Nov 11, 2009 - collaborative practices that tax controller and pilot attention and memory. .... altitude command, the pilot might respond "I don't think we can ...
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Nonroutine transactions in controller‐pilot communication Daniel Morrow Lee a
a b
c
, Michelle Rodvold & Alfred
b
Decision Systems, Stanford, CA
b
Department of Psychology, University of New Hampshire, Conant Hall, Durham, NH, 03824 c
San Jose State University Foundation, Published online: 11 Nov 2009.
To cite this article: Daniel Morrow , Michelle Rodvold & Alfred Lee (1994): Nonroutine transactions in controller‐pilot communication, Discourse Processes, 17:2, 235-258 To link to this article: http://dx.doi.org/10.1080/01638539409544868
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DISCOURSE PROCESSES 17, 235-258 (1994)
Nonroutine Transactions in Controller-Pilot Communication DANIEL MORROW
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Decision Systems, Stanford, CA MICHELLE RODVOLD
San Jose State University Foundation ALFRED LEE Decision Systems, Stanford, CA
People use a variety of strategies and devices to make themselves understood, partly in response to different communication constraints. The present study examined how communication during routine Air Traffic Control operations is shaped by accuracy and efficiency constraints. Controllers and pilots use a combination of English and special conventions that have developed in response to these constraints. One convention is the collaborative scheme, in which the speaker initiates a transaction, presents new information, and collaborates with the addressee to accept the information as mutually understood and appropriate (Clark & Schaefer, 1987). We examined how this scheme is used to balance the demands of accuracy and efficiency during routine pilot-controller communication. This scheme also organizes nonroutine communication, where pilots and controllers interrupt routine communication in order to resolve communication problems. Findings suggest that several communication problems can be traced to nonstandard collaborative practices that tax controller and pilot attention and memory. In addition, the accuracy and efficiency constraints influence which strategies and devices are used to resolve these problems.
Speakers and addressees do more than produce and understand utterances. They also work together to ensure that the utterances are mutually understood. The strategies and devices they use to achieve this mutual understanding depend on constraints imposed by participant goals, the medium, and other aspects of the communication situation (Clark & Brennan, 1990). This article explores how controllers and pilots understand each other by using a combination of English and special conventions that have developed in response to two broad constraints Daniel Morrow is now at the University of New Hampshire. This research was supported by NASA-Ames Research Center under a contract to Sterling Software (#2000-00342240). We thank the FAA for permission to obtain the communication samples. We also thank Herbert H. Clark for his many comments on the research and the paper. Partial results were presented at the Psychonomics Society Meetings, New Orleans, LA, November 1990. Correspondence and requests for reprints should be sent to Daniel Morrow, Department of Psychology, Conant Hall, University of New Hampshire, Durham, NH 03824. 235
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MORROW, RODVOLD, AND LEE TABLE 1 Example of Procedural Deviation, Inaccurate Readback, and Nonroutine Transaction With Understanding Problem
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Controller:
Pilot:
Cessna 223 (Callsign identification) Turn left heading 180 Intercept the Tracy 186 Radial Resume the Link 4 Departure Climb maintain 5000 Intercept 180 Radial / 5000 Cessna 223
Controller:
Pilot:
Cessna 223 That's the Tracy 186 Radial. Roger
[Incorrect Readback: Confuses heading and radial] [Partial Readback: Does not read back heading and SID commands] [Nonroutine Transaction: Controller corrects readback] [Missing Readback and Callsign]
in the Air Traffic Control (ATC) system. First, accurate understanding of each piece of information is often essential for air safety. This accuracy constraint has led to explicit acknowledgment procedures such as readbacks, where pilots repeat the ATC message so that the controller can check its interpretation. Second, ATC communication must be rapid because pilots and controllers talk about dynamic situations, and because many pilots talk to one controller over the same radio frequency. In response to this efficiency constraint, ATC language is highly compressed, with abbreviated terminology and phrasal syntax (see Table 1 for an example). The present study used a model of collaboration (Clark & Schaefer, 1987) to examine controller-pilot communication. According to this approach, communication takes place against a background of shared knowledge about language (English), ATC communication conventions (e.g., readbacks), and the operational environment (the navigation task, air space conditions). One important convention is the collaborative scheme. We explored how speakers and addressees use this scheme to organize routine as well as. nonroutine transactions, where the speaker or addressee interrupts routine communication in order to resolve a communication problem. COLLABORATION IN ROUTINE AIR TRAFFIC CONTROL COMMUNICATION People usually follow the collaborative scheme in order to ensure mutual understanding. Speakers initiate a transaction with one or more addressees, present new information about a topic, and collaborate with their addressees to accept the information as mutually understood and appropriate to the context (Clark &
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Schaefer, 1987; Ringle & Bruce, 1981). The scheme is illustrated by the following conversation:
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Rod: Felicia: Rod: Felicia:
Hi there. I'm on my way to the library. Mh hm. Gotta study for an exam. Yeah, me too. I'm behind as usual.
Rod initiates the conversation with a greeting and then presents information about some topic. Felicia accepts this information with a minimal acknowledgment, and Rod mutually accepts by continuing with the next turn. Similarly, Felicia implicitly accepts Rod's next presentation by making a relevant response. These minimal accept devices are often used in conversation (Clark & Schaefer, 1989). In ATC communication, controllers and pilots usually initiate transactions with aircraft identifications (e.g., "Cessna 223") and facility identifications (e.g., "Oakland Tower"). Typically, controllers next present information with command ("Turn left heading 180") and report speech acts ("Traffic at 2 o'clock [location with respect to direction of travel], A citation [type of aircraft], southbound [direction of travel of the traffic]") so that the pilots can update their mental model of the navigation task and carry out the intended actions (Human Technology, 1991; Morrow, Lee, & Rodvold, 1993). Because of the accuracy constraint in ATC communication, controllers and pilots often use more explicit devices than in other types of conversation to accept information as mutually understood. According to the Airman's Information Manual (Federal Aviation Administration [FAA], 1989), pilots should acknowledge ATC messages with their callsign and a readback, or repeat, of the commands in order to demonstrate that the intended pilot understood the message. In the transaction presented in Table 1, the pilot reads back the controller's commands. In routine transactions, controllers often implicitly accept pilot acknowledgments by beginning a new turn or transaction, or they explicitly accept with their own acknowledgment (Morrow et al., 1993). Pilots and controllers also accept the information as appropriate—complete, accurate, and timely (Billings & Cheaney, 1981). In short, controllers and pilots must agree that they share the same mental model before continuing to the next turn or transaction.
COLLABORATION IN NONROUTINE ATC COMMUNICATION The collaborative scheme also organizes nonroutine communication, where controllers and pilots resolve communication problems. These problems may relate to nonstandard initiation, presentation, and acceptance practices that tax pilot and controller cognitive abilities. Once a problem occurs, pilots and controllers must collaborate to resolve the problem. To do this, they deviate from the
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standard collaborative scheme, producing a nonroutine transaction. We focused on several problems related to nonstandard acceptance procedures, examining how often they occurred in samples of ATC communication, why they may occur, how they are resolved, and what their consequences were. Understanding and Information Problems Two general kinds of communication problems were examined. With understanding problems, addressees do not correctly update their mental model from the presented information (or speakers do not receive evidence that addressees did so). For example, addressees may not hear the message (Billings & Cheaney, 1981). Even if they hear the message, they may misunderstand all or part of it. Finally, even if they identify the words in the message, they may not correctly integrate the information with their mental model in order to identify the intended message. Ringle and Bruce (1982) refer to the latter as "model" rather than "input" errors. So, after "Cessna 223, Cross Seton [a navigation reference point] at altitude 4000 feet," a pilot may not hear the controller at all (no response), may hear but only partially understand ("Was that 4000 on the altitude?"), or may be unable to interpret the message even though all the words were identified ("Where is Seton"?). With information problems, addressees correctly understand the message but decide that it is inappropriate because the information is inaccurate, incomplete, or mistimed. For example, in response to the previous altitude command, the pilot might respond "I don't think we can descend that fast." Causes of Communication Problems We examined transcripts to determine if understanding and information problems are caused in part by cognitive demands imposed by nonstandard collaborative practices. Communication requires both individual and collaborative effort (Clark & Wilkes-Gibbs, 1986). Individual effort is defined as working memory capacity needed to initiate transactions (e.g., attract the addressee's attention) and to produce and understand messages (Levelt, 1989; van Dijk & Kintsch, 1983). Collaborative effort is also required because speakers and addressees must take the time to mutually accept information as understood and appropriate. For example, pilots keep ATC messages in working memory in order to read back the commands. In turn, controllers keep both the readback and their original message in working memory in order to "hear back," or check the accuracy of the readback. Cognitive constraints are particularly important in ATC communication because of the efficiency constraint—there is often little time to produce and understand messages and explicitly accept them. Nonstandard initiating, presenting, and accepting practices may create misunderstandings or disagreements by taxing limited attention and memory. 1. Initiation. Transactions may be unsuccessfully initiated because callsign problems (callsigns that are incorrect, partial or similar to other callsigns)
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2.
3.
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create confusion about the intended addressee (Golaszewski, 1989; Monan, 1983). In an earlier paper, we analyzed callsign problems in the present communication samples (Morrow et al., 1993). Presentation. Speakers may present too much information in one turn. For example, misunderstandings (indicated by incorrect readbacks) and nonstandard acceptance procedures (procedural deviations such as partial readbacks) are more frequent after longer messages (Morrow et al., 1993). Acceptance. Nonstandard acceptance procedures such as partial acknowledgments often prompt speakers to repeat messages in order to make sure they are understood, again producing nonroutine transactions.
This article focuses on how nonstandard acceptance procedures lead to nonroutine transactions. Resolving Communication Problems: Nonroutine Transactions In order to resolve an understanding or information problem, participants interrupt routine communication with a side-sequence in which they indicate and repair the problem so that the original message can be fully accepted (Clark & Schaefer, 1987; Jefferson, 1972). In the following transaction, the pilot begins a side-sequence by indicating an understanding problem, and the controller closes the sequence with a repair. Controller: Pilot: Controller: Pilot:
Cessna 223, Turn left heading 180, Climb and maintain 8000 feet. Cessna 223, Say again the heading. (Problem indication) Cessna 223, Turn left heading 180, (Problem repair) Climb and maintain 8000 feet. 180, 8000 on the altitude, Cessna 223. (Final acceptance)
Collaboration in nonroutine as well as routine transactions should be influenced by the accuracy and efficiency constraints. Controllers and pilots should use explicit acceptance procedures in order to satisfy the accuracy constraint. They should also resolve problems as quickly as possible because of the efficiency constraint. Problem indication-repair side-sequences were examined in order to see how pilots and controllers trade off efficiency and accuracy. For example, indication-repair sequences should result in explicit acceptance, such as acknowledging corrections, even though leaving off this final step would save time. Accuracy may also influence how problems are repaired. For example, speakers in other types of dialogue use more abbreviated repairs if addressees indicate that they understood part of the message rather than missing the whole message. By building on evidence provided by the addressee, speakers can minimize repair time and thus collaborative effort (Clark & Schaefer, 1987; Jefferson, 1972). However, pilots and controllers may use more elaborate repairs than necessary because of the accuracy constraint.
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Three understanding problems were examined. First, the speaker receives little or no evidence of being understood and repeats or otherwise prompts the addressee for an acknowledgment. Second, the speaker receives evidence of being misunderstood because the addressee gives the wrong interpretation (incorrect readback). In response, the speaker corrects the addressee (see Table 1 for an example). In both cases, the speaker simultaneously indicates and repairs the problem by repeating the message. Finally, addressees indicate that they misunderstood the message, prompting the speaker to clarify (as in the earlier example). We examined the devices used to indicate and repair these problems, as well as the level of misunderstanding these devices imply. For example, requesting a repeat of a message implies not hearing the message, while asking for a repeat of a heading command implies partial understanding. Several information problems were also examined. First, speakers noticed that they presented inaccurate information and corrected themselves within the same turn (first controller turn in Table 2). Second, addressees noticed that the speaker's message was inaccurate (see Table 2) and then updated it. Third, addressees noticed that a message was incomplete, and they filled in the information or asked the speaker to do so (Table 2). Fourth, speakers had to ask for a message that should have been given already (mistimed message). Finally, addressees challenged the message as inappropriate (for example, a pilot challenged a heading command with, "We're already on that heading"). We examined the consequences of nonroutine transactions by investigating how much nonroutine transactions reduced communication efficiency while ensuring accuracy. Nonroutine transactions should be longer than routine transactions because of the time needed to resolve the problem. Efficiency will be reduced if this extra time is spent accepting old information rather than presenting new information. Controllers and pilots may also use nonstandard language and procedures in TABLE 2 Example of Nonroutine Transaction With Information Problem Pilot:
Controller:
Dallas Approach (ATC facility identification) Cessna 223 (Pilot callsign identification) with Gulf Cessna 123 Correction, Cessna 223 Dallas Approach Radar contact Hotel is current Say altitude
Pilot:
Cessna 223 Out of 20,000
[Incomplete Contact] [Inaccurate report of ATIS (airport conditions)] [Controller self-correction]
[Controller corrects pilot ATIS report] [Controller requests information]
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TABLE 3 Example of Emergency Transaction Controller:
Cessna 223 Turn right heading 290
Pilot:
Okay, 290 /for Cessna 223 and uh sir, we got a little flap uh problem here/ it looks like uh we got them uh extended out,/ we can't get them up,/ we're going to have to have uh a come around I guess.
Controller:
Cessna 223 All right, Did you want to return to the airport then?
Pilot:
Uh, it looks like it right now, Uh give us another minute or two here.
Controller:
Cessna 223 All right, Just slow heading 290 and uh keep me advised.
Pilot:
Roger
nonroutine transactions. When talking to pilots, controllers typically use a command-oriented language that is governed by ATC conventions about terminology, syntactic form (phrases rather than full clauses), and the organization of speech acts in messages (Human Technology, 1991; Morrow et al., 1993; see Table 1 for a typical transaction). When resolving problems, however, controllers and pilots may switch to language and strategies that they normally use in conversation. They may do so for at least two reasons. First, they do not have many ATC conventions for resolving communication problems. Second, they may use conversational strategies because ATC conventions do not give them the flexibility to discuss nonstandard topics, whether or not miscommunication is involved. To examine this second possibility, we analyzed emergency as well as nonroutine transactions. In these transactions, controllers and pilots do not have a communication problem, but they discuss nonstandard topics such as a problem with flaps (see Table 3). Nonstandard language should be frequent in emergency as well as nonroutine transactions if controllers and pilots shift to conversational language when discussing a nonroutine topic. METHODS Communication Samples We analyzed audio tapes of controller-pilot communication during Terminal Radar Control (TRACON) operations, which require complex, frequent commu-
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nication (Lee & Lozito, 1989). Twelve hours of communication (half from Departure and half from Approach sectors) were randomly selected from four level-5 TRACONs (minimum of 300,000 operations per year) in the United States. However, not all of the communication was clear enough to be accurately transcribed. Table 4 presents the number of hours of transcribed communication and the number of transactions for each TRACON sample. Coding the Communication The communication was transcribed verbatim and divided into units that roughly correspond to utterances with a specific communication function. These units ranged from one phrase (e.g., callsign identification) to several phrases (e.g., traffic report), and complex units were further divided into units with distinct subfunctions (e.g., a traffic report was subdivided into phrases conveying different traffic information). The units were coded in two passes. Findings from firstpass coding were presented in Morrow et al. (1993). This paper presents findings from the second-pass coding. First-Pass Coding. As described in Morrow et al. (1993) and Rodvold and Morrow (1991), all transactions in the four TRACON samples were coded on the following dimensions. Transaction Organization. We defined a transaction as a set of turns between the same controller and pilot, with no more than 5 s of silence between turns (interturn intervals in conversation are often less than 50 ms; Walker, 1982). Transaction length was measured by the number of turns and speech acts. Transactions were coded for several factors that may influence turn and speech act organization, including speaker (pilot/controller), sector (Approach/Departure), and aircraft (air carrier unscheduled). Table 1 presents a transaction with two controller and two pilot turns.
TABLE 4 Description of TRACON Samples Nonroutine Transactions
