Evaluation of Pilot and Air Traffic Controller Use of Third Party Call Sign in Voice Communications with Pilot Utilization of Cockpit Display of Traffic Information

July 2013
Topics: Air Traffic Management, Avionics, Human Factors Engineering
Randall S. Bone, The MITRE Corporation
William J. Penhallegon, The MITRE Corporation
Leslie M. Benson, The MITRE Corporation
Gregory L. Orrell, The MITRE Corporation
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To take advantage of projected benefits afforded by Automatic Dependent Surveillance-Broadcast (ADS-B) In enabled Aircraft Surveillance Applications (ASAs), the use of call sign has been proposed as the method for pilots and controllers to refer to other (third party) aircraft on a common voice frequency. However, using these “third party call signs” (TPCS) to talk about (rather than talking to) other aircraft on the same frequency introduces a potential for confusion for controllers and pilots. The Federal Aviation Administration (FAA) Surveillance and Broadcast Services (SBS) program office identified TPCS as a program risk and initiated an activity to examine the topic. This Human-in-the-loop (HITL) simulation is part of that effort.

The simulation was intended to evaluate TPCS voice communications alternative candidates proposed by subject matter experts participating in the SBS activity and to provide research results that establish a basis for narrowing down the alternatives. It employed pilots, en route controllers, and terminal controllers as participants and evaluated the TPCS candidates within the context of two ASAs during an arrival and approach operation. Three TPCS formats and two placements were evaluated within the context of a traffic advisory and an Interval Management clearance. The study was framed around three central research objectives. These objectives and a summary of the corresponding results are presented below.

  1. The first objective was to determine whether deviating from the use of current day call sign format phraseology was necessary for pilots and controller to reference a Third Party Aircraft (TPA). The simulation found no evidence to suggest that deviating from current phraseology is necessary to reduce Third Party Pilot (TPP) confusion. Additionally, controllers generally preferred the use of current phraseology (Telephonic format), though pilots preferred the pronunciation of the individual letters (Letters format) in the airline designator. In some cases, the Letters format helped pilots more accurately identify the TPA on their Cockpit Display of Traffic Information (CDTI) traffic display than the current Telephonic format. As such, and despite reported controller misgivings, there may be advantages for deviating from the current Telephonic call sign format to convey TPCS.
  2. The second objective was to determine whether user acceptability and performance trade-offs existed between the chosen TPCS alternatives. Pilots showed a subjective preference for the Letters format, likely because it helped them better identify the TPA on the CDTI traffic display. A third format, termed “Delimiter,” was evaluated and consisted of placing the word “reference” between the airline designator and numeric flight identification. The Delimiter format was consistently rated poorly and associated with the most performance issues for both pilots and controllers. Overall, the Letters format appeared to be superior to the Delimiter format and it is not recommended that Delimiter formats be explored any further.
  3. The third objective was to determine the user acceptability and performance trade-offs related to the placement of TPCS within the controller clearance or advisory (i.e. earlier versus later). Simulation results show that TPCS in the later position was more acceptable and had fewer performance issues than in the earlier position. The improved performance could be because the later position allowed for a more natural and logical flow, and provided the least deviation from how pilots and controllers currently convey information in voice communications.

An appropriate phraseology solution needs to minimize the potential for TPPs on the frequency to become confused about transmissions referring to them, as well as allow pilots and controllers to establish a clear awareness of the aircraft being referenced. Based on the results of this simulation, two possible approaches with respect to TPCS format are recommended for the next and final activity in the SBS effort. Assuming that TPP confusion will be rare and solvable as it occurs, one approach is to allow controllers to use a Telephonic format as the normal method of conveyance, with the option to use the Letters format when the controller believes there may be pilot confusion about the airline three letter designator. The pilot would be expected to reply with the format used by the controller. However, if situations arise where the controller uses the Telephonic format and the pilot has confusion about which TPA is being referred to, the pilot could reply with a question asking for clarification of the TPA using the Letters format to resolve any ambiguity.

A second approach, that proactively mitigates the potential for TPP confusion, involves a required controller deviation from the current phraseology for TPCS. Despite less controller acceptability than the Telephonic format, simulation results suggest that the Letters format showed performance advantages for pilots and controllers in some instances. For this approach, follow-on research to further explore the acceptability of mandating the use of the Letters format for TPCS, particularly with controllers, is recommended.   

For either approach, TPCS placement should be carefully considered to maintain a natural flow and minimize the deviations from current phraseology for the individual clearance, instruction, or advisory in which it is expected to be used. In addition, a safety analysis may be desirable to fully understand the likelihood and impact of TPP confusion, which will always remain a possibility in voice communications.

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