I can say for sure that there are fluctuations (sometimes big) on the glideslope. Flying manually, assuming you are stable you just ignore and keep flying through them. Having the a/p coupled could get messy I imagine.
It hooks on Back Course LOC19 but no vertical path 
Since when does Oxford have an ILS to runway 01?
I actually skipped testing with KAP140, I was late for a friend wedding: departing at 1045LT in France with church service at 1230LT about 20 km from Oxford airport, hectic arrival after noticing “that I am late”: removing life jackets and wearing suits at 5kft over land 
Not much patience to fly all the way north for ILS19, so hand flew ILS01 with circle to land on RWY19 on 180kts clean descente, KAP140 is not designed for that !
It’s CAT1 approved, it flies beautifully on LPV & ILS near 200ft DH (if speed is kept higher than 80kts otherwise goes crazy on pitch on the back of the curve and without auto-trim it will hand a surprise), it’s only hooking to LOC & GS near FAP on radar vectored ILS while flying faster cruise speeds: it does not get it, I have to drag it slowly and pull up to catch it
In the other hand, with GPS (LPV or ILS procedural overlay), KAP140 hooks nicely on LPV or LNAV+V near FAP/FAF, even at 160kts, not sure if it’s the CDI progressive scaling and sensitivity versus cruise & approach speeds? or if GPS signal has wide coverage and is smoother than ILS signal?
A single channel puddle jumper A/P. I think the KAP140 is CAT 1 approved, not sure my faith is strong enough.
Thomas28 wrote:
So I’m guessing the radio telescope does something that interferes with that 300mhz frequency range.
That sounds like the only explanation, I will test GP on KAP140 next week and see if it slides all the way down on it, the AP has many problems of capturing LOC+GP on ILS already, even without issues with signal and it needs some babysitting, anyway, carefully watching an AP is not a bad thing (it can’t catch LOC above 120kts: needs NAV mode and can’t hook to GS from under: needs gentle pull up)
Ibra wrote:
Why it affects GS and not LOC? they run on different frequencies but paid on one frequency
They’re on different frequencies, the LOC is the frequency you set in the radio, the GP is somewhere in the lower 300mhz range. So I’m guessing the radio telescope does something that interferes with that 300mhz frequency range.
So the GS will wiggle in last part near the ground at 300ft (AP gets disconnected by then) or it happens higher?
Why it affects GS and not LOC? they run on different frequencies but paid on one frequency
Radio telescopes one mile from threshold cause glide slope fluctuations. There is also a warning on the approach plates.
