Re: Safety and design rankings (was Re: Flight controls)

From:         Robert Dorsett <>
Date:         11 Dec 92 17:42:28 PST
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In article  <airliners.1992.138@ohare.Chicago.COM> kls@ohare.Chicago.COM (Karl Swartz) writes:

>> These aren't safety-critical items (well, maybe the lighting is: it didn't 
>> work at Habsheim).
> I believe both intercom and lighting are considered safety-critical
> items.  

Sorry: that was poorly phrased.  It is a must-have, and, yes, it did
fail.  However, I understand the problem was mechanical in nature (CCF?); the
software problems were eventually fixed.  

I don't know about the intercom, but the PA system is, as well.

>Lighting in general may not be deemed critical, though certainly the
>directional lighting in the floor is.

Floor directional lighting is relatively new.  It complements, but does not 
replace, the regular emergency floods: both are now considered critical.

For the semantics fans: we should probably be careful in our use of the term 
"safety-critical" with respect to these systems: it is not, for instance, in 
the same league as the EFCS, and the software likely doesn't require the 
same confidence.  Anyone known for sure?  I would suspect emergency lighting 
is listed as an "essential function," not critical.

> Is the MD-11 comparable to the 747-400 in this regard?  I would assume
> so since they are of comparable vintage.

I would suggest not: the former is more of a derivative, the latter more of
a new type, with its new wing (which was designed to support the all-upper-
deck concept, plus maybe one more derivative after that), electrical system, 
extensive use of composites, new APU, etc.  Each has a high degree of direct 
commonality with its predecessor, but from a technology basis, I don't think 
they're in the same league.

One commenter to the paper Pete and I are brewing up took exception to my
comparison, though: he feels the 767 was more of an equivalent to the A320.
I disagree, from both design and avionics perspectives.

Perhaps some of the Boeing people posting here can comment on the 
commonality of the various versions of the 747.

> Where do the new generation 737s (-300/-400/-500) fit into this?

FMS, new engines, composites, just about everything else is derivative.  The
"glass" in the cockpits is hackwork, IMHO, nowhere NEAR as integrated as
the "all-new" glass airplanes such as the 747-400.  I don't believe systems
control has changed much at all.

> And, for completeness, where do the glass-cockpit version of the MD-80
> family fit into the picture?

My PERSONAL mental "ranking" of the sophistication of these airplanes is 

                   High-high automation/integration    
One philosophy        
  777                                                     Another philosophy
                     HIgh automation/integration
             757/767<--------------------->A310, A300-600
              FMS only, varying or no glass, no standards
                747-300,737-300,-400,-500, MD-8X, F.100
                    INS/PMS, conventional otherwise
              INS only, very smart autopilot, fair integration
        INS only, simple, coupled autopilots, fair integration
                        747-100/200, DC-10
          First/second-generation design, little integration
             two-man            |                    three-man
                                 --------------->727, DC-9, 707, DC-8

Two-man airplanes have always used more automation than three-man crews;
hence, I give them a slight edge among the "first-generation" airplanes.

Others may have differing impressions; there's no hard and fast rule to

Of all these airplanes, the original 747 family has the best internal
cockpit consistency, by far.  Otherwise, the new Airbusses have the best 
design consistency.  But I count some 19 fundamental cockpit designs in 
operation, countless permutations existing in most of them, depending on 
customer preferences in avionics and cockpit layout.  

The FMS's used on these airplanes are generally done by Honeywell, except
that Boeing's using Smiths Industries for the 737, for some reason.

Note that INS's on older-generation airplanes were often not purchased by 
customers who intended to use them for domestic service: EAL's A300-B4's, for 
instance, didn't even have them for service to South America.  All of the 
first-generation airplanes currently have INS retrofits available; there are 
also on-again, off-again plans to offer a relatively sophisticated glass 
cockpit for the 727, with new engines.  

But it's important to note that INS interfaces were pretty much localized, 
with maybe a coupled mode for the autopilot.  The devices were nowhere near 
as integrated in the cockpit design as 1980's/1990's crop, even if they were 
explicitly sold with airplanes (such as the early 747).  They were "packages,"
not the "essence."

LASTLY, note that the manufacturers are MUCH more assertive about preventing
customers customizing their cockpits.  This really got out of hand: for 
instance, I have a picture of a KLM 747-200 with some seven HSI's and CDI's 
and four full-sized ADI's, blanketing every spare square inch of the pilots' 
panels--that's what THEIR chief pilot apparently felt comfortable with. :-)  
Options are much more limited on modern airplanes; all customer variations 
are much "closer" to the manufacturer standard cockpit (the one that gets 
in all the publicity photos) than they used to be.  Then again, nearly all 
the major airlines don't have anything resembling the engineering and design 
departments  that they used to have, so they've forfeited the right to 
comment, to a large degree.  Performance is now ensured by legal contract, 
rather than design, with the dollar being the bottom line.

Caveat: I generally don't know that much about Douglas products 
(except for the DC-10 :-)); Boeing and Airbus have always caught my 

Robert Dorsett!!rdd