777 FLCH in climb and a/t going into HOLD, no low speed prot

[Houba]

Did anybody experienced this? And if yes, would you think that it could be a safety issue.

I've observed that upon engaging the FLCH during a climb and holding back the throttle they'll stop moving and the thrust mode annunciation is showing HOLD. Bottom line, you're sinking. The bad part about it is that even with the speed going into the foot with lowspeed alert, the autowake up of the autothrottle (low speed prot) is not engaging.

Thanks.

[I'mbatman]

Its a safety issue if your not paying attention. If you are acting like a pilot you should push the thrust levers up if you are getting too slow. If you use FLCH and get into HOLD, you have complete authority over the TL's.....if your not comfy with that.....engage VNAV(make sure its set correctly ;)

[fourgolds]

Why would you want to climb , holding back the thrust levers ?

Have you noticed what would happen if you descend whilst holding the thrust levers with cruise thrust ( cant wait to hear)

[Heilhaavir]

Good one fourgolds!

[ACMS]

experience HOLD in a CLB? NO I've never seen that in 7 years on the 777 or 8 years on the 744 before that.

Must have had a major upcock in the A/T system to get HOLD in climb.

You should have had THR REF FLCH SPD

Still, that's why were Pilot's. Were supposed to WATCH out for these little gotchas that CAN lead to a flight safety issue.

:ok:

[halas]

I just hope you were trying this stunt in the sim.

Why would you hold the thrust levers closed in climb, FLCH or otherwise, and let it get into a lowspeed situation, and then not advance them to get out of it?

God help all of us all if you are practicing this on the paying-public in open and shared skies in one of the shareholders aircraft.

[shakealeg]

Have a look at the FCOM, Autoflight, autothrottle system and understand there is no "wakeup" in FLCH.
And I have to echo the theme why climb with no thrust, doesn't seem that sensible.

[Houba]

Thanks for your replies.

I did try this in a box and the only time I could see myself holding back the A/T in a FLCH CLIMB would be to comply with an ATC order like "xxx stop climbing now and maintain 3000 feet" or TCAS or even windshear. Besides that I have to check if the box behave exactly like the sim and by looking at FCOM and AMM this point was obscur.
Happy landings and safe flights.

[ACMS]

Why would you pull the thrust levers back against the A/T even if ATC said stop climb now?????????????????????

Surely you'd select ALT HOLD and let the machine do it for you? Including any required thrust reduction to keep the speed under control. Selecting ALT HOLD generates a much faster pitch response than selecting VS, try it yourself and see.

If a TCAS RA requires manoeuving then you are supposed to disconnect the A/P and A/T.

Likewise manually flying a Windshear escape manoeuver you have to disconnect the A/T and manually advance to max thrust.

Even hand flying I can't see myself fighting FL CH and pulling the thrust off, just disconnect the damn thing if you need to.

[Houba]

Yeahh, I know I'm not following the Boeing procedures by the book but I'm payed for this (in a box of course).
This ship is so smart that I could not beleive that Boeing left an open door into the protection modes.
According the AMM the systems monitors the TLA and if they are blocked for more than 2 seconds they go into HOLD. (aka pilot holds them or something mechanical like too much friction). That's how you can have the HOLD in FLCH climb.

[Beeline]

I know on the 757/767 TMS, if 8 degrees TLA aft is manually selected during FLCH using N1/EPR Ref, Hold mode is entered.

2lbs force pilot induced or unnatural force generally disconnects A/T clutch.

Never worked the 777, maybe sim set up?

[FullWings]

In FLCH, the autopilot (or FD, if AP not in) will try and keep the commanded speed by adjusting the pitch/pitch demands. If you don't follow the FD in manual flight, you won't get speed protection as there is no 'wakeup' in FLCH.

Summary: If you disengage the AT then pull the nose of the aircraft up in the air and leave it there, the aeroplane will slow down towards the stall. This is normal behaviour!

[Lookforshooter]

Maybe we need 'low speed pilot detection'

[GlueBall]

Houba . . . If you're a real pilot flying real airplanes, I hope that I won't ever be paxing on your airplane. Because you are a busybody; perhaps overly bored sitting in the cockpit for hours doing nothing, who constantly needs to dabble with systems, . . . pulling the throttles back in a climb . . . like a mechanic who needs to fix something that isn't broken. :eek:

[Bungfai]

During descent,with hand flying, using FLCH mode THR in hold mode, for some reason like try to level off before the target altitude, then low speed condition could occur. Or during descent in severe turbulent auto pilot using FLCH mode.That might lead to that situation.

[ACMS]

What are you trying to do here?

Yes there are ways to stall the 777 if you REALLY WANT TO?

While handflying the A/C during descent using FLCH why would you level off BEFORE the MCP ALT then NOT BOTHER TO SELECT ALT HOLD? You know that the speed will decay if you don't.

While you at it why don't you try a barrel roll too:ok: The A/C FBW will object BUT you could still do it with your flying skill I'm sure!!

There will invariably always be holes in the swiss cheese, just try not to knowingly line them up ok?

[Port Strobe]

Here's (http://randhem.estar.se/Info/SimpleText.aspx?MenuID=17) the Boeing recommended fix for these back doors

[ACMS]

I'm sure the Bus has a few back doors too

[Houba]

Whoaw, some posts coming from real "invicible" pilots (from a CRM prospective). There are pilots and then ... God himself, but he does not know how to fly a plane.
BANDH = That's where I have a problem, the AT switches are ON but it does not protect it for low speed (in the box). Bottom line I've asked folks in Seattle to tell me if the ship is doing the same. Might be an aims issue, but I know that some are going to say that I'm stupid and irresponsible but that's I'm payed for.

[FullWings]

If the AT is armed on the MCP it will ALWAYS go into wake up mode regardless of FMA annunciation at the time. That is why it is called "Protection"
Not quite my understanding: (from manual) "When the pitch mode is FLCH or TOGA, or the airplane is below 400 feet above the airport on takeoff, or below 100 feet radio altitude on approach, the autothrottle will not automatically activate."

So a deliberate design decision. If the PFCs are in "normal" mode and the AP is not inhibited you will still have envelope protection, i.e. you will get an increasing nose-down force approaching the stall, with no ability to trim it out.

As mentioned by other posters, a likely scenario is manually descending in FLCH, then reducing the ROD or attempting to level off above the selected altitude. There is no wakeup so the speed will decay; the clue is that the FDs will be commanding an ever increasing pitch down. If the FDs were switched off (as you're not going to follow them) AT wakeup would be available.

This is typical of what I call "mixed mode" flying: half automatic, half manual where neither half fully understands what's going on. All in or all out! Unfortunately, our SOPs are for AT in at all times, so we fly the example above in the sim. to demonstrate the "level change trap".

[Re-entry]

As fullwings pointed out, Boeing designed the AT not to autowake-up in FLCH mode.

However, the AP (if in CMD) or the flight control system (if manual flight) provide independent envelope protection.

If in CMD, the AP will prevent the aircraft from going below min maneuver speed, so it will transition to a descent, and you will get an AUTOPILOT caution message.

If manual flight, the aircraft will not trim below min maneuver speed. The pilot would have to apply continuous column force to go below min speed, with higher force than that required for an equivalent out-of-trim condition above min speed.
So in manual flight, you could stall it but you would have to really mean to.:(