747-400 Go Around

[QAVION]

Not quite sure what happens during an Autoland if you push the TOGA switches twice....

If once, the aircraft goes into THR Mode and climbs at 2000fpm.
If twice, the aircraft goes into THR REF, but.... how is the extra thrust used?

Is it used for extra V/S or extra airspeed? If it is used for extra airspeed, what happens when you reach the flap speed limit? Does the thrust reduce... or does the aircraft start climbing faster?

This sort of stuff isn't mentioned in our engineer training notes.

Thanks.
Regards.
Q.

[Cornish Jack]

Q
for most operators, the TO/GA initiation is just a means of starting the go around. Thereafter, dependent on the company SOPs there will be a reselection to other modes - e.g. at 1000' agl select FL CH and hit the THR switch (to reduce to CLB power). Some companies use V NAV in place of FL CH but the principle is the same.... get it going skyward, then, at a safe height, sort out the procedural bits. I don't know of anyone who uses TO/GA with no subsequent intervention but, even if they did, the aircraft would level at ALT capture and the power would come back to hold dialled IAS.

[QAVION]

Thanks, gents.... Am now a little bit wiser :)

CJ...

"I don't know of anyone who uses TO/GA with no subsequent intervention but, even if they did, the aircraft would level at ALT capture and the power would come back to hold dialled IAS."

Not sure if we've talked about this before, but I read something, somewhere which suggested that thrust level in TOGA climb (THR or THR REF) is maintained at level out (If no mode change was made). If maintained, I can't see the aircraft maintaining airspeed, but accelerating. Actually, I thought the change of mode to FLCH or VNAV was to prevent this(?).

Cheers.
Q.

(Edit)
P.S. (Ooops) Just found it.... In our company AOM.

"A/T remains in THR or THR REF until SPD mode is selected. Speed protection prevents exceeding the maximum operation, gear extended, or flap placard speed."

Are they saying here that you have to select SPD to prevent overspeed... or that it is done automatically prior to this?

[SMOC]

The A/T even in THR or THR REF won't fly into the red blocks it'll just hold a few knots below it.
So I'd say it's good practice to select SPD or arm SPD with FLCH rather than forget or run out of time and end up bouncing off the red blocks in THR REF / LNAV / ALT or whatever.

[QAVION]

Thanks, SMOC.

I was a little worried that level-off at THR REF thrust might have been some weird APFD submode without speed protection.

Cheers.
Q.

[Cornish Jack]

Q
Apologies :o
Yes, you're correct - brain was in neutral !!
The speed control in the continued TO/GA case is simply that of 5 kts below 'red blocks'. It is one case where the A/T FMA is 'telling lies'. It will continue to show THR REF (or THR for a single push)even though the A/T has intervened to control to airspeed.

[QAVION]

Thanks, CJ.

Yet another piece of the 747-400 jigsaw puzzle.

Cheers.
Q.

P.S. "brain was in neutral !!"

Having reached retirement, I think you/your brain has earned that privilege ;)

[Notso Fantastic]

Our Go-around procedure calls for manual intervention quickly. You've barely started climbing on reduced power when at 1000' agl, you select FLCH, 200kts, and get accelerating to retract flaps to at least (or most) Flaps 5. Exceeding Flap20 speed up to 1000' isn't really a factor at all.
PS- please don't ask about the THR button! I try and ignore it.

[Cornish Jack]

NSF
THR button? The ONLY problems with the THR button are the way it is described in the Boeing manual and the indicated response when it is operated. Your ground training notes (assuming that you're Birdseed) should have included a little piece I penned many years ago on the THR button (or switch, if you prefer). It was intended to simplify matters but it may well have been removed. Shame really, 'cos, like Ronseal - "it does what it says on the tin" :D