NY320Capt

Anyone venture to guess why "Autopilot not authorized" would be on an approach (For example KCRQ), relatively flat prethreshold terrain, nothing too fancy type of approach? Why knock it off by 960' ?

thanks

rickair7777

Might be due to possible oscillations in the LOC or GS. Same thing at KMRY IIRC.

Or maybe it's something with the equipment design, maybe not certified as stable in close.

I don't remember any funnyness on that approach though, and I've done it enough times.

KIGONYE

what is this autopilot you speak of.

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ce650

A while back at Flightsafety for recurrent, there was an ILS into MIA (dont remember which one) that has the "no autopilot below whatever altitude". Anyways, the instructor told us it was because there is a large parking lot on short final and all the cars hose the radar altimiter.

I dont know if he was full of s*&t or not?! But that was the reason he gave us.

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NY320Capt

That would be my guess, some sort of unexpected and perhaps sporadic interference with the signal.

rickair7777

That could very well be. There should in theory be no electromagnetic interference on the NAVAID frequencies (FCC laws) but the government can't control objects or terrain on private property that might affect a RAD ALT. Also I don't think RAD ALT freqs are protected, they might be used by a variety of sensors on the ground (door openers, etc).

Next time you fly in there, stay on GS to 960' and then see what is right in front of you on the ground. Actually it might simply rapidly rising or dropping terrain.

Autopilots doing a CAT-I should not of course even use the RAD ALT but on GPWS equipped airplane they might disconnect if the RAD ALT sensed rapidly rising terrain.

clipperskipper

It's the ILS 8R at MIA reads "Autopilot coupled approach not authorized below 500 feet". This would put you near the VDP, however it doesn't read how tall you would be at the VDP on glide slope.

rickair7777

Huh? VDP is not applicable to an ILS...

It's published in case you are using the LOC.

jonnyjetprop

In MIA, the G/S is unstable below that altitude. That's why you can't autoland on that runway.

I checked the plate of the ILS 24 to CRQ and the restriction is "autopilot coupled approach NA below 960"

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