Hi
I'm a A320 enthusiastic.
My favorite Boeing is the B777, so i started reading the FCOM, FCTM....
i also purchased PMDG 777. never flew a GA aircraft directly on A320 ( virtually with Qpac A320: most realistic C* law simulated so far)
But I really having a hardtime maintaining the desired flight plath with the PMDG 777
i use to fly the PMDG 737 NG ( NGX) from PMDG, PMDG always does top notch add on :
With the NGX, when i want to change the flight path, I just pitch up or down until i get the flight path I wanted, then adjust thrust to maintain the desired speed and trim to remove the force on the work, the NGX then maintain the FP provided the speed is not changing and the config too.
What i understood from the b777 is that it has an autotrimming feature like the A320 but only for config change, thrust, turbulence, bank, gear , so if you want to change speed you need to do it with the trim on the yoke which will change the trim speed reference, the aircraft will then target the trim reference speed with phugoid phenomenon.
But how do you maintain the flight path with a such feature.
for example I was flying level at 3000 feets, LOC captured. 2 NM from FAP, I select flaps 20, when the GS is captured, I select gear down and then I disconnect the AP and AT. selct then flaps 30, the autotrim will compensate for the flaps change, but speed will decrease toward VREF30+5 KTS (assuming no wind) and I haven't yet change the Trim reference speed which is still at Vref 20 (when AP disconnected), so if no input are given, the AC will pitch down to accelerate and target the VREF25 speed.
So when I select flaps 30 after disconnecting both AP and AT, i trim up as long as the speed is decreasing in order to maintain the Flight path, need also to move the yoke too tough, but i'm not trimming for releasing the force on the yoke but I'm ordering a new trim reference speed, so,when i release the yoke, the flight path is not maintain as te AC will pitch up to maintain the new trim reference speed. PMDG add a trim reference speed indicator on the speed tape so that we simmer can know where the trim reference is currently until we get used to how the trim reference system work.
So after disconnecting the AP and AT, i select flaps 30 and I trim so that the TRS is at VREF30+ 5kts, when the AC speed is within 5 kts of the TRS, i trim once so that the blip trim enters in action and set the trs to the current AC airspeed but even when I'm perfectly trimmed, the AC doesn't maintain the flight path, the aircraft is always pitching down and I can't trim up because of the Blip trim function.
flying a A320 is mush more efficient to maintain the fligh path, but that's only my opinion.
i could post avideo in a couple of hours.
I hope that some 777 pilots can sheld some light on this topic
Regards
CMB