Every week I attend an evening course to help me get through the studying required for my PPL ground exams. Debriefing each session should help me with reinforcement of what I have been taught.
We are currently studying navigation in preparation for my that exam. In previous sessions we have been working with the whizzy wheel this day was the final navigation session we focused on radio navigation.
When you fly away from a point you are flying a Radial and when you fly towards a point you are flying a Bearing.
Here is a quick example: If I am flying 180 degrees away from from a point am flying the Radial 180. If I were to turn around and fly towards the point I am flying the Bearing 360.
A radio transmits information in the form of waves, which has a few properties: wavelength, the length of one wave going up and down and back to its starting point; frequency, how many waves are fit into a one second period and amplitude, how tall is the wave.
Some nitty gritty about radios
There are three types of radio:
- Low Frequency / Medium Frequency (LF/MF) – They aren’t reliable at night and are susceptible to costal refraction, static interference can happen due to thunderstorms. The waves follow the earths curvature. LF operates at 30-300kHz and MF operates between 300-3000kHz.
- Very High Frequency (VHF) – The radio operates with line of sight. Is susceptible to propagation errors, dead spots and waves reflecting off of buildings. VHF operates between 30-300MHz.
- Ultra High Frequency (UHF) – Operates on line of sight and it operates between 300-3000MHz.
Types of radio
There are a number of different radio aids that can be used to help with navigation whilst in the plane.
VHF Direction Finding (DF/VDF)
DF is used to find your position relative to the transmitting beacon. It uses radio transmissions to identify your position. ATSUs that can offer the VDF are noted in the AIP. As it works in conjunction with radio transmissions only a single aircraft can be located at a time.
There are four helpful ‘Q’ codes that are helpful to know:
- QDM – Magnetic bearing from the aircraft to the station.
- QDF – Magnetic radial from the station to the aircraft.
- QUJ – The true track to the station from the aircraft.
- QTE – The true track from the station to the aircraft.
There are multiple classes of VDF accuracy:
- Class A +/- 2°
- Class B +/- 5°
- Class C +/- 10°
- Class D Accuracy worse than Class C
The primary radar is a UHF transmission and works based on line of sight, so the higher the better. It transmits a pulse that can be reflected back by an object. The distance of the object is calculated using the time between sending and receiving the pulse.
Primary radar is commonly used by Radar or Approach ATSUs.
Secondary Surveillance Radar (SSR)
A secondary surveillance radar is very similar to the primary radar except the transponder returns a coded pulse back towards where the original pulse came from. The data returned from the transponder will appear on the same screen as the location of the plane.
Non-Directional Beacon (NDB)
NDB’s operate in the low frequency range and have a maximum specified range, this will change on a per station basis. When within the specified range there should be no more than a 5° error.
VHF Omni-Directional Range (VOR)
VOR is the trickiest of the different radio navigational aids to explain and it is also one of the most helpful.
Using a VOR a pilot can fly a bearing or a radial from the station. A VOR might be found at an airfield or just placed somewhere to aid with navigation.
The bearing or radial a pilot wants to fly is set using the Omni-Bearing Selector (OBS). A “to” or “from” flag is also set to tell the VOR whether the pilot wants to fly a radial or a bearing.
With the important information set the Course Deviation Indicator (CDI) will move to tell the pilot what direction to fly to get back onto course.
There are a couple of other important pieces of information about VORs to keep in mind. The VOR instrument is completely independent of the actual heading of the aircraft. The heading points on the VOR on a map won’t appear to be straight; VORs use magnetic headings so North is actually in Canada and not the North Pole.
Whilst I do not know the specifics of how it works, I can tell you that VORs work by measuring the phase difference of two different waves (black magic to me).
Distance Measuring Equipment (DME)
A DME is used to measure your distance from somewhere. They are actually in the UHF frequency band but are listed as VHF as they are commonly co-located with VORs.
I should end this blog post by saying that I have written the above based on my messy notes. I am also learning this as I am writing; if I find something wrong I will update the post.