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Boeing 737 Rudder PCU Problem Investigation  
User currently offlineKBGRbillT From United States of America, joined Sep 2004, 155 posts, RR: 0
Posted (3 years 6 months 4 weeks 1 day 18 hours ago) and read 5192 times:

Does anyone know the name of the investigator and/or individual that theorized that the Boeing 737 rudder pcu problems during the 90's could stem from thermal shock? This theory basically solved the problem of 2 mysterious crashes and several other inflight malfunctions, however, on the Air Emergency episode "Deadly Components" an investigator refrences this person as a 'fellow' who proposed this theory based on some similar issues witnessed in the U.S.A.F. This individuals name show be widely publicized as a smart man and potential saver of many lifes!

12 replies: All unread, jump to last
 
User currently offlineUTAH744 From United States of America, joined Jul 2009, 200 posts, RR: 0
Reply 1, posted (3 years 6 months 4 weeks 1 day 18 hours ago) and read 5139 times:

Quoting KBGRbillT (Thread starter):

What this smart man saved was Southwest Airlines. The FAA was very close to grounding ALL B737's.



You are never too old to learn something stupid
User currently offlinetxagkuwait From United States of America, joined Aug 1999, 1803 posts, RR: 42
Reply 2, posted (3 years 6 months 4 weeks 1 day 17 hours ago) and read 4976 times:

Quote:
What this smart man saved was Southwest Airlines. The FAA was very close to grounding ALL B737's.

I would be very interested in seeing some sort of proof as to how close the FAA was to grounding the aircraft.

Considering their safety record (a runway overshoot in dismal wx which tragically killed a young boy in an automobile as the sole fatality over a 40 yr period - with infinitely more cycles/day than practically any other carrier I can think of) I would be hard pressed to think that a grounding was imminent.

So kindly share the source of your information. If a grounding was imminent, certainly there are articles or statements in the public record you can cite.

Or....if this was merely speculation on your part....you can tell us that, too.


User currently offlineFlyASAGuy2005 From United States of America, joined Sep 2007, 7004 posts, RR: 11
Reply 3, posted (3 years 6 months 4 weeks 1 day 17 hours ago) and read 4963 times:

Quoting txagkuwait (Reply 2):

I'm pretty sure he was referring to the rudder problems the 737s had in the 90s and the fact that WN has an all 737 fleet. Not the incident in MDW..

It would have directly affected them (and all '37 operators for that matter) but with no other a/c type, I think it would have been a huge issue as well.

[Edited 2011-01-25 20:41:25]


What gets measured gets done.
User currently offlinetxagkuwait From United States of America, joined Aug 1999, 1803 posts, RR: 42
Reply 4, posted (3 years 6 months 4 weeks 1 day 16 hours ago) and read 4802 times:

ASA guy:

I agree with you completely and wasn't suggesting a rudder had anything to do with the MDW incident.

I try to stay in the loop and while the unexplained 737 crashes were a concern - I cannot, for the life of me, recall any threat by the FAA to ground the aircraft type.

We were not looking at a Martin 202 or Lockheed Electra deal. The 737 had acquired a very enviable safety record before the 3 or so crashes attributed to the rudder.

Without a doubt the FAA wanted to know what caused those crashes. And it is/was no comfort to the survivors of those lost in 737 crashes that the aircraft type had demonstrated its airworthiness and had not theretofore experienced any sort of ongoing problem which would have led to the crashes.

But in all of the literature I recall and in a number of accident investigation reports I do not recall ever seeing anything, anwhere that the FAA contemplated a grounding.

Yes, as an all 737 operator it would not have been a good time for WN. Then again, it (the grounding) never happened. Nor have we experienced a plethora of 737s falling out of the skies.

What I don't understand, and perhaps I never will (I am a petroleum engineer rather than an aerospace type) is why did this problem (if it were a rudder) wait so many years before it reared its ugly head? Design flaws usually come out and bite fairly early in an aircraft's life - the DH Comet, the Martin 202, the Lockheed Electra. They don't usually wait 8 or 10 or 15 yrs before a trend develops.

Suffice it to say --- whatever it was, it appears to be fixed, and the 737 continues to ply the skies as a safe, durable, and rugged workhorse in the fleet of many airlines throughout our world.


User currently offlinewjcandee From United States of America, joined Jun 2000, 5152 posts, RR: 22
Reply 5, posted (3 years 6 months 4 weeks 1 day 15 hours ago) and read 4674 times:

Quoting txagkuwait (Reply 4):
, it appears to be fixed

Also the flight envelope has been changed to eliminate catastrophic results from the known failure modes.


User currently offlinePlaneInsomniac From Canada, joined Nov 2007, 678 posts, RR: 0
Reply 6, posted (3 years 6 months 4 weeks 1 day 13 hours ago) and read 4519 times:

Quoting KBGRbillT (Thread starter):
Does anyone know the name of the investigator and/or individual that theorized that the Boeing 737 rudder pcu problems during the 90's could stem from thermal shock?
Quoting txagkuwait (Reply 4):
I try to stay in the loop and while the unexplained 737 crashes were a concern - I cannot, for the life of me, recall any threat by the FAA to ground the aircraft type.

I can recommend the excellent book "The Mystery of Flight 427: Inside a Crash Investigation" by Bill Adair, which is a detailed and suspenseful description of the USAir 427 crash investigation. It also discusses in detail the rudder valve issues and how the investigation team - in a series of controlled experiments performed on the very rudder valve salvaged from the crash site - finally narrowed the probable cause down to a weak valve design.

I think both of the questions stated above are answered in the book, if my memory serves me right.



Am I cured? Slept 5 hours on last long-haul flight...
User currently offlineUSAIRWAYS321 From United States of America, joined Jul 2001, 1847 posts, RR: 9
Reply 7, posted (3 years 6 months 4 weeks 1 day 2 hours ago) and read 4034 times:

"Flight 427: Anatomy of an Air Disaster" by Gerry Byrne is a great book on this subject as well.

User currently offlineKBGRbillT From United States of America, joined Sep 2004, 155 posts, RR: 0
Reply 8, posted (3 years 6 months 4 weeks 1 day ago) and read 3873 times:

Quoting txagkuwait (Reply 4):
But in all of the literature I recall and in a number of accident investigation reports I do not recall ever seeing anything, anwhere that the FAA contemplated a grounding.



In the Air Emergency episode I referenced in the original post one or two of the NTSB and/or FAA investigators of the USAir flight 427 crash specifically mentioned that they did seriously consider grounding the 737 fleet because of the shocking similarity to United 585 as well as the close call with Eastwind flight 517 which exhibited nearly identical rudder control issues.


User currently offlineUTAH744 From United States of America, joined Jul 2009, 200 posts, RR: 0
Reply 9, posted (3 years 6 months 4 weeks 21 hours ago) and read 3723 times:

Quoting txagkuwait (Reply 2):
http://seattletimes.nwsource.com/news/local/737/

In 1996 I was living in the Puget Sound area and the Seattle Times did an excellent multi part piece on the Boeing 737 ruder PCU. If you have the time read all of the articles, or just go to part 5 which tells of the relationships between Boeing, NTSB and the FAA. Much of the delays on fixcing the rudder PCUs was due to Boeing (or cost reasons) and the FAA (conflicting mandates - protect flying public & advance aviation industry.)

As to how close the FAA was to grounding the B737's a friend in gthe FAA told me he had heard that it was being considered. After reading all of the articles you sure hope they were considering such an action. I now have not even a second thought about riding on a B737.



You are never too old to learn something stupid
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 10, posted (3 years 6 months 4 weeks 20 hours ago) and read 3639 times:

Quoting txagkuwait (Reply 4):
What I don't understand, and perhaps I never will (I am a petroleum engineer rather than an aerospace type) is why did this problem (if it were a rudder) wait so many years before it reared its ugly head?

It was an extreme corner case condition and not reliably repeatable. There was no way to positively confirm it, and no way to know you'd positively eliminated it. You needed a PCU that was within particular portions of the allowable tolerances for manufacture, coupled with exactly the right thermal environment, coupled with exactly the right pilot input with the spool valve in exactly the right condition. Much like most aviation disasters, several things had to line up exactly right at the same time.

Tom.


User currently onlineXT6Wagon From United States of America, joined Feb 2007, 3394 posts, RR: 4
Reply 11, posted (3 years 6 months 4 weeks 20 hours ago) and read 3610 times:

Quoting tdscanuck (Reply 10):
Much like most aviation disasters, several things had to line up exactly right at the same time.

Worse its the kind of thing that can fix itself in the crash. Nothing harder to find than a problem that is no longer a problem when you are searching for it.


User currently offlineKBGRbillT From United States of America, joined Sep 2004, 155 posts, RR: 0
Reply 12, posted (3 years 6 months 4 weeks 18 hours ago) and read 3519 times:

Researhed this topic all day today and found the answer finally in an article in Air & Space magazine from 2002. The gentlemens name is Ralph L. Vick, he was an engineer for Bendix Corp. in California. With over 6600 737's built and flying around the world at one time or another this man's name should be widely know in the aviation community as a hero!!

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