Approach
Join Date: Jan 2002
Location: UK
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Both inbound QDMs are defined by radials from the beacon, the difference is the display on the cockpit instrument. (ie one CDI fly left fly right, the other a single needle the pilot interprets.)
As I understand it, only a VOR has radials . An NDB has bearings . FF is correct in saying that VORs generally have a Course Deviation Indicator on which the radial is dialled to give a left/right indication, while NDBs have only a needle which the pilot must interpret to fly a desired bearing to or from the station.
Both approaches utilise a transmitter to provide navigational signals that can be interpreted by the pilot to fly a pre-determined flight path that maintains a certain level of safety while transitioning from flying withouth being able to see the ground, to flying to a point where sufficient ground references can be seen to safely land the a/c.
An NDB is one type of navigation aid. It transmits a simple signal in a frequency range just below the AM broadcast radio band.
The receiver (an 'ADF') is able to display the information determined from this signal in relation to the a/c's heading ie it tells the pilot where the transmitter is in relation to where the a/c is pointing eg directly ahead (000/360 deg), directly behind (180 deg), to the left (270 deg), to the right (090 deg) and bearings in between.
The pilot must do the thinking to convert this information into something a bit more useful ie "Where is the a/c in relation to the beacon?" instead of "Where is the beacon in relation to the a/c?".
Some slightly more advanced displays can use compass information to do this for the pilot. It still uses a basic compass rose display show this information.
A VOR is another type of navigational aid. It transmits in a frequency range just below the FM broadcast radio band.
Unlike the NDB/ADF system, the VOR system provides a more complicated type of signal that allows the a/c equipment to determine position & deviation from this positon in relation to the ground aid with reference to a specific 'bearing' from the transmitter. This type of 'bearing' is called a 'radial'.
The dispay uses a 'left/right' needle to show a/c position in relation to a selected radial.
The methods of using these two types of navigational aids are different, as are the errors & limitations involved with each of them.
This means that approaches that use each of these aids must be specifically designed. Often they will be very similar, but not necessarily so.
An NDB is one type of navigation aid. It transmits a simple signal in a frequency range just below the AM broadcast radio band.
The receiver (an 'ADF') is able to display the information determined from this signal in relation to the a/c's heading ie it tells the pilot where the transmitter is in relation to where the a/c is pointing eg directly ahead (000/360 deg), directly behind (180 deg), to the left (270 deg), to the right (090 deg) and bearings in between.
The pilot must do the thinking to convert this information into something a bit more useful ie "Where is the a/c in relation to the beacon?" instead of "Where is the beacon in relation to the a/c?".
Some slightly more advanced displays can use compass information to do this for the pilot. It still uses a basic compass rose display show this information.
A VOR is another type of navigational aid. It transmits in a frequency range just below the FM broadcast radio band.
Unlike the NDB/ADF system, the VOR system provides a more complicated type of signal that allows the a/c equipment to determine position & deviation from this positon in relation to the ground aid with reference to a specific 'bearing' from the transmitter. This type of 'bearing' is called a 'radial'.
The dispay uses a 'left/right' needle to show a/c position in relation to a selected radial.
The methods of using these two types of navigational aids are different, as are the errors & limitations involved with each of them.
This means that approaches that use each of these aids must be specifically designed. Often they will be very similar, but not necessarily so.
