Regional navigation operation mode

The RNAV unit based on VOR/DME works in at least three modes: VOR, route and approach. A fourth mode can also be found on some models: VOR parallel. The regional navigation unit needs VOR and DME signals to operate in any RNAV mode. If the selected navigation device is VOR without DME, then RNAV mode will not work.

In VOR (or non-RNAV) mode, the RNAV unit only acts as a VOR receiver with DME function. As shown in figure 14-30. The unit display on the VOR indicator is conventional in all aspects. For operations on established routes or any other conventional VOR navigation, VOR mode is used.

To use the RNAV function of the device, the pilot should select one or a series of waypoints to determine the course. In order to operate in any RNAV mode, the unit needs direction and distance signals; Therefore, it is necessary to choose VORTAC as the navigation facility. In order to establish waypoints, points within the service range of VORTAC are defined according to directions and distances. Once the waypoint is input into the unit, the route mode of RNAV is selected, and the heading deviation indicator will display the heading guidance of the waypoint instead of the original VORTAC. In route mode, the heading deviation indicator indicates the direction of the route, not the VORTAC of the voyage to which the route belongs. DME will also display the distance to the waypoint. Many units have the ability to store several waypoints, allowing them to plan before flight and call them in flight if necessary.

RNAV waypoints are entered in units of magnetic azimuth (for example, 275.5 degrees) and distance to the sea (for example, 25.2 nautical miles) to the nearest tenth. When drawing RNAV waypoints on charts, pilots will find it difficult to measure this accuracy, but in practical applications, it is not necessary in most cases. Many flight plan publications publish airport coordinates and waypoints with such accuracy that RNAV units can accept these figures. In RNAV mode, there is an incomprehensible but important difference between CDI operation and display.

In RNAV mode, the heading deviation is displayed according to the deviation of the straight line. In RNAV route mode, the maximum deflection of CDI usually means 5 nautical miles on both sides of the selected route, regardless of the distance from the waypoint. In RNAV approach mode, the maximum deflection of CDI usually means 1.25 nautical miles on each side of the selected route. When the aircraft approaches a waypoint in RNAV mode, the sensitivity of CDI does not increase.

RNAV approach mode is used for instrument approach. Its precise scale width (quarter route mode) can track the selected waypoint back and forth very accurately. In cross-country navigation with visual flight rules, it is not worthwhile to track a route in approach mode, because it requires a lot of attention and will soon become boring.

The fourth mode is VOR parallel mode, which is rarely used on some units. This allows CDI to display straight line (non-angular) deviation when the aircraft is facing backward VORTAC. It is named because the pilot deviates from the selected course or course at a selected fixed distance (if necessary). VOR parallel mode has the same effect as putting waypoints directly on VORTAC. Some pilots choose VOR parallel mode when using their autopilot navigation and tracking functions, so as to smooth the route after nearby VORTAC.

When using the RNAV based on VOR/DME to navigate the aircraft, confusion may occur, so it is necessary for the pilot to be familiar with the installed equipment. As we all know, some pilots can't see the switch position or signal, which leads to unexpected operation, so they don't pay attention to running in RNAV mode. On the contrary, because the pilot missed the switch position or signal, he neglected to set the crew to run mode. From beginning to end, cautious pilots are not only familiar with the equipment used, but also can't fully trust a navigation method when cross-checking can be done by other methods.