Talk:Boeing 737 rudder issues

Merge

Should this be merged to the main article on 737's?--Torchwood Who? (talk) 09:03, 24 March 2008 (UTC)

Other Suspected 737 Rudder PCU malfunction incidents

I removed the Sahara Airlines crash, since the only source we have on that one, declares it was a case of a trainee pilot pushing the wrong (opposite) rudder, during engine out training at low altitude. There have been other crashes, with that same probable cause, in a variety of airliners, and those had nothing to do with a malfunctioning PCU, any more than that one (according to that lone report). EditorASC (talk) 01:18, 26 September 2009 (UTC)

Elevator PCU too?

Seems that an EasyJet B737 has been having problems with a similar symptom, but affecting control in pitch - see here: [1] —Preceding unsigned comment added by 213.40.249.181 (talk) 16:06, 27 October 2009 (UTC)

Cause Of Superheating Of Hydraulic Fluid To Create Rudder Reversal Not Found

I've just watched the National Geographic tv programme which features the NTSB investigation into the United FL585, USair FL427 and Eastwind FL517 related mystery air disasters. The overall conclusion after extensive testing, was that superheated hydraulic fluid forced into the supercooled, -40 degree due to previous high altitude, rudder dual servo valve caused the unit to function in reverse. If a pilot pressed the right rudder peddle to counteract a slight roll to the left, then the opposite of the desired effect would result i.e. the plane would suddenly continue to roll alarmingly further left and create complete confusion for the pilot, leading to a stall and nosedive. Autopilots would similarly be affected. The NTSB seemed satisfied that a remodelling of the rudder dual servo unit was a good resolution of the investigation.

There is an elephant in the room here though. No-one actually mentioned why the hydraulic fluid would suddenly become superheated in the first place. This relates to the section above concerning similar symptoms in elevator PCUs, which affects control in pitch rather roll with the rudder PCU. Unfortunately, this apparently random and sudden superheating of hydraulic fluid remains a complete mystery which still has the potential to strike any aircraft today or in the future. Why is this vital element of the overall NTSB investigation missing from the article? 176.24.226.120 (talk) 06:58, 5 July 2013 (UTC) Alan Lowey.

The temperature of the fluid in a hydraulic system is raised by the increase in pressure when the system is operating, i.e, when the servo is responding to a control input.

The test fluid was heated to a high temperature so as to increase the temperature differential between the fluid and the extremely cold servo housing. On the aircraft the servo valve system is outside the aircraft pressurization and heating and is subjected to intense cold when flying at high altitude for long periods, resulting in 'cold soak'. The test fluid was heated simply to make it easier to stage the test without specialized freezing equipment or extended periods of freezing. — Preceding unsigned comment added by 95.150.11.144 (talk) 11:19, 22 July 2017 (UTC)

Suspected PCU Problem In Afghanistan 747 Cargo Plane Crash (Video)

http://www.youtube.com/watch?v=intuj4SKyFk

The unfortunate aircraft can be seen to perform the same kind of maneuvers as seen in the simulations of reverse rudder PCU function. If a pilot pressed the right rudder peddle to counteract a slight roll to the left, then the opposite of the desired effect would result i.e. the plane would suddenly continue to roll alarmingly further left and create complete confusion for the pilot, leading to a stall and nosedive. Autopilots would similarly be affected.

The mystery force which superheats the hydraulic fluid in the first place is the culprit, rather than a mechanical fault or pilot error. 176.24.226.120 (talk) 12:16, 5 July 2013 (UTC) Alan Lowey.

The 'mystery force' is the pressure within the system when application of rudder is applied. This heats the fluid. The problem was due to the difference in temperatures between the hot fluid and the extremely cold PCU mechanism which is outside of the pressure hull and uninsulated.

The cause of the crash in the linked video was the cargo shifting due to it not being secure properly. See: National Airlines Flight 102. — Preceding unsigned comment added by 95.149.55.42 (talk) 08:45, 12 March 2019 (UTC)

Rudder?

I'm having trouble with the idea that a rudder hard over, rolls a plane onto it's back. Ailerons are used for roll control. Anybody have any thoughts. ThanksLonginus876 (talk) 01:59, 2 July 2014 (UTC)

The rudder applies roll as well as yaw, in opposite directions. Usually the ailerons are used to compensate, however a hard over on the rudder without warning will cause a plane to roll before the pilot can compensate. If the pilot isn't trained for it, that adds to the delay before corrective action is taken. With a large plane, there is a lot of inertia to overcome, so once it starts moving it takes a lot of force to stop it, and at low speeds the flight controls are not as responsive. I've heard of other accidents where unexpected input flipped a plane before the pilot could correct, so this doesn't strike me as unusual. //not a pilot, but I've crashed a simulator a few times. (68.150.172.12 (talk) 04:42, 6 July 2014 (UTC))

Most rudders apply a bit of roll (in addition to yaw), because the middle of the rudder is not aligned with the center of mass of the airplane. Notice how the tail is up above the main body. The rudder is right in the tail, so the middle of it exists up above the fuselage. DrZygote214 (talk) 07:24, 8 September 2014 (UTC)

When yaw is applied , i.e., rudder, the aircraft rotates around its vertical axis in the direction of the applied rudder and because of this the wing on the outside of the yaw is travelling faster than the opposite wing relative to the aircraft direction of travel and airflow, the opposite wing in turn, is travelling more slowly. Therefore the outside, faster travelling wing creates more lift and rises, the inner wing, less lift, which then causes that wing to drop. In case of very low aircraft forward speeds, such as on the approach to a stall, the inner wing may even be going backwards to the direction of airflow. This is why a wing drops at application of full rudder when stalling the aircraft to deliberately enter a spin.

Thus application of rudder results in a tendency to roll in the direction of the applied yaw/rudder deflection. — Preceding unsigned comment added by 95.150.100.128 (talk) 11:07, 26 July 2016 (UTC)

What versions of the 737 are affected by this?

I'm surprised the article doesn't mention which versions, or if it's all version, of the 737 are affected. The 737 was introduced in 1968, but the first crash related to this rudder-servo problem seems to be in 1991. This makes me think that only the latest versions of the 737 would be affected. However I compiled this list:

a 737-291, United Airlines Flight 585 (1991 Mar 03)

a 737-3B7, USAir Flight 427 (1994 Sep 09)

a 737-2H5, Eastwind Airlines Flight 517 (1996 Jun 06)

The list is incomplete but it looks like the early 200 and 300 versions are affected. Seems very strange to me because these versions also made their commercial debut in the late 1960's. So can someone clarify? Do all 737 versions have the same rudder-servo? Seems hard to believe that it would never fail until 23 years later, but the obvious suspicion is age-related failure. DrZygote214 (talk) — Preceding undated comment added 07:35, 8 September 2014 (UTC)

These are all Boeing 737-200 or Boeing 737-300 series aircraft (note the "737-2xx" or "737-3xx" number format). It's not clear to me when they first started using this servo design, or if its use was limited to the 737 "Classic" models such as the -200 and -300, though I may research that fact and add it to the page if it's relevant. No 737s in service (at least in the United States) should be affected by this issue anymore; I updated the article recently to show that the US Federal Aviation Administration mandated a replacement of all affected 737 rudder servos by the end of 2002.

Content removed

I have removed a re-write of the article by an editor with a conflict of interest, because the edit broke the wiki formatting and does not properly cite its sources and contains extensive unattributed quotations. There might be some useful information there, but it's not the kind of content we are looking for. -- Diannaa (talk) 01:59, 21 April 2015 (UTC)

Rudder redesign image used in this article lacks fair use rationale

File:737 rudder redesign.jpg is used in this article. I tagged it with {{Di-no fair use rationale}} unable to solve the problem immediately myself, although I believe it could be useful for demonstrating the article within Wikipedia's non-free use policy. Please add a fair use rationale, or if it's already deleted by that time, request undeletion. 84.250.17.211 (talk) 20:57, 22 September 2018 (UTC)

imgur

There is a good writeup and picture/screenshot series on imgur that has been circulating on the web: https://imgur.com/a/5wcFx8M

I don't know the origin but maybe someone here can recognize it. Also it has some good stuff that seems worth researching and writing up in the article (we obviously can't use it directly). 173.228.123.166 (talk) 01:17, 20 March 2019 (UTC)

This article was written by Admiral Cloudberg, who posts frequent articles to a subreddit: https://www.reddit.com/r/AdmiralCloudberg/ . This user responds to Private Messages so worth asking for input

Boeing Meddling

One thing I don't see mentioned on this page, is how suspiciously Boeing acted throughout the whole ordeal. Based upon their actions, it's likely they knew or were at-least aware of the cause long before the FAA. Specifically several key parts of United Airlines Flight 585's tail servo went missing after being accessed by a Boeing employee, which would later be determined as likely cause of the failure occurring.

Source: - under "Three pieces missing"

"The investigators gathered on the morning of March 21, 1991, at United's San Francisco base to discuss taking the dismantled servo valve to Parker Bertea's plant in Irvine for further testing. That was because United didn't have the equipment to extensively test the servo's slides.

Walz, of Parker Bertea, was assigned to hand-carry the servo valve to Irvine. John Calvin, the quality-control engineer from Boeing, instructed an assistant to pack up the parts. According to court records, the assistant left the room and returned with a taped package, which he handed to Walz, who carried it on a flight to Southern California.

When Walz opened the package that afternoon at the Parker Bertea plant, he discovered that three servo-valve parts were missing: a spring, spring guide and end cap.

Boeing, citing ongoing litigation, has never explained why those three parts were left out of the package forwarded to Irvine. "

I don't expect Wikipedia to be acting as an investigative source here, but this information would be useful to include in some form or another.

--67.248.136.53 (talk) 18:56, 17 September 2020 (UTC)

References

MetroJet Flight 2710

I clicked on the link but it redirected me to the same page, making the link completely useless, should I remove it? SomeoneWiki04 (talk) 09:38, 17 March 2024 (UTC)