A/T thrust mode question 744

[Jeff Nielsen 1,386]

Ok, having just tried a flight for the first time in a while with the 744 my question is this.When using the auto throttle can't thrust/speed mode be selected from the FMC/CDU or do you have to select it from the CDU then also select the appropriate function from the MCP?Just a little confused here, because I still can't seem to get this right anymore.Thanks.

[Guest AJ]

The A/T follows one or the other, but never both. It depends on which mode the autopilot is in. Basically, when VNAV is active, the A/T listens to the FMC-CDU. In other modes, such as FLCH or Speed, the A/T folows the MCP. You will notice that when VNAV is selected, the MCP window goes blank. This is your big cue that the A/T is following the FMC-CDU.Andrew

[Jeff Nielsen 1,386]

Andrew, I understand all that. For some reason even after reading the above sticky on the care of the A/T I still can't get it to work.I dont' fully quite understand the sticky either. I think I need a 1-2-3 now on what to do because it's not what I used to do...lol. I've also double checked that I don't have it overiden in the options menu also.

[Guest D17S]

Once you have the AT engaged, the AFS will take care of switching thrust modes to match up with whatever pitch mode you have selected. For every pitch mode, there is a corresponding thrust mode. Thrust and pitch are such close partners, they really can not work safely . . . one without the other. That's where the AFS comes in. AFS will watch what pitch mode is engaged and automatically select and engage the appropriate thrust mode. All you have to do is make sure the AFS is on the ball. Actually, IMO, it's a hazard that an "AT Disconnect" switch even exists. You should never be able to shut off the AT system while the AP is engaged. (Note: Watch for the MD11. The AT arm_disarm switch has been completely removed from the MCP. The MD11 has it right. The 744 has it wrong . . but here we are! So how do we deal with this?) Mainly, be careful. If that AT discos with a pitch mode still engaged, a crisis is not far behind (That was the reason behind the "Care and feeding . . ." article. Folks were flying with the AP engaged and the AT disengaged.)As before, once the AT is initially engaged, it will shift modes to coordinate with any pitch mode. . . but what if it becomes disengaged? How do you get the dawg-gawn thang re-engaged? I'm not 100% sure, but the model may be a bit buggy here. Try this little test flight. Set up a Vnav Path cruise. Disarm (Shut- off) the AT, then select the AT switch back to arm. The AT will not re-engage. This is normal. However if you are in a Vnav pitch mode, a re-press of the Vnav button should re-engage the AT into the appropriate thrust mode. Sometimes is does and sometimes not. That could be a bug. Here's a workaround. Momentarily select the MCP's V/S mode, then press the MCP's "SPD" button. The AT will engage in SPD. Now that the AT is re-engaged, it will NOW shift modes to match up with whatever pitch mode you want to select. Press Vnav. The left FMA (thrust) will provide the appropriate thrust mode. Select any pitch mode you want. The AFS will autoselect the appropriate thrust mode. You're back in the groove.The only real problem is getting the AT re-engaged if you should shut if off. However if the AP is engaged, the AT should NEVER be shut down independently . . . unless you specifically want this for some specific purpose (After all, you're still the boss!) Another for instance: You are hand flying and you want to engage the AP in a non-Vnav mode. Say Altitude Hold. When you engage the AP in Altitude Hold the AT will not automatically re-engage even though it is armed (Note once again that it will engage in PMDG's upcoming MD11. That is a much safer system! The MD11 will never need a

[Jeff Nielsen 1,386]

I thought that it should switch modes also, Sam, which it is not.I have the A/T switch on before I even taxi out. It's a part of my panel/MCP crosscheck setupI've been starting out from T/O manually to V/S and Speed hold until I'm all cleaned up, then to VNav which should engage the CLB mode I thought. In climb is when I happened to notice that the A/T wasn't controlling the thrust/speed. In any case I thought I should have been protected as soon as I was off the ground. I doubled checked the FMC also to make sure everything was selected correctly and it was.I've never had to re-engage the A/T so I don't know about that.Baffeling.Thanks to all for posting.

[crvm 0]

Never ever use V/S in this situation go FLCH................Randy J. Smith................A PROUD MEMBER OF THE PMDG BETA TEAM[h4]Evolution is a process that results in heritable changes in a population spread over many generations[/h4]

[Jeff Nielsen 1,386]

LOL, from 0 AGL to say about 1500 AGL. My guess is that most real pilots actually hand fly it following the flight director then go VNAV.I'm not sure why you'd use that mode while you're cleaning up. I used the V/S mode as a cheat.Then again, I'm not a real pilot I just play one on TV. LOL.Soz, Randy, couldn't resist.:-)Edit: That was a crack on myself, btw, not you. :-)

[michal 44]

>LOL, from 0 AGL to say about 1500 AGL. My guess is that most>real pilots actually hand fly it following the flight director>then go VNAV.True, but when you depart a busy airport you may be out of VNAV very quickly because of special ATC instruction, then back on it ... if you ever watched some DVD video from a real flight things can be very hectic.Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://sales.hifisim.com/pub-download/asv6-banner-beta.jpg

[Guest D17S]

Did a little test flight using V/S as an initital climb mode. Works fine . . but it's not "Murphy proof." Actually we don

[Jeff Nielsen 1,386]

Sam,Thanks for the lengthy post, but I'm not in a V/S climb except for the few few seconds of the departure. Just long enough to stabilize. VNav should take over properly anyways when engaged.In any case, the A/T is never disco'd either, so I'm not sure what the point of your post is other than to point out you're using the FLCH mode.

[Tabs 2,790]

>>LOL, from 0 AGL to say about 1500 AGL. My guess is that>most>>real pilots actually hand fly it following the flight>director>>then go VNAV.>>True, but when you depart a busy airport you may be out of>VNAV very quickly because of special ATC instruction, then>back on it ... if you ever watched some DVD video from a real>flight things can be very hectic.Why would you have to leave VNAV in climb due to ATC instructions - just dial the altitude they request on the MCP and press the knob... the plane will level and go into VNAV ALT - when you get further clearance, just dial it up and hit the knob again - away you go in VNAV SPD.

[Jeff Nielsen 1,386]

That's exactly how I've been doing it in the 37. I go from V/S on the takeoff to VNav, then keep dialing the altitude up as cleared.On the 47' I can't get that to work, lol.

[MarkRey 16]

>>Then again, I'm not a real pilot I just play one on TV. LOL.>If you were a tv pilot you would not have vnav, just a big red button marked 'AUTOPILOT' :-erksI long for Travolta to do a plane movie - then maybe we'd see reality for a change :-lol Being a pro I doubt he'd stand for the kind of bolloslush we usually see up front.that's my opinion from the ol' armchair anyway :-lolregards,Markhttp://www.precisionmanuals.com/images/forum/747400.jpgXPHomeSP2/FS9.1/3.2HT/1024mb/X700pro256

[Guest D17S]

You might try Vnav as your initial climb mode and using that to stabilize the initial climb . . . then allowing it to continue the climb. It will stabilize just like V/S but use the much safer method of targeting airspeed to do it (rather than V/S's ROC target). You will get the maximum ROC that is possible for the target airspeed. Below Acceleration altitude this will be a V2 speed. Above, a speed limit. But it's still the pilot's choice . . . at least in our sim world. If a RW pilot engaged V/S as an initial 1st-2nd segment climb mode, the Chief Pilot would certainly want to join that conversation. Maybe he would end up prescribing it as an operational imperative or all of his pilots . . . or not. The point is . . . in our sim world we can experiment. V/S is a great tool for this because you have to manually control rate (pitch) to maintain speed for various operational scenarios. Events like accelerations altitude and thrust reduction require the pilot to get involved. Vnav does this all automatially so the pilot doesn't really get to 'touch it' like V/S force a pilot to do. That's all I meant.

[Jeff Nielsen 1,386]

Sam,In V/S with the A/T engaged you do not have to have manual control of the aircraft except for some sort of lateral navigation going (LNav or control wheel).My problem is I can't get A/T's to work during any mode.