A/T mode confusion in TOGA 744

[Qavion 19]

"I would still prefer to see this with my own eyes so take it for what it is worth.I know how you feel, Steve.... )))Too many experts out there with different opinions :(The change to THR doesn't make sense at all (is that a fixed derate or a temp derate? Or both?)"The AT will then change to SPD and accelerate to the current flap limit speed less 5 kts."If it's in SPD mode, why does the aircraft accelerate???Thanks, anyway.Cheers.Q>

[Guest D17S]

Tend to agree. I still like Cornish's theory that THR REF is not just a reference/power set to an EICAS thrust limit. THR REF always seemed like too big a name for something as simple as that. For instance, the MD11 calls this simple, referenced power setting to TO thrust something that makes much more sense for this function. The MD11 calls this thrust mode "CLAMP." But on the other hand, in the model, the THR REF mode still works exactly like the MD's "Clamp." . . . And to a degree, when in the shadow of doubt; I've come to lean toward the model's version. There's just SO much right. "THR" is a variable thrust mode and seems to have a lot more "A.I." than any other thrust mode, but its TDY as a

[cowpatz 243]

We only do temp derates. Sorry my mistake. It will stay in REF or THR REF until approaching the flap limit less 5 then change to SPD.Must say that I havent looked close enough to note the difference between a derated and non derated TO as to the THR mode. Next time I am in the sim I will try it.CheersSteve

[cowpatz 243]

>Tend to agree. I still like Cornish's theory that THR REF is>not just a reference/power set to an EICAS thrust limit. THR>REF always seemed like too big a name for something as simple>as that. Sam I am not sure what you mean by this. My manuals are very vague about this subject and do not address it in enough detail but from what I can gather the thrust limits are determined by the EEC's, called up by the FMC, and displayed on EICAS so if THR REF is not referenced to an EICAS thrust limit then what is it referenced to?As an aside remember the thread that discussed the merits or otherwise of EPR V's N1 as the primary thrust indicator? Well I dont want to reopen it but on the Rollers if the EEC's are in ALTN then N1 and not EPR becomes the controlling figure. Why? I have no idea. Just another little useless piece of information.Need to get in the sim................CheersSteve

[Qavion 19]

"but on the Rollers if the EEC's are in ALTN then N1 and not EPR becomes the controlling figure. Why? I have no idea."Usually the necessity to switch to ALTN (automatically or manually) is because you have lost EPR data or it has become unreliable. Eg. During reverse thrust, the turbulence generated during this time upsets the EPR sensors, so N1 becomes the reference.Cheers.Q>

[Guest D17S]

". . . so if THR REF is not referenced to an EICAS thrust limit then what is it referenced to?"The "Cornish Theory" is that THR REF is also airspeed REFerenced to flap and airframe Vmo(s). In THR REF, the airplane will not overspeed flaps or exceed Vmo.That's the theory I was referring to.

[cowpatz 243]

Sam from my reading those fundamentals are associated with the FCC's in TOGA and FLCH. They are most likely part of the THR REF logic as well.Q might know more on this aspect.CheersSteve

[Guest BAW1085]

>"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>Sorry if I've confused you, I'm only a simple Airbus Engineer as in A380...who's only "Flown" a big military sim when I was younger.. Having said that a close look at one of the ITVV videos mentioned in another thread does show this sequence as well...and come on it's only a Boeing....}(regardsDMAirbus

[cowpatz 243]

Haven't been playing with any cables in the A380 have you DM??? ;)CheersSteve

[Guest kame]

Dear Sam,>What you really want to do is set the MCP to your intermediate >airspeed of 250 before the AT shifts into SPD. But watch this >too.

[Guest D17S]

That's some great test-flying, Kan-ichiro. See what you started? This is getting more interesting all the time. So, how's the #4 lesson going? Let's get another thread going for that one too. This is just too much fun. (The mods all go "Oh no. Not again." )But hey, it was all Dirk's fault last time. That got-to-know spirit just wouldn't let loose till we all got it figured out (and I say good for him), and we're the ones that get all deleted and locked-up. It's just not fair . . . let's go some more!

[Guest kame]

>So, how's the #4 lesson going? The TRC #4 is VNAV active and it's no ploblem in this matter.Sincerely,Kan-ichiro Fushihara

[kevinh 409]

CLAMP is the MD equivalent of Boeing's HOLD, not THR REF. In other words the A/T drive is disengaged so thrust setting cannot inadvertently change during the takeoff manoeuvre.When you select FLCH, the FCC switches to SPD hold (with pitch) and the Thrust Management System goes to THR. On some aircraft this drives the A/T command straight to CLB thrust (737, 757), on others the A/T command increases more slowly, but will end up at CLB fairly quickly. As thrust increases, pitch increases to maintain speed. Once thrust is at CLB, rate of climb is determined by aircraft weight and the selected speed. This will certainly occur before altitude has changed by more than a few hundred feet. So the notion that THR in FLCH is somehow to do with time to target altitude is totally incorrect. This is the kind of wrong conclusion such theories based on observation can lead to.These "theories" are all very well, but ultimately irrelevant. If you had access to Honeywell or Collins designs, you might be able to define all the subtleties, but defined they are. Pprune is a good place to get information from pilots, but sometimes even pilot's don't fully understand how these things work. I have no idea whether THR REF includes any speed protection. It may well do. FFRATS auto-throttle systems (which preceeded the integrated A/T and AP systems common today) certainly used to, so in THR mode, thrust will reduce to avoid exceeding flap speed limits ( Vmo was not protected).Kevin

[Guest BAW1085]

Judging by todays news, I have a feeling the odd short cable is the least of our worries.

[falcon999 24]

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