SXDFC
Topic Author
Posts: 1977
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Classic 737 Krueger Flap Droop, Why?

Mon Dec 23, 2013 6:39 am

Hello All:

Was working "California One" tonight, ( Boeing 737-3H4 ) when I noticed that the inboard Krueger flap dropped down. I know this is common on the older Boeing A/C ( 727,737-200 thru -500 ) and wanted to know why this was the case. I also like to know if this is also prone to the 737NG series?

http://i1208.photobucket.com/albums/cc368/737-8H4/912DD0B4-C5F3-4EE6-85F1-8B8EF919CA6E_zpsi9n9ogjg.jpg

http://i1208.photobucket.com/albums/cc368/737-8H4/2A2BD7EE-2DC7-4EAC-809F-C60929F4A452_zpsxzvd7q7c.jpg

http://i1208.photobucket.com/albums/cc368/737-8H4/D21DAEF9-974C-49ED-BEEF-53AC91A38C38_zps4ib7znhh.jpg

Although a bit unrelated, here she is in full glory..

http://i1208.photobucket.com/albums/cc368/737-8H4/A16F0AE9-E51D-428F-ABF0-2B61A14E886C_zps2hqc54pz.jpg
 
boeing767mech
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RE: Classic 737 Krueger Flap Droop, Why?

Mon Dec 23, 2013 3:50 pm

Quoting SXDFC (Thread starter):

Was working "California One" tonight, ( Boeing 737-3H4 ) when I noticed that the inboard Krueger flap dropped down. I know this is common on the older Boeing A/C ( 727,737-200 thru -500 ) and wanted to know why this was the case. I also like to know if this is also prone to the 737NG series?

Was told in class it has to do with the shut off valves and the actuators relaxing with no hydraulic pressure on them, and was also told this isn't an issue with the 737NG's since they updated and or changed the design of the actuators.

But this was in a gen fam class and not a factory class.

David
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SPREE34
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RE: Classic 737 Krueger Flap Droop, Why?

Mon Dec 23, 2013 5:19 pm

Quoting boeing767mech (Reply 2):
Was told in class it has to do with the shut off valves and the actuators relaxing with no hydraulic pressure on them,

^^^^^^^That right there. Same reason you will see both ailerons droop on various aircraft at the gate. Pressurize the system and they all move to their present commanded position.
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boeing767mech
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RE: Classic 737 Krueger Flap Droop, Why?

Mon Dec 23, 2013 6:21 pm

Also little side note. Someone pulled that Krueger Flap to the fully extended position. When they droop because of no pressure on the system there in the mid positions.

David
Never under-estimate the predictably of stupidty
 
yeelep
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RE: Classic 737 Krueger Flap Droop, Why?

Mon Dec 23, 2013 8:17 pm

There are limits to the amount of allowed droop. One minute after hydraulics are turn off, the allowed droop is two inches for new/overhauled actuators, four inches for in service actuators, measured from the lower wing surface to the flap trailing edge.

Don't recall ever seeing a large droop on any of our NG's.

[Edited 2013-12-23 12:21:17]
 
YYZatcboy
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RE: Classic 737 Krueger Flap Droop, Why?

Fri Dec 27, 2013 5:26 am

Something like this is also why on the 727 you have to make sure the ground crew is clear before you pressurize the hydraulic system. The landing gear doors droop and will snap shut. If someone is standing nearby it can amputate limbs or worse.
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FlyMKG
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RE: Classic 737 Krueger Flap Droop, Why?

Fri Dec 27, 2013 6:39 am

Quoting YYZatcboy (Reply 5):
Something like this is also why on the 727 you have to make sure the ground crew is clear before you pressurize the hydraulic system. The landing gear doors droop and will snap shut.

Close but not quite. The landing gear doors are powered by A system hydraulic pressure which comes from engine driven pumps. The main landing gear doors can either be up, down and locked, or down and unlocked.

My company starts engines with the A pumps off. That way, when the engines are being started, there is still no A system pressure being generated. The captain, after verifying that all ground personal are clear, will call "after start checklist, A pumps on." If A pumps aren't called for the flight engineer will query the captain before turning them on. Once they are turned on two exterior components usually move. The krueger flaps will retract and the main gear doors will close only if they were down AND unlocked. Other components can move like the nose gear and the trailing edge flaps but rarely do since they are left in the neutral or up position.

If nobody lowered the main gear doors then nothing happens and if they are down and locked nothing happens. There are handles in the gear well area that can lower and lock the main doors down. It is part of the engineer's preflight to unlock the main gear doors.

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YYZatcboy
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RE: Classic 737 Krueger Flap Droop, Why?

Fri Dec 27, 2013 8:10 am

I should have specified before moving the ground interconnect to power the A system off of the electrical B system with the gear unlocked during pre start.
DH1/3/4 MD11/88 L1011 A319/20/21/30/50/80 717 727 735/6/7/8/9 744 762/3 77E/W 788/789 E40/75/90 CRJ/700/705 CC150
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HAWK21M
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RE: Classic 737 Krueger Flap Droop, Why?

Fri Dec 27, 2013 9:31 am

The Importance of Ensuring certain areas are clear of personnell/equipment before oressurizing the hydraulics.....
The Droop caused by the Unpressurised Actuator moving out of flush position due weight & can snap back when pressure is supplied.
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barney captain
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RE: Classic 737 Krueger Flap Droop, Why?

Fri Dec 27, 2013 10:09 am

Quoting boeing767mech (Reply 3):
Someone pulled that Krueger Flap to the fully extended position. When they droop because of no pressure on the system there in the mid positions.

I would agree...
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Venus6971
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RE: Classic 737 Krueger Flap Droop, Why?

Sun Dec 29, 2013 2:27 am

NG's also droop after a awhile, I work at a MRO that does C checks on 737-400's and NG's. When we pull the inboard thrust reverser off we use speed tape to keep the flap stowed so it will not into the way.
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DocLightning
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RE: Classic 737 Krueger Flap Droop, Why?

Sun Dec 29, 2013 6:37 am

Why does the flap extend all the way? Wouldn't gravity stop it before it started its upswing into position?
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CALTECH
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RE: Classic 737 Krueger Flap Droop, Why?

Sat Jan 04, 2014 2:51 pm

Quoting SXDFC (Thread starter):
Was working "California One" tonight, ( Boeing 737-3H4 ) when I noticed that the inboard Krueger flap dropped down. I know this is common on the older Boeing A/C ( 727,737-200 thru -500 ) and wanted to know why this was the case. I also like to know if this is also prone to the 737NG series?
Quoting boeing767mech (Reply 1):
and was also told this isn't an issue with the 737NG's since they updated and or changed the design of the actuators.

There are Notes in the 737NG AMM that say the leading edge Flaps can droop.

Quoting boeing767mech (Reply 3):
Also little side note. Someone pulled that Krueger Flap to the fully extended position. When they droop because of no pressure on the system there in the mid positions.

The LE Flaps only have fully retracted and fully extended positions IIRC. There is no mid position for the LE Flaps, unlike the LE SLats.

Quoting yeelep (Reply 4):
Don't recall ever seeing a large droop on any of our NG's.

Not like the 727s and Jurassic 737s, those always drooped.

Quoting YYZatcboy (Reply 5):
Something like this is also why on the 727 you have to make sure the ground crew is clear before you pressurize the hydraulic system. The landing gear doors droop and will snap shut. If someone is standing nearby it can amputate limbs or worse.
Quoting FlyMKG (Reply 6):
Close but not quite.
Quoting YYZatcboy (Reply 7):
I should have specified before moving the ground interconnect to power the A system off of the electrical B system with the gear unlocked during pre start.

Do not remember the 727 landing gear doors having droop, unless the respective gear door handle was moved to the down position and there was no hydraulic pressure. IIRC, the doors would slowly fall with gravity. If you have the two handles in the up position with the doors down and unlocked with no hydraulic pressure, then when Ground Interconnect or A System is powered up, they will shut.

The DC-9/MD-80 Main Gear Doors however would droop with bad springs on the uplocks. Had a MD-80 out of MIA or FLL divert here to MCO years ago with a Rt Main Gear Door that had bad uplock/springs and had a light. He ground the skid pad down pretty good.

Years ago, had a 727, # 412, have a video of it somewhere, that had the Lt Main Gear Door Actuator bracket break which jammed the Main Landing Gear in a intermediate position. He did a nice 2 point landing here in MCO.
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VC10DC10
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RE: Classic 737 Krueger Flap Droop, Why?

Fri Jan 10, 2014 6:44 am

Probably a really obvious answer to this question, but for 737s that are being stored outdoors or on a long ground stop, are the Krueger flaps locked in position so that debris, dirt, etc., don't cause any damage? Or are they masked off in some way?
 
barney captain
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RE: Classic 737 Krueger Flap Droop, Why?

Fri Jan 10, 2014 9:30 am

Quoting CALTECH (Reply 12):
The LE Flaps only have fully retracted and fully extended positions IIRC. There is no mid position for the LE Flaps, unlike the LE SLats.

Correct.

But when the Kruger flaps "droop" due to no hyd pressure, they do in fact hang at a mid position - exactly where gravity dictates they should.
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CALTECH
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RE: Classic 737 Krueger Flap Droop, Why?

Fri Jan 10, 2014 2:31 pm

Quoting VC10DC10 (Reply 13):
Probably a really obvious answer to this question, but for 737s that are being stored outdoors or on a long ground stop, are the Krueger flaps locked in position so that debris, dirt, etc., don't cause any damage? Or are they masked off in some way?

Long ground stop, never have seen it. Long term storage, a piece of tape would probably do the trick. Awaiting scrapping, why bother.

Quoting barney captain (Reply 14):
Correct.

But when the Kruger flaps "droop" due to no hyd pressure, they do in fact hang at a mid position - exactly where gravity dictates they should.

Right. The dreaded 'droop' position.
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HAWK21M
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RE: Classic 737 Krueger Flap Droop, Why?

Mon Jan 20, 2014 10:41 am

Quoting CALTECH (Reply 15):
a piece of tape would probably do the trick. Awaiting scrapping, why bother.

Makes sense to follow a preservation schedule, never know when they could be sold to a freighter company one day......has happened in the past.
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