B777 - FMA Modes: THR vs SPD
Hello,
I have some questions that I would appreciate the answers to.
1) In flight school, we are taught that pitch controls speed and thrust controls flight path angle. For example, if one is slightly below the GS, in order to get back on the GS, the theory is that one would first increase thrust in order to regain the vertical flight path. Then, this would require a compensatory increase in pitch in order to maintain the speed. Is this how it is done in airliners as well? Or are airliners flown with pitch for flight path and thrust for speed since their engines take longer to spool up? I recently talked to a real-life A330 pilot who told me that airliners are flown like Cessnas - IE pitch for speed and thrust for flight path.
2) I am confused as to the difference between THR and SPD on the 777. If airliners also inherently follow the "pitch for speed, thrust for flight path" philosophy, does that mean that in SPD mode on the 777, the autopilot still uses pitch for speed and thrust for flight path? For example, assume that one is flying in V/S mode at -1000 FPM, speed 250 knots. Assume that one wants to increase speed to 270 knots. In order to accomplish this, does the plane first pitch down to accelerate to 270 knots, and then increase its thrust to maintain the v/s at -1000? Or does the autopilot use thrust to accelerate to 270 knots and reduce pitch to maintain the -1000 FPM?
3) In the 777 FCOM, it says this:
"THR – autothrottle applies thrust to maintain the climb/descent rate required by the pitch mode ".
So if I got it right, in a climb, when FLCH is selected on the MCP, the MCP speed window opens at the current
airspeed and the aircraft’s speed is still controlled through the elevators but the FMA pitch
mode changes to FLCH SPD. The FMC considers the MCP altitude setting and commands
the autothrottle to provide thrust (THR) as required to achieve the resulting altitude change in
two minutes (120 seconds).
If a climb is commanded that exceeds the ability of the autothrottle to achieve the change in
two minutes the thrust goes to the current thrust reference maximum setting.
If the airliners like the 777 are indeed flown like a GA plane (i.e. pitch for speed and thrust for flight path), then wouldn't this mean that there is essentially no difference between the THR mode and the SPD mode? In that case, what exactly is the difference between THR and SPD then?
4) Finally, what is the difference between ATHR on Airbus and AT on Boeing? I heard they worked quite differently.
Any answer would be highly appreciated.
Thanks a lot.