B737-300 autoland on one autopilot
 

Some years ago, a Boeing instructor pilot told me the 737-300 does a perfectly satisfactory autoland on one autopilot except there is no stabiliser back trimming at 400 ft. Have since seen this demonstrated many times in the 737-300 simulator and it works nicely even though no stab trim operation at 400 ft. The flare is perfect.

What is the purpose therefore of the stab trim winding back at 400 ft RA on a two autopilot autoland when it doesn't happen on a single pilot autoland?

The back trim is there to assist in a Go around. Whilst the aircraft can auto land in single channel, its not approved.

I don't think it's about the go around. I believe it is a fail safe so that in the unlikely event of an uncommanded disconnect the aircraft won't fly straight into the ground but level off slightly giving you enough time to take manual control. It doesn't happen with a single channel approach because the assumption is you will be landing manually.

We tried this a long time ago. It would have ploughed onto the rwy if we didnt disconnect and flare

Ive tried it in the sim and heard of guys doing it on the line, with no problems at all.

But why would you? If it's not authorised, legally, and you can do 1 CH down to 200' then manual land, is that not enough if the RVR is OK. I suspect most of us might pause a little at disconnect time. The a/c will be in trim and a gentle breath on the elevator is all that is required. With the approach ban criteria is anyone suggesting they would commence an approach to autoland outside specified criteria; both RVR and suitable ground aids? Is this discussion not just a academic? Perhaps it can, but can it be used? Rules would have to change. Until then, except in a dire emergency, who s going to try and risk it?

Not my area of expertise, but perhaps it is worth bearing in mind that just because the sim will do something doesn't mean the aircraft will do it. Bear in mind that if the aircraft isn't certified to do it there is no virtue in spending money simulating it realistically. We aren't talking real aircraft hardware in most cases.

In reality, the aircraft will NOT flare, no matter what you see in the simulator.
Sim is NOT the real aircraft. No back-trim at 370' is no flare in real life, and both will not occur with single autopilot approaches.

So do not try it, not only is it not approved, there is also a reason for it not being approved😏

I am now on B744 and that is a completely different story 😀

The automatic trim isn't to facilitate the flare.

A friend at FR done it on the line and asked did I know the aircraft could do it? My reply was yes it can do it but why the hell do it and put yourself in a vulnerable position?!!