
-ASRS

Pope (1986)
-ASRS

Monan (1988)
-ASRS

Morrison & Wright (1989)

-ASRS

ASRS (7990)

Spence (1992)
-ASRS

Geliman Research Associates
(1987)
-ATC tapes

Golaszewski (1989)
-ATC tapes

Morrow, Clark, Lee &
Redvold (1990)
-ATC tapes

Morrow, Lee & Rodvold
(1990)
-ATC tapes

Clark, Morrow & Rodvoid
(1990)
-ATC tapes

Morrow, Rodvold & Lee

{under review)

-ATC tapes

Morrow, Lee, & Rodvoid (1591)
-ATC tapes

Billings & Cheaney (1981) Cardosi & Boole (1991)

-ASRS

Monan (1983)
-ASRS

Work Group on Human

Factors Relating to

Controtier and Pilot Errors

(1991)

-ASRS
Acoustical Ruiz, Legres & Guell
Approach = (1991)

-Literature survey

Tomilin & Pikovskiy
(1979)
-Personal accounts

-ATC tapes

ATH Report on September
Readback Survey (1989)
-ATC tapes and survey data

Williams & Stevens (1972)
-Tapes of Hindenburg
radio voice broadc7st

Dornheim (1991)
-LA tower tape

Kanki & Foushee (1939)
-Simulation study

Human Technologies, Inc. (1991)
-Simulation study
-Audio/video ATC tapes

Foushee, Lauber, Baetge &
Acomb (1989)
-Simulation study

Brenner, Shipp, Doherty & Morrisey
(1985)
-Lab study

Brenner & Shipp (1987)
-Lab study


Table 10
Cardosi and Boole (1991). Time components in ATC/Pilot verbal communications (seconds).

Source and Type of Communication Mean S.D.

Communication involving maneuvers for traffic (n = 80)
Controller issues communication involving maneuvers for traffic.
Lag time for pilot to respond to contro!ler message
Pilot's initial reponse to controller's first transmission.
Controller's second transmission to the same pilot
Duration of pilot's second reponse ..
Total communication duration .

Communications involving turns not for traffic (n = 250)
Controller issues communication involving turns.
Lag time for pilot to respond to controller message
Pilot's initial reponse to controller's first transmission
Controller's second transmission to the same pilot
Duration of pilot’s second reponse ..
Total communication duvation ....

Communications involving traffic advisories (n = 178)
Controller issues communication involving traffic advisory
Lag time for pilot to respond fo controiler message
Pilot's initial repo.se to controller's first transmissior
Controller's second transmission to the same pilot
Duration of pilot’s second reponse
Total communication duration .....

Table 11

Human Technologies, Inc. (1991). Air route traffic control center
(ARTCC) ground-air communications.

Category Percent

Command
Observation .
Suggestion
Statement of Intent
Inquiry ...

reement
Disagreemen
Acknowledgment
Answer ..
Repetition
Correcting Response..
Clarify Response
Courtesy

* The categories left blank occurred in less than 2% of the communications.
15



Table 2

An overview to the taxonomic approach literature.

Aviation Safety Reporting System

Data Source
Audio Tape Analyses

Labaratory-Based Studies

Grayson & Billings (1981)
-Communication problems in flight
operations

Manan (1986)
-The hearback problem

Pope (1986)
-The hearback problem

Monan (1988}
-The hearback problem

Morrison & Wright (1989)
-Communication problems in ATC

ASRS (1990)
~Human factors workshop briefing

Spence (1992)
-Communications probtem

Billings & Cheaney (1981)
-Information transfer problem

Monan (1983)
-The callsign problem

Work Group cn Human Factors
Relating to Controller and

Pilot Errors

-Controller and pilot er.ors

Gellman Research Associates (1987)
-Pilot-controller readback errors

Gclaszewski (1989)
-Read-back errors

Morrow, Clark, Lee & Rodvold (1990)
-Collaboration in controller-pilot
communication

Morrow, Lee & Rodvold (1990)
-Routine pilot-controlier
communication

Clark, Morrow & Rodvoid (1990)
-Routine communication in the
ATC system

Morrow, Rodvold & Lee (under review)

-Nonroutine controller-pilot
communication

Morrow, Lee & Rodvold (1991)
Collaboration in controiler-pilot
communication

Cardosi & Boole (1991)
-Pilot response to control calls

ATH Report on September Readback
Survey (1989}
-Readbacks

Kanki & Foushee (1989}
-Communication as group process
mediator of aircrew per‘ormance

Human Technologies, Inc. (1991)
-Controller communication in en
route contral

Foushee, Lauber, Baetge, & Acomb
(1989)
—Crew factors in flight operations



Information Processing Approach

Bisseret (1971) proposed one of the first information
processing approaches to understanding the mental
processes involved in air traffic control. By gaining 2
better understanding of thy thought processes and
mental operations that a controller performs, he
proposed that it might be possible to automate those
Processes and operations thereby improving upon air
safety. Bisseret viewed the air traffic contro! system as
serving two distinct functions: surveillance and
correction. With the surveillance function, the air
traffic controller, as a system, scanned fer and detected
the presence of air conflicts. With the correction
function, the controller activated problem solving
strategies and selected the best solution. The primary
task that a controller performed was categorization.
Categorization consisted of “dividing a set of objects
into different classes in accordance with the given aim”
(p. 566). Objects were classified in accordance with
their attributes and to che values assigned to these
attributes; that is, the importance the attributes had
was determined by the situation (aim).

Within the air traffic control environment, main-
taining aircraft separation was an important attribute
whose value became increasingly important to the
controller if the risk of minimal sepata-ion distance
was threatened. Thus, Bisseret argued that controllers
categorized aircraft not by type but into groups: paten-
tial conflicting pairs and all others. Information about
aircraft attributes (type of aircraft, flight level, pasi-
tion, airspeed) weather condition attributes (clouds,
wind, ice) and other relevant information was used in
a working memory to monitor and categorize aircra%
inte groups and pairs. An experienced controller de-
veloped what Bisseret termed “operative memory.”
Operative memory consisted of all the relevant know!l-
edge and information of the air traffic contro! posi-
tion/sector that a controller had memorized, organized,
and structured. Today, it may be called 2 “mental
model” or acquired “situational awareness”.

Navarro’s (1989) method for studying fight crew
communications errors that used an information pro-
cessing taxonomy of communications is presented in
Table 14. As with many information processing mod-
els, he propesed that information was processed se-
quentially. information from the environment served

as the inprt to the human information processing
system, where it was detected, identified, interpreted,
and output by the performance of some action. Using
this model, Navarro believed that errors could be
evaluated and corrections in cemmunications applied
to individuals or to groups. Although no data were
presented, this model could be easily applies to the
interactive communications between air traffic con-
trollers and pilots. The necessity of ATC to repeat
communications could be attributed to Hight crews
not detecting the message; “say agains” might have
occurred during the identification piocess, and queries
more likely to have occurred during the data interpre-
tation when values were being verified (cf. Morrow, et
al., 1991, 1992).

McCoy and Funk (1991) presented a taxonomy of
ATC operational errors based on Wickens’ (1984}
functional model of human cognition. The major
components in their model included sensation, percep-
tion, working memary, long term memory, central pro-
cessing, and response. Table 15 presents definitions and
limitations for each of the major components in their
model. A simplified version of Wickens’ model is
presented in Figure 1. Information from the external
world is sensed and some of the raw sensory input is
acted upon by pattern recognition operations in work-
ing memory. Information and procedures from long-
term memory in conjunction with central processes,
such as attention and reasoning, contribute to the
further processing of that content in working memory.
The input is identified, interpreted, made meaningful,
potentially stored, and so on, and could result in the
execution of a selected response.

Based on this type of 2 model, McCoy and Funk
categorized accidents involving the ATC System from
1973 through 1989, Abstracts were obtained from the
Aircraft Accident Reports maintained by the National
Technical Information Service Government Report
Announcements and Index database. Of the 29 se-
lected abstracts, 18 abstracts cited probable or contrib-
uting controller involvement in the accident.
Approximately 5% of the accident: were attributable
to attention, 10% to memory, and 20% te perception
{situation awareness). The remaining accidents were


DOT/FAA/AM-£3/26

Office of Aviation Medicine
Washington, D.C. 20591

AD-A274 457
Se

94-00005
Een

C

ATC/Pilot Voice
Communications — A Survey
of the Literature

O. Veronika Prinzo
Thomas W. Britton

Civil Aeromedical Institute
Federal Aviation Administration
Oklahoma City, Oklahoma 73125

November 1993

Final Report

This document is available to the public
through the National Technical Information
Service, Spripgfield, Virginia 22161.

TIC

PBELECTE ws
aie |

@

U.S. Department
of Transportation

Federal Aviation
Administration

94 4 08 075


Table 4
Monan (1986). Types of hazardous incidents resulting from misheard ATC/Pilot communications.

Types of Incidents No. of Incidents

Deviations from Assigned Altitude/flignt Levels

Deviations in Headings...

Failures to “tlold short” of the Active Runway
and Similar on-the-ground Mishaps

Deviations in Airway Routings

Totai 417
Table 5
Monan (1986). Link failures in the ATC/Pilot communications chain.
Failure Number of
Modes Citations

ATC message numerics tr2smitted correctly bui heard
incorrectly, and heasback failed

* — Misheard ATC clearance/instruc*ion numerics......

* — Cockpit mismanagement resulting in readback
errors: complacency, fatigue, etc...

* Inadequate acknowledgements with subsequent
flight deviations (“Roger”, “So Long”, “Okay”}....

- 46

. Apparent inattention to amendments to ATC
clearances/instructions ..

ATC message numerics transmitted, heard, and read back
correctly but followed by deviations due to cockpit
mismanagement

* — Misuses of altitude alerier display...

© Other - - primarily “forgetting” ...

Acknowledged controller hearback failures ....

e Failure to hear error in pilot readback..

e Source of numeric error unknown (either in
transmission or rece.ving - - insufficient

detail in report), but not heard in readback .-. 86
. Clearance amendment not acknowledged by pilot
and noi challenged by controller... 38



Table 3

Grayson and Billings (1981). Categorization of pilot/ATC oral communication problems.

Category

Incomplete content

Absent (not sent)

Number of
Reports Definition
Other inaccuracies in content 792 1) erroneous data (formuiation errors:
2) errors in judgment
3) conflicting interpretation
Ambiguous phraseology 529 message composition, phraseology,
or presentation could lead to a
misinterpretation or misunderstanding
by the recipient
296 originator fai!s to provide all the
necessary information to the recipient
to understand the communication
tnaccurate (transposition) 85 misunderstanding cue tc the sequence of
numerals within a message
Misinterpretable (phonetic similarity) 71 stmilar-sounding names or numerics led to
confusion in meaning or in the identity of the
intended recipient
1,991 failure to originate or transmit a required
Of appropriate message
Untimely transmission 710 message not useful to the recipient because
it arrived too early or too late
Garbled phraseology aval content of the message last or severely
distorted to the point where the recipient
could not understand the intended message
Absent (equipment faiiure) 153 equipment malfunction resulting in a
complete loss of a message
553 failure to maintain listening watch,

Recipient not monitoring

proper lockout, or read available
correct information



behaviors. Only a small number of communications
problems were attributable to equipment failures, fre-
quency saturation, or other system problems. Monan
(1986, 1988) identified the frequent absence of hearback
as a major issue in ATC communications. That is,
ATC failed to actively listen to a pilots’ readbacks of
ATC clearances containing numbers. Morrison and
Wright (1989) separated environmental and task per-
formance factors from communications problems.
Controller overload, brought on in_part by heavy
traffic and radio frequency congestion, was cited as
contributing to clearance compesition, phraseology
and delivery technique, and readback/hearback com-
munications errors.

‘The ASRS database is a valuable resource that has
been used to identify some of the communications
problems in information transfer. ir has provided
direction for researchers. In communications-based
questions, the ASRS can be used to: 1) distill informa-
tion pertaining to the efficiency and effectiveness of
maintaining air safety; 2) examine and compile narra-
tive reports to get a sense of what's happening in daily
flights; and 3) help researchers develop stimulus mate-
rials for experimental ATC/pilot communications stud-
ies.

There are several inherent weaknesses with using
the ASRS that should be considered: 1) sampling is
biased, in that reports are voluntary and are subjective
interpretations of the circumstances that led to the
event; 2) many more pilots than air traffic controllers
submit reports, which could bias interpretations of the
database; 3) the accuracy of the narrative descriptions
of the event has not been established (memories are
malleable and subject to distortion); 4) use of a stan-
dardized narrative to zeformat the reports is subjective;
5) coding is subjective; 6) reliability in coding (inter-
rater and intra-rater reliability and consistency) needs
to be verified and periodically updated; 7) more objec-
tive operational definitions need to be established; and
8) base-line error rates pertaining to the incidence of
specific problems are not available (Cardosi, personal
communication, 1993).

Voice tape-based communications taxonomies ad-
dressed more specific issues in ATC/pilot communica-
cons derived from the ASRS based-communications
taxonomies. Researchers developed speech act com-

28

munications taxonomies that examined communica-
tion problems resulting from message composition,
timeliness, or coordination in controller errors as part
of the dynamics in information transfer. TRACON
controllers used identification and commards most
frequently and pilots used acknowledgments and iden-
tification most often. Headings end altitudes were the
most frequently used topics in all transactions. Enroute
radar controilers issued more commands and acknowl-
edgments than reports or inquiries. Additionally, more
expert enroute teams delivered more commands than
jess expert teams when they were under heavy workloads
(HTI1,1991). Ac TRACONSs, longer messages were
more likely to contribute to incorrect or partial
readbacks. Some of the strategies and devices used in
TRACON/pilot communications te achieve accurate
and efficient information transfer included: ask for
repeat (say again?), question (was that 2402), and
paraphrases (signaled understand problem). Voice
quality was an important signaling device that indi-
cated a lack of understanding and that improved the
accuracy of information transfer (Morrow, et al., 1991).

An advantage of using audio-taped communica-
tions databases is that they provide an objective, reli-
able, and verifiable real-time record of the information
transferred between air traffic controllers and pilots.
By developing and consistently using the same basic
speech act categories, different researchers can exam-
ine different aspects of the same types of voice commu-
nications. Transcripts are valuable sources of data, but
they have limitations. A complete analysis of voice
radio communications would require that an evalua-
tion of the information content of the speech signal be
included with message content. The contributions of
overlapping speech, as well as the role of pauses and
hesitations in signaling understanding, would need to
be determined. Speakers can lengthen words by draw-
ing them out and alter the spacing between words, and
use changes in intonation, as signaling devices. Gener-
ally a rising intonation at the end of a phrase indicates
more information is forthcoming. A falling intonation
indicates the end of a message. When people are the
recipients of a message, this information aides the ease
of interpretation of speech signals.


mutual understanding of the assigned radio frequency
has occurred. The pilot displays full hearing (see Table
13) by correctly repeating the radio frequency and
ending the transmission with the word “Roger,” indi-
cating a confirmation acknowledgment during pilot
turn number 3. The controller and pilot, through
collaborative effort, ensure that they both understand
the transmitted information through the process of
presenting, correcting, and confirming that a mutual
understanding of the intended meaning has occurred.
The radio frequency was presented, corrected, and
then confirmed before 2 new topic was initiated.

In their analyses, Morrow, Rodvold, and Lee (1999)
focused on nonroutine transactions with misunder-
standing errors similar to the example presented above.
They found that the most common type of problem
disrupting routine communication consisted of diffi-
culty understanding previously presented informa-
tion. The other 2 types of misunderstanding errors
were repeating unacknowledged commands and cer-
recting an inaccurate pilot readback. Also during
nonroutine transactions controllers spent more time
accepting information and less time initiating transac-
tions and presenting new information. Controilers
repaired understanding problems by repeating, para-
phrasing, or answering pilot questions, while pilots
repaired by repeating or acknowledging messages.
Nonroutine transactions were shown to have reduced
efficiency since they were longer, yet presented little
new information, and the organization of nonroutine
transactions resembled “normal” speech more than
standard ATC communications.

Morrow, Lee, and Rodvold’s (1991) analysis of
pilot/controller recorded TRACON communications
identified different types of problems that disrupt
routine communications. They found that problems
were infrequent when counted as a percent of the total
transactions; however, they suggest that identifying
the communication factors that influence problems
may provide insight into why they occur and how to
eliminate them. There was a connection between com-
munication problems and collaborative effort; that is,
when 1 party produced long messages with several
commands to decrease overall transaction time, the
other party might have tried to abbreviate acknowl-
edgments, thus increasing collaborative effort.

Tl, SUMMARY AND
RECOMMENDATIONS

‘This section isa briefsummary of the research contained
in each of the previous sections, followed by some
strengths and shortcomings of each approach. Several
recommendations are presented.

Summary aad Discussion

Areview of the literature on communication taxonomies
using the ASRS database and voice tapes was presented,
followed by che acoustical correlates approaches and
the cognitive/ psycholinguistic approaches to voice radic
communications berween air taffic controiiers and
pilots.

The ASRS-based communications taxonomies iden-
tified problem areas in voice radio communications
associated with operational errors/deviations. The com-
munications taxonomy for voice tape-based speech
acts described ATC/pilot communications, message
conient, differences in speech act use, and how prob-
lems in understanding were resolved. The communi-
cations taxonomies literature consistently found that
miscommunications occurred more often when con-
troflers experienced overload due to heavy traffic,
frequency congestion, message length, etc. (cf. Morrison
& Wright, 1989; Morrow, et al., 1990). Observational
reports and ASRS reports consistently state that air
traffic controllers speak too fast (cf. Mitre Report,
1990). However, retrospective voice tape analyses that
examined ATC delivery techniques have not validated
pilot and observer reports that speech rate is too rapid.
(Morrow, Lee, & Rodvold, 1990; Cardosi, in prepara-
tion). Morrow and co-authors used the number of
syllables spoken per second to measure speech rate on
49 message pairs; however, this was too small a number
on which to base a conclusion.

ASRS-based communications taxonomies addressed
basic, general issues involved in identifying factors in
communications that compromised air safety. Grayson
and Billings (1981) concluded that the preponderance
of ATC/pilot oral communications problems involved
human errors related to a failure to deliver timely,
potentially important information, problems in mes-
sage content and phraseology, and poor monitoring

27


other researchers have analyzed actual ATC/pilot voice
tapes of routine operations to 1) identify and classify
the frequency of occurrence of various types of infor-
mation (i.c., speech acts) contained in a communica-
tion (Morrow, et al., 1990; Clark, et al., 1990), 2)
record the frequency and type of communication ertor
present in operational errors (Golaszewski, 1989), and
3) identify and report the frequency of occurrence of
ATC communication task components during live
and simulated environments (Human Technologies,
Inc., 1991).
The draft of the Work Group’s final report further
states,
A review of relevant research work and opera-
tional analyses on errors in pilot-controller com-
munication by the Work Group indicated that
current analyses have focused primarily on the
counting and description of pilot-controller com-
munication errors, with little systematic work on
developing explanations or examining the causes
of errors (Work Group on Human Factors Relat-
ing to Controller and Pitot Errors, draft of the
Final Report, 1992, p. 9).

Purpose of the Report

Although there are many potential uses for this report,
it was initiated to address 3 basic questions: 1) What is
known about ATC/pilot voice communications and
the issues pertaining to miscommunications? 2) What
approaches have been used to study miscommunica-
tions? 3) What research needs to be perforrned so that
real solutions can be offered to the aviation community?

To answer the first question, a survey of the existing
ATC/pilot communications literature was performed.

To answer the second question, the literature was
organized according to the different methodological
approaches employed. This allowed identification of
research gaps relevant to understanding ATC/pilot
communication problems.

Finally, once the problems were identified, then the
third question could be addressed by providing recom-
mendaiions and guidelines for considering these is-
sues. This report provides 2» evganized smmary of
the ATC/pilot voice communications .crature and a
framework for the systematic study of interactive ATC/
pilot verbal communications,

Il. LITERATURE REVIEW

This literature review addresses some of the human
factors issues that may contribute to air traffic control/
pilot verbal miscommunications. The materials are
presented in a general, chronological progession in
each of the 3 major sections. The Communications
“faxonomic Approaches Section presents communica-
tions taxonomies developed from data obtained from
the Aviation Safety Reporting System (ASRS),
audiotaped voice radio communications, and
laboratory-based studies. These taxonomies defined
types, frequencies, and possibie sources or catalysts of
verbal miscommunications. The Acoustical Correlates
Approaches Section presents several methodological
approacles that examined changes in some acoustic-
phonetic properties of the human voice under
conditions associated with miscommunications. The
Cognitive/Psycholinguistic Approaches Section
provides an information processing perspective to air
traffic control (ATC) communications, research on
short-term memory and communications, and how
interactive conversation strategies reduced voice-based
communications problems.

Communications Taxonomic Approaches

Overview

Various individuals, groups, and organizations have
systematically arranged ATC/pilot voice communiza-
tions into groups or categories according to some
criteria; that is, they developed taxonomies. Two major
groups of communications taxonomies are presented:
ASRS-databased communications taxonomies and the
speech act communications taxonomies, Reports were
derived from survey (45%), field (41%), and laboratory
(14%) data sources. The materials presented in this
section made up approximately $1% of the 43 collected
reports and are summarized in Table 2.

Early research in communications taxonomies fo-
cused on identifying the frequency of miscommunica-
tions between air traffic controllers and pilots. The
NASA ASRS database was used in all the early studies;
from this, the readback/hearback loop was developed.
Early on, a taxonomy of miscommunications was de-
veloped, which basically divided miscommunications


Ruiz, Legros, and Gueli (1990) summarized the
major research efforts over the past 50 years that
measured the acoustic modifications of the human
voice as it was influenced by workload. Psychologica!
or emotional stress and physical fatigue can be identi-
fied by examining the acoustic properties of a speaker's
voice. Orc-, two-, and three-dimensional acoustic
characteristics were evaluated. Their primary conclu-
sion was that the fundamental frequency of the human
voice rises in a stressful situation. The frequency of the
firs: formants also are modified by emotional stress or
workload. Energy level (volts or decibels) is less stable
a measure. Although a speaker's total speaking time
increases with stress, the speaker tends to decrease the
number of syllables spoken per second. The two-
dimensisnal spectral analysis indicated that the time
contours of the fundamental frequency became more
irregular and discontinuous under high stress. Three-
dimensional sonagrams indicated that workload modi-
fied frequencies above 2,000 Hz. Although a
relationship exists between stress, fundamental fre-
quency, energy level, or speech raie, causality cannot
be inferred from these correlations; that is, they should
not be taken as estimators of individual reactions to
workload. Empirically derived research is needed to
decermine whether a causal relationship of practical
and statistical significance exists.

Field Studies: Accident Audio Tape Analyses

Williams and Stevens (1972) analyzed the voice
characteristics of radio announcer Herb Manson of
radio station WLS describing the approach of the
Hindenburg, the famous Zeppelin that suddenly burst
into flame, while landing at Lakehurst, New Jersey,
May 6, 1937. Three narrow-band spectrograms of his
voice were made, in which the phrase “ladies and
gentlemen” was present prior to, during, and
immediately following the disaster. Following the
incident, the announcer’s average fundamental
frequency (£) was noticeably higher. A comparative
analysis made of an actor reading the transcripts and
acting the role of the radio announcer showed striking
similarities. Various actors were asked to act out anger,
fear, sorrow, or neutral situations. The general
conclusion was that the normal contour of the
fundamental frequency, 2s a function of time, was

18

characterized by smocth, slow, and continuous changes
occurring in syllables. Generally, sorrow lowered
baseline f, and decreased f, range while anger ox fear
brought about an increase in both measures over
baseline performance.

Tomilin and Pikovskiy (1979) presented a psycho-
physiological method for studying oral and acoustic
information following airpiane crashes. Accident in-
vestigators who examined voice qualities generally
looked for changes in the frecuency spectrum and
temporal amplitude of identical words or parts of
words (i.c., phonemes) spoken by the same individual
at different times. Generally, a frequency shift to the
tight was indicative of emotional stress whereas a
frequency shift to the ieft indicated a reduciion in
stress. Pilots flying under complex conditions demon-
strated similar changes in speech: Speech became more
rapid, more frequent, longer pauses were present be-
tween words or phrases, and more slips of the tongue
were present.

As part of the study involving the acoustical corre-
lates of psychological stress, Brenner, et al. (1985)
analyzed crew conversations reco:ded before and dur-
ing emergency situations prior to aircraft crashes.
Tapes were obtained from recordings at air traffic
control facilities and from a cockpit voice recorder.
Identicai words or phonetic segments produced by the
same speakers during routine and emergency commu-
nications were extracted and analyzed. in ali of the
tapes, beth the mean and standard deviation of the
fundamental frequency increased significantly in the
emergency air ta ground communications. Although
preliminary, jitter scores decreased in emergency com-
munications and may provide an additional acoustical
component measure indicative of psychological stress.

Brenner and Cash (1991} completed an acoustic-
phonetic analysis of selected voice radio communica-
tions by the master of the oil tanker Exxon Valdez.
Speech analysis provided a technique for identifying
secondary evidence of alcohol impairment. A total of
42 statements were analyzed at 5 different time peri-
ods: 1) 33 houis before the accident, 2) ! hour before
the accident, 3) immediately following the accident, 4)
1 hour after the accident occurred, and 5) 9 hours after
the accident. Speaking rate was measured by the num-
ber of syllables spoken per second. Repeated measures


Non-routine transaction ---- Purposeful interruption in the standard cominunication chain used to
signal a problem in information transfer.

Operative memory --------------- All the relevant knowledge and information of the air traffic contro!
position/sector that a controller had memorized, organized, and
structured.

Phoneme ---------------------------- Smallest unit of speech that distinguishes one utterance from another

in all the variations that it displavs in the speech of a single person or
particular dialect as the result of modifying influences.

Pitch perturbations ----------- --- Minute variability that occurred in the spacing of fundamental fre-
quency periods when measured on cycle-by-cycle variability in the
amplitude pattern.

Pian View Display (PVD)--~--- CRT and related computer hardware and software which displays on
a screen radar-detected aircraft.

Pop-ups --- wee A previously unidentified aircraft requesting IFR or VFR clearance.
Readback --------------------------- The act of a pilot repeating the information in a ATC clearance.
Shimmer --------------------------- Cycle-by-cycle variability in the amplitude pattern.

Speech act ------------—---— An utterance which serves one discourse function.

Transaction —----~-----—-------- The delivery and receipt of a communication between a minimum of
two people.

Understanding problems ------- Problem in understanding the intentions of a communication due to
faulty mental model updating.

Visual flight rules (VFR) --------- Rules that govern the procedures for conducting flight under visual
conditions. The term VFR is also used in the United States to indicate
conditions that are equa! to or greater than minimum VFR require-
ments. In addition, it is used by pilots and controllers to indicate type
of flight plan.

Working memory ----------------- An active system of memory in which information is assembled and

organized prior to recall.

35



comparison between the typical trial in the Brown-
Peterson task and an experimental trial in the Loftus.
et al. (1979) task is presented in Table 16. in the
Brown-Peterson paradigm, subjects were presented
with three consonants to remember followed by a brief
retention interval in which the subject performed a
non-relate-! task to prevent rehearsal, and then recalled
the 3 letters once a signal was presented. The emount
of time given following the consonants and preceding
recall varied from 0 to 30 seconds. Loftus, et al.
replaced the components with numeric information
commonly transmitted in ATC messages. The types of
memory messages used were place/frequency (e.g., 2
place to contact with a 4-digit radio frequency) and
transponder code message (e.g., a 4-digit radar
transponder code). Four female college students were
required to remember either a place/frequency,
transponder cede, or both. in addition to the types of
memory messages, subjects either encoded the
transponder code sequentially as 4 separate values or as
2, 2-digit values. For example, in sequential encoding
the transponder code 2772 would be encoded as “two,
seven, seven, two.” In the chunked encoding, the
transponder code would be encoded as “rwenty-seven,
seventy-two.” Chunking is an encoding strategy that
allows for more information te be processed in a
limited capacity memory system.

The results showed high recall for place informa-
tion, medium recall for transponder code information,
and poor recall for radio frequency information at
immediate, 5-, 10-, and 15-second retention intervals.
Also, the number of pieces of information to be re-
calted had a large effect on the probability of correct
recall, as did the time interval between presentation
and recall. Radio frequency information was less likely
to be recalled correctly, even with a G-second retention
interval and a smali memory load, Chunking the
transponder code seemed to increase correct recall of
the radio frequency under a high memory load condi-
tion. Chunking did not improve correct recall of
transponder codes. In general, the finding supported
the idea that chunking some types of aviation-related
information, that is, making the amount of informa-
tion per message smaller with a larger interval between
messages, may increase the probability of a pilot cor-
rectly reading back that message.

24

An alternative approach to coun
chunks (quantity constraint) that could be actively
held in a short-term memory assumed that short-term
memory was limited by the amount of time (time
constraint) for which chunks could be retained
{Schweickert & Hayt, 1987). That is, a chunk of
information had to be actively engaged; otherwise,
activation levels diminished, and the informational
content of the chunk decayed and was forgotten. Some
researchers reported that the number of items immedi-
ately recalled correctly $0 percent of the time (i.c.,
memory span) depended on the type of information
that could be pronounced {icad) in about 1.5 seconds
(Mackworth, 1963; Baddeley, Thomson, & Buchanan,
1975; Schweickert & Boruff, 1986). Any infermation
not retrieved after approximately 1.5 seconds was lost.
Schweickert and Hayt’s results showed that reading
time was a better predictor of recall then the aumber
of items presented for unpracticed subjects. Both read-
ing time and number of items were equivalent predic-
tors for practiced subjects. Longer word lists required
more time to be read than shorter word lists, thereby
increasing the chances for trace decay. However, longer
word lists were more distinctive and increased the
chances of correctly guessing the item. The applied
suggestion was to make infrequently encountered
messages shorter to pronounce (i.e., readback), but
Frequently heard messages distinctive, even if the mes-
sages had to be longer.

A study of ATC/pilot miscommunications was un-
dertaken az the Sale Lake City terminal (McCandless,
1991). Random samplings of voice radio trensmis-
sions and behavioral observations of ground-to-air and

g the number of

air-to-ground communications were obtained.
McCandless interpreted the preliminary findings to
suggest that miscommunication errors were common
and that miscommunications 1) led to operational
errors, 2) caused operational inefficiencies, and 3)
were cominitted most frequently by private pilots. The
study suggested that ATC/pilot miscommunications
were caused by several factors including: variabiliry in
equipment quality, poor speech-to-noise ratios, indi-
vidual differences in communications ability, effects
of excessively long transmission, and workload. There
was a significant increase in controller speech rate and
number of speech acts contained in a transmission



TABLE OF CONTENTS

INTRODUCTION
A. Overview of the Problem ae
5. Purpose of the Report ......ccc ce ceeeccsessessenscssscrssecsscssasseeseessesserecesereersseenssesaees 4

LITERATURE REVIEW.
A. Communications Taxonomic Approaches
1. Overview...
2. Aviation Safety Reporting System
3. Audio Tape Analyses
4. Simulation, Survey, Field Studies .
B. Acoustical Correlates Approaches
1. Overview
2. Laboratory Studies.
3. Field Studies ...
Cc. Cognitive/Psycholinguistic Approaches
1. Overview
2. Information Processing Models of Communications .
3. Short-term Memory
4. Interactive Conversations

SUMMARY AND RECOMMENDATIONS

A. Summary and Discussion .
B. ReECOMMENAATIONS .........sssecscscesseetesseseceeenesesenreessesseeneeseaesesseenenesseseseneeeeceaeee
REFERENCES

GLOSSARY OF ATC TERMS...

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sseession oF yp
NTIS GRA&E
= DTIC TAB a
INSPECTED 8 Unannounced o

* Justifieation_____g

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Distribution/

javail and/or
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(1989) analyzed audio tapes containing zeadback errors
using this coding scheme. Six general types of
communication errors were identified:

1) Uncorrected pilot readback of an ATC clear-
ance,

2) Uncorrected controller readback of 2 pilet com-
munication,

3) Pilot readback of a clearance intended for an-
other aircraft,

4) ATC instructions given to the wrong aircraft,

5) Pilot non-compliance with ATC instructions,
and

6) Uncorrected controller readback of information

from another controller.

Erroneous pilot readbacks not corrected by a con-
troller (i.e., a hearback error) were involved in 50% of
the 22 analyzed events. Pilot readback errors of clear-
ances intended for another aircraft often resulted when
aircraft with similar cail signs were being worked on
the same frequency without a controller alert to pilots.
These 6 types of communications errors were classified
as either environmental situations or “true” errer situ-
ations. Environmental situations involved difficulties
with the task environment and included:

1) ATC position/sector working aircraft with simi-

lar call signs,
2) VER pop-ups for IFR clearance,
3) Garbled/inaudible transmission, and
4) Interphone communications distractions.

Aspeech act coding scheme developed by Kanki and
Foushee (1989) to analyze flightcrew communications
has been used and modified by several researchers to
answer different types of questions involving voice
communications. A speech act “Roughly corresponds
to an utterance serving one discourse function” (Mor-
row, Clark, Lee, & Rodvoid, 1990, p. 4). See Table 8
for the definitions of the various categories of speech
communications.

Morrow, Lee, and Redvold (1990) and Clark, Mor-
row, and Rodvold (1990) developed a method for
cataloging routine and nonroutine pilo/ATC radio
communications using a similar communications tax-
onomy to examine routine pilot/ATC radio communi-
cations (see Goguen, Linde, & Murphy, 1983). Their
goals were to identify, undezstand, and explain why
problems occurred in routine operations. In their

1h

preliminary study, the communications problems iden-
tified were inaccuracies (e.g., incorrect readback), pro-
cedural deviations (¢.g., omission of readback or
acknowledgment), and nonroutine transactions (e.g.,
detec. aad repair a misunderstanding). Focus was on
identifying the possible causes of inaccuracies, proce-
dural deviations, and nonroutine transactions. The
possible causes included: 1) length of message, 2)
procedural deviatior s, and 3) nonstandard language.
Their paper describ:s the coding methodology.

In a related paper, Clark, Morrow, and Rodvold
(1990) used the Morrow, et al. (1999) coding scheme
to 1) describe the organization of routine communica-
tions between a single TRACON and air carriers, 2)
identify the types and frequency of probiems that
interrupt routine information flow, and 3) identify
factors associated with communication problems. They
analyzed audio tape samples of approach and depar-
ture TRACON communications twice. The first pass
focused on discourse organization, speech acts, avia-
tion topics, problem transactions, and factors associ-
ated with problem transactions. The second pass
focused on how controllers and pilots indicated and
repaired communications problems. Once the audio
tapes were transcribed, each communications sample
was divided into coding units. Consider the transac-
tion presented below:

Pilot: Cactus 123 siz, request direct Charlotte

Controller: Cactus 123 unable, contact Adzata Center one-
rwo-eight-point-seven-five

Pilot: One-twenty-four-seven-five, switching

Controller: That's one-two-cight, one-twenty-cight seventy-
five, Cactus 123

Pilot: One-rwenty-cight point seventy-five, roger

This transaction involves 2 controller turns and 3
pilot turns. The transactions making up 2 communica-
tion occur sequentially. First, 1 person initiates a
message to be received by the recipient. The speaker is
responsible for delivering meaningful utterances. The
recipient is supposed to actively listen to the speaker
and indicate whether or not that message was under-
stood. Thus, communications proceed 1 turn at a
time. Each turn contains at least 1 speech act. Each
speech act serves a specific communications function.
The pilot’s first turn contains 2 speech acts: a call sign


identifying the pilot and a request. The first controller
turn contains 3 speech acts: a cali sign identifying the
pilot, and 2 commands. Each command can be further
broken down into topics: denial of a request and a
radio frequency change. Nested within this transac-
tion is an incorrect readback of a frequency change.
During the second turn the controller detected and
provided the pilot with the correct frequency, followed
by the cal! sign. This turn contained 2 speech acts.

The analysis examined the following ‘typical’ pilot-
controller transactions: 1) duration of communica-
tion, 2) who talked the most, and 3) what types of
actions were used most frequently to obtain the desired
peal, Generally, in rootine wansactions, most of 2
controller’s speech acts centered around presenting
information to pilots. However, when understanding
problems occurred, a controller’s speech acts involved
accepting of information from pilots (Morrow,
Rodvold, & Lee, under review). As shown in Table 9,
problems in communications were identified as distur-
bances that interrupted the flow of normal, routine
information transfer. Morrow and co-authors pointed
out that these problems did not necessarily lead to the
occurrence of an operational error or incident; how-
ever, they did reduce the efficiency of information
transfer.

Morrow, Lee, and Rodvold (1991) attempted to
identify the types of problems that disrupted routine
communications and determine how frequently each
type of problem was likely to occur in ATC/pilot
communications. The data from voice radio commu-
nications obtained from 4, level-S TRACONSs indi-
cated that errors in routine communications were
relatively infrequent; however, the majority of partial
and incorrect readbacks were preceded by messages
swich mraltiple commands or messages that combined
commands with requests or traffic reports. Appar-
ently, pilots or controllers sometimes produced longer
messages of abbreviated acknowledgments, but these
strategies had the tendency to increase the probability
of more nonroutine transactions-

Forty-six hours of ATC/Pilot Air Route Traffic
Control Center (ARTCC) communications obtained
from 4 Centers were examined 10 determine the time
required for 2 controlier to transmit successfully time-

critical messages to pilots (Cardosi & Boole, 1991).
Communications were divided into those that re-
quired maneuvers for traffic, turns not for traffic {sic],
and traffic advisories. As shown in Table 10, it cook an
average of 10 seconds for an en route controller to
transmit accurately a message involving traffic infor-
mation to a pilot. “The only controller second mes-
sages that were counted as such were ones in which the
controller had to repeat of clarify some part of the
original message” (p. 2-2). Approximately 14% of the
transmissions involving traffic maneuvers were re-
peated, 13% of the time controllers had to tepeat
instructions izvolving turns not for traffic, and on 8%
of the transmissions controllers had to repeat or clarify
traffic advisory information. It is not possible to deter-
mine from this study why controllers needed to repeat
their transmissions. Apparently, some of the frequency
congestion problem may be attributable to controllers
repeating previous transmissions, either fully or in
part. Pilots may rot be able to completely process the
message because too much information was presented
in a single transmission.

Simulation, Survey, and Fieid Studies
Involving ATC/Pilot Communications

An analysis of controller communications obtained
during live and simulated en route air traffic control
environments was conducted by Human Technology,
Inc. (HTH (1991). The communications categories,
modifications of the Foushee, Lauber, Baetge, and
Acomb (1989) coding scheme, and speech acts were
identified and tallied. The data analyses examined
differences in communications patterns and controller
task category (e.g., issue advisory, initiate handoff,
manage arrivals; see Cognitive Task Analysis, Human
Technology inc., 1990, 1991). As shown in Table 11,
more than half of the communications between en
route radar controlless and pilots involved delivering
commands to pilors and about 25% involved
acknowledgments, Team ratings were made by FAA
Academy subject matter experts’ observations. The
simulation data indicated that as workload inczeased,
controllers in top-rated teamis issued more reperzs to
pilots than did lower-rated teams. Additionally, top-
rated controllers tended to issue smaller message units

4 Air Route Traffic Control Center or ARTCC alse is synonomeus with en route, and center-

13


Technical Report Documentation Page

1, Report No. 2. Government Accession No. 3. Recipient's Catalog No.
DOT/FAA/AM-$3/20

%. Title and Subtitle 3. Report Date

ATC/Pilot Voice Communications -- A Survey November 1993

of the Literature ©. Performing Organization Code

7. Author(s) O. Veronika Prinzo, Ph.D. 8. Perfurming Organization Report No.

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

FAA Civil Aeromedical Institute
P.O. Box 25082

Oklahoma City, OK 73125 47. Contract or Grant No.

12. Sponsoring Agency name and Address 13. Type of Report and Period Covered
Office cf Aviation Medicine
Federal Aviation Administration
800 Independence Ave., S.W.

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

18. Supplementaf Notes

76. Abstract

The first radio-equipped control tower in the United States opened at the Cleveland
Municipal Airport in 1930. From that time to the present, voice radio communications
have played a primary role in air safety. Verbal communications in air traffic

j control (ATC) operations have been frequently cited as causal factors in operational
errors and pilot deviations in the FAA Operational Error and Deviation System, the
NASA Aviation Safety Reporting System (ASRS), and reports derived from government -
sponsored research projects. Collectively, the data provided by these programs
indicate that communications constitute a significant problem for pilots and
controllers. Although the communications problem was well known the research
literature was fragmented, making it difficult to appreciate the various types of
verbal communications problems that existed and their unique influence on the quality
of ATC/pilot communications.

This is a survey of the voice radio communications literature. The 43 reports in the
review represent survey data, field studies, leboratory studies, narrative reports,
and reviews. The survey topics pertain to communications taxonomies, acoustical
correlates and cognitive/psycholinguistic perspectives. Communications taxonomies
were used to identify the frequency and types of information that constitute routine
communications, as well as thcse communications involved in operational errors, pilot
deviations, and other safety-related events. Acoustical correlate methodologies
identified some qualities of a speaker's voice, such as loudness, pitch, and speech
rate, which might be used potentially to monitor stress, mental workload, and other
forms of psychological or physiological factors that affect performance.
Cognitive/psycho-linguistic research offered an information processing perspective
for understanding how pilots' and controllers' memory and language comprehension
processes affect their ability to communicate effectively with one another.

This analysis of the ATC/pilot voice radic communications literature was performed to
provide an organized summary for the systematic study of interactive communications
between contrellers and pilots. Recommendations are given for new research
initiatives, communications-based instructional materials, and human factors
applications for new communications systems.

17. Key Words 78. Distribution Statement
ATC-Piliot Communications Document is available to the public
Communication Taxonomy through the National Technical

Information Service, Springfield,
Virginia 22161

19. Security Classif. tof this report) 20. Security Classif. tof this page) 21. No. of Pager 22. Pree
Unclassified Unclassified 39

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



V. GLOSSARY OF ATC TERMS

ATC Instructions ------------------ Directives issued by air traffic contro! for the purpose of requiring a
pilot to take specific actions; e.g., “Turn left heading two five zero,”
“Go around,” “Clear the runway.”

Communications error -------- -- A causal factor associated with the exchange of information between
two or more people (e.g., pilots and specialists). It refers to the failure
of human communication not communication equipment, FAA Form
7210-3. Final operationai error/deviation report, p. 15.

Collaborative scheme ~

A hypothetical construct which serves to organize two-party commu-
nications into a meaningfu! shared mental model; consists of one or
more transactions.

Formant ------------------------------ Vocal tract resonance; formants are displayed in a spectrogram as
broad bands of energy

Fundamental frequency --------- The number of glottal openings per second. It is perceived by humans
as the speaker's pitch.

Handoff -------------------------—- An action taken to transfer the radar identification of an aircraft from
one controller to another if the aircraft will enter the receiving
controllet’s airspace and radio communications with the aircraft wili
be transferred.

Hearback ---------------------------- The act of a controller’s actively listening to a pilot’s readback of an
ATC clearance.

Information problems--------—- Problems in communications due to information which may be
inaccurate, incomplete, or mistimed.

Instrument flight rules (IFR) -- Rules governing the procedures for conducting instrument flight. Also
a term used by controllers and piiots to indicate type of flight plan.

Level-five ----------------—---~ Air traffic control facility conducting between 100.00 and 999.99
operations per hour.

34


Table 15

McCoy and Funk (1991). Functional elements of human information processing model.

Type Function Limitation

Sensing Samples raw stimuli from environment and passes Sensory thieshoids and discrimination
information to perception limits

Perception Assigns information to perceptual categories Suboptimal adjustment of critical

detection thresholds, vigilance loss,
and limits to perceptuai attention

Working Memory —_ Bottleneck between sensing/perception, !ong-term — Capacity and duration
memory, and the central processing functicn of
reasoning and response selection

Long-Term Memory Retains parameters used in perception, general No apparent limits on storage, but many
factual knowledge, and has role in mainiaining factors limit retrieval
internal model of the worid (including self}

Central Processing Decision-making and response selection, allocates Confirmation bias and the interrelated
menial! resources to functions required to perform _ limits to speed and accuracy of

various competing, concurrent tasks responses
Response Transforms selected responses into mechanical Speed and strength
energy

classified as response selection errots involving issuing effort. Adams and Hwoschinsky argued that people
clearances, coordination, and a variety of non-specific have limited memory capability. Memories were re-
situations trieved by associative recali and were reconstructions
Adams and Hwoschinsky (1991) discussed some of _ of prior life experiences. As such, memories were not
the human factors limitations in ATC information _ perfect copies of actually experienced events. Although
transfer. They argued that the major limitationsonthe — no empirical, study, or survey data were presented, the
human information processing system included: per- authors categorized communications errors using their
ception, how information is processed, capacity, and model and specified causality, For example, they pro-
memory. Perception was selective and determined, in posed that “readback errors, hearback errors, read
part, by prior knowledge and experience (expecta- forward crrors, and transcript:un errors were caused by
tions). Processing of information was not simulta- expectancy problems” (p. 494).
neous and itstancancous. “Processing is mainly done
by paralicl processing of several types ofinformationin Short-term Memory
a sequential manner” (p. 492). During peak operas While inany studies examined ways to encode
tions, time may become compressed whereby control- information so as to minimize perception errcrs, few
fers may be forced to implement decisions based on studies addressed the question of how to minimize
partially processed information. Processing capacity is encoding crrors. Loftus, Dark, and Williams (1979)
affected by the procedures and rules that people used _ used the Brown-Peterson (1958, 1959) paradigm and
to make mental comparisons, decisions, and so on. designed an experiment to simulate a pilot's memory
Using the rules appropriately could reduce mental task in a controlled laboratory environment. A

22



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.


more information is transmitted. Very few aviation-
based cognitive/psycholinguistic studies examining
voice radio communications exist (cf. Loftus, et al.,
1979; Schweickert & Hayt, 1987). Loftus and co-
authors’ results, although consistent with the litera-
ture on working memory, used four female college
students withour aviation backgrounds as subjects.
Whether the same results would occur using control-
jers or pilets is presently being determined in an
experiment by Cardosi (in preparation).

Some problems associated with performing a cogni-
tive/psycholinguistic analysis on the information pre-
sented on voice tapes acquired from centers or
TRACONS inciude: 1) poor quality tapes that have
unintelligible recordings are useless to researchers; 2)
interpreting voice tapes without access to the context
in which the communications occurred reduces the
validity of the interpretation; 3) retrospective analyses
of audio tapes do not allow for causal explanations; and
4) the tapes provide only a limited focus on the
problem.

Much of the research presented in this survey in-
volved the expenditure of effort in examining only a
subset of miscommunications. For example,
Golaszewski (1989) and Morrow, et al., (1990, 1991,
1992} examined incorrect, partial, and missing
readbacks; Cardosi and Boole (1991) examined only
messages containing traffic information; and Clark, et
al., (1990) focused on strategies used to promote
understanding between controllers and pilots. A com-
plete picture of transactions or speech acts contained
*n daily communications has not been presented. A
more comprehensive analysis would provide the com-
with a total picture of normal and problematic
communications nested within an overall communica-
tions taxonomy. Only a few pieces of the communica-
tions puzzle have been presented without benefit of a
complete picture on which to base accurate conclu-
sions. Rather than ty to derive a picture from the
limited information, it might be better to start by
defining the characteristics of daily communications
and then extract the normal and miscommunications

subsets. This way, a better understanding of how big of
a problem miscommunications exert on daily ATC/
pilot operations can be obtained,

30

There has been only a limited focus on individual
differences among controllers and pilots in communi-
cating information to each other. The ability to trans-
mit information efficiently and effectively may vary
with the ability to: 1) speak clearly, 2) speak at optimal
rates, 3) compose messages, and 4) deliver messages
with minimal interruptions or “say agains.” Human
Technologies, Inc. (3991) has provided some direc-
tion for further studies on individual differences and
the Salt Lake City Terminal Communications Staff
study (1991) has also made some suggestions.

Recommendations

Recommendations derived from this review of
taxonomic, acoustical cotrelates, and the cognitive/
Psycholinguistic approaches include:

1. Determine whether a national database on voice
communications, as part of the operational er-
ror/deviation database, should be constructed.
As part of this database, the feasibility of having
the speech act become the standard unit of mea-
surement to examine voice communications
should be determined,

Determine whether an evaluation of the ASRS
data acquisition, coding, and entry system should
be performed. As part of this evaluation, the
reliability and validity of information coding
procedures should be examined.

Sample more air traffic facilities to determine
whether communications-based problems are of
national proportion or site specific. A variety of
data needs to be acquired including voice tapes
of live communications and visual information
so that the context within which voice commu-
nications occur can be determined.

Perform comprehensive experiments and corre-
lational studies to examine the relationships be-
tween workload performance factors and
communication ertors. Variables of interest
should include: 2) number of aircraft being
worked, b) radio frequency congestion, c) com-
bined positions/sectors, d) conflict, and e}
weather. Communication errors should include:
clearance composition, phraseology, delivery
technique, readback, and hearback.


during periods of heavy traffic. Pilots also accelerated
their speech rate during heavy workload. More re-
quests for repeated messages and corrections of incom-
plete readbacks were observed during moderate to
heavy workloads Although not measured directly,
subjective impressions lead McCandless to further
suggest that this resulted in increased controller stress
and anxiety (p. 8).

The McCandless study also offered specific recom-
mendations to improve communications. McCandless
suggested that controllers organize information into
“chunks,” that is, group-related information into a
single transmission for clarity (e.g., topically reiated
information, a main idea, or an idea unit} and increase
the inceliigibility of transmissions through good ar-
ticulation, normal speech rate, and low background
noise. Chunking has been used as 2 way to improve
retention of information in working memory by com-
bining individual pieces of information into a singular,
meaningful unit (cf. Loftus, et al., 1979). The
McCandless study suggested that pilots use brief, but
essential, radio transmissions, request clarification when
necessary, and increase the intelligibility of transmis-
sions through improved delivery techniques.

Morrow and Rodvold (1992) reported the findings
of 2 of their studies: a fieid study and a part-task
ulation study. The field study examined ATC/pilot
routine and non-routine communications sampled
from each of 4 tevel-5 YRACONs. The results demon-
strated that incorrect, partial, or missing readbacks
were infrequent events when daily communications
were considered. The results suggested that longer and
more complex messages preceded incorrect and partial
readbacks. Based on these findings, the part-task simu-
lation study varied message length based on the num-
ber of commands contained in a message. The results
of this study suggested that breaking longer messages
up into shorter ones was gererally better for commu-
nications if enough time were left between messages,
so thar a later arriving message did not interfere with
memory for the first message.

Taken as a whole, the studies presented here indi-
cated that: 1) only a few speech acts should make up a
single transmission; 2) the speech acts making up a

si

transmitted message should be topically related; 3) a
message should be brief; 4) a message should be mean-
ingful; and 5) time factors should be considered.

Interactive Conversations

Clark and Schaefer’s (1987) theoretical paper examined
the traditional view of conversational speech. The
traditional view holds that conversation is a single,
sequential process of turn taking between a speaker
and a recipient(s). That is, a speaker is tasked with
delivering understandable utterances. The recipient is
tasked with understanding those utterances. Within
this simplistic model there are 2 turns, i turn is made
by the speaker who initiates the conversation and the
other turn is made by the recipient. In this way,
conversations proceed 1 utterance ata time. Clark and
Schaefer state that conversations are social exchanges
thar require cooperation and collaboration among
those engaged in the act of conversing. Under such a
framework, conversations occur concurrently at 2 levels.
Level 1 (traditional view) consists of the conversation’s
topical focus; i.e., what the conversation is about (p.
20). Level 2 requires that the speaker and the recipie:.t
of the utterance share acommon understanding (mutual
belief’ of the utterance. Both the speaker and the
recipiert are responsible for the recipient gaining a
true understanding of whar the speaker meant to say
when an utterance was delivered.

In conversat onal speaking, collaborative effort is
expended through the process of presenting, correcting,
and confirming that the mutual understanding of ar
utterance has occurred before another utterance is
delivered. Clark and Schaefer present their model
using conversations that occurre+ between telephone
operators and telephone users who requested directory
assistance. Telephone communications often parallel
air traffic control communications in that both havea
structured grammar, both consist of minimal informa-
tion exchanges, both contain message interruptions,
and both are limited ro 2 participants at a time who
converse in a sequential order with minimal interrup-
tions. The structure of information transfer can con-
sist of either continuous utterances or as installment
utterances. With continuous utterances, a telephone
number has a sentential structure if the numbers are
preceded by a subject and verb in the form “It’s [prefix

25


this paper. Factors that predisposed controller perfer-
mance etrors were mainly errors cf omission; control-
lets failed to perform a faction as expected or needed.
The top 5 workload factors affecting controller perfor-
Marce were:

1) Large numbers of aircraft,

2) Frequency congestion,

3) Combined positions/sectors,

4) Conflict resclution, and

5) Inclement weather.

Frequency congestion included 1) stepped on trans-
missions due to large numbers of aircraft being worked
ona frequency, 2) continuous controller transmission
toa series of aircraft without a break for pilots to reply,
3) clipping, and 4) no breaks in communications
between the controlier and the aircraft being worked.
Combined positions/sectorsoccus when a single coptroi-
ler is assigned to work ali the positions making up a
sector (generally 3 positions). For example, a facility
may have ! controller work all the positions due to
staffing, traffic load, and time of day factors. Mid-shift
(midnight to 8 A.M.) may only require a single con-
troller to work the traffic making up the loca!, ground
and clearance delivery positions. Conflict resolution
involved an awareness of an impending corflict before
it become one; not its resolution. For example, 2
aircraft are on a converging course, the controller
becomes distracted, the CA symbol (conflict alert)
present on the radar screen brings the controller back
to the situation. The contrcller knew it was going to be
a problem but did not act upon all the available
information at the time. (Personal communication
with R. H. Wright, March, 1993). Communications
errors were primarily errors of commission that in-
volved either ATC procedural or verbat mistakes. A
further categorization of communications errors is
presented in Table 7. Heavy traffic, resulting in con-
troller overload and frequency congestion, was identi-
fied as the main factor associated wich communications
errors. No statistics were provided in this report.

The next major area of survey research developed
macro categories of miscommunications. For example,
5 key communication problems present withia the
aviation environment were identified (ASRS, 1990):

1) Frequency congestion,
2) Similar sounding call signs,

3) Pilot frequency monitoring failures,

4) Controller monitoring failures, and

5) Pilot failures to verify doubtful communica-
tions.

Pilot and controller communications techniques
included:

1) Problems during message composition,
2) Message production (i.c., transmission),
3) Message verification, and

4} Message comprehension.

According to the ASRS 1990 report, frequency
congestion was “clearly the worst communication prob-
lem confronting the aviation system” {p. 1). Proce-
dural shortcutting, phraseology truncation, and
improper controller or pilot communication tech-
niques were implicated with frequency congestion. A
comparison of the 1988-1989 ASRS incidents pre-
sented in the 1990 ASRS Report indicated 2 6%
increase in the frequency with which communications
techniques were cited as a contributing fuctor in the
filed incident reperts. There also was a 2% increase in
the citation of a faulty readback/hearback during the
same reporting period,

Reports generated from ASRS data have been help-
ful in developing broad classification communication
taxonomies and for elucidating areas for further expio-
ration. However, most ASRS analyses cannot be used
to determine the causal factors related to an incident or
operational error because of the subjective, post hoc
nature c- ‘he reports. Pilots generally file reports to
ASRS after they have been involved in a possible
violation ofa FAR. Their reports are filed after the fact
and are based on private interpretations. It is not
possible to verify the accuracy of their reports.

Audio Tape Analyses: Exploratory Studies
Involving Real-time ATC/Pilot Radio
Communication Tape Analysis

Intheearly part of 1990, new approaches for developing
communication taxonomies began to emerge. Audio
tape real-time recordings of pilot-controller com-
munications supplied the data for analysis. Gellman
Research Associates, Inc. (1987) developed 2
methodology and data reduction coding form for
analyzing pilot-controller readback errors. Golaszewski


Table 8

Kanki and Foushee (1989). Speech act coding scheme.

Category Definition

Command A specific assignment of responsibility by one group member to another
Observation Recognizing and/or noting a fact or occurrence relating to the task
Suggestion Recommendation for a specific course of action

Statement of Intent

inquiry

Agreement

Disagreement

Acknowledgement

Answer

Response Uncertainty

Tension Release

Frustration/Anger/Derisive Comment

Embarrassment
Repeat

Checklist
Non-task Related

Non-codable

ATC

Total Communication

Announcement of an intended action by speaker; includes statements
referring to present and future actions but not to previous actions

Request for factual, task-related information; not a request for action

A response in concurrence with a previous speech act; a positive evaluation
of a prior speech act

A response not in concurrence with a previous speech act; a negative
evaluation of a speech act

fa) Makes known that a prior speech acct was heard; (b) does not supply
additiona! information; (c) does not evaluate a previous speech act

Speech act supplying information beyond mere agreement, disagreement, or
acknowledgement

Statement indicating uncertainty or lack of information with which to
respond to a speech act

Laughter or humorous remark

Statement of displeasure with self, other persons, or some aspect of the task;
or a ridiculing remark

Any comment apologizing for an incorrect response
Restatement of a previous speech act without prompting
rompts and replies to items on a checklist
Any speech act referring to something other than the present task

Speech act which is unintelligible or unclassifiable with respect to the present
coding scheme

Flight-crew radio communication with Air Traffic Control, dispatch, “the
company,” etc.

Sum of ali the above

12