A friend called me the other day to say that several times in last few months he was vectored to an ILS in such a way that his autopilot was unable to capture the glideslope. For those who shun autopilots this may not be an issue, but for many professionals, especially those flying single pilot in high performance aircraft, routine autopilot use for an IMC approach is standard.
To my knowledge all autopilots, when armed for an approach, must intercept below the glideslope for capture to occur. Diving to capture a glideslope makes it tough to stabilize the approach.
My friend called the tower after landing and in the ensuing discussion found that there was some confusion about why this was important. The controller’s guidance says, “For a precision approach, (when vectoring an aircraft to an approach) at an altitude not above the glideslope/glidepath or below the minimum glideslope intercept altitude specified on the approach procedure chart.” That is, they should put you in a position to intercept from below the glideslope.
In the example above, by my interpretation, outside of FREST you should be at 2,400 and between FREST and MEANS it would be 2,100.
One way to make sure that happens is to ask for a “coupled approach,” which will remind ATC that the autopilot will do the honors.
Has anybody else had any difficulty in this area recently?