Real 767 autopilot question RE: Apprch Mode

[Guest]

Hi,It has been noted in previous threads here that the real 767 autopilot trims the stabilizer after commanding the proper pitch angle but does not trim the rudder or ailerons. It was also mentioned by real 767/757 pilots (HPSOV et al.) that the autopilot will initiate a forward slip in a crosswind landing situation with LOC APPRCH mode (non-autoland) engaged. Question: when the pilot disengages the autopilot in this situation (i.e., the autopilot has configured the aircraft on approach for a forward slip), how does he/she maintain directional control as the rudder will no longer be deflected properly by the autopilot? It would seem that the slip would get messed up in a gusty crosswind situation when the AP comes off. I'm assuming that it's normal procedure to disengage the AP in LOC APPCH mode before decision height in order to accomplish a manual landing? Thank you!

[Guest]

Hi James,The AP will never cross control into a slip. This would make the transition to manual flying too dangerous that close to the ground and the yaw damper would take out any slip that isn't input by the pilot anyway. What the AP does do is course correct for a crosswind while on a localizer approach. It's still the pilot's job to kick the nose straight with the rudder just prior to touch down.Cheers,JohnBoeing 727/737 mechanic

[michal 44]

As was said, the AP does not do "slip" method, it does regular crabbing into the wind. Michael J.

[Guest]

Are you guys super sure about this? I think HPSOV (a real 767 captain that participates in the forum) mentioned that the autopilot did use the forward slip method rather then crabbing. I've also read some training publications that affirmed this (I think). Maybe I'm confused, wouldn't be the first time :(

[michal 44]

I am 99.9% sure. Just think technically - it would actually be very difficult for AP to figure out the proper amount of slipping and keeping nose aligned with runway. Special software, certification would be needed. Crabbing is already used during enroute navigation so it is a known thing.Crabbing is a much more straightforward technique that lands itself better to automation. But according to some 767 pilots here, crabbing is the preferred technique even when flown manually - and it looks better too ;-)Michael J.

[Guest]

Not so sure on this one...I think we need Ian or HPSOV's input. I had thought, during an autoland, the rudder is used to gradually remove the crab starting at about 500' RA.Jon (KSEA)

[michal 44]

Correct, but like you stated yourself .. it is the crab, not a slip. This is what the discussion was about.Michael J.

[Guest HPSOV]

G'Day all!Sorry for late reply but I've been at work (if you can call it that).First I deny all knowledge of saying anything incriminating :-PHeres how it goes.... (bearing mind in aircraft I fly all three autopilot automatically engage at 1500ft).The autopilot will crab the aircraft in, that is will point the nose of the aircraft into wind, so that the aircraft tracks a straight line over the ground.If you have LAND 2 or LAND 3 displayed (ie, two or more autopilots are connected to an ILS in APP mode), AND the crab angle exceeds 5 degrees, the aircraft will introduce a small slip. This occurs at 500ft RA, and it not annunciated. It will use up to 2 degrees angle of bank in order to reduce the crab angle, the wings are levelled again during ROLLOUT mode, which engages at 5ft RA.In my company the captain is allowed to leave the autopilot engaged until 50ft, so it is possible that when he disconnects the autopilot, the aircraft will be in a slip condition. The way to avoid any problems with this is to "lock" your feet on the rudder pedals, so that when you disconnect the rudder cant move. Once you have positive control of the aircraft then you can remove the slip as you feel necessary.

[Guest Ian_Riddell]

Ditto :-)I don't know about 727's and 737's, but 767's and 747-400's use slip in the final phase of autoland (as required). Ain't modern technology wonderful !As previously mentioned on the forum, the Yaw Damper only has a few degrees authority, allowing the Autopilot to do what it wants with the aircraft. Slip, crab, crash, etc...Cheers.Ian.

[Guest Martin]

This "crash" AFDS mode that you're talking about... is it annunciated?MartinIt's a lot like life and that's what's appealing

[Guest Ian_Riddell]

>... is it >annunciated?Only in the newspapers the next day ;-)http://www.ozemail.com.au/~iriddell/767/Crash.jpgCheers.Ian.

[Guest]

All 3 autopilots autoengaging at 1500 feet is unusual. But in that circumstance, the autoland feature IS engaged and it WILL introduce a slip, although mainly in the flare mode, ie, below 50 feet.Our 75's and 76's (same autopilot) you have to manually engage the remaining two autopilots, and that can only be done after selecting approach mode, not LOC mode. With only 1 autopilot engaged, no slip is possible. In fact, the autopilot will not control the rudder at all unless in autoland mode (3 autopilots engaged). The Yaw Damper will do its thing, of course, but that will not result in any sort of slip.

[Guest Martin]

LOL... How did that picture come about? Someone with too mucht time on their hands...? ;-)MartinIt's a lot like life and that's what's appealing