My PSX Children of the Magenta experience

[torrence]

While flying one of my PSX regular routes (KLAX-KSFO) I found myself thinking I had a great CAT III approach into 28R SFO set up - then it when pear-shaped.  Had captured LOC and GS and was descending for a LAND 3 autoland when visibility improved and I sighted runway at about 2000.  I decided to land visually from that point and canceled autopilot and auto-throttle and took over manual control.  Ok until at about 600 ft when visibility went to 0/0 (not uncommon in foggy SFO vicinity and modeled well in PSX wxr).  At this point I must of lost me presence of mind (as the bricklayer said).  I tried to re-set up a LAND 3 autoland by re-enabling autopilot - but forgot I had also disconnected the auto throttle.  Landed very hot and crept to the gate with tail between my legs, cancelling various warning messages. 

I think I fell victim to the 'Children of the Magenta' syndrome discussed in several threads.

I think, in manual mode and at ~600 ft and still descending with no runway in sight, I should have have immediately pushed TOGA and bailed out, not started punching other buttons.  The fact that my virtual self survived more or less is no excuse.

Comments?

Cheers,
Torrence

[United744]

Hmm... you went from instrument landing with autopilot to visual manual landing (fine), but then tried to revert from visual manual landing back to autopilot controlled instrument landing (bad).

1) 600 ft is too low to get CAT III autoland (IIRC the system needs to pass through 1500 ft RA for best capture, though lower is possible if the aircraft is on path and stable). IIRC below 1000 ft RA autoland will not arm.

2) You attempted to "upgrade" the automation during a critical phase of flight. This is generally discouraged, as incorrect modes can be selected, with undesirable results at such low level.

3) It breaks the "stable approach" philosophy.

Having "downgraded" the automation (transition to manual landing), if the visibility screwed the manual landing at your decision height, your ONLY option is go-around.

If you're flying in marginal weather, it would be prudent to remain in the higher level of automation so you don't trash the approach/landing.

What was ATIS reporting for RVR? If it was below visual minima (considered 800 m, but may be stated higher on the approach plate - I personally prefer 2 SM or 3000 m), you wouldn't be able to visually fly the last part of the approach/landing anyway. If you are at decision altitude for the instrument approach you are flying and have visual with the runway, you can continue.

The biggest problem with the 744 in low viz, is the fact the flight deck is so high up. It generally has higher minima requirements due to this. The minima of the instrument approach may be too low for a visual landing.

Try an ILS approach at Cat II manual minima with a 15 kt straight crosswind. Extend the cloud layer so you're IMC at pattern altitude all the way down to minimums.

[emerydc8]

1) 600 ft is too low to get CAT III autoland (IIRC the system needs to pass through 1500 ft RA for best capture, though lower is possible if the aircraft is on path and stable). IIRC below 1000 ft RA autoland will not arm.

I can't find anything in my manuals, but there was a discussion on pprune about a letter purportedly published by Boeing that suggests it's 600' AGL.

From a letter from Boeing in response to a question about latest allowable AP engagement for Autoland:

"Provided that an ILS that meets the autoland criteria, has been tuned, the airplane is being manually flown on the published ILS path in trim and on speed, and APP has been selected prior to 1500 feet AGL, selecting the autopilot prior to 600 feet AGL (which is the lowest altitude for LAND 2 or LAND 3 to be annunciated) should satisfy the logic for autoland. The time required for the autoland system to perform a self-test and confirm correct operation will vary depending on conditions. We recommend that the crew engage the autopilot as soon as possible in order to satisfy approach logic.
Note: The autoland status must be confirmed by the crew at 500 feet AGL.
Note: Late autopilot engagement is not a recommended practice."

http://www.pprune.org/questions/539312-b777-asa.html#post8467405

[United744]

and APP has been selected prior to 1500 feet AGL

If you kill the FD like I do for manual flying, engagement below 1500 ft makes autoland unavailable.

I knew there was a specific reason for 1500 ft; I couldn't remember the exact detail (I thought I was confusing it with another aircraft).

Need to try this in PSX.

[torrence]

Thanks for the comments, guys - confirming that I should have done a go-around under the circumstances.  I did get LAND 3 announced and thought I was ok until I noticed the speed getting away from me.  I actually wasn't very surprised by the sudden low level loss of visual.  As I mentioned, I've seen it before in the SFO area with PSX native scenery and weather (and radar had indicated some returns in the area).  Don't have the METAR report in hand but this is usually triggered in PSX by some version of scattered or occasional low level clouds in the report (I forget the exact METAR-speak for this). My other sin was that I really wanted to land and get out to dinner and didn't want to stooge around for half an hour holding over Oakland to set up a new approach.  My sim version of real world head-office and schedule pressures I guess.  Gave myself a fail on this one. 

Cheers,
Torrence

[Hardy Heinlin]

... there was a discussion on pprune about a letter purportedly published by Boeing that suggests it's 600' AGL.

Quote from a Boeing FCOM:

"NO AUTOLAND also displays on PFD if multi-channel approach selected but multi-channel engage status (LAND 3 or LAND 2) has not been annunciated by 600 feet AGL."

"has not been annunciated by 600" -- My interpretation: When all CMD lights are illuminated below 1500 ft because two A/Ps are armed and one is engaged, and the engagement is not working because multichannel validation is detecting a fault, the system will try to revalidate all parameters until reaching 700 ft. Below 700 ft the validation cycle will give up, and NO AUTOLAND will appear after a short delay (at ca. 600 ft). In other words, the time until 600 refers to fault analysis, not to CMD button pushing. The FD mode is not a fault. Two A/Ps armed and one engaged, that is a fault. That's my present interpretation.

As far as I recall, in PSX the multichannel validation is modelled after some logic diagrams from maintenance books; the part with the height check looks like this:

valid = ( lower_glideslope_antenna_selected OR radio_alt > 700 ) AND ... etc. other stuff

The gear position has an influence on this as it needs to be extended to get the lower G/S antenna. So if the gear is up below 700 RA, NO AUTOLAND will appear.

However, I just discovered a side effect: If the gear is re-extended below 700, PSX keeps NO AUTOLAND until the pilot causes an AFDS mode change, e.g. cycling the FD or A/T switch. I think this needs to be modified. Gear re-extension should (A) re-activate LAND 3, or (B) the system should inhibit LAND 3 (as it does now), but if it does, it should also inhibit it when the pilot pushes a CMD switch. In that case I'll change my interpretation of the FCOM quote above.

I don't know what should be done -- (A) or (B). In PSX the minimum for multichannel engagement is 200 ft. Should I increase it to 650?


Cheers,

|-|ardy

[emerydc8]

Rather than an A/P fault, I was thinking more along the lines of a runway change to a parallel runway, where you don't get around to arming the approach until well below 1500' -- like 600' or 700'.

[United744]

The way I interpret is thus:

If APP mode is not SELECTED by 1500 ft RA (let's say you push APP at 1000 ft AGL) then Autoland is not available.

It's not that it can't validate, but the fact you didn't engage it early enough. The same way you can't get VNAV below 400 ft - no technical reason why not, but that's what the lawyers decided.

[Hardy Heinlin]

You can engage APP and autoland below 1500 ft on the real 744 (and in PSX).

[United744]

I'm not doubting it can be done, but why then do they say what they do about APP mode "and APP has been selected prior to 1500 ft AGL", if it can be selected later?? Is it a case of the manual not reflecting the actual situation?

[skelsey]

I can't offer anything in relation to the technical discussion as I cannot actually (yet) find any reference to any minimum A/P engagement heights for autoland in the documentation I have. There is reference to FLARE and LAND 3 annunciating "below" 1500R, and that autoland status must be verified at 500 ft AGL. There is also a note in the QRH that if an engine fails above 1500R ("before multi-channel engagement") the pilot must provide rudder pedal inputs to counter the asymmetry until descending through 1500R when multi-channel engages, but this obviously does not exclude the possibility of getting multi-channel if you engage below 1500R in the first place.

My assumption from all the above is that given that a CAT III approach is required to be stabilised by 1000R in any event, Boeing (or the airline) decided that whether or not you can get multi-channel/LAND 3 if you engage the A/P below 1000R is a moot point, which is not very useful in the context of the above discussion I know.

As far as the original post goes -- my comment, for what it's worth, is that if you have briefed and set up for one thing (i.e. a CAT III approach/autoland) it is probably not a good idea to change your mind halfway through and do something else -- in a multi-crew environment you'd be in danger of rapidly leaving your mate behind, especially when you then tried to go back to what you said you were going to do in the first place!

That said, if you'd decided you were actually going to fly a CAT I approach instead, then I would say there's actually no particular rush to hit the TOGA switches until you reach your CAT I minimums of around 200ft aal; personally I would have just carried on hand-flying the ILS, after all that's why it's there -- so you can land when the vis is poor! At the CAT I DH you then can either see enough to land = happy days, or if not = go around.

However, again the overall problem stems from having briefed and set up for a CAT III approach without considering the possibility of reverting to CAT I (i.e. -- what are the CAT I minima/DH, bottom lines for deciding when to make the switch or otherwise continue with the CAT III autoland etc) and then going 'off script'.

[Hardy Heinlin]

However, I just discovered a side effect: If the gear is re-extended below 700, PSX keeps NO AUTOLAND until the pilot causes an AFDS mode change, e.g. cycling the FD or A/T switch. I think this needs to be modified.

This stuff I quoted above is actually a bug I introduced when I implemented United Airlines' option re manual selection of all three CMD switches:

1.1.090. New option added on Instructor > Model > Programming: "Manual A/P multichannel engagement" (when APP is selected on the MCP for autoland, the pilot has to push all three CMD switches manually; as usual, above 1500 ft, two of the three A/Ps are just armed, and when below that height they are actually engaged).

This option requires a "CMD armed" check before the re-validation can start. But when the gear re-extends, they aren't armed but already engaged, and so the re-validation can't start in that case.


|-|


Now fixed in PSX 10.7: http://aerowinx.com/board/index.php?topic=4191.0