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Guest gremel

Flight Dynamics / USAir Flight 427

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Guest gremel

I was wandering about the flight dynamics of the PMDG 737-700 when I tried to replicate the crash of USAir Flt 427 in Pittsburgh back in 1994 or thereabouts. The problem was with the rudder valving and the rudder stuck in the full left position leading to a rollover to the left and resulting crash. The aircraft was a 737-200 and was at an altitude of 6000ft on approach to the airport when the rudder malfunctioned.I know that the PMDG is a 737-700 series and I was attempting to see if the flight dynamics were the same or close to the real 737-200 that went down. I was unable to get the PMDG to roll over at the config. altitude of 6000ft using extreme left rudder inputs..I did have the yaw damper in the 'OFF' position.Can anybody add their comments to this senario. I have tried the same approach with RFP 747 and it duplicates the flight path according to the flight simulators that were used to identify the problem with the 737-200 crash back in the mid-90's. Regards,Jack

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Guest Racer

Sounds like you know more about this accident than I do, but here's my take............The first three events of that crash were caused by the wake vortex of the preceeding 727, which caused the initial left roll and deflected the rudder to it's blow down limit. I think the reason you couldn't reproduce it in the PMDG is because FS2004 doesn't model things like wake vortex very well (or other exreme atmospheric conditions like wind shear). Also, the investigators don't know exactly how the rudder was behaving after the valve was damaged. So things like this are hard to replicate accurately in a sim.It's really intersting that you could reproduce it in the RFP... I would put that down more to inaccuracies in the RPF's flight model (no offense intended) than to PMDG's. that's just my relatively uninformed $.02, though my father is FAA near Pittsburg and we have discussed this accident some.I once tried to reproduce the initial stages of the Alaska 261 accident, but the results seemed pretty off to me as well. I just put it down to the limitations of FS2004.regards,Ryan Justesen

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Guest Racer

Jack, copy that, I realize my post wandered a bit, sorry :) I will give it a try tonight and see how my set up responds. (X-45) I'm curious now....Will report back.regards, Ryan

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Why would you want to replicate such a terrible event? Anyways, as I recall the NTSB tried to replicate this in the air with wake turbulance etc and could always recover under this situation. Truth be told for this particular case it will never be **100%** known why it happened although the rudder seems to be involved. I suggest testing the PMDG 737 against known things like a Boeing Flight Performance Manual and the like. Best Wishes,[h4]Randy J. Smith[/h4][h3]P M D G's 747-400[/h3][h4]coming to a runway near you[/h4][/font color]Caution! Not a real pilot, but do play one on TV ;-)AMD 64 3200+ | ASUS KV8 DELUXE | GFORCE 5700 ULTRA @535/1000 | Maxtor 6Y080M0 SATA 80 GIG | 512 DDR 400 | Windows Xp Pro | Windows Xp Pro 64 |

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Guest Racer

Randy, I can't speak for Jack, but speaking for myself I was interested in replicating it for the same reason as the NTSB; to better understand it, not out of some juvenile 'death wish' or what not... Such crashes are terrible tragedies, and I believe it is our duty as pilots to learn all we can from them. In regards to FS, it's value to me is mostly just to give a little hint as to what was affecting a pilot's decision making process during the emergency. Sorry if I wasn't 100% clear about that.regards,Ryan

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Guest pez_man

Hmm, I remember seeing a documentary on Discovery about that accident (where else?! :-)) Didn't that accident happend because some sort of malfunctioning rudder control unit making the rudder stuck? If my memory serves me correct Boeing had to replace the malfunctioning piston on all their 737's. So probably the 737NG has another typ of rudder mechanism, hence no crash with PMDGs NG! :-)rgrds fredrik granfors

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Guest Racer

Jack, just for the record, PMDG 737-600 @ 6000ft, 190 kts, 5400lbs. fuel, yaw damper off, AP off, rudder sensitivity set to high in control panel.Upon application of rudder hardover left aircraft has immediate and strong left yaw, followed 1-2 seconds later by onset of roll coupling, roll rate increasing as bank angle increases. Autothrottle still engaged, marked engine spool up (which was noted in the report) even with airspeed passing 230kts.I could not induce yaw with the AP on, b/c even with yaw damper off it will not allow you to command that amount of rudder (in FS, my opinion). Of course, in the real accident the AP could not prevent the rudder from being deflected to it's blowdown limit. regards,Ryan

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After the incidents in question, a directive was issued that raised approach speeds by 10 kts for the Classic and New Gen 737's. This is to keep the airspeed up to a point where the ailerons can overpower the rudder in the event of a hardover. The FAA ordered a retrofit/redesign of the rudder actuator systems for all 2000+ US registered 737-2/3/4/5 aircraft in 11/01.Next Gen 737's already have the redesigned rudder actuators, and are not subject to this particular anamoly, as Fredrik says. Hopefully, with the retrofit, the Classic and New Gen's are in better shape as well.Obviously, there is alot more to it than this, but the details are little on the long side.Soooo....no, the PMDG 737 should NOT be able to reproduce this.

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