[SystemSafety] "FAA chief '100% confident' of 737 MAX safety as flights to resume"

[Peter Bernard Ladkin]

On 2020-11-20 15:21 , Tom Ferrell wrote:
> Couple of quick thoughts on this:
> 
> Re the Max.  .... All of this does not, however, change my basic point concerning the level of scrutiny applied to the MAX.

Nor mine that the current procedures are known to be inadequate and that has been remarked by the 
two investigative bodies JATR and House Transportation Committee.

> Re: Sioux City.  My understanding of that event is very different than what you noted in your brief post.  The first two events associated with the cargo door was a structures issue.  Explosive decompression leading to cabin floor collapse which in turn compromised multiple aircraft systems including the hydraulics.  

Yes, and Ermenonville was the third time it had happened. It had happened before in pressurisation 
test, and in a revenue flight over Windsor, Ontario.

> As I understand it, that scrutiny included the routing of hydraulics throughout the airplane.  > The hydraulics routing passed that scrutiny based on the best knowledge at the time. 

I don't think so. Neither did the NTSB. See below.

> The subsequent unconstrained rotor burst in the Sioux City created shrapnel patterns that far 
> exceeded what the earlier analyses had assumed.  

As far as I know, no it didn't. I am looking at the fragment distribution diagram. All pretty 
standard. And I am looking at the routing of all three hydraulic systems in the tail. It is 
*obvious* looking at those two together that there is the potential for a turbine disintegration to 
sever all three lines.

The NTSB said it "considers in retrospect that the potential for hydraulic system damage as a result 
of the effect of random engine debris should have been given more consideration.... Douglas should 
have better protected the critical hydraulic system(s) from such potential effects."

Basically, they say that engine fragmentation specialists should be more involved in hazard analysis.

The event showed clear violation of 14 CFR 25.903(d). They actually used a "special condition" 
during DC-10-10 certification because 25.903(d) was in process of being revised. There was 
subsequently an FAA Order 8110 11, and AC 20-128 which addressed engine frag/critical system 
involvement and contained advice on how to conform with 903(d), but neither were effective at time 
of certification.

> The idea that ALL the hydraulics were routed through the tail such that one event disabled all
> the systems is erroneous.  

No it is not. It is, in fact, what happened.

There are three hydraulic control systems, which all run through the tail and which were all severed 
in the tail section in various ways, and there is no backup. Backup was considered subsequent to a 
recommendation in the NTSB report.

Systems Numbers 1 and 3 had parts that were found severed or missing on the right horizontal 
stabiliser. System 2 pumps were attached to and obtained power from the Number 2 engine, the tail 
engine which fragmented. Parts of the Number 2 hydraulic system components were found "in the Alta, 
Iowa area", which is some 80km or so from Sioux Gateway Airport, which means Number 2 went also at 
the time of Nr. 2 frag. See AAR-90-06 Section 2.3.

> The hydraulics were compromised due to multiple impacts in at least two different locations, 
> only one was the tail which disabled two of the three redundant systems. 

Nope, all three. Lines for Number 1 were severed; a portion of the stabilizer contained part of 
Number 1 and Number 3 was missing on landing; critical parts of Number 2 which had been attached to 
the Number 2 engine accessories were found underneath where the engine blew.

PBL

Prof. Peter Bernard Ladkin, Bielefeld, Germany
ClaireTheWhiteRabbit RIP
Tel+msg +49 (0)521 880 7319  www.rvs-bi.de





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