FAA Aviation Mechanic General (AMG)Aircraft Drawings, Weight and BalanceMedium
A wiring diagram identifies a connector location as 'BL 24 LH.' What does the 'BL' portion of this designation represent?
- AVertical distance above a horizontal reference plane
- BA numbered maintenance access zone
- CLongitudinal distance aft of the datum
- DLateral distance left or right of the aircraft's centerline
Show answer & explanationAnswer & explanation
Correct answer: D. Lateral distance left or right of the aircraft's centerline
Butt Line (BL) is a lateral measurement, in inches, left or right of the aircraft's centerline (BL 0). It is used with Fuselage Station and Water Line to precisely locate structure, components, and wiring.
Why the other options are wrong
- A. That describes Water Line, a vertical reference.
- B. Zone numbers are a separate maintenance manual location system, not BL.
- C. That describes Fuselage Station, a longitudinal reference.
Butt Line (BL)
A location reference measuring lateral distance, in inches, to the left or right of the aircraft's centerline (BL 0), used with FS and WL to locate a point in three dimensions.
- Centerline is BL 0
- Left/Right designations distinguish sides
- Used together with FS and WL for precise 3-D location
Memory trick: BL = 'Beside the Line' — how far sideways from centerline.