Hazard to ILS to runway 23 in BUF - Safety Alert 2009-1

[DeltaAVL]

Instead of providing a nice smooth 3 degree glideslope it oscillates up and down, if you leave the AP on it will pitch up and down quite a bit because it's attempting to follow the glideslope.

I feel certain this is a stupid question, but - it's not designed to do that? i.e., it doesn't do that to avoid the various hills and small mountains on the approach course?

 

[Roger, Roger]

Nope. It's designed to be a straight glide path all the way down. Different ILS's have different characters. One bad one I've flown was the ILS 32 at GPT-glideslope was wavering the whole way down. It was VFR so I could see we were right on glidepath.

It seems (in my very limited experience) that ILS's that also cover a Cat 2 or 3 approach tend to be steadier and smoother.

 

[JaceTheAce]

I go into BUF a lot. I always see the false glideslope that appears beyond 5 degrees of intercepting the localizer while using the ILS 23 at BUF. During those times I've been visual and ignored it, but I can see it confusing some autopilots if APP mode was armed, not just NAV (or LOC) mode.