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SAA380
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B732 Flap Incident

Sat Apr 18, 2009 3:59 pm

Hello all,

A B732 traveling from JNB to GRJ in South Africa had problems with it's flaps on Friday 10th of April.

The aircraft landed safely and no one was injured. I am just curious to what you guys think the cause of the problem was. I am guessing a hydraulic failure. And how crucial are flaps on landing?

I have a friend that traveled on that flight, and he said that the flaps did not deploy on approach. The AC diverted to Overberg AFB which has a longer runway.

Has something similar ever happened to other 732's?

http://www.capeargus.co.za/?fSection...ticleId=vn20090415051218234C869315

Thanks for the replies,

SAA380  airplane 
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wilco737
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RE: B732 Flap Incident

Sat Apr 18, 2009 4:06 pm



Quoting SAA380 (Thread starter):
And how crucial are flaps on landing?

Flaps are pretty important for landing to reduce the approach speed and so the landing distance.

Here is a picture of a B738 which landed without any flaps at all, only the slats were extended, they used the whole runway and were escorted by fire trucks (hot brakes). but everything was ok.


View Large View Medium
Click here for bigger photo!

Photo © Wilco737



I don't know the reason why that happened, but a problem with hydraulic is possible. Or maybe during extension they didn't travel at the same speed left and right and then the flaps stop to travel to avoid a flap assymetry.

wilco737
 
OPNLguy
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RE: B732 Flap Incident

Sat Apr 18, 2009 4:34 pm

Quoting SAA380 (Thread starter):
Has something similar ever happened to other 732's?

The article (and not a half bad one, considering) mentions an indication problem, which tells me that they had a "split flap" in which the flaps (one side) jam at some point and quit operating so as to not cause an asymetrical condition. It's not the most common type of failure, but there are procedures for it in the QRH. Depending upon how much the flaps come out before they jam/stop, the landing speeds will vary accordingly, i.e. less extension = higher speeds and more extension = lower, more normal speeds.

Quoting SAA380 (Thread starter):
I am guessing a hydraulic failure.

If there was a hydraulic failure involved, there would probably be other symptoms, but my money would be on physical malfunction like a jackscrew, track, or maybe even some type of spindle issue.

http://www.b737.org.uk/flightcontrols.htm#Trailing_Edge_Flaps



There are actually two needles on the indicator, and they normally overlap each other. Should an assymetry commence, the needles split, hence the term "split flap."




[Edited 2009-04-18 09:50:32]
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
Tristarsteve
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RE: B732 Flap Incident

Sat Apr 18, 2009 5:02 pm



Quoting SAA380 (Thread starter):
I am guessing a hydraulic failure.

The B737 trailing edge flaps have a standby electrical motor. This will deploy the flaps with a hydraulic failure.

Quoting OPNLguy (Reply 2):
There are actually two needles on the indicator, and they normally overlap each other. Should an assymetry commence, the needles split, hence the term "split flap."

These needles are driven by a transmitter on each wingtip. If one of the transmitters stops sending a signal, the needles split on the flap indicator. The flap asymmetry is sensed by the flap indicator which stops the flaps.
 
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HAWK21M
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RE: B732 Flap Incident

Sun Apr 19, 2009 5:04 am

As mentioned above....The B732 TE flap has an Electric backup drive motor,driving the common TE flap mechanism,used in case Hyd drive does not function.
a jam or assymetry slat/flap mvmt can cause the Flap to stay put.

The article talks of a light....probably the TE flap or LE flap light near the Flap Indicator.

regds
MEL.
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SAA380
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RE: B732 Flap Incident

Sun Apr 19, 2009 9:59 am



Quoting OPNLguy (Reply 2):
If there was a hydraulic failure involved, there would probably be other symptoms, but my money would be on physical malfunction like a jackscrew, track, or maybe even some type of spindle issue.

http://www.b737.org.uk/flightcontrols.htm#Trailing_Edge_Flaps



There are actually two needles on the indicator, and they normally overlap each other. Should an assymetry commence, the needles split, hence the term "split flap."

Thanks for the link. It's really helpful and explains it thoroughly in detail.

Quoting TristarSteve (Reply 3):
Quoting SAA380 (Thread starter):
I am guessing a hydraulic failure.

The B737 trailing edge flaps have a standby electrical motor. This will deploy the flaps with a hydraulic failure.

Did not know that there was a backup electrical motor in to use in a hydro failure.
There must have been most likely a assymetry problem or a physical problem as mentioned by OPNLguy.

Thanks for the info!

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AA737-823
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RE: B732 Flap Incident

Mon Apr 20, 2009 9:25 pm



Quoting TristarSteve (Reply 3):
The B737 trailing edge flaps have a standby electrical motor. This will deploy the flaps with a hydraulic failure



Quoting HAWK21M (Reply 4):
As mentioned above....The B732 TE flap has an Electric backup drive motor,driving the common TE flap mechanism,used in case Hyd drive does not function.



Quoting SAA380 (Reply 5):
Did not know that there was a backup electrical motor in to use in a hydro failure.

As a 737-200 and -NG mechanic, please allow me to elaborate on this. These statements are only true depending on the type of hydraulic failure. The 737 standby/emergency flap system is HYDRAULICALLY POWERED. Yes, it has a third fluid reservoir, and an electrically driven pump, so that if you've lost systems A and B there's still a good chance that you'll have enough fluid for flap/slat deployment.
But the flaps are NOT electrically powered in standby mode and more than they're elctrically powered when you're running A or B electric pumps on the ground.

It's picking nits, but it IS a difference.

So, all that to say that this problem could still have been hydraulic somehow.
If, say, the hydraulic failure was AT the Flap Drive Unit, there's a good chance that you're out of luck on that one.

But I, too, think an asymmetry is more likely.
Between torque tubes, transmissions, angle gearboxes, etc., there's a lot in there to go awry.

As far as the consequences, it's an unpleasant situation to find yourself in, but certainly manageable IF you have enough runway to deal with, which would seem to be the contributing factor to the decision to divert! Landing speeds can very QUITE high in this situation, depending on how far out the flaps went before failure.

A US Airways A330-300 (N670UW or 672 at the time, can't remember now which one, and they've changed registrations since the merger) had a hydro failure on approach to Manchester UK, and had to land with a very high AOA and a high airspeed, AND only one thrust reverser. But they made it okay.

Quoting OPNLguy (Reply 2):
or maybe even some type of spindle issue.

There IS an AD out for outboard spindles shearing in half. It requires a periodic inspection, and I believe offers a reengineered spindle for replacement. Not sure- it came out a few years before I was working on FLUF's.
 
AA737-823
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RE: B732 Flap Incident

Mon Apr 20, 2009 9:29 pm

Just as a follow-up and to clarify, allow me to explain my "not electrically driven" statement by comparing it to a 747, which is the only other Boeing I have first-hand experience on.

The 747 leading edge Kruger Flaps are pneumatically powered, with an ELECTRIC alternate. In the event that the pneu system fails, they are actually driven out by electric motors.
I believe that's also true of the trailing edges.
Compared to that, you can see what I mean when I say that the 737 LE/TE flaps/slats are NOT electrically powered in alternate mode- they're still powered by fluid going to actuators for slats and LE flaps, and fluid going to a hydro motor, twisting the same torque tubes for the TE flaps.

Hope that clarifies for you.
 
PGNCS
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RE: B732 Flap Incident

Wed Apr 22, 2009 12:32 am

We have to practice flap malfunctions in the simulator in initial and recurrent training. It's all about airspeed management and picking the longest runway available. It's not a crisis unless you have no other options than a very short and/or contaminated runway, although speeds and pitch angle are considerably higher than on a normal approach, so the visual picture on final approach is unusual.

To answer the OP's question; yes I have heard of this on other 732's and most other types from time to time, too. You don't hear about these very often because they are dealt with without much drama or difficulty in the majority of cases.
 
roseflyer
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RE: B732 Flap Incident

Wed Apr 22, 2009 2:18 am

Planes are designed typically to have their max capable landing (and tire) speed be the landing speed at Max Landing Weight with no flaps. It will take a long time to stop, but it is not a catestrophic condition.

Quoting OPNLguy (Reply 2):
The article (and not a half bad one, considering) mentions an indication problem, which tells me that they had a "split flap" in which the flaps (one side) jam at some point and quit operating so as to not cause an asymetrical condition.

That could be it. It's hard to tell.

Quoting WILCO737 (Reply 1):
I don't know the reason why that happened, but a problem with hydraulic is possible. Or maybe during extension they didn't travel at the same speed left and right and then the flaps stop to travel to avoid a flap assymetry.

Asymmetric flap (flap skew) detection was created for the 737NG using 777 technology. The Jurassic only has the needles, which can show a problem AFAIK.

Quoting AA737-823 (Reply 6):
But the flaps are NOT electrically powered in standby mode and more than they're elctrically powered when you're running A or B electric pumps on the ground.

It's picking nits, but it IS a difference.

And on the NG, that problem is fixed!
If you have never designed an airplane part before, let the real designers do the work!
 
Tristarsteve
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RE: B732 Flap Incident

Wed Apr 22, 2009 8:21 am



Quoting AA737-823 (Reply 6):
But the flaps are NOT electrically powered in standby mode

I dont know if you are nit picking but.
B732 and B733/4/5 are nearly the same.
Flaps have NORMAL mode and ALTERNATE mode. There is no standby.
Trailing edge flaps are hydraulically driven by a hyd motor in the wheel well. The L/E slats and driven by individual hyd actuators, sequenced from the flap power unit.
If the main hyds fail, the crew can select ALT FLAPS to arm.
This isolates the flap hyd motor and arms the ALT flap electric motor. The crew can then select flaps down by the ALT flap selector switch.
Selecting ALT flaps also runs the STANDBY hyd pump. As the flaps extend electrically, the slats will extend using standby hyd pressure.

On the ground (no air loads) the flaps can be retracted also using the electric motor, but this is frowned upon as it overloads the motor.

This is for non-NG B737s (as per original question)
Go and look in the wheel well. Above the keel beam the flap drive unit has two motors, one hyd and one elec, driving the flap torque tubes through the same gear box.
 
AA737-823
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RE: B732 Flap Incident

Mon May 25, 2009 10:08 pm



Quoting TristarSteve (Reply 10):
Flaps have NORMAL mode and ALTERNATE mode. There is no standby.
Trailing edge flaps are hydraulically driven by a hyd motor in the wheel well. The L/E slats and driven by individual hyd actuators, sequenced from the flap power unit.
If the main hyds fail, the crew can select ALT FLAPS to arm.
This isolates the flap hyd motor and arms the ALT flap electric motor. The crew can then select flaps down by the ALT flap selector switch.
Selecting ALT flaps also runs the STANDBY hyd pump. As the flaps extend electrically, the slats will extend using standby hyd pressure.

You're calling them "ALTERNATE," which is the correct term- I was calling them STANDBY, which I think got the point across.

Yes, the trailing edges are driven by an electric motor in ALTERNATE mode- my apologies.

However, our books say that the leading edges CANNOT be retracted in ALTERNATE mode. Whether there's some qualifications to that statement, I do not know.
 
Viscount724
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RE: B732 Flap Incident

Tue May 26, 2009 1:45 am

A WestJet 737-700 was unable to lower the flaps approaching YYC on April 22 and performed a flapless landing. Excerpt from Transport Canada daily occurrence summary.

TSB reported that the WestJet Boeing 737-700, registration C-FWBL, operating as flight WJA 268, was en route from Vancouver to Calgary when the autopilot disengage alert sounded. CMD A (autopilot A) would not re-engage so CMD B (autopilot B) was selected. It was then observed that the horizontal bar on the captain's flight director was not in view. Control of the aircraft was transferred to the first officer. When flap 1 was selected on approach to Calgary there was no flap movement or indication. The aircraft was cleared to maintain 8,000 feet while the checklists were run and maintenance was consulted. The crew subsequently performed a flapless landing on Runway 28 with ARFF standing by.
Update 5 May 2009: Transport Canada Maintenance and Manufacturing reported that upon inspection, an electrical connector in the LH flap well was determined to have high resistance. The connector was replaced and the fault cleared with no further issue.


A CO 737-700 also had flap problems approaching YYC in February.

The Continental Airlines Boeing 737-700, N33714, was operating as flight COA1429 from Houston, TX to Calgary, AB. Upon flap selection on approach into Calgary, the flaps ceased movement at 6°. The flight crew conducted a missed approach and consulted the QRH. A second approach and landing was conducted with the flaps at 6° with ARFF standing by. Maintenance performed a FSCU and PSEU bite check which identified a lagging fault in the left flap position sensor. The fault was cleared, the system ground checked and aircraft returned to service.
 
YYZYYT
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RE: B732 Flap Incident

Tue May 26, 2009 4:18 pm



Quoting Viscount724 (Reply 12):
A WestJet 737-700 was unable to lower the flaps approaching YYC on April 22 and performed a flapless landing. Excerpt from Transport Canada daily occurrence summary.

I was in a 340 that once had a flap problem, and did a flapless landing at YVR. Fun - extra hour of circling, 2nd approach so I could get a really good look at the city and lost of trucks with shiny red lights next to the runway. Didn't know that it was necessary to report to TSB, though.

But here's my question: Are the leading edges (or can they be) lowered spearately and is this done when there is a trailing edge problem?

I recall discussions regardig the distinciton between the two for the purpopse of take off, but do not know whether that applies to a landing as well.

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