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.
Plain English
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.
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.