Plain English Meaning
It is a signal from the airport that tells the pilot whether they are left or right of the runway centerline while flying away from the runway, used after a missed approach or on departure.
Full Definition
In a Microwave Landing System (MLS), back azimuth is a guidance signal that provides lateral course information to aircraft after a missed approach or during departure, projecting outward from the departure end of the runway. It allows the pilot to fly a precise centerline track away from the runway, opposite in direction to the front azimuth signal used for the approach.
Context Anchor
Seen in MLS discussions of approach guidance, departure guidance, and missed-approach guidance.
Derivation
‘Azimuth’ comes from the Arabic ‘as-sumut,’ meaning ‘the directions,’ and refers to a horizontal angle or bearing. ‘Back’ here simply means ‘in the reverse direction’ — so back azimuth is the horizontal guidance signal pointing the opposite way from the normal approach azimuth.
Why Pilots Care
Provides accurate lateral guidance during a missed approach without requiring a separate navigation aid.
Grounding Statement
Picture an aircraft climbing away after deciding not to land; back azimuth is the MLS left-right guidance for that outbound path.
Intuition Check
Do not read back azimuth as just any “backward” compass direction. In MLS use, it means a specific left-right guidance function for flying away from the runway.
Example Sentence 1
After executing the missed approach, the pilot followed the MLS back azimuth course straight out to the holding fix.
Example Sentence 2
The back azimuth signal allowed the aircraft to depart the airport on the reciprocal course using the same MLS installation.