737 autoland nose up

[Dzosefs]

Anyone know for how many units is aircraft aiming when trimming at 400' during autoland? I couldn't find this information in the fcom. Only states it nose up trim.
Regards

[goeasy]

It likely variable, depending on the FMC current MAC

[Capt Pit Bull]

I wouldn’t know, but on the 737 the FMC isn’t anywhere near as fundamental as more modern types so my gut instinct is that it wouldn’t be involved in pitch trim. But I don’t have al the manuals and haven't flown one for 15 years so I could well be talking bollocks (why change the habit of a lifetime!).

[Gin Jockey]

goeasy

ah negative, you give aircraft too much credit for information transfer, we talking about !!!! heap from the 60s at heart, pretty sure you can do auto land with double FMC failure

[FlyingStone]

Anyone know for how many units is aircraft aiming when trimming at 400' during autoland?

The amount of flare spring bias is not fixed. It is calculated by the FCCs based on the stabilizer position and flap setting.

depending on the FMC current MAC

FMC on the 737 has nothing to do with the autoland. You can dispatch without both of them and still retain full Cat III capability.

[Banana Joe]

Originally Posted by Dzosefs

Anyone know for how many units is aircraft aiming when trimming at 400' during autoland? I couldn't find this information in the fcom. Only states it nose up trim.
Regards

On average the trim wheel is wound 13 times. I think you have to wind the trim wheel 10 times and 15 times respectively on the CL and NG for one unit of trim.

I am going by memory. I don't claim this to be exact information and I don't know how relevant this would be.

[fdr]

Interesting question, it does but the amount I cannot recall. The B747 classic in. dual-channel used to add 2 units ANU, and that predated the 737 ALAND capability, would think it would be close to that, which is around the incessant whirring that Banana Joe indicates.

[turbidus]

The Autopilot is flying the aircraft. The FMC provides mach trim and speed trim, hence the comment about performing CAT III autoland W/O FMC is valid. (as long as the AP is fully functional)
The pilot will have to manually trim the ac if the FMC's are inop. and can still perform a CAT III autoland procedure.

Is the question how to manually trim the ac below 400' on final???

[FlyingStone]

FMC provides speed and mach trim on the 737? Are you sure​​​​​​?

[FullWings]

Well, the 737s without FMCs could still do autolands and had mach trim, so...

[Gin Jockey]

Originally Posted by turbidus

The Autopilot is flying the aircraft. The FMC provides mach trim and speed trim, hence the comment about performing CAT III autoland W/O FMC is valid. (as long as the AP is fully functional)
The pilot will have to manually trim the ac if the FMC's are inop. and can still perform a CAT III autoland procedure.

Is the question how to manually trim the ac below 400' on final???

Ah you got some bogus info in there. Yes, you can do an auto land with no FMCs. That part is correct. However, the FMC has nothing to do with trimming for an auto land, so the trim will work just fine without the FMCs. Not sure where you are getting this info. The proof of the pudding is in the “auto land limitation summary” in the QRH. It lists all the equipment requirements, nowhere does it mention an FMC.

[ImbracableCrunk]

Originally Posted by turbidus

The Autopilot is flying the aircraft. The FMC provides mach trim and speed trim, hence the comment about performing CAT III autoland W/O FMC is valid. (as long as the AP is fully functional)
The pilot will have to manually trim the ac if the FMC's are inop. and can still perform a CAT III autoland procedure.

Is the question how to manually trim the ac below 400' on final???

F *C* C, perhaps?

[BraceBrace]

Originally Posted by turbidus

The Autopilot is flying the aircraft. The FMC provides mach trim and speed trim, hence the comment about performing CAT III autoland W/O FMC is valid. (as long as the AP is fully functional)
The pilot will have to manually trim the ac if the FMC's are inop. and can still perform a CAT III autoland procedure.

Is the question how to manually trim the ac below 400' on final???

Manual trim with AP(s) engaged on a 737?