Air Traffic Controller and Flight Crew Conduct of a No-Closer-Than Spacing Task utilizing a Cockpit Display of Traffic Information

March 2016
Topics: Air Traffic Management, Avionics, Human Factors Engineering
Randall S. Bone, The MITRE Corporation
Andrew S. Mendolia, The MITRE Corporation
Eric Vallauri, Egis
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A Human-In-The-loop (HITL) simulation involving air traffic controllers and flight crews was conducted to examine a new Automatic Dependent Surveillance-Broadcast (ADS-B) Aircraft Surveillance Application (ASA) called Cockpit Display of Traffic Information (CDTI) Assisted Pilot Procedure (CAPP). The purpose of the simulation was to determine CAPP feasibility and operational acceptability from the perspective of the following topics: cloud ceilings, spacing between aircraft, benefits, transition to another ASA, roles and responsibilities, workload, displays, and communications. The CAPP concept examined in the simulation was that most recently defined in ADS-B standards bodies (additional implementations may be possible).

The main objective of CAPP is to begin a spacing reduction in arriving aircraft during the transition from Instrument Meteorological Conditions (IMC) to visual separation operations, such as CDTI Assisted Visual Separation (CAVS), where further spacing reductions are expected. CAPP includes new display elements, procedures, and communications. CAPP involves a controller issuing an instruction to the flight crew of a CAPP aircraft to use their traffic display information to space from a Traffic To Follow (TTF) during final approach operations. The instruction includes the call sign of the TTF and a No Closer Than (NCT) distance value. The NCT distance is expected to be close to, but not less than, the applicable separation standard (as the controller remains responsible for separation). The flight crew’s task is to make spacing judgments and manage speed using information provided on the traffic displays to stay at or outside of the spacing value issued by the controller while achieving their desired spacing. The flight crew task is supported by an advisory level alert for the NCT value. When conducting CAPP, the flight crew is expected to continue an Out-The-Window (OTW) visual scan for the TTF and for reaching visual conditions. When the sighting occurs, it is reported to the controller so a transition to visual separation can occur.

Eleven controllers and eleven flight crews conducted CAPP under four conditions examining the independent variables of cloud ceiling (3300 and 1800 feet [ft]) and NCT value (3.2 and 3.5 Nautical Miles [NM]). The participants also conducted CAPP in four other events that examined additional outstanding questions: a CAPP aircraft overtake, no transition from CAPP to CAVS, CAPP with pilot separation responsibility, and extra flight crew actions to transition from CAPP to CAVS.

Overall, the results support the hypotheses of CAPP being feasible and acceptable to controllers and pilots under both ceiling and NCT value conditions. The results also support the hypotheses related to the pilot’s ability to conduct CAPP and remain at or outside the NCT value, as well as the controller’s ability to detect spacing / separation issues during CAPP. The 3300 ft ceiling was generally found to be more acceptable to pilots and controllers. The NCT value appeared to be less of a factor for pilots, but the 3.2 NM NCT value appears to better approximate the spacing desired by the controller. The 3.2 NCT value may be sufficient for ceilings that allow for additional closure after a transition into CAVS / visual separation operations.

The displays and communications used in the simulation were reported as providing the necessary information for CAPP.

Controllers were generally more positive than pilots about the concept due to reduced workload, having more time available to monitor non-CAPP aircraft, and additional support for the spacing task during approach. Pilots reported increased traffic awareness but also increased workload.

Both pilots and controllers had questions about separation responsibilities. From a controller perspective, their positive questionnaire responses suggest they may be willing to retain separation responsibility (as done in this simulation). However, it appears the controllers prefer to have the flight crew be issued separation responsibility during CAPP. From a flight crew perspective, it appears that while some pilots may prefer the controller maintains separation responsibility, a majority would be willing to accept it and the transfer is desirable.

Based on the results, CAPP appears to have benefits and is worth pursuing when there is a transition to CAVS / visual separation. Without this transition, not enough data was available to draw final conclusions on the benefits of conducting CAPP. With the transition to CAVS, pilots used the NCT value as a goal (versus a distance to remain far away from) and set in an even lower spacing for the CAVS operation. The lowest ceiling examined in the simulation gave little time to gain the benefit of additional closure during CAVS. Therefore, the exact ceilings under which CAPP is most beneficial should continue to be examined. The separation responsibilities of the controller and flight crew should also continue to be examined since greater benefits, and a more acceptable and desirable implementation, may be possible. Regardless of separation responsibilities, controllers will continue to have a key role in the successful implementation of CAPP. A wide initial spacing within the CAPP pair is unlikely to be reduced significantly by the pilots. Tighter initial spacing will result in reduced spacing at the threshold, and potentially reduced variability, while retaining the ability of pilots to “fine tune” their spacing.

The recommendations and results of this simulation are intended to be used by the FAA, European Organisation for Civil Aviation Equipment (EUROCAE), and RTCA in developing CAPP conceptual and technical standards. The technical sponsors of this research in FAA’s Office of Aviation Safety (AVS), who develop the regulatory and guidance material for ASAs, are also expected to use the recommendations and results in the development of Advisory Circulars (ACs) and Technical Standard Orders (TSOs) based on the international standards.

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