On Balance Betwixt Safety And 'common Sense'

[Mitch Cronin]

Our 'common sense' tells us when the little light on the car's dashboard that means we've only got so much gas is illuminated, we can make it to the next convenient gas station.... we wouldn't push it so far in an airplane.

Our 'common sense' tells us when there's a rattle in the front end, we'll have lots of time to diagnose and address the problem. In an airplane, we have an MEL.

etc......

But then.... our 'common sense' might tell us it's ok to fly with something out of sync with the book.... and maybe it's right.... Maybe it's something really silly.... like an indicator that won't.... or a light that doesn't.... and we decide we know better than the book, because we're here, and the folks who wrote the book weren't.

And you know what? I'm here to tell you I'd very likely handle things just like that -- with my own 'common sense' -- if I were alone in my own airplane.

And I've been ragged upon, to some degree, for my 'online' stance regarding such 'common sense'.... but here;s the rub:

Once we accept our own 'common sense' as our guide for judgement on such matters.... once we've decided the book doesn't always have to apply...

....the lines get cloudy.... grey can creep into areas which - should something ugly happen, our 'common sense' would then tell us were really black and white, and we "should" have stuck with the book.

That, dear friends, is the roots of "the normalization of deviance" It can get really ugly... and people can get really dead. Grey has no place in this business.

To answer some critics..... Yessir. In a "this bird must fly" situation, I'm as much inclined as the Captain would be to look for real solutions in real-world operations. .....but I think it's incumbent upon us all to consider such notions when ad-libbing.

Personally, I'd rather see a bloody great big airplane sit idle with a silly glitch, than see it fly with a problem nobody understands.

[GDR]

Sheeeesh Mitch. Where is your sense of adventure?

[J.O.]

I want to know the rest of this story. This hornets nest doesn't get stirred up over a burned out light in the cabin.

[boestar]

The MMEL for the aircraft was written by the "Experts" These guys took into account the possible ramifications of an inactive system (or light). While we may think it silly, we may not see the possible interactions within the aircraft systems.

Besides......Common sense is not all that common so for the rules to be aplied equally the books must be followed.

[Don Hudson]

boestar - soooooo true.

In addition to possible interactions within aircraft systems which pilots cannot always know about, the MMEL doesn't (and can't) take into account the effects upon an operation with multiple MEL'd items. Assessing the effects of multiple MEL items on the operation is a complex decision and should be made by the captain in discussion with the crew and with Maintenance.

[Moon The Loon]

boestar - soooooo true.

In addition to possible interactions within aircraft systems which pilots cannot always know about, the MMEL doesn't (and can't) take into account the effects upon an operation with multiple MEL'd items. Assessing the effects of multiple MEL items on the operation is a complex decision and should be made by the captain in discussion with the crew and with Maintenance.

I'm sure there are others (I haven't seen them), but the Dash 8 actually has a Supplement Compatibility Guide as part of the AFM. With an item MEL'd, the aircraft operates by way of a Supplement (i.e. ECU, nose steering, anti-skid inop). Additionally for certain runway conditions, there are supplements for Slippery Runway, Contaminated Runway, Reduced Power Takeoff, etc.

The Compatibility table tells you specifically which supplements can be used together, and which cannot. An example of the "cannot" is an inoperative ECU with inoperative nose steering.

With this aircraft, at least, the manufacturer has attempted to remove the discussion Don refers to.

Surely though, the AFM cannot address every issue.

[IFG]

The MMEL for the aircraft was written by the "Experts" These guys took into account the possible ramifications of an inactive system (or light). While we may think it silly, we may not see the possible interactions within the aircraft systems.

Besides......Common sense is not all that common so for the rules to be aplied equally the books must be followed.

I'm sure there are others (I haven't seen them), but the Dash 8 actually has a Supplement Compatibility Guide as part of the AFM .... The Compatibility table tells you specifically which supplements can be used together, and which cannot. An example of the "cannot" is an inoperative ECU with inoperative nose steering.

With this aircraft, at least, the manufacturer has attempted to remove the discussion Don refers to.

Surely though, the AFM cannot address every issue.

I'm not convinced that the taking "into account" of implications, for each individual unserviceability, is anywhere near as deep as you chaps are implying - altho' some of that must have gone into deHav's incompatibility list. I remember that list from my DH-8 days.

As for individual deferrals, I inquired of Downsview's boffins once about what I saw as over-zealous restriction on Day-VFR flight (complete dual AHRS etc. etc. req'd for dispatch) I'd asked why there was limitation beyond the general minimum Day-VFR instrumentation listed elsewhere in the CAR's (or the predecessor reg's at the time) & was told that the aircraft was simply not put through certification testing with lesser equipment requirements.

It seemed that most of the MMEL allowances were for over-redundancies, e.g. 1 DC Gen allowed as there were still multiple DC sources.

For all that, I'll agree with the posters here who caution about reliance on the prevalence of "common" sense. Ironically, I was trying to make that point, about adherence to sillier rules, to my friend Mitch on a thread about speed limits - Great to see you're coming round, ol' Buddy

Cheers, IFG

[Don Hudson]

Moon, re, "Surely though, the AFM cannot address every issue."

No, I agree it can't. That's what crews and captains are for - to assess operational and downstream effects of MEL'd unserviceabilities.How many have had to defend their decision not to take an aircraft with a u/s radar, being told it was acceptable under the MEL?, (which it was but the airplane was going to the Caribbean in summer)...

I can recall taking an aircraft with about six MEL items, all legally dispatchable (go, with conditions), and individually acceptable though complex, but in combination with other factors, (winter ops, icy runway at destination / de-icing, max duty-day due delays at both terminals), was as close to no-go / airplane change as I ever got, and it just got worse. But that's what crews are for - to assess and determine what no AFM, MEL or Chief Pilot can or should. The day was a unadulterated mess.

IFG, probably I have misperceived but if I may, the fact that there over-redundancies arise and incompatability lists exist speak to the very issue of trying to plan for contingencies which can't be known except by the crew at departure. I think the fundamental idea is that crews can quickly understand operational implications in circumstances never contemplated in MMELs, but as you say, the notion is a not-so-subtle work-around such judgement calls, but as I say I have probably misperceived and the procedure probably worked well. But as you correctly observe, no, it's not deep. Ninety-nine percent of the time it's a non-issue. It's just airmanship. Sometimes taking an airplane with six items MELd is just fine and even a good challenge for the "little grey cells" !

[boestar]

IFG,

I agree with you that is does not go as deep as perhaps it could or should. Don makes a valid point that, that it what the aircrews are there for.

HOWEVER

In this age of technology and electronic flight bags there is the possibility of having an electronic MEL that could cross reference individual MEL items and alert when 2 MELs are placed on an aircraft that may cause issues if both systems are inop at the same time as Don alluded to with the 6 MELs. We currently need approval to apply more than 3 MEL to an aircraft mainly to avoid situations like that.

As for the MMEL, no company that I know of uses the full MMEL in operation and I am not even sure you can. the MEL is a subset of the MMEL and is more restrictive as well.

[IFG]

IFG,

I agree with you that is does not go as deep as perhaps it could or should. Don makes a valid point that, that it what the aircrews are there for.

HOWEVER

In this age of technology and electronic flight bags there is the possibility of having an electronic MEL that could cross reference individual MEL items and alert when 2 MELs are placed on an aircraft that may cause issues if both systems are inop at the same time as Don alluded to with the 6 MELs. We currently need approval to apply more than 3 MEL to an aircraft mainly to avoid situations like that.

As for the MMEL, no company that I know of uses the full MMEL in operation and I am not even sure you can. the MEL is a subset of the MMEL and is more restrictive as well.

Hi Boestar - Agreed re: MMEL, not sure why I typed in the 2nd M. It is my understanding that the MEL must not be less restrictive than the MMEL (as established by the manufacturer), but may place additional restriction. I believe this opportunity is seldom exercised, but could stand corrected.

.... IFG, probably I have misperceived but if I may, the fact that there over-redundancies arise and incompatability lists exist speak to the very issue of trying to plan for contingencies which can't be known except by the crew at departure. I think the fundamental idea is that crews can quickly understand operational implications in circumstances never contemplated in MMELs, but as you say, the notion is a not-so-subtle work-around such judgement calls, but as I say I have probably misperceived and the procedure probably worked well. But as you correctly observe, no, it's not deep. Ninety-nine percent of the time it's a non-issue. It's just airmanship. Sometimes taking an airplane with six items MELd is just fine and even a good challenge for the "little grey cells" !

Also in agreement with you, Don. My comment on 'depth' of consideration was not an encouragement to be fast and loose about unserviceabilities

& no intent at all to trivialize the concerns about multiple deferments. As 'Moon pointed out, deHav' published a compatibility list (& I assume Bombardier would now?); I believe it listed concurrent deferrals that were not permitted (as opposed to those permitted - again open to correction), which still leaves the almost infinite possible combinations not listed up the the crew's best judgement. The '27 I fly now has no such list, but of course was certified slightly before the DH-8. Are they commonly provided on 'todays' A/C?

Cheers, IFG

[edited to add] Incompatibility of some deferments is indicated in the deferral allowance or the associated Operating Procedures (as in XXX must be operative), so even where no separate compatibility list is published, the overall A/C serviceability has been considered.

[Don Hudson]

Understand all, IFG... D.