VOR tracking and QDM

This weekend I will be looking at Low level flying, VOR Tracking and QDM flying.
If this sounds confusing then here is my notes:


(PLEASE LOOK AT THE INTERNET FOR VOR INSTRUMENT DIAGRAM USED ON THE BELOW)

VOR, short for VHF Omni directional radio range, is a type of radio navigation system for aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice (if equipped), and navigation signal. The identifier is morse code. The voice signal is usually station name, in-flight recorded advisories, or live flight service broadcasts. The navigation signal allows
the airborne receiving equipment to determine a magnetic bearing from the station to the aircraft (direction from the VOR station in relation to the Earth's magnetic North at the time of installation). VOR stations in areas of magnetic compass unreliability are oriented with respect to True North. This line of position is called the "radial" from the VOR. The intersection of two radials from different VOR stations on a chart provides the position of the aircraft.


VOR Tracking – Exercise 18C (1)

Aim: How to track/intercept a track to and from a VOR

Airmanship: Lookout. Safety altitude. FREDA. AIP latest information.

General Notes:

The ground radio facility is known as the VOR (VHF omni-range) Station.
Each station transmits signals in all directions, hence the term Omni directional. The signals are arranged to produce an infinite number of courses or tracks, 360 of which can selected and identified by the VOR receiver in the aircraft. Each bearing from a station is called a radial.
The audio signals from the station carry an identification feature and sometimes an ATIS transmission. As stated, VHF band is used (between108MHz and 117.95MHz), the signals are line of sight and are relatively free from interference.

Basically, the aircraft equipment comprises antennae, receiver, frequency selector, and course deviation indicator (CDI). Warning ‘flag’ device is fitted to show when the equipment readings are likely to be unreliable.

Likely range of the equipment is as follows:
Aircraft Altitude Approx Range
1,000ft 40nm
2,000ft 55nm
4,000ft 78nm
8,000ft 110nm

It should be realised that each radial subtends an arc of approximately 1nm at 60 nm from the station, so intercepting a radial some distance from the station can require a larger closing angle than when close in.
The VOR station’s signals, one fixed and one rotating- are in phase when aligned with Magnetic north. Thus all bearings or radials are in degrees Magnetic.


To Track To A Station

Check before flight in the UK Air Pilot (AIP) and obtain ‘frequency’, ‘ident’, ’hours of operation’, ‘precise location’, and ‘designated operational coverage’.

The user should having tuned and identified the station:
 Select required radial on the CDI
 Confirm no warning flag
 Ensure correct TO/FROM indication (i.e. Aircraft heading and CDI reading similar)
 While maintain heading, CDI needle L or R will indicate which way to turn
 The number of dots that the needle is off will show the amount of track error
 Assess track error, multiply by 3, plus drift allowance and select new heading
 A normal ‘bite’ would be 30 degrees.
 As the needle moves to the centre, reduce the angle. Remember, full needle deflection is 10 degrees.
 As the aircraft nears the station, the radial width will reduce considerably.
 When very close in, it becomes impractical to fly using the CDI. Best option is to fly using your established heading.


Example:
If CDI needle shows 2 dots to the left, this means deflection of 4
degrees. 4 x 3 = 12 degrees, so change heading 12 degrees to left (+ or -) wind allowance.

To Track From A Station

As before and having tuned and identified the station

 Select the required radial on the CDI.
 Confirm no warning flag.
 Ensure a correct TO/FROM indication i.e. CDI says FROM and both the CDI reading and the aircraft heading are similar.
 Maintain heading and CDI needle either left of right will indicate which way to turn.
 The number of dots that the needle is off will show the track error.
 Assess the error, multiply by 3, plus or minus a drift allowance and select a new heading. A Normal ‘bite’ would be 30 degrees.

Note: If the needle was deflected fully to one side, the safest way to assess the track error is to find the QDR by rotating the OBS knob in order to centralise the needle. The difference between the QDR and the required track will be the track error. Reassess, return the CDI to the required radial and fly the new heading. As the needle centres, reduce the ‘bite’. Remember, as the aircraft flies away from the station the radial will widen and accuracy becomes important To Assess Time To A Station

Tune and identify the station as before, assuming it is wished to establish the approximate time to the station, proceed as follows:

 Turn the aircraft so that it is flying at 90 degrees to the radial being tracked
 Centre the CDI and note the time
 As soon as the CDI starts to move, turn the OBS to set a new radial 10 degrees ahead
 When the needle centres again, note the elapsed time. Then apply the following formula:


TIME (SECONDS)
--------------------------------- = MINUTES FROM STATION
DEGREES OF CHANGE