Two beams
The localiser gives lateral guidance along the runway centreline; the glideslope gives vertical guidance, normally 3°. Together they define a narrow corridor to the touchdown zone.
Categories
CAT I has a decision height of 200 ft and 550 m visibility. CAT II lowers this to 100 ft. CAT IIIb allows landings in visibility as low as 75 m with an autoland system and a certified crew.
Flying it
Intercept the localiser first, then join the glideslope from below to avoid false lobes. Rate of descent in feet per minute is roughly ground speed in knots times five for a 3° slope.
Key points
- Standard glideslope is 3°; descent rate ≈ ground speed × 5.
- Never intercept the glideslope from above — false lobes exist.
- CAT IIIb autoland requires aircraft, crew and airport certification.
Knowledge check