A/T mode confusion in TOGA 744

[Guest BAW1085]

>Just to join the conversation: >>TOGA will guide to a pitch attitude only until you are>airborne. Then it will provide flight guidance to a "speed on>pitch" climb at the MCP airspeed. THRust remains REFerenced to>takeoff power. You, el Cap-i-tan, control speed with the pitch>of the airplane. Thrust is just locked at TO power. >>I expect you had your MCP set to 197-25, or 172kts as your>initial V2 climb speed. Without Vnav in the picture, that>initial MCP airspeed hop is based on the initial MCP setting.>>>If you really want to stay with this MCP airspeed, recognize>that thrust just pulled back (big time) and you are now going>to be using pitch to maintain your climb to the MCP altitude. >Now thrust is controlling speed and you are now controlling>altitude with pitch. Note that you and thrust just swapped>jobs.>>You were probably going faster than the 197 when thrust>shifted to "SPD", so watch out. You are probably going to slow>down. Thrust is now controlling speed and you now have to use>pitch to climb. >>You will be manually pitching up to maintain the climb while>thrust is automatically backing off to capture a slower>airspeed. Like I said above, this is a bad combination and>definitely not the place I want thrust to be slowing me down >. . . especially when I now need to pitch up to maintain a>climb . . . and I

[Qavion 19]

"Where did you collect this information (1-4 as you listed above?)"Robert...Here's what the guys at PPRuNe had to say. I know at least one of these guys used to be a Technical Pilot (A pilot specializing in the technical side of flying 744's... A "what if..." guy)http://www.pprune.org/forums/showthread.php?t=229400Cheers.Q>P.S. I'm hoping someone has some 744 big sim time coming up soon. I'm especially interested in whether the A/T will switch to THR REF at 400'.A while ago, there was a Notice To Crew saying that RB211 EEC's needed to see a thrust lever position change at the thrust reduction point (height or FLAPS 5), otherwise the EEC's would remain in a kind of HOLD mode until other parameters told them to unlock. A/T unlock (HOLD to THR REF) is somewhat different however.

[Guest D17S]

Hey, great site. Thanks for the tip. This seemed to be the best guess."1. The thrust levers advance to the selected T/O thrust (THR REF) and the vertical mode will be TO/GA.2. At 65 kts the autothrottle annunciates HOLD3. At 400' the autothrottle again indicates THR REF"That's fine, I'm OK to here. Here's our discussion kick-off point. "4. At the selected altitude, the vertical mode changes to ALT but the A/T remains in THR REF and the aircraft accelerates up to the flap placard speed or VMO as applicable.So,The MCP airspeed setting does not matter andThrust mode will shift to SPD at a flap limit or Vmo? It's OK with me (kinda), but that means PMDG's non-reset, MCP "previously set airspeed" (PSA) increasing to PSA +25 needs to be reviewed. And, a reset PSA adding 10 knots might be due a second look too. Both of these AFS behaviors seem odd to me.But from an operational view, the #4's suggestion of not having the ability to set an intermediate speed is concerning. I would WANT to have the capability to set an intermediate max airpeed somewhere below Vmo. Therefore, I like the PMDG version of this better because it gives me the ability to set a critical airspeed "stop." I just don't like the 10 knot addon part. "Therefore SPD mode needs to be selected or alternatively, select FLCH SPD while still climbing."First, a SPD thrust mode cannot be selected independently from an engaged TOGA thrust mode. It has to drafted into the game as a teammate of a pitch mode. But, that's OK. Select FLCH, or V/S for that matter. Why not? Couldn't hurt, because . . . These button presses would be largely irevelant A THR/FLCH or SPD/VS climb will be extremely similar to a THR REF/TOGA climb anyway. It will be an existing vertical or air, speed on pitch climb at an (~)EICAS thrust limit However this way, the implied sugggestion is that a SPD/ALT altitude capture will be assured (as if it wasn't before!). In summary, the SPD/ALT capture that PMDG has modeled still seems the most logical (sans that +10 addon). Why would I design an AFS to continue to accelerate (at blast-off power) to a Vmo at an initial altitude capture? I would want flap speed protection part. I like that. But to then to allow it to blow by my MCP airspeed on an adrenaline pumpin

[Qavion 19]

"In summary, the SPD/ALT capture that PMDG has modeled still seems the most logical (sans that +10 addon)."Not sure what point you're tying to put forward here, Sam... Do you want the sim to work the way you logically think it should work... or the way the real aircraft does?Robert is talking about A/P options, but I'm not sure this is an option on the 744.Cheers.Q>

[Guest D17S]

"I find that the Aircraft does not accelerate to a placard speed, the speed just decays when reaching the MCP altitude. Thereafter the heading is not maintained either and the aircraft simply departs."Actually it sounded to me like you were doing a great job test flying. Kirchu and Dirk found this too. I really hadn't seen it till you guys found it, but I found it odd as well. Good eye.About all that mode swapping stuff: If nobody knows, I'll just reason out a best guess. The most rational choice and reality don't match up too often, but it's always fun to take a shot. Although I did get a dash number bumped up a notch for an ACARS MU once What a suprise that was. My big contribution to aviation.

[Guest BAW1085]

>>P.S. I'm hoping someone has some 744 big sim time coming up>soon. I'm especially interested in whether the A/T will switch>to THR REF at 400'.From what I've seen it does ! Check the MODE as you climb through 400ft

[Qavion 19]

"From what I've seen it does !"What have you seen, BA1085? This identical scenario in a big sim or real aircraft? (VNAV not armed)"Check the MODE as you climb through 400ft"Er... how?Q>

[Guest kame]

Dear Sam,>So it you want 250, set 240. Set 250, get 260 . . .and a ticket!I have experimented the same. Is this (+10) a bug? If so, I would like to propose fixing it in the near future.Sincerely,Kan-ichiro Fushihara

[Qavion 19]

"So,The MCP airspeed setting does not matter andThrust mode will shift to SPD at a flap limit or Vmo?" There is still some debate on this issue.. See Cornish Jack's latest contribution..."http://www.pprune.org/forums/showthread.php?p=2631239#post2631239"I still think we need some big (Level D) sim time here.Cheers.Q>

[Guest D17S]

Cornish Jack:

[Guest BAW1085]

Top LINE of the PFD...Three Blocks known as the Autopilot Mode annunciator. MAThrottle/Roll/Pitch Throttle sector mode changes through the TO regime.1. After selecting TOGA (THR REF) Indicates in the throttle MA and the Roll/Pitch MA indicate(TOGA).2. At 65 kts the throttle MA annunciates (HOLD)3. At 400' the throttle again indicates (THR REF)

[Qavion 19]

"From what I've seen it does ! Check the MODE as you climb through 400ft"OK... "BA"... I don't know who the most confused is, here... As a real world 744 maintenance engineer, I know where to look ;) .. I also know what the PMDG sim does and what PS1 does... Unfortunately, my RW manuals don't cover this scenario.What I wanted to know was what you meant by "what I've seen". Have you had real world or big sim experience AND have had to test this non-standard scenario?You're suggesting I check what happens.. but I'm not a RW 744 test pilot... and I don't have access to a big sim.Cheers.Q>

[cowpatz 243]

There needs to be some clarification made to an earlier comment made by Robert regarding TOGA pitch attitude and what is actually commanded."What that sentence means is:TOGA is commanding the pitch angle to which you should rotate during takeoff. Once you have left the ground and the tail is clear of the strike hazard zone, TOGA pitch provides you with the correct pitch angle to maintain speed."The flight director pitch command is not used for rotation only after lift off. Usually a 3 eng pitch attitude is used to rotate to and these are normally obtained from either the take off tables or the PTOC (Pre TO certificate). These typically vary from 12 to 15 or more degrees dependant on weight. For a derated TO lower the pitch value by 1 degree.If you rotate to 8 degrees you wont get airborne (maybe if the a/c is empty). For a flap 20 TO the liftoff attitude is around 10 degrees and will give a tail clearance of 40 inches. Tailstrike attitude is 12.5 degrees.At VR a smooth rotation should be commenced at approx 2.5 degrees/sec to the calculated target attitude not the FD pitch bar. Liftoff should be acchieved in 3 to 5 secs. Rotaing too fast or at too lower an airspeed could result in a tail strike. Too slow a rotation speed and you could compromise the eng out obstacle clearance should you be unforunate to lose an eng after V1.At lift off the commanded pitch attitude is V2+10. If the current speed remains above this target for 5 secs then the target speed is reset to current airspeed (up to V2 + 25). After liftoff if an eng fails the pitch commanded target speed would be: .V2 if spd below V2 .Existing spd if between V2 and V2+10 .V2+10 if above At 400 ft VNAV activates, if armed, and pitch is commanded to maintain current speed and autothrottle sets selected ref thrust and annunciates THR REF.As for VNAV not being armed prior to TO....that is an interesting topic.Normally if VNAV is not available then internal FCC speed limits are used for TOGA and FLCH. But as for the thrust and when or if it would change from HOLD to THR REF is a curly one. I have seen this scenario in the sim a long time ago when VNAV was inadvertantly not armed (This can happen a lot because of the number of TO resets used in the training scenarios but is usually picked up quickly). I will try and have a sim instructor mate run the scenario and if I get an answer I will let you all know.CheersSteve

[Dirk98 354]

Thanks Steven. Definitely some of the numbers that you mentioned look familiar to me (unless someone else will give different ones, lol).Dirk. :-)

[cowpatz 243]

I managed to speak to one of our sim instructors about this. He commented that he has seen this many times.Assuming VNAV was not armed then after lift off the pitch mode would remain TOGA and the AT would reamin in HOLD. At 400 ft the AT annunciation will change to THR (if the TO was derated) or THR REF if full thrust used. The pitch mode will remain in TOGA and still command the original speed V2+10 to 25 kts. There will be no thrust reduction at Flap 5 or whatever altitude you have programmed in (normally 1500ft)and there will be no acceleration. This will remain until reaching an altitude limit. The AT will then change to SPD and accelerate to the current flap limit speed less 5 kts. The pitch mode will be ALT.I would still prefer to see this with my own eyes so take it for what it is worth.CheersSteve