Jump to content
Sign in to follow this  
tunnelcat

Taiwan Jet Explodes Into Fire in Japan

Recommended Posts

For years I have worked in the computer industry, specifically around infrastructure.You would not believe the amount of patches (AD's) that are issued for the network and hardware that supports it. I know planes and networks ain't the same, but the reality is, in this context, they're pretty close.My 2 cents,bt

Share this post


Link to post

the 737 rudder issue is a good example of how many things need to be in place for a 'fault' to occur. as also stated here, much like computers and finding the cause of a network/software crash ... may look easy at first glance; but hard to find the exact sequence to identify and then create a fix.--


D. Scobie, feelThere support forum moderator: https://forum.simflight.com/forum/169-feelthere-support-forums/

Share this post


Link to post

>The loose bolt is just another little problem that seems to>be adding to continuing list of defects that are showing up in>the venerable Boeing 737 series.>It was never a defect but a design that when not replaced correctly would not work. That is what happened in this case. The mechanics forgot to put the washer back in and the bolt fell out simple as that.But at approach speeds and altitudes, they could get into what is called a>'crossover stall' whereas one wing would stall before the>other at low speeds when a sudden yaw occurred, especially>dangerous during crosswind landings. When the rudder slammed>over on the United flight, the aircraft violently rolled over>when the right wing stalled and the pilots had no chance to>recover from the resulting roll.This is known as a cross-control stall

Share this post


Link to post

>>Pilots could recover from this occurrence at higher speeds and>altitudes (that's how the investigators figured out the>problem when it happened to two other airliners that the>pilots were able to recover from the roll). But at approach>speeds and altitudes, they could get into what is called a>'crossover stall' whereas one wing would stall before the>other at low speeds when a sudden yaw occurred, especially>dangerous during crosswind landings. When the rudder slammed>over on the United flight, the aircraft violently rolled over>when the right wing stalled and the pilots had no chance to>recover from the resulting roll.>>As best as I can remember, I think Boeing had to issue new>higher landing speeds to all 737 pilots while the cause was>being sorted out.>>Kim You are confused. There is no such thing as "crossover stall." There is such a thing as "crossover speed." This was something discussed with regard to the USAir and United 737 crashes and A300 crash. If you were above crossover speed, you had enough aileron authority to overcome any uncommanded rudder hardovers, while below that speed, you did not.If the loose bolt was because CAL maintenance did not comply with a maintenance bulletin for a known problem, then you can't blame Boeing for this one. Every single airplane out there has its problems. The longer a plane has been in service and the greater their numbers, the more which will come to light. Once a problem comes to light, one of three things will happen. The problem can be redesigned by the manufacturer, a maintenance procedure can be instituted for it, or a cockpit procedure can be added for it. All of which are valid for making the plane safe. If a required maintenance procedure was not followed, then there is nothing either the manufacturer nor pilots could have done to prevent anything.

Share this post


Link to post

You're right, I meant 'crossover speed stall', my mistake when I was interrupted writing the post. The 'one wing stall' is a more dangerous quirk of swept wing aircraft when a quick or excessive yaw occurs during slow speed flight. The wing that moves backwards during the yaw will lose far more lift because of it's angle relative to the airflow. This problem is not as severe on aircraft with wings positioned ninety degrees to the body of the aircraft, although it can still happen.The resulting stall will roll the aircraft violently to the stalled wing side, and if there is insufficent airspeed and altitude, recovery is not possible.When I lived in Colorado Springs, I had to connect between Denver and KCOS many times. Pilots used to do a very steep (more than 30 degrees) and short final turn onto runway 35L. I assume that they were in a hurry to land, but that practice seemed to stop after the United accident. Nice gentle 25 degree turns and less views of the ground through the windows while sitting on the opposite side of aircraft.These one wing stalls don't seem to be modeled very well with the jetliners in FS. The aircraft don't roll enough that you can't recover.Kim

Share this post


Link to post

There is no such thing as a "crossover speed stall" either. What you are describing is a cross-control stall. The only term in aviation that includes the word "crossover" is "crossover speed." Crossover speed was a factor in the crashes because at the time of the uncommanded rudder deflection, they were below crossover speed, which meant that they did not have enough aileron roll authority to overcome the rudder input. The Tradewinds 737 survived the rudder hardover because they were flying fast enough above crossover speed that they had enough aileron authority to overcome the rudder hardover. Those planes did not crash because of cross control stalls in the sense in which you are describing it. None of them were turning onto final at the time. They were just minding their own business in straight and level flight several thousand feet up and miles from the airport when they crashed. The rudder malfunction caused the rudder to deflect in the opposite direction of the pilot's command. Once the planes were already deep in their death spirals, you can perhaps say that they were in a potential cross control stall situation because they had a continuous rudder deflection with opposite aileron and stick back. But that is secondary to the actual situation, which is the plane entered an uncontrolled roll because of an uncommanded rudder deflection at a point where their airspeed was insufficient for the ailerons to counteract the rudder malfunction. Those crashes had nothing to do with whether people are turning final more gently or not. Any differences you think you noticed between how a plane was flown before or after those accidents as a passenger or observer are imagined or coincidental at best.

Share this post


Link to post

Let me do some research on where I got the terminalogy. I'll post back on what I find. 'Crossover speed' is a known term, but I read a descriptive term somewhere that referred to the particular type of stall which occurs when the aircraft is near that speed and a sudden yaw occurs, stalling only one wing and causing a roll, so I'll look for where that was referenced.As for the steepness of a percived bank angle, one time on approach to KCOS in a DC-10, the turn on final was definately beyond normal proceedures. It was so noticeable that other passengers even commented on it and g-forces were definitely felt. Due to the common occurrances of rotor winds off of the front range, there was mention in the news of proceedure changes for final approach turns into KCOS until the cause of the United crash could be determined.Kim

Share this post


Link to post
http://www.apstraining.com/article3_fci_training_dec02.htmThis looks like the article you may have read. They use the words "crossover speed" and "stall" in close proximity, but read closely because nowhere is he using the phrase "crossover speed stall." The discussion is about the result of the relation of the crossover speed and the accelerated stall they ended up in. A plane will stall at any speed, that is why you have normal stalls, power off stalls, power on stalls, accelerated stalls, etc. but nowhere is the word "speed" attached. Speed has nothing to do with stalling an airplane.

Share this post


Link to post

O.K. readers. I've finally done my due diligence and read through Bill Adair's 2002 book, The Mystery of Flight 427, to find the correct information. The term I was one I hadn't heard before, so I guess my memory failed me in my last posts, my apologies. Passages from Bill's book are in quotes.The term is called 'crossover point', defined by the author Bill Adair as: "The critical airspeed at which a full swing by the 737's rudder cannot be counteracted by the ailerons. When a plane has a rudder hardover while flying slower than the crossover point, the pilot must speed up to regain control."He also referred to the crossover point as; "the precarious moment in flight when the plane is at the mercy of the rudder. It was an aerodynamic quirk that Cox called the 'hole in the flight envelope'". John Cox was a USAir pilot and incident investigator for the airline pilot's union at the time of the USAir crash. Essentially, this is the speed at which the ailerons cannot counteract a sudden movement or a full hardover of the rudder. If the aircraft is going slower than the crossover point, a roll occurs that will result in loss of control unless there is sufficient altitude for recovery and the pilots are trained in the proper procedures for regaining attitude and speed. This quirk can also be far more unforgiving in swept wing aircraft.When the 737 aircraft was certified in 1967, the crossover point was not considered to be a problem. Boeing stated that if there was ever a rudder control valve failure, the ailerons were more than capable of countering the roll. This was found out years later to be incorrect. While flight-testing a 737 in 1995 after the USAir crash, John Cox and the other investigative pilots and engineers used the speed and flap settings that the USAir pilots were using just prior to the crash. After Cox got set up at flaps 1 and 190 knots, he began to apply a rudder input until he had full deflection. He maintained this steady-heading sideslip and began to reduce speed. At 187 knots, he found that he had to push forward on the yoke to lower the nose and regain airspeed in order to recover and aileron use alone was insufficient to counter the roll. He and the other pilots came to the conclusion that the crossover point was too high, not what they were expecting from the 737. It was also the exact approach speed that USAir Flight 427 was traveling at when it flipped over. The USAir pilots "ran out of roll authority". At normal 737 approach speeds, this could be a very precarious position for pilots to be in.The other contributing factor was the design of the 737's hydraulic rudder control unit, called the "dual concentric servo valve". The valve had two pistons, one inside the other. If one piston ever seized during flight, the unit was supposed to return to a neutral position. However, it was found during testing that thermal shock could cause one piston to seize, e.g. a cold valve getting a dose of hot hydraulic fluid. Hydraulic overpressure would then slam the other piston to full extension. Not only did full rudder deflection occur but it would do it in the opposite direction from the rudder pedal position. The confused pilots would be pushing hard on one pedal while the rudder was actually in the opposite position!In the USAir incident, wake turbulence from an earlier aircraft and in the Colorado Springs incident, severe rotor crosswinds off of the Front Range Mountains were determined to be the initiating causes in both fatal events. Boeing claims that all 737's will be refitted with newer two valve systems by 2007 (an improved valve was installed in the meantime). Pilots have now been alerted to the crossover point and are trained in the proper recovery techniques in case of anomalous rudder movements.Sorry for the long post but I hope all those interested in accident investigation give this book a read. It gives a very interesting view of an NTSB investigation.Kim

Share this post


Link to post

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  
  • Tom Allensworth,
    Founder of AVSIM Online


  • Flight Simulation's Premier Resource!

    AVSIM is a free service to the flight simulation community. AVSIM is staffed completely by volunteers and all funds donated to AVSIM go directly back to supporting the community. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. Thank you for your support!

    Click here for more information and to see all donations year to date.
×
×
  • Create New...