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View Full Version : B738 both minimums selectors required for dispatch?


LMX
29th Aug 2013, 15:46
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?

Denti
29th Aug 2013, 16:07
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.

LMX
29th Aug 2013, 16:19
Of course, it just seems odd to me when you are allowed to dispatch without for example autopilots or GPWS.

Denti
29th Aug 2013, 17:20
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.

LMX
29th Aug 2013, 17:28
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.

flyboyike
29th Aug 2013, 17:43
Wouldn't this be a better question for your company than for pprune?

ImbracableCrunk
29th Aug 2013, 23:36
MEL 34-48M in my book says 2 INS/0 REQ. Can't do CAT II or III. That's it.

REMARKS AND EXCEPTIONS
May be inoperative provided approach procedures do not require its use.
NOTE:
Must be operative for CAT II/III approaches

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

go around flaps15
29th Aug 2013, 23:48
Where I work we require two for dispatch. No exceptions.

B737900er
31st Aug 2013, 16:09
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.

777AV8R
31st Aug 2013, 16:55
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.

framer
31st Aug 2013, 23:26
Wouldn't this be a better question for your company than for PPRuNe
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.

A Squared
1st Sep 2013, 07:59
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.


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.

LMX
1st Sep 2013, 15:51
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.

flyboyike
2nd Sep 2013, 01:44
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.


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.

High Energy
2nd Sep 2013, 06:25
My company MEL states; 2 Installed and 0 Required for Dispatch.
" May be inoperative provided approach procedures do not require its use. "