So you CAN'T do a full autoland with only a fail passive AP correct? So what categories of ILS approaches can you still shoot? Is the only difference being that you'd disconnect at DH and land manually? While shooting an ILS approach with fail passive, would you still engage both CMB A and B for the approach? I understand the difference between fail op and fail pass. autopilots, but am still not sure what you can and cant do with a fail passive only system, or whether you can still shoot CAT II and CAT III approaches. Thanks!

A fail passive autopilot is a 2 channel autopilot. A fail operational autopilot is a 3 channel autopilot. You can do a full autoland with both. The difference is that if one of the two channels on the fail pass fails, the autopilot will couple out. On the fail ops autopilot it will continue with the landing. There are a lot of technical details involved. This was only a very basic answer.

A fail passive autopilot is a 2 channel autopilot. A fail operational autopilot is a 3 channel autopilot. You can do a full autoland with both. The difference is that if one of the two channels on the fail pass fails, the autopilot will couple out. On the fail ops autopilot it will continue with the landing. There are a lot of technical details involved. This was only a very basic answer.

That is true and with fail passive there is no rollout so the pilot must steer the plane after touchdown.and yes both autopilots must be engaged !! Fred.

That is true and with fail passive there is no rollout so the pilot must steer the plane after touchdown. Fred.

Ahh, forgot that point, thanks Frederic!

excellent guys, much appreciated! so would you engage both autopilots even for a standard ILS approach, or in in other words a non-autoland approach?

No you wouldn't. You could, but there's no point and it's not SOP. During a normal "assisted" approach, with the intent to disco the AP at some point in order to take over manually, you'd fly on the master AP and have the SINGLE CHANNEL indication. Oh and BTW, fail-ops are usually three-channel, correct, see T7, 757/67, 744, and similar. Still, the 737 has no three channels and can still be fail-op. There really is no third channel somewhere in the back or something. What it does have though is an actuator that can move the rudder and hence provide full rollout capability. This is a requirement for IIIB approaches with no DH.

and why is there two different systems afterall? Is it related to the tech evolution in systems ? /Michael

seeings as you can still do an autoland with a fail passive ap, couls you still do a CAT IIIb approach? even though you'd have to manually control the rollout?

and why is there two different systems afterall? Is it related to the tech evolution in systems ?

As you might imagine a fail-operational system adds another level of safety. Hence it allows lower minima as well (IIIB vs IIIA). And yes, it's probably a tech evolution thing too, but for most it will be a $$$ thing and furthermore there are not so many areas where you'd really *need* IIIB all the time. E. g. from where I am from it happens on a handful of days per year tops, so that might not really make people consider a fail-op purchase.

seeings as you can still do an autoland with a fail passive ap, couls you still do a CAT IIIb approach? even though you'd have to manually control the rollout?

No you can't. Fail-pass is IIIA maximum, IIIB however requires fail-op. Remember, even IIIA is only possible manually with a certified HUGS. Normal manual approach is only permitted up to CAT II.

I guess I'm still confused (whats new lol) So with a fail passive AP, what's the maximum category in which you could perform an autoland? From PPPrune "Lets take a Boeing.A pilot is not allowed to automatically land an aircraft that has not got either LAND2 or LAND3 displayed. If you go back to our previous posts on autolands you will be well aware that land 2 is still technically cat 3 capable. The next step down from land 2 is cat 2.No autoland allowed." This is what I'm not understanding, with a fail passive only AP, if I understand what is said above, you cannot carry out an autoland? I guess my final question is, what is a 737NG with a fail passive autopilot and no HUGS certified as, CATII max?

excellent guys, much appreciated! so would you engage both autopilots even for a standard ILS approach, or in in other words a non-autoland approach?

No you wouldn't. You could, but there's no point and it's not SOP.

It was at my last airline. Autolands were very common and therefore easy. At my current gig, dual channel approaches are only used if you're going to actually do the autoland.

I guess I'm still confused (whats new lol) So with a fail passive AP, what's the maximum category in which you could perform an autoland?

IIIA.

"Lets take a Boeing.A pilot is not allowed to automatically land an aircraft that has not got either LAND2 or LAND3 displayed. If you go back to our previous posts on autolands you will be well aware that land 2 is still technically cat 3 capable.

Technically speaking that's already wrong. A fail-passive Boeing simply never shows LAND2 or LAND3 at all. It shows CMD, even with two engaged channels, that's it. It's still autoland. And yes, LAND2 is certainly CAT III capable, but you have reduced redundancy (and probably higher minima, depending on procedures).

The next step down from land 2 is cat 2.No autoland allowed."

Sorry but it's just plain wrong. CAT II, of course, like any category, may use autoland but the difference to CAT III is you don't have to. You can practically always autoland, no matter what category. Technically, you could autoland CAT I if the signals are protected, you monitor the system closely and are prepared to take over (or go-around) at any point, just as usual.

This is what I'm not understanding, with a fail passive only AP, if I understand what is said above, you cannot carry out an autoland?

No. A fail-passive AP can still carry out an autoland. Fail-passive means that a system failure will not allow an automatic landing anymore, however it will transfer a stable and in-trim aircraft to you that does not need excessive corrections in order to maintain its intended trajectory. That's the main difference to fail-op - it would still carry out a safe (automatic) landing even in the event of a failure (below AH anyways).

I guess my final question is, what is a 737NG with a fail passive autopilot and no HUGS certified as, CATII max?

No, CAT IIIA. Even with a certified HUGS it would still be IIIA, with the big difference you could carry out the IIIA landing manually. Which you couldn't without the HUGS.

It was at my last airline. Autolands were very common and therefore easy. At my current gig, dual channel approaches are only used if you're going to actually do the autoland.

Interesting. Well after all, I guess technically it makes not a great difference in the approach phase if you run on one or two channels, so why not actually.

Interesting. Well after all, I guess technically it makes not a great difference in the approach phase if you run on one or two channels, so why not actually.

Two channels will mean the autopilot remains coupled in the event of a go around, it'll disconnect with only one. (IIRC)

Correct. Oh and just another complete lockup upon hittin TOGA at DH... sigh Bug smell.