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severniae

engaging speed hold mode correctly

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Hi all,
So when I'm descending I often use FLC mode to descend, and often by a certain point I'll need to level off and maintain a certain speed.
If I try and input a speed on the MCP, nothing happens, but also if I press the speed hold button the AP seems to stay in the previous mode. It also seems to do this when in VNAV mode. To engage speed mode I first have to engage alt hold/VS then I can engage speed or thrust mode.
 

What I'm asking is what is the correct way? How should I be doing this? Reason being I once disengaged the AP but left the AT on, I leveled off (maybe a little early) and instead of the AT either disengaging or applying more power, it kept itself in FLC mode and kept power at idle and I almost stall spun in!

Advice greatly appreciated.

James Walker

 

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When you‘re in a mode that hides the speed on the MCP (only VNAV) it means that the speed is taken from the FMC. To override it simply press the speed dial knob. 

The FLC mode climbs with full allowed thrust and decends with idle thrust. This is as long as you won‘t move the thrust levers manually (they are in HOLD mode so you can move them) However when you choose FLC mode the speed window must activate to select the speed.

what does your FMA tell you while you have this happen? What modes are active?

and what do you mean with „you leveled off a little early“? How? When you press ALT HOLD then FLC must disengage as it‘s a vertical mode only. Also when you activate another vertical mode such as VS. 

Edited by Ephedrin

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3 hours ago, severniae said:

What I'm asking is what is the correct way?

The correct way is the way that gets you what you need. Seems a bit...obvious and unhelpful, but the question is a bit like asking "what is the correct way to unscrew a screw?"

Is it a tight spot? Then you may want a ratchet with a Phillips or flathead adapter. If it's open, you could probably use a power drill. If it's fragile, then you might want to get it out by hand with a screwdriver.

The first issue is understanding what tools you have, and when and why you should use them.

3 hours ago, severniae said:

How should I be doing this?

When flying, it's always good to ask yourself "why." Why are you using FL CH, and then having to level off, and then manually handling all of this? VNAV handles all of this for you, so why make it more difficult in a particularly busy time of flight?

This might sound off-putting at first, but I'll say this bluntly: there are no points or awards for making things more complicated. I think a lot of simmers get this idea that if you do things manually, or use the most complex way of doing something, then it somehow increases your pilot cred. I'd argue the opposite. Do whatever taxes you the least, and leaves you less prone to...well...as you say in this next quote: stalling and spinning in because you either don't fully understand the AP mode, or are so busy that you fail to notice a bad situation getting worse.

3 hours ago, severniae said:

Reason being I once disengaged the AP but left the AT on, I leveled off (maybe a little early) and instead of the AT either disengaging or applying more power, it kept itself in FLC mode and kept power at idle and I almost stall spun in!

FL CH is a pitch-for-speed mode on either rated thrust, or idle, so I imagine that your altitude was set to some altitude below where you chose to manually level off, and the A/T was still at idle because that's how the mode is designed to work for a descent. When the AP is on, it will modulate the pitch to maintain a rated-power climb, or idle descent. When the AP is off, that's your responsibility.

I made this for the 737, but the modes have the same core concepts:

 

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12 minutes ago, severniae said:

Wow, great reply that explains perfectly! Many thanks - your right, I should try and make things easier!

Glad to hear it. A lot to keep up with. Let the plane take care of as much as it can (as long as you're still keeping up with it). Of course, if there's any confusion, let us know!

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13 hours ago, severniae said:

What I'm asking is what is the correct way? How should I be doing this? Reason being I once disengaged the AP but left the AT on, I leveled off (maybe a little early) and instead of the AT either disengaging or applying more power, it kept itself in FLC mode and kept power at idle and I almost stall spun in!

Advice greatly appreciated.

James Walker

This is a man-machine interface problem where you need to be fully aware of what the automatics are doing.. 

The first bit of advice is to read the aircraft manual so that you know how to program and use the automatics correctly, because a good knowledge and close monitoring of the B744's AP/FD and FMS modes is essential.  Secondly, do not refer to the mode control panel (MCP) for mode annunciations, but rather always monitor the mode annunciations on the PFD instead; and make sure they are what you meant to select and therefore expect to see.  Third, when you are not using the autopilot you should always ensure that the Flight Director is programmed correctly for the desired maneuver and if you decide not to follow its commands for any reason it should be turned off.  Last but not least, do not rely on the FMS to fly the aircraft for you, because this can lead to automatic complacency and one day the aircraft will bite you again (as you discovered when you almost stalled)!

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