Chapter 16
Navigation
Generally, the same techniques apply when tracking outbound as those used for tracking inbound. If the intent is to fly over the station and track outbound on the reciprocal of the inbound radial, the course selector should not be changed. Corrections are made in the same manner to keep the needle centered. The only difference is that the omnidirectional range indicator indicates “FROM.”
If tracking outbound on a course other than the reciprocal of the inbound radial, this new course or radial must be set in the course selector and a turn made to intercept this course. After this course is reached, tracking procedures are the same as previously discussed.
Tips on Using the VOR
- Positively identify the station by its code or voice identification.
- Remember that VOR signals are “line-of-sight.” A weak signal or no signal at all is received if the aircraft is too low or too far from the station.
- When navigating to a station, determine the inbound radial and use this radial. Fly a heading that will
maintain the course. If the aircraft drifts, fly a heading to re-intercept the course then apply a correction to compensate for wind drift.
- If minor needle fluctuations occur, avoid changing headings immediately. Wait a moment to see if the needle recenters; if it does not, then you must correctly recenter the course to the needle.
- When flying “TO” a station, always fly the selected course with a “TO” indication. When flying “FROM” a station, always fly the selected course with a “FROM” indication. If this is not done, the action of the course deviation needle is reversed. To further explain this reverse action, if the aircraft is flown toward a station with a “FROM” indication or away from a station with a “TO” indication, the course deviation needle indicates in a direction opposite to that which it should indicate. For example, if the aircraft drifts to the right of a radial being flown, the needle moves to the right or points away from the radial. If the aircraft drifts to the left of the radial being flown, the needle moves left or in the direction opposite of the radial.
- When navigating using the VOR, it is important to fly headings that maintain or re-intercept the course. Just turning toward the needle will cause overshooting the radial and flying an S turn to the left and right of course.
Time and Distance Check From a Station Using a RMI
To compute time and distance from a station, first turn the aircraft to place the RMI bearing pointer on the nearest 90° index. Note the time and maintain the heading. When the RMI bearing pointer has moved 10°, note the elapsed time in seconds and apply the formulas in the following example to determine the approximate time and distance from a given station. [Figure 16-33]
The time from station may also be calculated by using a short method based on the above formula, if a 10° bearing change is flown. If the elapsed time for the bearing change is noted
in seconds and a 10° bearing change is made, the time from the station, in minutes, is determined by counting off one decimal point. Thus, if 75 seconds are required to fly a 10° bearing change, the aircraft is 7.5 minutes from the station. When the RMI bearing pointer is moving rapidly or when several corrections are required to place the pointer on the wingtip position, the aircraft is at station passage.
The distance from the station is computed by multiplying TAS or GS (in miles per minute) by the previously determined time in minutes. For example, if the aircraft is 7.5 minutes from station, flying at a TAS of 120 knots or 2 NM per minute, the distance from station is 15 NM (7.5 × 2 = 15).
The accuracy of time and distance checks is governed by existing wind, degree of bearing change, and accuracy of timing. The number of variables involved causes the result to be only an approximation. However, by flying an accurate heading and checking the time and bearing closely, the pilot can make a reasonable estimate of time and distance from the station.
Time and Distance Check From a Station Using a CDI
To compute time and distance from a station using a CDI, first tune and identify the VOR station and determine the radial on which you are located. Then turn inbound and re-center the needle if necessary. Turn 90° left or right, of the inbound course, rotating the OBS to the nearest 10° increment opposite the direction of turn. Maintain heading and when the CDI centers, note the time. Maintaining the same heading, rotate the OBS 10° in the same direction as was done previously and note the elapsed time when the CDI again centers. Time and distance from the station is determined from the formula shown in Figure 16-34.
Course Intercept
Course interceptions are performed in most phases of instrument navigation. The equipment used varies, but an intercept heading must be flown that results in an angle or rate of intercept sufficient for solving a particular problem.
Rate of Intercept
Rate of intercept, seen by the aviator as bearing pointer or HSI movement, is a result of the following factors: