Glossary of Trajectory / Intent Terms
Active Trajectory. The active trajectory or flight segment refers to the current path and automation states being used for guidance and control of the aircraft. Command Trajectory. The command trajectory refers to the path an aircraft will fly if the pilot does not engage a new flight mode nor change parameters for active or future flight segments. Non-Precision Trajectory.A non-precision trajectory refers to an aircraft path with no specific containment bounds between the intended path or flight parameters and the actual path flown. Typically, transitions to an intended trajectory such as Direct To segments are non-precision, whereas aircraft flying RNP path segments with known lateral and vertical containment are precision trajectories. (A trajectory can also be a precision flight path in the horizontal and non-precision in the vertical plane.) Planned Trajectory. The planned trajectory includes intent information that is conditional upon the pilot engaging a new flight mode. Without pilot input, the aircraft will only fly toward the command trajectory. If the aircraft system is unable to determine whether a trajectory segment is planned or command, then the default type is a planned trajectory. Selected Altitude. Selected Altitude is an altitude value which is dialed in an autopilot interface such as a Mode Control Panel to specify a desired limit value for climb or descent segments, or to specify a desired target altitude to maintain for level flight segments. Selected Heading / Track. Selected Heading is a desired air reference heading value that is dialed into an autopilot interface such as a Mode Control Panel to specify a target value to transition towards and maintain for constant heading angle flight. Selected Track is similar to selected heading except that the directional reference is inertial track angle rather than heading. Short Term Intent. Short Term (TS report) Intent refers to the intended path and intended flight parameters on the currently active flight segment. Short-term intent can refer to either autopilot or FMS/ RNAV parameters associated with the current flight segment. Target Altitude. Ideally, Target Altitude is the aircraft’s intended level-off altitude if in a climb or descent, or the aircraft’s current intended altitude if it is being commanded to hold altitude. However, since many aircraft only have limited ability to communicate target altitude, it is acceptable to broadcast alternatives to target altitude based on aircraft capability. Target Heading / Track. Target Heading / Track is the heading or track angle target used by the aircraft guidance system to acquire or maintain the lateral path. The actual value used depends on the active guidance source, i.e. allowed values include Selected Heading / Track for direct autopilot specification, Heading/ Track Hold for autopilot maintenance of the current heading or track angle, and FMS / RNAV specified track angle to the next lateral waypoint. Time of Applicability. Time of Applicability is defined in the DO-242 MASPS as the time of report validity. Since Time to Go (TTG) is defined as the “estimated remaining flight time to the TCP point”, we here interpret time of applicability for TC reports as the current time for newly received report data. TTG then represents time to TCP relative to current time of applicability. Trajectory Change Point. A Trajectory Change Point is a point where an anticipated change in the aircraft’s velocity vector will cause an intended change in trajectory. The change in trajectory may be either a change in path or a change in speed.
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