ILS Question

[Pete491]

Has anybody else noticed that different ILS approaches perform differently?  For example the glide slope on the ILS19R at KSNA fluctuates a lot about half way down and my autopilot will never lock on.  The ILS25L at KLAX works perfectly every time.  The glide slope is smooth and my autopilot handles the approach perfectly.

Maybe it's my autopilot or pilot.

Thanks!

[Keith Smith]

Nope, haven't heard of that one. Can't think of what's causing it. Are you getting intercepting the glideslope from below in both cases? Are you intercepting and tracking the localizer without a problem on both of them?

[Mark Hargrove]

Are you using FSX by any chance?

Next time you fly the ILS at KSNA pay particular attention to whether what you're seeing is the ILS signal wandering or the airplane itself wandering due to FSX's classically bad 'turbulence' model. Unless I check 'Disable turbulence and thermal effects on aircraft' (on the Settings/Display/Weather tab), I *always* get a pocket of severe turbulence about 1/2 to 2/3 of the way down the ILS at KSNA. More than once it's knocked me right out of the "pocket" that the autopilot would track. Usually *that* doesn't happen, but it has happened more than once.

Also, as Keith suggested, make sure you've got a good intercept of the GS and LOC before you switch your autopilot over to 'APR' mode. The FSX autopilot, in particular, will not intercept the GS from above.

If you're flying X-Plane, then -- never mind.

-M.

[Pete491]

Mark,

Yes, I'm using FSX and that's exactly what was causing this. I checked 'Disable turbulence and thermal effects on aircraft' and the problem was solved.

Thanks!