Re: A3XX vs B747-600 (was: Airbus lawsuit coming?)

From:         Mark Ingram <>
Date:         21 Oct 96 02:29:18 
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On 11 Oct 1996, Terrell D. Drinkard wrote:

[Quoting Mark Ingram:]

> >I do suspect that there could be any number of significant "grandfathered"
> >737 systems that would not meet current certification criteria.  In one of
> >the _AW&ST_ articles discussing the NTSB's ongoing investigation of 737
> >uncommanded rudder inputs (United and USAir, among others), it was
> >reported that the rudder PCU (power control unit, I believe it is) could
> >not be certified under today's regulations.
> I've not worked the 737 in a year or so, but I don't recall anything like
> that.  That sounds like a suspiciously irresponsible statement to me.

> Do you recall exactly where you read that?

Perhaps someone with the _AW&ST_ CD-ROM (or complete back issues) can help
me out here, as far as the exact date and issue.  It has been within the
last six months that this particular article was published.

I find _AW&ST_ at times exasperatingly conservative, on rare occasions
dead wrong, but irresponsible - hardly ever.  As to the design problems
"grandfathered" into the main and standby rudder PCU's, and the yaw damper
system, one has only to read the latest NTSB recommendations to know that
there are significant problems here (_AW&ST_, October 7, 1996, p. 20,
"NTSB Seeks Upgrades to 737 Rudder System").

> FWIW, there cannot be "any number" of significant systems that do not meet
> current criteria.  Each manufacturer has to request a specific
> "grandfathering" action from the appropriate regulatory agency, and they
> are all subject to negotiation with that same regulatory agency.  The
> regulatory agency keeps very close tabs on what systems are in the airplane
> as well as their cert status.

Besides the PCU's dual-concentric servo valves, which are susceptible to
galling, there are definitely any number of 737 -100's and -200's flying
with old-technology flight data recorders (five-channel foil models,
perhaps?).  While these are indeed "certified" for their use on certain
aircraft, they nonetheless are not "certifiable under current criteria"
for installation under new Type certificates.

Each and every one of these exemptions may indeed have been negotiated
with a certifying ageny, but it still doesn't make the exempted technology
"currently certifiable."


Mark E. Ingram

MarkT@Mo-Net.Com (also