Abstract

RTCA Special Committee 186 has recently adopted a series of changes to the original Minimum Aviation System Performance Standards (MASPS) for Automatic Dependent Surveillance Broadcast (ADS-B).1 The new document will be published as DO-242A. Major changes to the MASPS include a significant restructuring and expansion of the intent parameters for future ADS-B systems. ADS-B provides a means for aircraft to exchange information about their intended trajectories with each other and with ground systems. NASA and Boeing have played significant roles in recommending these changes and providing supporting analysis. The intent changes are anticipated to provide substantial benefits to several programs and operational concepts under development by the two organizations.
There are four primary changes in the specification of intent broadcast for DO-242A ADS-B systems:
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Introduction of Target State (TS) reports for broadcasting current flight segment target states, including target altitude and target heading or track angle. These reports provide information about an aircraft’s short-term intent.

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Adoption of a broader definition of Trajectory Change Points (TCPs) that includes 2-D Area Navigation (RNAV) waypoints, 3-D and 4-D trajectory change points under DO-242, and level-off changes in vertical transitions. The expanded definition accommodates uncertainties that can exist along an aircraft’s trajectory.

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Introduction of Trajectory Change (TC) reports for broadcasting successive flight segment parameters and TCPs. (TC reports are the DO-242A equivalent of next TCP and TCP+1 reports in DO-242, but with an expanded report format for more generic TCPs, and capability for transmitting up to four TCPs.)

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Introduction of new transmission update rates and broadcast conditions for aircraft broadcasting TS and TC reports.

These changes have been designed to better reflect the capabilities of existing and future aircraft avionics, while providing benefits to current and proposed applications. DO-242A implements intent information elements that can be supported by current avionics systems and data buses. Provisions are made for future incorporation of other intent elements, as needed to meet operational requirements. This document summarizes the reasons for the DO-242A intent changes and provides a detailed overview of current and future intended ADS-B MASPS changes related to aircraft intent.
1 Introduction

The revised Minimum Aviation System Performance Standards (MASPS) for Automatic Dependent Surveillance Broadcast (ADS-B) document (DO-242A) incorporates significant changes related to the exchange of aircraft intent information. Aircraft intent refers to information known about an aircraft’s intended trajectory and is considered to be an enabling technology for the future National Airspace System.2 ADS-B is a means by which aircraft can exchange intent with each other and with ground stations. As primary sponsors of the MASPS changes related to intent, NASA and Boeing have worked to ensure that the ADS-B MASPS is supportive of future intent applications under consideration by both organizations.
The reason for considering broadcast of intent information in ADS-B systems is to extend the domain of predictability of aircraft trajectories beyond short-term extrapolations using current aircraft position and velocity states. Most current ADS-B applications under development only require state vector data. However, future applications of ADS-B could require intent information to extend look-ahead time for trajectory predictions beyond the current flight segment, or as a means of enhancing integrity of extrapolated path predictions. Proposed air-air applications of intent information include airborne separation planning where more than a few minutes look-ahead time is desirable for conflict detection and conflict prevention, and conflict resolution, where broadcast of intended resolution maneuvers may be important for situation awareness of all nearby equipped aircraft.
　
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