Another 737 rudder incident

[Cyclic Hotline]

NTSB Investigates Boeing 737 Rudder

By DENNIS CONRAD, Associated Press Writer

WASHINGTON (AP) - The National Transportation Safety Board is investigating whether a rudder problem caused a United Airlines Boeing 737 to suddenly bank while descending for a landing in Chicago last week. The plane landed safely.

Rudder problems on 737s are suspected in two deadly U.S. air crashes in the early 1990s. Last month, the Federal Aviation Administration proposed requiring airlines to install new rudder control systems on 737s, the world's most popular commercial jets.

The rudder is the flap on the vertical tail of the aircraft. Moving the rudder left or right causes the plane to turn in that direction.

The pilots flying United Airlines Flight 578 from St. Louis to Chicago's O'Hare International Airport last Thursday afternoon reported the plane's nose suddenly swung to the left and right when the aircraft began descending at around 9,000 feet, FAA spokesman Paul Turk said Monday.

The pilots disconnected the autopilot and the plane then banked sharply, Turk said. They had to apply pressure on the rudder pedals to level the wings and regain control.

After the plane touched down, the pilots said the rudder swung left and then fully to the right, causing a loud bang, Turk said.

The plane stopped safely and all 93 passengers got off without incident.

NTSB spokeswoman Lauren Peduzzi said investigators checked the plane during the weekend and are studying its flight data recorder and cockpit voice recorder.

"We're still reviewing all the data to see exactly what caused the incident,'' said Peduzzi, who described it as a "rudder anomaly.''

Boeing spokeswoman Liz Verdier said a number of factors could have been responsible, including the aircraft itself, the pilot or the weather.

"We don't know what that anomaly is,'' she said.

Verdier said Boeing considers the incident serious and would consider checking its entire fleet if the NTSB investigation indicates it could be more than an isolated occurrence.

United spokesman Joe Hopkins declined to comment.

Boeing announced in September that it would train pilots in how to handle jammed rudders and would begin installing new rudder systems on 737s in 2003.

The FAA's rudder proposal would give the airlines five years to install the new systems. The FAA estimates that 2,000 U.S. airplanes would have to be refitted, at a cost of $364 million.

The FAA is seeking public comments for 60 days before issuing the new directive.

The NTSB blamed rudder problems for a US Airways crash outside of Pittsburgh in 1994 that killed 132 people and a United Airlines crash at Colorado Springs, Colo., in 1991 that killed 25.

[knackered]

The rudder is the flap on the vertical tail of the aircraft

My, my! These journalists shouldn't try to explain aviation terms in their own words. It only comes out worse.

And of course they had to mention the possibility of it being the pilot at fault. Some things never change (and never will).

[TR4A]

It probably was the yaw damper acting up.

Uncommanded Yaw or Roll Checklist:

1. Maintain Aircraft Control With All Available Flight Controls.
2. Increase Airspeed And Reduce AOA (if required).
3. Autopilot (if engaged)...Disengage.
4. Yaw Damper...Off.

[Meering]

knackered,

I understand why the professional users (I'm just SLF with an interest in the industry) of PPRUNE castigate journalists from time to time, but in this case the writer was quoting a Boeing spokesperson. Would you expect them to censor the quote?

Meering

[Hicks]

Knackerd.
I agree with you that 'Control Surface' may have been a better term but I guess 'flap' will do for the general public don't you think? Second, as far as I can make out from the above it was Liz Verdier, a Boeing Spokeswoman who mentioned Pilot Error -however unlikely that is. Nevertheless, I hope that we won't leave any avenue unexplored to explain this upset though.
What concerns me more is that this may be yet another example of a 737 with a rudder problem. How many more are there that have been diagnosed as Yaw damper problems? Boeing are only starting in [b]2003[\b] to install a modified rudder control system when it is known (suspected??) that there are problems?

Cheers

hicks

[ 18 December 2001: Message edited by: Hicks ]

[liquidgold]

was this the 100/200 or 300 onwards, anybody know?
Well done to the crew, could have been accident no 3.

[CashDrive]

Looks like a classic case of wake turbulence from here .... :p

[moggie]

Wake turbulence at 9000' in the descent? Wake up!

This will probably turn out to be yet another "unexplained" rudder hard over from the B737. However, of course, Boeing have had a really good look at them and nothing is wrong. So why then have they re-designed for the NG and the FAA ordered reengineering all B7373 in service?

If it was wake turbulence, why the bang and swing soem time later after touchdown.

How does Boeing get away with this kind of thing?

[ 18 December 2001: Message edited by: moggie ]

[Puritan]

I've had a B737-300 roll through > 45° on me - twice !

First time, we were following a B747, and the second time was behind a A321 - but both times were during the descent (former at 12,000' on the way into STN, the later just as we were joining the localiser into CPH)

QRH drill actioned accordingly - and not really a problem.

[PaperTiger]

was this the 100/200 or 300 onwards

United 200s are retired. Only have -300s and -500s now.

[320DRIVER]

Any other industry source for this news?

Thanks.

[knackered]

Meering,

As I read the above article, the reference to 'flap' was not part of the Boeing quote.

Hicks,

'Control surface' would have been a better term, yes, but I don't agree that 'flap' will suffice. We often complain of the public's perception of things aviation but if we are going to feed them rubbish then what?

I didn't mean to imply that the reporter was implying possible pilot error. The 'they' I refer are the usual industry spokesmen, in this case Boeing, who find it convenient to keep the old 'pilot error' cause as a standby always.

Anyway, this is a side issue to the main thread here, but these issues always come up with these type of reports and I find it unnecessary and misleading.

[GearUp CheerUp]

Moggie

'Wake turbulence at 9000' in the descent? Wake up!'

You obviously have no experience of commercial flight operations or you would know its possible to encounter another aircraft's wake anywhere at any stage of flight. :D

[Rocket Ron]

Hey Puritan, somebody been letting you practice your hand flying?! :p G'luck mate.

[Montt]

There has also been a problem with the tail (rudder?) of a Transavia 737 towards the end of 96 or early 97, I believe when landing at FRA; this was shortly after the aircraft came back from check at TAP.

Can anyone shed any light on this incident/accident, and clarify whether it was the same class of problem as the one discussed on this thread or whether it was a different one?

[hobie]

quote ....

The FAA's rudder proposal would give the airlines five years to install the new systems. The FAA estimates that 2,000 U.S. airplanes would have to be refitted, at a cost of $364 million. ..... end quote

364 million divided by 2000 aircraft = 182,000 dollars each ..... now lets say that a 737 might fly an average of 300 days per year at 600 passengers per day .... thats equal to 180,000 passengers per year ..... could we please all give the airline that we are flying, an extra dollar each trip and solve this problem now!!!!

(if my passenger load estimates are low then let the airlines send any excess in the one dollar charge to charity)

spelling corrected .....

[ 18 December 2001: Message edited by: hobie ]

[David Hurst]

Montt

So far as I remember this was an mx problem in that a bolt had not been fastened correctly during the checks and the nut unwound. Brilliant flying by the crew saved the day. Never did hear what happened to the TAP maintenance people. Probably the lawyers were the only ones who gained anything.

[Hicks]

Knackered

Very true.

Cheers

hicks

[Cyclic Hotline]

Boeing 737 Problem Investigated
By DENNIS CONRAD, Associated Press Writer

WASHINGTON (AP) - Federal investigators are looking at whether a wire brush left under the cockpit floor of a United Airlines Boeing 737 led to a rudder problem that caused the plane to suddenly bank while descending into Chicago last week.

United Airlines spokesman Chris Brathwaite confirmed the brush was found in the cockpit area but declined to say how it got there.

He said the company is cooperating with investigators to determine whether the brush caused the problem on the Dec. 13 flight from St. Louis to Chicago's O'Hare International Airport.

The Air Line Pilots Association, which also is looking into the matter, believes the brush was left behind by a mechanic and jammed the rudder cables, spokesman John Mazor told The Seattle Times.

National Transportation Safety Board spokesman Paul Schlamm said investigators have not drawn any conclusions.

"The investigation is still continuing on many fronts,'' he said Thursday.

The pilots flying United's Flight 578 reported the plane's nose suddenly swung to the left and right when the aircraft began descending at around 9,000 feet. The pilots disconnected the autopilot and the plane then banked sharply. They had to apply pressure on the rudder pedals to level the wings and regain control.

The plane landed safely and all 93 passengers got off without incident.

The rudder is the flap on the vertical tail of the aircraft. Moving the rudder left or right causes the plane to turn in that direction.

Rudder problems on 737s are suspected in two deadly U.S. air crashes in the early 1990s. Last month, the Federal Aviation Administration proposed requiring airlines to install new rudder control systems on 737s, the world's most popular commercial jet.

[AtlPax]

I hope the FAA doesn't try to brush this one off . . .

[bblank]

I now fly the A320 and that is also perfect........

Don't forget that the Direction Generale de l'Aviation Civile can sue you for libel if you suggest otherwise. And win.

Back to the 737. From the first AP article:

"After the plane touched down, the pilots said the rudder swung left and then fully to the right, causing a loud bang

Boeing spokeswoman Liz Verdier said a number of factors could have been responsible, including ... the weather."

Say what you want about Boeing but don't say that its spokeswoman is humourless.

According to a Reuters report of this incident, "Boeing spokeswoman Liz Verdier said the company has designed a new rudder system to comply with the [FAA] directive and is ready to retrofit all of the nearly 2,000 Boeing 737s in the American fleet."

According to AP, "Boeing announced in September that it would ... begin installing new rudder systems on 737s in 2003."

The second statement casts doubt on the readiness expressed in the first: if Boeing is "ready" for the retrofit, then why wait until 2003? I seem to recall reading that the new design has not been tested for unanticipated adverse consequences. Anyone know the status?

A detailed preliminary incident report of UAL 578 can be found here:
<a href="http://www.ntsb.gov/ntsb/brief.asp?ev_id=20011219X02423&key=1" target="_blank">http://www.ntsb.gov/ntsb/brief.asp?ev_id=20011219X02423&key=1</a>

[GlueBall]

L337: Having survived the 737 rudder calamity, be mindful of your A320 composite tail! <img src="rolleyes.gif" border="0">

[Dagger Dirk]

This UAL 737 rudder incident below is so similar to the Bournemouth 737 event

So toilet-brush or not, my money goes on it being a wee-run of this one:

at <a href="http://www.aaib.detr.gov.uk/formal/gbgji/gbgji.htm" target="_blank">http://www.aaib.detr.gov.uk/formal/gbgji/gbgji.htm</a>

Pee-pee in the E&E
Those electrolytes in the crystalline deposits can give you more swings than Benny Goodman (or the baton in front of the Boston Philharmonic).

[BIG PARTYR]

GLUEBALL
With a "let's defend everything American even if it's no good" comment like that, you should be calling yourself S--TBALL!

[Avman]

I thought B737 pilots may find this (taken from the NTSB site) of interest:

NTSB Identification: CHI02IA050

Scheduled 14 CFRPart 121 operation of Air Carrier United Airlines (D.B.A. United Airlines)
Incident occurred Thursday, December 13, 2001 at Chicago, IL
Aircraft:Boeing 737-322, registration: N359UA
Injuries: 99 Uninjured.

This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed.

On December 13, 2001, at 1203 central standard time, a Boeing 737-322, N359UA, operated by United Airlines as flight 578, declared an emergency due to a reported "rudder malfunction" during decent to the Chicago O'Hare International Airport (ORD), Chicago, Illinois. Visual meteorological conditions prevailed at the time of the incident. The 14 CFR Part 121 passenger flight was operating on an instrument rules flight plan. The 2 pilots, 4 flight attendants and 93 passengers reported no injuries. The flight departed from the Lambert-St. Louis International Airport, St. Louis, Missouri, at 1129, en route to ORD.

The first officer reported in a written statement, "... At approximately 9,300', during the descent the aircraft began to bounce and slowly bank to the left, which led me to believe we were experiencing wake turbulence. With the A autopilot still engaged the airplane began a correction back to the right while continuing with the bouncing sensation. The airplane rapidly achieved approximately 10 degrees of bank when the captain announced that he was disengaging both the autopilot and the autothrottles. The rate of bank accelerated in a fashion similar to when one turns the airplane with the speed brakes deployed to the flight detent. As a result of the yawing and bouncing sensation I instructed the flight attendants to 'be seated immediately' via the PA. The airplane was now in an approximate 45 degree bank to the right."

"The captain was very obviously opposing the roll with both left rudder pressure and left aileron. The captain stated something to the effect 'I think it's a rudder problem'. I then looked at the A and B system hydraulic quantity and pressure gauges and saw normal indications. I then began assisting the captain on the controls with both the left aileron and left rudder pressure. At this point I noticed the airspeed was diminishing from 250 KIAS to about 238 KIAS. I then pushed forward on the control column to increase the airspeed in hopes of increasing control effectiveness. As our airspeed increased the effect of left control inputs began to move the airplane to a more controllable attitude. The captain appeared to regain control of the airplane at approximately 8,200'."

"At this point the captain still had both hands on the control wheel with significant left aileron input. As a result I initiated an increase in power to maintain 250 KIAS and 8000'. The captain then asked me to declare an emergency. I stated that we were declaring an emergency due to a rudder malfunction. I stated we had 100 souls on board and approximately 10,300 pounds of fuel and I would get back to ATC as time permitted. I then initiated the QRC for the 'uncommanded rudder' checklist. The reference actions in the checklist did not provide any relief to the amount of left aileron and left rudder pressure required to maintain control of the aircraft."

"Upon completion of each item on the checklist I tried to verify the hydraulic pressure and quantity indications to see if there was a change. I did not see any change on either. The captain requested that I let ATC know that we needed 27L. I did so. I asked the captain if I should tell the purser to prepare the cabin for evacuation. The captain agreed. I then called the purser and stated 'we have declared an emergency due to a rudder problem, prep the cabin for evac, you have approximately five minutes'. The purser acknowledged my instructions."

"Approach then cleared us to 4000' and vectored us to downwind. We were then cleared to 2500' and 210 knots. At 220 KIAS the captain called for flaps 2, I did so. The captain then stated 'looks like a slam dunk'. He then utilized speed brakes and called for flaps 5. ATC then turned us on a base leg and cleared us to 2100' and 180 knots. The captain then stowed the speed brakes. At approximately 195 KIAS the captain called for flaps 10 and 'gear down final descent checklist'. At this time we were given a final vector and cleared for the ILS 27L. I armed the approach mode after identifying the ILS frequency. It became obvious that the captain's flight director was not giving accurate localizer guidance when the captain discovered his course was still set to 220. He then selected 270 and joined the localizer and glideslope for 27L. I contacted the tower just inside the marker and stated again that we were an emergency aircraft and would like the trucks. Tower acknowledged and cleared us to land."

"We flew a flaps 30 approach and landing to 27L The captain was stabilized per UAL criteria well before 1000' AGL. Between 1000' and 500' AGL the captain commented on how it was becoming increasingly difficult to control the airplane with left rudder pressure and left aileron. At 500' I joined the captain on the controls per his request."

"The airplane landed on the centerline in the touchdown zone on 27L. The speed brakes automatically deployed upon wheel spin up. The captain utilized some engine reversing and the autobrakes began to decelerate the aircraft also. Together the captain and I attempted to maintain directional control of the aircraft throughout the landing rollout with the use of rudder input. It became increasingly difficult to do this as the airplane slowed. About when I called '100 knots' I heard a loud ping or thud when the rudder simultaneously locked out all control input causing the left pedal to push against my foot."

"The airplane was brought to a stop just short of the Tango highspeed taxiway..."

[Few Cloudy]

What can make an aircraft swing?

The rudder itself, Thrust assymetry (short pop or otherwise) Dragging Brake, Yaw Damper input, Atmospheric condition (wake or general) Other flight control assymetry.

As did 'L337', so did I experience a sharp swing on T/O about a year and a half back. It happened in ZRH in a 737-300.

Before the investigation could be completed, the incident had reached these pages, accompanied by lots of polemic "Problem rears its ugly head again"- etc. As this is a very sensitive subject, I didn't want to comment until sure of my facts. maybe now is the right time.

In my case, the rudder pedals were not displaced to the left (the direction in which the aircraft swung). The swing was sharp and of short duration. We were close to Vr and engine instruments were all OK (my first thought was a surge)- the ship was quickly under control and we took off.

I have to say that Boeing were super - organised an immediate telephone conference and asked many pertinent questions, as well as filling us in in great detail on the history of the problem, as well as possible failure modes. We pulled the flight recorder and had a read out made as soon as possible.

It turned out that the swing was visible on the recorder - the ship swung a couple of degrees (it felt like a lot more because it happened fast) and there was even a half degree of left bank shown as the left oleo compressed. The rudder position was straight ahead (as was the pedal position) and immediately the Yaw Damper corrected the swing with a kick to the right - ie. working as it should. We went through a list of other possible reasons and all we could come up with was a local atmospheric effect - possibly caused by a slight quartering tailwind being deflected by a small forest.

In my case, the ship was not to blame. Before any result could be obtained however, it had received bad press. The tendency is to put incidents into neat pre-conceived categories and apportion blame with too little knowledge sometimes. I hope this helps to put the record straight, as far as the ZRH incident was concerned.

[PaperTiger]

FWIW one of the Seattle TV stations reported the UA578 incident as being caused by a 'wire brush' tool left by mtx somewhere in the run. I find no reference to this on the NTSB site, so it may just be typical media er.. reporting. Any AME care to comment on how likely is this scenario ?