An Analysis of Tower (Ground) Controller-Pilot Voice Communications
Preface
We thank the Federal Aviation Administration Office of the Chief Scientist for Human Factors (AAR-100) for supporting this and other air traffic control (ATC) communications work. Bryan Brett of Science Applications International Corporation (SAIC) coordinated the voice-tape and raw-data analysis, and, together with Dave Malek, promptly fielded many follow-up questions. Ben Cameron, John Chevalier, Joe Jarboe, and Joe Moyer, also from SAIC, analyzed the voice tapes. We appreciate their effort in this difficult and sometimes tedious task. Dr. Kim Cardosi provided insightful comments on an earlier draft of this report. Finally, we thank the quality assurance specialists at the participating ATC facilities who supplied the tapes for this analysis.
Table of Contents
1. Introduction
2. Materials
3. Controller Instructions
4. Pilot Responses
5. Communication Problems
5.1 Overview
5.2 Requests for Repeats
5.3 Readback/Hearback Errors
5.4 Callsign Confusion
5.4.1 Overview
5.4.2 Callsign Confusion by Controllers
5.4.3 Callsign Confusion by Pilots
5.5 Conceptual Errors
5.5.1 Conceptual Errors by Controllers
5.5.2 Conceptual Errors by Pilots
5.6 Communication Problems and Transmission Density
6. Summary and Comparison With Previous Studies
7. Recommendations
8. References
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Executive Summary
This analysis of ground-control communications is part three of a four-part effort to capture not only the qualitative, but also the quantitative aspects, or incidence, of air traffic control miscommunications. The approach taken is to examine representative samples of pilot-controller communications recorded in four air traffic control (ATC) environments; tower-ground control (this report), air route traffic control centers (Cardosi, 1993), tower-local control (Cardosi, 1994), and terminal radar control (TRACON) (in progress).
Despite initial applications of datalink, voice communications between air traffic controllers and pilots remain at the center of ATC operations. Given this prominent role, it is not surprising that communication problems have been identified as a factor in over 70 percent of operational errors and pilot deviations in the FAA's Operational Error and Deviation System (OEDS) (Danaher, 1993). Accidents such as the 1977 collision between two Boeing 747s at Tenerife, demonstrate the potentially fatal consequences of inadequate communication. (One aircraft taxied down the runway while the other used the same runway for an unauthorized takeoff.) Additional evidence for communication problems stems from incidents reported to the Air Safety Reporting System (ASRS; see, e.g., Monan, 1988). Although evidence from such (potential) accidents and incidents is very valuable for pinpointing and/or investigating specific areas of concern, it represents a biased sample, counting only the cases in which something went awry.
At the Department of Transportation's Volpe Center for Transportation Human Factors Research, we are taking a three-pronged approach to the investigation of air-traffic control communications. In addition to communication problems reported to the ASRS, we are examining voice tapes recorded at ATC facilities during actual operations. This endeavor is the subject of the present report. Furthermore, we are verifying some of the conclusions drawn from the two previous approaches and investigating other issues relevant to effective controller-pilot communication in carefully controlled laboratory studies (see, e.g., Bürki-Cohen, 1995 a, b).
This report is based on an analysis of over 48 hours of pilot-controller communications recorded from the ground-control frequency at twelve air traffic control towers. We examined the complexity of controller instructions, that is, how many pieces of information a single controller transmission contains. We also looked at how pilots respond to these instructions, and whether the type of response is affected by the complexity of the instructions. Particularly, we studied the effect of complexity of the instructions on communication problems, such as when pilots ask controllers to repeat their instructions or when they make an error in the readback. Other communication problems examined include aircraft callsign discrepancies and conceptual errors (e.g., when a controller sends a pilot to the wrong runway or a pilot dials in the wrong frequency.)
The following recommendations to further improve ATC communications and thus the margin of safety in the ground-control environment arise from this investigation:
- Controllers should keep instructions short. The shorter an instruction, the more likely will it be correctly read back by the pilot.
- Controllers should listen to what a pilot reads back, especially regarding hold-short and taxi instructions and frequencies. More emphasis should be given to hearback during controller training (ASRS Callback, 1992).
- Controllers should try to speak slowly especially when they are under pressure and don't have time to repeat information.
- When talking to foreign pilots, controllers should take into account the potential for phraseology differences and reduced English language proficiency. TheFAA should compile a list phraseology differences to be distributed to controllers and pilots, especially those flying internationally. Controllers also should speak "staccato," that is, to break the instruction up into its component words by inserting short pauses. Recognizing where one word ends and the next begins is notoriously difficult for any inexperienced listener of a foreign language. Repeating numbers in grouped format, i.e., "seven-teen," instead of sequential format, "one seven," as recently authorized for emphasis of altitudes (FAA, 1992), may backfire with foreign pilots who group numbers differently in their native language.
- Pilots should ask when they are not sure about a piece of information. But even if pilots are sure that they have heard and remembered correctly, they should at least read back hold-short instructions and frequency changes.
- Whenever possible, controllers should point out similar callsigns on the same communication frequency. All instructions and readbacks should include the full callsign.
- Both controllers, when listening to readbacks, and pilots, when taking instructions, should be aware of how their expectations may affect what they hear. Pilots expecting certain instructions must wait for complete aircraft identification before taking action on the instructions.
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References
ASRS Callback Number 163, 1992. Readback/hearback - Some fresh ideas.
Bürki-Cohen, J. 1995a. Say again? How complexity and format of air traffic control instructions affect pilot recall. 40th Annual Air Traffic Control Association Conference Proceedings.
Bürki-Cohen, J. 1995b. How to say it and how much: The effect of format and complexity on pilot recall of air traffic control clearances.
Cardosi, K. 1993. An analysis of en route controller-pilot voice communications. DOT/FAA/RD-93/11.
Cardosi, K. 1994. An analysis of tower (local) controller-pilot voice communications. DOT/FAA/RD-94/15.
Danaher, 1993. Close encounters of the wrong kind; accidents/incidents involving communications. Paper presented at "Communicating for Safety." A Seminar for Pilots and Air Traffic Controllers. Phoenix, Arizona, May 18-20.
Federal Aviation Administration 1991. Runway Incursion Plan. Associate Administrator for System Engineering and Development (ARD-100).
Federal Aviation Administration 1992. Air Traffic Control (7110.65G). Air Traffic Rules and Procedures Service.
Federal Aviation Administration 1993. Statistical Handbook of Aviation. Office of Aviation Policy, Plans and Management Analysis, FAA APO-95-5.
Monan, W.P. 1988. Human factors in aviation operations: The hearback problem. NASA Contractor Report 177398.
Morrow, D., Lee, A., & Rodvold, M. 1993. Analysis of problems in routine controller-pilot communication. International Journal of Aviation Psychology, 3(4), 285-302.
Morrow, D., & Rodvold, M. 1993. The influence of ATC message length and timing on pilot communication. NASA Contractor Report 177621.
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