approach surface

"approach surface" means an inclined plan above an approach area normal to the vertical plane containing the longitudinal centre line of the aerodrome and intersecting that centre line at the boundary between the aerodrome runway strips and that approach area;
PU(A) 358/1997 - AERODROME (CONTROL OF OBSTRUCTIONS) (KUALA LUMPUR SEPANG AERODROME) ORDER 1997
2. Interpretation.