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Old 6th Mar 2009, 14:34
  #1544 (permalink)  
cargun
 
Join Date: Mar 2009
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Shouldn't be a sudden change of 1958 feet in RA1 reading considered as malfunction?

I'm a non pilot, tech savvy curious Turkish guy. I read all the 78 pages so far and many other forums. I'll try to be objective yet forgive me if I'm wrong.

First of all I agree that the crew's initial mission is to fly the airplane by continuously checking altitude & speed. So so far it seems that pilots deserve some (it depends how much) part of the blame here. I also agree with both the cultural issues & the military crew members' seniority rank issues having prevented the safety pilot to intervene. Yet I also consider that pilots can't be all to blame. 100 seconds is a lot and without CVR we do not know what on earth happened there in the cockpit.

You pay zillions of dollars to Boeing for state of the art avionics masterpieces that you can rely. You expect the autopilot mechanism to be close to fail proof. Here I really can not understand the design of the 737ng flight computer system, if RA1 feeding the FCC B, why on earth the pilot commanding FCC B looks at RA2. There is supposedly a "sudden" change of 1958 feet (1950 to -8) in RA1 reading, how on earth Boeing engineers could not have foreseen that such a huge variation should deactivate auto pilot?

This is easy you do not have be engineer to figure this out. Suppose you are very punctual and carry two watches, one on your right hand and one on your left. You usually check the left one, let's say every hour. All of a sudden you realize that the left one has gone behind/forward like "5 hours" since the last time you checked. What would you do? Would you just think that 5 hours went by? You cross check the one on your right. You realize the left one is kaput and you keep checking the right one until you have the left one fixed.

If the RA1 reading variance was like 100/200/10/50 feet you would be right, no way a computer might have just by cross checking with the RA2 realized that RA1 was malfunctioning. Come on guys! It's a sudden change of 1958 feet. t0 you are at 1950 feet, t1 you are at -8. And the reading is so negative even below what should the 737 RA read on the ground. (-4) This is a major engineering and design scandal. Boeing is there to blame, not for a faulty RA, that can happen, but for a faulty flight computer safety system. Now Boeing claims that in case of malfunction of RA 1, FCC would consult RA 2. Yet I'm sure by Feb 11 alert they didn't know that a negative reading and a huge variance in altitude counted as a malfunction. On Feb 11, they focused on the faulty RA to be fixed and serviced, rather than focusing on what would a faulty RA cause at 737ng's state of the art avionics. They should have issued the recent detailed warning back then in Feb 11. Yet we all know that even highly skilled and experienced 737 avionics experts do not know for sure the protocole when & how FCC consult RA2 instead of RA1. A lot of pilots confessed her and there they didn't know FCC B was fed by RA1, while they were looking at RA2.

One other issue is that, as back as in September 2007, I read in local forums that THY 737 pilots were complaining about negative left RA readings. They were told and believed this to be harmless and explained with "yet another cell phone activated". Due to such a repetitive error, resolved with a stupid explication, crew may have ceased to report this "harmless error". That might be the reason the previous errors are there on the FDR, yet not on the airplane's maintenance log book. Here all THY 737 pilots, airlines maintenance and training & Boeing technical crew are to blame.

Yet this fault, initially reported at THY, dates back to 2007 and Boeing didn't figure out that it would interfere with flight safety processes on auto pilot, as this is the lead RA feeding the FCC. I'm sure many other airlines' 737's had the same (-8) reading issue, reported or not. Not fixing it is much worse than designing a faulty computer system. No design is fail proof. Microsoft does major mistakes, but they issue patches, try to fix things. Why Boeing didn't fix this earlier?

Having said all this. Can anyone clear me on the ATC's role in 100 seconds of crew paralysis. Shiphol ATC having a radar and ILS should have closely monitored the 737's approach on their screens, starting at around 2500 feet. They would know its altitude, speed and distance from the airport at any given time. Why on earth haven't they warned the crew? Why anybody doesn't talk about this? Or am I too wrong in assuming they should have.
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