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BA 747 Flap Jam  
User currently offlineLambourne From United Kingdom, joined Sep 2001, 81 posts, RR: 0
Posted (6 years 6 months 3 weeks 1 day 13 hours ago) and read 9055 times:

Does anyone know anything about last night's return to LHR of BA011 to Singapore? I gather it had flaps jammed after take off and had to dump fuel over the North Sea coast before returing safely about midnight.
I'm always intrigued to know how this can happen with all the backup systems nowadays.

18 replies: All unread, jump to last
 
User currently offlineCHRISBA777ER From UK - England, joined Mar 2001, 5964 posts, RR: 62
Reply 1, posted (6 years 6 months 3 weeks 1 day 12 hours ago) and read 8884 times:



Quoting Lambourne (Thread starter):
I'm always intrigued to know how this can happen with all the backup systems nowadays.

Only takes one hydraulic actuator to jam and the flap isnt going anywhere - nothing that you can do from the flightdeck. Not a huge deal but it does happen sometimes.



What do you mean you dont have any bourbon? Do you know how far it is to Houston? What kind of airline is this???
User currently offlineAA737-823 From United States of America, joined Mar 2000, 5771 posts, RR: 11
Reply 2, posted (6 years 6 months 3 weeks 1 day 8 hours ago) and read 8491 times:



Quoting CHRISBA777ER (Reply 1):
Only takes one hydraulic actuator to jam

Uh, what?
I'm a 747 mechanic... they don't use actuators, they use jackscrews, powered by hydraulic motors. The jamming of such devices is very rare.
Dash 8-400 use actuators in landing gear... and THOSE seem to jam up in Europe fairly regularly!!!!
Haha.

But anyway, I guess if a jackscrew jammed, then the alternate flap system wouldn't be able to do anything about it, so yeah, you're pretty much a no-go at that point.


User currently offlineCHRISBA777ER From UK - England, joined Mar 2001, 5964 posts, RR: 62
Reply 3, posted (6 years 6 months 3 weeks 1 day 8 hours ago) and read 8482 times:



Quoting AA737-823 (Reply 2):
Quoting CHRISBA777ER (Reply 1):
Only takes one hydraulic actuator to jam

Uh, what?
I'm a 747 mechanic... they don't use actuators, they use jackscrews, powered by hydraulic motors. The jamming of such devices is very rare.
Dash 8-400 use actuators in landing gear... and THOSE seem to jam up in Europe fairly regularly!!!!
Haha.

But anyway, I guess if a jackscrew jammed, then the alternate flap system wouldn't be able to do anything about it, so yeah, you're pretty much a no-go at that point.

They dont use hydraulic actuators? Wow. Didnt know that - thanks  Smile



What do you mean you dont have any bourbon? Do you know how far it is to Houston? What kind of airline is this???
User currently offlineLHR777 From , joined Dec 1969, posts, RR:
Reply 4, posted (6 years 6 months 3 weeks 1 day 7 hours ago) and read 8304 times:

The BA11Y finally departed this evening (11th February) at 19:01hrs. A mere 21 hours and 46 minutes behind schedule.

User currently offlineFr8mech From United States of America, joined Sep 2005, 5400 posts, RR: 14
Reply 5, posted (6 years 6 months 3 weeks 1 day 6 hours ago) and read 8206 times:



Quoting Lambourne (Thread starter):
I'm always intrigued to know how this can happen with all the backup systems nowadays.

The backup systems in place are typical for control, not flight control, failure. Except for a very few instances, there are no backups for a mechanical failure (jammed flaps, gear, flight controls, etc.).



When seconds count...the police are minutes away.
User currently offlineAA737-823 From United States of America, joined Mar 2000, 5771 posts, RR: 11
Reply 6, posted (6 years 6 months 3 weeks 1 day 1 hour ago) and read 7881 times:



Quoting CHRISBA777ER (Reply 3):
They dont use hydraulic actuators? Wow. Didnt know that - thanks

You're welcome!

Quoting Fr8mech (Reply 5):
Except for a very few instances, there are no backups for a mechanical failure (jammed flaps, gear, flight controls, etc.).

That's not entirely true. All of the systems you've mentioned have a backup system in place. Now, in the odd case of a jam, you're pretty much out of luck.
A quick review:
The gear (on a 747, since that's the aircraft I know, and also the one in question) have mechanical pull-cable releases for the locks. When activated, the doors and gear drop simultaneously, which is a daunting prospect to begin with, but whatever works, works. The doors for the main gear have large grease pads, so that as the wheels drop, they can slide across the door, pushing it open.
INCIDENTALLY, if you're in the main wheel wells walking around to replace light bulbs or whatnot, it can be VERY tricky to not step on the grease pads and find yourself skidding in any direction with a twisted ankle. Sigh.

Now, flaps. Both the leading edge (kreuger on a 747) flaps and trailing edge (triple-slotted, except for 747SP) flaps have electrical backups. They take a PAINFULLY LONG TIME to extend or retract, but they get the job done. In fact, the aircraft is dispatchable if some of the pneumatic leading edges are INOP. You simply write up the MEL number, and have the crew deploy them electrically. Surprising, but true. The trailing edge also has electrical backup systems in place. They use a tremendous amount of current, and take a long time, which is why they're not proctucal for typical use, but again- they get the job done.

Now, flight controls. By this, I assume you mean elevators, rudders, ailerons, spoilers.
The way backup systems work on these is mianly system redundancy.
First of all, there are FOUR elevators on the 747- two each side. The left outboard section is controlled by hydraulic system 1, with the inboard run from systems 3 or 4. The right side elevator, outboard, is powered by system 4, with the inboard powered by 1 or 2.
There are also two rudder sections. The upper section runs off of system 1 or 3, while the lower runs off of system 2 or 4.
The ailerons (four of them) are as follows:
Left outboard: system 1 or 2
Left inboard: system 1 or 3
Right outboard: system 3 or 4
Right inboard: system 2 or 4

The brakes are typically powered by system 4, and alternate brakes are run off of system 1, with reserve braking handled by system 2. Yep, that's three systems capable of doing the braking. Braking is kinda important.

Spoilers.... geesh, get confusing. Suffice it to say that each panel is powered by only one system, but there are 12 panels, and they are divided up among systems 2, 3, and 4.


I hope that I have added to the discussion, and increased the general knowledge of the 747 aircraft systems and backups!


User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 7, posted (6 years 6 months 3 weeks 1 day ago) and read 7770 times:

In a previous life, I did quite a bit of flight test for a US carrier that had a very sizeable 747 fleet. I can remember doing a test flight on a 747 that had a very similar issue. The TE flaps would not extend all the way to 25 or 30 using the normal extension system and the alternate system would not drive the either.

We must have flown that aircraft 10 times. Each time Boeing and the ground engineers would have changed a little more of the drive system. Finally, the jackscrew transmission and the jackscrew itself was changed. It worked and solved the problem. The flap drive (transmissions and jackscrews) were sent back to Boeing and it was discovered that there was a burr on the jackscrew itself. With the wing flex and loads on the transmission that was enough to stop the jackscrew at about 22 degrees of flaps.

The normal extension for the trailing edge uses Hydraulics to drive the jackscrew transmission, with electric motors being the backup. From 0 flaps to 25 it takes just about 6 minutes using the alternate extension. The LE are normally driven by pneumatics with electrics as a back up.

Quoting AA737-823 (Reply 6):
The gear (on a 747, since that's the aircraft I know, and also the one in question) have mechanical pull-cable releases for the locks. When activated, the doors and gear drop simultaneously, which is a daunting prospect to begin with, but whatever works, works. The doors for the main gear have large grease pads, so that as the wheels drop, they can slide across the door, pushing it open.

People often ask why in a Boeing is the landing gear lever placed in the OFF position (middle). The answer is in the off position the landing gear are not hydraulically locked up but actually rest on the inner landing gear doors. In case of an alternate extension, the gear doors will drop open and gravity takes care of the rest.


User currently offlineGh123 From , joined Dec 1969, posts, RR:
Reply 8, posted (6 years 6 months 3 weeks 23 hours ago) and read 7686 times:

Looks like an opportunity for the BA boys to pull out their Flap-Jacks.

I recommend Marks and Spencers'.


User currently offlineAA737-823 From United States of America, joined Mar 2000, 5771 posts, RR: 11
Reply 9, posted (6 years 6 months 3 weeks 19 hours ago) and read 7467 times:



Quoting PhilSquares (Reply 7):
People often ask why in a Boeing is the landing gear lever placed in the OFF position (middle). The answer is in the off position the landing gear are not hydraulically locked up but actually rest on the inner landing gear doors. In case of an alternate extension, the gear doors will drop open and gravity takes care of the rest.

I'm sorry, but that's partially incorrect.
The landing gear themselves don't typically rest on the doors, even with the lever in the 'off' position. They are mechanically latched up. In the 'off' position, you're correct in stating that the hydraulic power is removed. But the mechanical locks are still holding the gear up.
Other Boeings do rest the gear on the doors, but not all of them. Heck the 737 doesn't even HAVE doors.


User currently offlineGkirk From UK - Scotland, joined Jun 2000, 24928 posts, RR: 56
Reply 10, posted (6 years 6 months 3 weeks 18 hours ago) and read 7460 times:



Quoting AA737-823 (Reply 9):
Heck the 737 doesn't even HAVE doors.

Hell, I always wondered why it was so cold and windy in the cabin of a 737  duck 



When you hear the noise of the Tartan Army Boys, we'll be coming down the road!
User currently offlineOldeuropean From Germany, joined May 2005, 2090 posts, RR: 4
Reply 11, posted (6 years 6 months 3 weeks 18 hours ago) and read 7414 times:



Quoting Gkirk (Reply 10):
Hell, I always wondered why it was so cold and windy in the cabin of a 737

Yeah, while flying over Scotland you also can hear the sheep.  duck 

Sorry, I couldn't resist.  rotfl 

Axel



Wer nichts weiss muss alles glauben
User currently offlineTjc2 From United Kingdom, joined Feb 2006, 141 posts, RR: 0
Reply 12, posted (6 years 6 months 3 weeks 17 hours ago) and read 7030 times:



Quoting Gh123 (Reply 8):
Looks like an opportunity for the BA boys to pull out their Flap-Jacks.

Haha! I recommend my Mother's recipe, but then again each to your own..



The only time I made a mistake was when I thought I was wrong...
User currently offlineAlbird87 From , joined Dec 1969, posts, RR:
Reply 13, posted (6 years 6 months 3 weeks 15 hours ago) and read 5967 times:

did the 744 land with full flaps or were the flaps actually jammed into a position?

we had a incident like this here on KX with our 732QC which was carrying freight at the time and coming into GCM and they couldnt get the flaps past 5 degrees! people have posted that there are suppose to be backups but this aircraft cam in with 5 degrees flaps at aroun 160 knots. This aircraft nearly ended up in the water cause of this but they were able to use the turning extensions at the end of the runway to turn the aircraft in time to stop them having a wet end!

Now if the 744 had a stick in the flaps at 5 or 10 degrees then i wouldnt want to be approaching in that bird even if i had 12000 feet of runway!


User currently offlineSpeedbird2263 From Jamaica, joined Jul 2006, 470 posts, RR: 1
Reply 14, posted (6 years 6 months 3 weeks 14 hours ago) and read 5327 times:

Quoting Albird87 (Reply 13):
Now if the 744 had a stick in the flaps at 5 or 10 degrees then i wouldnt want to be approaching in that bird even if i had 12000 feet of runway!

This is taken care of in the FAR's which state that for T-Category Airplanes, the required landing distance shall not be more than 60% of the total runway length, including stopway if available and if the runway is wet you divide the distance by 1.15. So in the case of a 12000ft runway, by the FAR's the landing distance should not be more than 7200ft for a dry runway and not more than 10434ft for a wet runway. In the event of an emergency, you have either 4800ft(dry runway) or 1566ft(wet runway) to play with.
So in the case of the 747 and a high-speed approach, it would translate that given the appropriate weight (*fuel dump), a 12000ft runway should be more than adequate.

P.S. The more experienced aviators here, please feel free to correct me If Im misguided in my rationale.  Smile

[Edited 2008-02-12 05:49:48]


Straight'n Up 'N Fly Right Son ;)
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 15, posted (6 years 6 months 3 weeks 12 hours ago) and read 4983 times:



Quoting AA737-823 (Reply 9):
The landing gear themselves don't typically rest on the doors, even with the lever in the 'off' position.

When the main landing gear on the L-1011 in the fully retracted position and the control handle is placed in off position, the gear rests on the inboard main landing gear door. The is up-lock is on the door not the door. The gear is allowed to float between two shock absorbers (called snubbers on the L-1011). The L-1011 shares this feature with most Boeing aircraft.


User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 16, posted (6 years 6 months 3 weeks 4 hours ago) and read 4747 times:



Quoting Albird87 (Reply 13):
did the 744 land with full flaps or were the flaps actually jammed into a position?

It was a 747-200B, but it did land with partial flaps. There was just one section, port inboard, that did not extend fully. The alternate flap system didn't work either. So, the QRH has you select landing flaps on the unaffected portion and leave the affected portion where they are (about 22degrees). Not a big deal.


User currently offlineAA737-823 From United States of America, joined Mar 2000, 5771 posts, RR: 11
Reply 17, posted (6 years 6 months 3 weeks ago) and read 4626 times:



Quoting 474218 (Reply 15):
When the main landing gear on the L-1011 in the fully retracted position and the control handle is placed in off position, the gear rests on the inboard main landing gear door. The is up-lock is on the door not the door. The gear is allowed to float between two shock absorbers (called snubbers on the L-1011). The L-1011 shares this feature with most Boeing aircraft.

That may be on the L-1011, but the aircraft in question is a 747, which does NOT rest the gear on the doors when the lever is placed in the 'off' or any other position. It rests on the GEAR uplocks. The doors have their own mechanisms.

Would you like a photo?

Anyhow.

Quoting Gkirk (Reply 10):
Hell, I always wondered why it was so cold and windy in the cabin of a 737



Quoting Oldeuropean (Reply 11):
Yeah, while flying over Scotland you also can hear the sheep.

You guys get outta here!!!!!  Smile


User currently offlineUAL747 From , joined Dec 1969, posts, RR:
Reply 18, posted (6 years 6 months 3 weeks ago) and read 4585 times:

This can happen too, but according to the photographer, the flight went on as scheduled, but at a slower speed and lower altitude. From what I understand though, that if the avionics detects an asymmetric flap extension, it automatically locks the flaps...not sure though:

http://cdn-www.airliners.net/photos/photos/2/7/6/1005672.jpg

UAL


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