"Ask ATC" Blog

ILS Approaches

At almost every major aerodrome in almost any developed nation, the primary instrument approach will be an ILS or instrument landing system. The reason behind this is no mystery - an ILS offers precise vertical (glide path) and lateral (localizer) guidance and affords the best altitude minimums of any instrument approach. Due to this very accurate guidance, the ILS is considered by many to be the easiest instrument approach to fly.

When setting the aircraft up for an ILS approach, whether it be a straight-in or full procedure, it is generally best practice to intercept the localizer before intercepting the glide path. This is as much for safety as it is for technique. Glide path indications are only evaluated for terrain clearance within the lateral confines of the approach, therefore, any vertical guidance should be ignored until the aircraft has intercepted the localizer. Air traffic control should never vector an aircraft to intercept the localizer closer than a point 1-mile from the point at which descent will begin unless they have first obtained the consent of the pilot.

Once established on the approach, there are often altitude markers indicated on the approach plates which show the approximate altitude the aircraft should be flying at over certain navaids or DME fixes. It is important to cross reference your altitude with these points as in at least one instance, erroneous glide path indications caused a Learjet to descend into the ground well before it ever reached the threshold. Always be sure you have the correct altimeter setting before conducting any instrument approach.