B738 both minimums selectors required for dispatch?
 

In flight, I discovered I couldn't decrease the minimums on my selector with the "fast" mode of the selector; only the slow (single digit) increment was working.

We called engineers after landing, had a look in the MEL and were quite surprised to see that it simply says that 2 DH/Mins selectors are required for dispatch with no exceptions. Considering that the minimums can easily be copied from the other side with the Displays Control Panel switch, I don't see why one couldn't dispatch with just one DH/Mins selector, or even none if in VMC.

Does anybody know the reasoning behind this?

As usual, loss of redundancy. If you dispatch with both working and one stops working you still can set the minimum on both sides. If you dispatch with only one working and that fails you have no way to set a minimum.

Of course, it just seems odd to me when you are allowed to dispatch without for example autopilots or GPWS.

Without autopilot is fine provided the flightplanning takes that into account (non RVSM, alternate etc). Absolutely no problem to fly without it. GPWS is a bit more tricky and it actually depends on operation. However it is quite possible to fly without doing a CFIT even without having a GPWS active. Granted, most pilots used to it would be startled by the missing auto height callouts.

Actually, just checked my MEL and it allows dispatch without Decision Minimum Height Selectors, you just have to make sure that you use an approach that doesn't require its use. Basically you are restricted to VFR flight or visual approaches.

That makes sense and is what I would have expected to see! Nonetheless our MEL shows 2 required, no exceptions.

Wouldn't this be a better question for your company than for pprune?

Not required in my MEL
 

MEL 34-48M in my book says 2 INS/0 REQ. Can't do CAT II or III. That's it.

I see someone posted the same. My MEL has a "change bar" next to this item. I wonder if the update this difference.

Where I work we require two for dispatch. No exceptions.

But they are working though, just not the fast 10 increment! I can see why engineers take the piss, if we are refusing to go, saying its broken when Infact one part of it is playing up but the overal system works.

The Why..
 

The MEL is developed from the Master MEL published by the manufacturer and must not be less restrictive than the MMEL.

For whatever reason, your Flt Ops Engineering department developed an MEL with this restriction. As such, the CAA approved it. As the MEL is revised frequently, it may be a good idea to drop by the office and ask about it. These things do get involved and seemingly minor things. An be missed, overlooked or need a 'tweak'. In any event, the MEL that you are working with governs your operation.

It has been my experience that really useful and thought provoking information can come from asking the forum questions like this. Often links to background information are posted that would have taken hours of dedicated research to uncover. I think it is a good idea as long as the OP is validating opinions for themselves.

So how did you arrive at the conclusion that a minimums selector is required for any instrument procedure? I flew for a number of years (US Part 121) in airplanes which didn't have any installed, so from that perspective it seems like one of those nice to have but not necessarily required items.

Thanks for your input! It's interesting to see that some operators have some different requirements for the DH selectors. Maybe comes down to regulatory requirements in different states? Anyway I doubt I would have got such info from my own company.

That hasn't been my experience. More commonly these types of questions lead to people parading their vast knowledge and not actually answering the question.

My company MEL states; 2 Installed and 0 Required for Dispatch.
" May be inoperative provided approach procedures do not require its use. "