737 Rudder Problem.
Ich bin ein Prooner.
Thread Starter
Join Date: Feb 2003
Location: Home of the Full Monty.
Posts: 511
Likes: 0
Received 0 Likes
on
0 Posts
737 Rudder Problem.
Having watched an aviation prog. earlier tonight, several references were made to the problem which apparently caused the rudder on some 737 aircraft to go to full deflection and cause the aircraft to crash.
I know the prog. in question is now quite old. What I would like to know is, was the cause of these incidents ever irrefutably solved, and if so, what was it?
Thanks. N.Z.
I know the prog. in question is now quite old. What I would like to know is, was the cause of these incidents ever irrefutably solved, and if so, what was it?
Thanks. N.Z.
Join Date: Mar 2004
Location: The Pub
Posts: 46
Likes: 0
Received 0 Likes
on
0 Posts
Err.....I fly the 737 and when I see it parked up and shut down the rudder is in the normal postion and not deflected to one side unless as already pointed out there is a bit of a wind and it may move to one side.
Join Date: Mar 2004
Location: The Pub
Posts: 46
Likes: 0
Received 0 Likes
on
0 Posts
It says on your profile that you only hold a PPL so I can assume you have never done a 737 type rating or any other rating?
Does the 757/767/Airbuses have a problem with the rudder as well because I have also seen them when powered down their rudders deflected to one side in a strong wind.
Does the 757/767/Airbuses have a problem with the rudder as well because I have also seen them when powered down their rudders deflected to one side in a strong wind.
Join Date: Aug 2001
Location: Europe-the sunshine side
Posts: 755
Likes: 0
Received 0 Likes
on
0 Posts
mike,with hyd sys off ,the rudder will go into wind,and you'll have a chance of being hit by the yoke on some sensible points if you won't pay attention.
I agree with you ,it will probably be dificult to move the actuator by hand,but the wind on the rudder surface has a lot more force than your muscles.
I agree with you ,it will probably be dificult to move the actuator by hand,but the wind on the rudder surface has a lot more force than your muscles.
Join Date: Apr 2004
Location: Mostly hotels
Posts: 130
Likes: 0
Received 0 Likes
on
0 Posts
although i agree that the issue of the 737 rudders has been side stepped by introducing rpr ,ffm or intially by increasing the block speeds in the classics[before the rpr etc]. but but the rudder does move because of the wind if not powered by the hydraullics.the argument given above about the actuator being absolutely not necessary as anyone with bit of knowledge of physics can explain it easily.and boys do you actually believe in the profile page.....
Join Date: Mar 2004
Location: The Pub
Posts: 46
Likes: 0
Received 0 Likes
on
0 Posts
Your very touchy Mike, pick up your toys and put them back in your pram (Pillock!!!)
A lot of people seem to agree that without hydraullics the wind will move the rudder, I have sat in the flightdeck when the hydraullics are not powered and the control yoke can and does move about in a strong wind.
A lot of people seem to agree that without hydraullics the wind will move the rudder, I have sat in the flightdeck when the hydraullics are not powered and the control yoke can and does move about in a strong wind.
Join Date: Oct 2001
Location: farrrr east
Posts: 263
Likes: 0
Received 0 Likes
on
0 Posts
If you honestly think that the rudder would be blown to full deflection by the wind on the ramp you honestly have issues,
B737-3/4/500 AMM 27-21-00 Rudder and Trim Control System Adjustment and Test Block 501 page 520 Para 5
Do a test of the rudder hinge friction.
Last edited by allthatglitters; 25th Sep 2005 at 19:48.
Join Date: May 2005
Location: Near LHR
Posts: 24
Likes: 0
Received 0 Likes
on
0 Posts
I don't know if this will help the debate, but here goes. In my day job, I was involved in an investigation into a 747 uncommanded elevator input a few years ago, and also in the 737 rudder system redesign conferences in Seattle.
The cause of the 747 elevator deflection was a combination of two things - a bit of grit in one of the selector spools on the tandem actuator preventing full closure, and return lead rather than return lag on the other spool. As the design of the 747 elevator and 737 rudder PCU's are almost identical, this caused a light bulb to illuminate over the head of one of the development engineers, and much finger pointing ensued towards the 737 actuator.
Parker Hannifin have redesigned the spools to prevent return lead, and have increased the overlap margins to make some allowance for contaminants in the system.
Mr. Boeing has redesigned the entire system; the only salvageable bit is the standby actuator. Even the yaw damper coupler is different, as is the wiring and the magic boxes. There is a redefined hydraulic limiter, and a mechanical limiter.
The Speed increase was an attempt to ensure that the aircraft operated above crossover speed and so give the pilot a fighting chance at controlling it if the rudder declared UDI. I don't know much about flying 737's, but from a systems perspective I'd suggest that as the 737 has manual reversion, the best course of action in the event of a rudder hard over would be to dump the hydraulics and fly manually.
Other Boeings have non return valves in their systems to prevent the wobbly bits flapping around in the wind in the event of a total hydraulic fluid loss; as the 737 has manual reversion, that would be a bit of an own goal, so it is quite normal for the control surfaces to move about in the wind, whereas it would be a bit worrying if a 747, 767 or any other true Boeing flying control did so.
I'm now sitting back and awaiting the inevitable character assassination..............
The cause of the 747 elevator deflection was a combination of two things - a bit of grit in one of the selector spools on the tandem actuator preventing full closure, and return lead rather than return lag on the other spool. As the design of the 747 elevator and 737 rudder PCU's are almost identical, this caused a light bulb to illuminate over the head of one of the development engineers, and much finger pointing ensued towards the 737 actuator.
Parker Hannifin have redesigned the spools to prevent return lead, and have increased the overlap margins to make some allowance for contaminants in the system.
Mr. Boeing has redesigned the entire system; the only salvageable bit is the standby actuator. Even the yaw damper coupler is different, as is the wiring and the magic boxes. There is a redefined hydraulic limiter, and a mechanical limiter.
The Speed increase was an attempt to ensure that the aircraft operated above crossover speed and so give the pilot a fighting chance at controlling it if the rudder declared UDI. I don't know much about flying 737's, but from a systems perspective I'd suggest that as the 737 has manual reversion, the best course of action in the event of a rudder hard over would be to dump the hydraulics and fly manually.
Other Boeings have non return valves in their systems to prevent the wobbly bits flapping around in the wind in the event of a total hydraulic fluid loss; as the 737 has manual reversion, that would be a bit of an own goal, so it is quite normal for the control surfaces to move about in the wind, whereas it would be a bit worrying if a 747, 767 or any other true Boeing flying control did so.
I'm now sitting back and awaiting the inevitable character assassination..............
Join Date: Jul 1999
Location: 58-33N. 00-18W. Peterborough UK
Posts: 3,040
Likes: 0
Received 0 Likes
on
0 Posts
NTSB's findings here - all you need to know about 737 rudders.
http://www.ntsb.gov/events/usair427/images.htm
http://www.ntsb.gov/events/usair427/images.htm
Prop Jocket
Nicely summarised. The 744 incident was extremely interesting, both for the theories which made the rounds and the rather puzzling initial lack of connection made to the 37 rudder problem. Most bizarrely, I seem to recall that much speculation favoured "air in the system". Our resident hands-on technical expert at the time (genuine, not self appointed) came close to bursting a blood vessel at that one!!
I never saw the company follow-up but, some time later, Pilot magazine carried a full report and put forward the same conclusion as you. As I see it, that "dots the I's and crosses the T's" on the the '37 rudder saga but being aware of crossover speed and its implications would seem to be a sensible exercise for 37 operators.
For any who are not fully "up to speed"
on that I would highly recommend a part of AA's training video dealing with Performance and Control issues which includes an animation of a sequence of Boeing test flights looking at the control implications - fascinating, and it shows the problem and corrective action vividly. The rest of the video presents a strong caveat as regards the relevance of the remedial action which he boils down to the unarguable "Fly the aircraft first"!!! Highly watchable and superbly done.
Nicely summarised. The 744 incident was extremely interesting, both for the theories which made the rounds and the rather puzzling initial lack of connection made to the 37 rudder problem. Most bizarrely, I seem to recall that much speculation favoured "air in the system". Our resident hands-on technical expert at the time (genuine, not self appointed) came close to bursting a blood vessel at that one!!
I never saw the company follow-up but, some time later, Pilot magazine carried a full report and put forward the same conclusion as you. As I see it, that "dots the I's and crosses the T's" on the the '37 rudder saga but being aware of crossover speed and its implications would seem to be a sensible exercise for 37 operators.
For any who are not fully "up to speed"
on that I would highly recommend a part of AA's training video dealing with Performance and Control issues which includes an animation of a sequence of Boeing test flights looking at the control implications - fascinating, and it shows the problem and corrective action vividly. The rest of the video presents a strong caveat as regards the relevance of the remedial action which he boils down to the unarguable "Fly the aircraft first"!!! Highly watchable and superbly done.
