Definition
A formula used with the Automatic Direction Finder (ADF) to calculate the magnetic bearing to a non-directional beacon (NDB). Magnetic Heading (MH), the direction the aircraft's nose is pointing relative to magnetic north, is added to the Relative Bearing (RB), the angle measured clockwise from the aircraft's nose to the station as shown by the ADF needle. The sum is the Magnetic Bearing (MB) to the station. If the result exceeds 360 degrees, subtract 360 to obtain the correct magnetic bearing.
Plain English
Add the direction your nose is pointing (in degrees from magnetic north) to the angle from your nose to the station (shown by the ADF needle). The answer tells you the actual compass direction from your aircraft to the station.
Context Anchor
Seen in ADF navigation when a pilot turns a needle indication into a usable bearing to a ground radio beacon.
Why Pilots Care
Converts the ADF needle reading into a usable compass direction for tracking to or from the station.
Analogy
Think of standing in a field facing a direction on a compass. Someone tells you a tree is 40 degrees to your right. To tell a friend the tree's compass direction, you add your facing to that 40 degrees. The aircraft does the same with the ADF needle.
Grounding Statement
The formula changes “where the needle points relative to the nose” into “which magnetic direction the station is from the airplane.”
Intuition Check
Do not treat RB as already being a magnetic direction. RB is only an angle from the airplane’s nose, so MH must be added to find MB.
Example Sentence 1
Flying a magnetic heading of 270 with the ADF needle showing a relative bearing of 045, the pilot applied MH + RB = MB and determined the magnetic bearing to the station was 315.
Example Sentence 2
If magnetic heading is 270 and the ADF shows a relative bearing of 180, the magnetic bearing becomes 090 after subtracting 360.