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audio19
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Forklift V. Engine Cradle

Wed Apr 21, 2004 10:04 am

Hi,
When AA Flight 191 crashed in 1979, the investigators said one of the probable causes was damage to the aft bulkhead flange due to maintenance, and they said that one of possibilities was that the use of a forklift instead of an engine cradle caused the damage. Can anyone explain the difference between a forklift and an engine cradle? What do DC-10 mechanics use today when they remove engines?
Audio
 
MD11Engineer
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RE: Forklift V. Engine Cradle

Wed Apr 21, 2004 1:55 pm

Hard to explain without a picture. An engine cradle is aframe that supports an engine during transport and installation. It is usualy mounted on a low trolley for moving. The engine is attached to it by pins. Mostly bootstrp equipment is used to remove or install engines, this means a set of beams and struts, which get temporarely attached to hardpoints of the pylon or wing, from which chain hoists are suspended (3 or 4 depending on the aircraft or engine) which in turn lift or lower the engine cradle with the engine. Between the hoists and the cradle dynamometers are installed to measure the load on each hoist.
After removal of the cowlings and disconnection of all lines (fuel, electrics, hydraulics), an empty cradle is positioned under the engine and hoisted up until the mount points of it can be attached to the engine. Then the the hoists are being pretensioned by watching the dynamometers, on one hand you want to prevent the sudden weight of the engine causing the whole shebang to drop, on the other hand you don´t want to overstress the engine mounts on the pylon. Afterwards the engine mount bolts are loosened. Now the cradle with the old engine in it is being lowered to the ground and pushed away. Now the new engine is being pushed in position under the pylon and hoisted up until the engine mount points contact the pylon mounts. The hoists are pretensioned and the mount bolts fitted and torqued. Then the the cradle is disconnected from the engine and lowered to the ground, after which all the lines are connected to the new engine.
The critical factor is the pretensioning of the hoists, if the tension is not enough, the old engine will drop a bit, if it is too much you´ll damage the pylon. If you use a forklift instead of the proper hoists, you don´t have any control over the force you excert to the pylon, which might cause overstressing and cracks.

Jan
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AUAE
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RE: Forklift V. Engine Cradle

Wed Apr 21, 2004 9:25 pm

Very nice explanation Jan,

The difference is all about control. Fork lifts can slip or get away from you, but so can just about any method of raising or lowering engines. Just a bit on semantics, we use Load Cells instead of dynamometers. :P Same difference, I know.
Air transport is just a glorified bus operation. -Michael O'Leary, Ryanair's chief executive
 
audio19
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RE: Forklift V. Engine Cradle

Wed Apr 21, 2004 9:57 pm

Thanks for that detailed explanation! So, I take it that fork lifts are no longer used in raising/lowering the engine and pylon? What other maintenance operations are they used in?
 
AUAE
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RE: Forklift V. Engine Cradle

Wed Apr 21, 2004 10:31 pm

No, forklifts are still used for raising and lowering engines. You just have to exhibit care when you do. Actually, I should say cranes are used. In my mind I wasn't really making a distinction, but I guess I should. Cranes are much better suited to the precision lifting you need to do.
Air transport is just a glorified bus operation. -Michael O'Leary, Ryanair's chief executive
 
broke
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RE: Forklift V. Engine Cradle

Wed Apr 21, 2004 10:50 pm

The maintenance action that led to the loss of the number 1 engine on the American DC-10-10 at ORD was as follows;

American was performing a modification or repair that required removal of the pylon. The manufacturer's recommendation was to remove the engine from the pylon and then remove the pylon from the wing.
What American did was to leave the engine on the pylon and remove the pylon and the engine as an assembly.

The combined weight of the engine and pylon made it difficult to align and install the assembly without stressing the pylon/wing mounts. The rear mount was damaged and later failed, resulting in the accident.
 
MD11Engineer
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RE: Forklift V. Engine Cradle

Thu Apr 22, 2004 1:32 am

In SXF we used a ceiling mounted crane in the hangar to change engines. We would attach a T shaped frame to ther crane, from which a manual chain hoist and a dynamometer would be suspended for fine adjustments. The other changes I´ve done were done on the ramp using bootstrap equipment.

Jan
Je Suis Charlie et je suis Ahmet aussi
 
FDXmech
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RE: Forklift V. Engine Cradle

Thu Apr 22, 2004 12:05 pm

>>>The critical factor is the pretensioning of the hoists, if the tension is not enough, the old engine will drop a bit, if it is too much you´ll damage the pylon. If you use a forklift instead of the proper hoists, you don´t have any control over the force you excert to the pylon, which might cause overstressing and cracks.<<<

With the chain hoists having some slack, we normally back off the mount nuts allowing the engine to unseat, attaining a gap with the pylon.

Then we raise the hoists to assume the engine weight. Meanwhile the gap between the engine mount and pylon allows the hoist to take up the engine weight without the engine mount contacting the pylon. Then remove the nuts & drop the engine.

Installing the engine we hoist the engine up leaving an engine mount /pylon gap. We then raise it the rest of the way by running the nuts down (the nuts raising and seating the engine mount/pylon) and torquing.
You're only as good as your last departure.
 
MD11Engineer
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RE: Forklift V. Engine Cradle

Thu Apr 22, 2004 1:47 pm

I´ve been doing engine changes on 737s (-200 and classic) long ago, so I don´t remember the specifics anymore, but I´ve done at least ten engine changes recently on 757-200s with P&W 2040 engines and a 767-200 with GE CF6-80 engines. Acc. to the AMM you´ve got to pretension the chains, both on removal as on installation. On installation you slowly lift the engine until the shear pins are fitted in the holes of the mounting plates and then you tension the hoists (I don´t have the AMM at home, so I can´t give the tension values). Then you insert the bolts and torque them.

Same on removal, you tension the hoists to a certain force (don´t exceed the maximum given in the AMM), and then loosen and remove the bolts.

Jan
Je Suis Charlie et je suis Ahmet aussi
 
FDXmech
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RE: Forklift V. Engine Cradle

Fri Apr 23, 2004 5:42 am

Hi Jan,

I was referring to the DC10/MD11 and 727 #2 engine. I don't recall the A300-600 though.

The concern with these aircraft was applying an excessive upward force on the pylon/mount.

I know, looking back aways, we used to seat the engine using the hoist equipment. But now the engine is seated the last fraction of an inch or so by tightening down on the mount nuts.

But this is just talk, of course this critical step is done verbatim by the M/M.

FDX
You're only as good as your last departure.
 
nudelhirsch
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RE: Forklift V. Engine Cradle

Fri Apr 23, 2004 5:46 am

http://www.rolls-royce.com/media/gallery/civil/lrg_br710_3.htm

Jan, is this an engine cradle?


guess so...
Putana da Seatbeltz!
 
MD11Engineer
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RE: Forklift V. Engine Cradle

Fri Apr 23, 2004 5:53 am

This looks more like a trolley used in the engine factory for moving the engine, not like the things to lift the engine under the pylon. I will see if I can find a picture, maybe copy one out of the AMM when I´m back at work on saturday.

FDXMech,
When I´m signing for the engine change I always make sure that the hoist loads are as the AMM prescribes and I personaly torque the attachment bolts. I also do the dye penetrant inspection of the bolts and barrel nuts (if we don´t get new ones) and the inspection of the mounts myself.

Jan
Je Suis Charlie et je suis Ahmet aussi
 
nudelhirsch
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RE: Forklift V. Engine Cradle

Fri Apr 23, 2004 6:11 am

Oh, ok, Jan, I forgot the lifting mechanism, but i can imagine, what it looks like then...

Thanks anyways...

Putana da Seatbeltz!
 
FDXmech
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RE: Forklift V. Engine Cradle

Fri Apr 23, 2004 8:20 am

Jan,

Yep. That's the big one in my mind.

These terrible accidents increase ones awareness immensely. Nothing is taken for granted.

FDX
You're only as good as your last departure.
 
FDXmech
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RE: Forklift V. Engine Cradle

Fri Apr 23, 2004 8:45 am

Hi Nudelhirch,

These are examples of shipping stands/engine cradles.

The bottom right photo of the Delta 737-200 with the JT8D is an example of a workstand. The workstand has the engine sitting high up making the engine more accessable to work on (especially the bottom).
The other pictures show engines in their cradles which are mounted to the shipping stand.

Note on the bottom left photo, the red bootstap arms which the hoists attach to.


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Mr Spaceman
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RE: Forklift V. Engine Cradle

Fri Apr 23, 2004 9:04 am

Hi guys.

This link shows some more jet engine stands. If you scroll down, you can see the different stands that are used for different makes & models of engines. Some are one piece and some have a base and cradle. There's also a Gantry Crane which doesn't appear to be a mobile crane, but, perhaps it attaches to a jet engine in the same maner as a mobile crane.

http://www.airspares.com/engine_stands.htm


Chris  Smile
"Just a minute while I re-invent myself"
 
FDXmech
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RE: Forklift V. Engine Cradle

Fri Apr 23, 2004 9:31 am

Hi Mr Spaceman,

Your being a truck driver, you might find it interesting that these engines cannot be transported by train for their lack of suspension, unless things have changed.
You're only as good as your last departure.
 
dairbus
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RE: Forklift V. Engine Cradle

Fri Apr 23, 2004 10:15 am

When I worked at BWI, we had an MD88 do an air return due to an engine failure. The engine needed to be replaced so a new engine was trucked from Dallas I believe and our station had to call around to different local companies for a mobile construction crane to help change the engine. The crane was needed due to the aft mounted engines. I guess they would of sent equipment for a bootstrap lift device if it was wing mounted.
"I love mankind. It's people I can't stand." - Charles Shultz
 
TimT
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RE: Forklift V. Engine Cradle

Fri Apr 23, 2004 1:40 pm

The bootstrap on the #2 engine for a DC-10 is a complicated thing- if I remember there are 8 pieces that all have to be attached to the pylon before the hoist(s) are even hung. We never used a dynamometer to keep track of stress for that engine, but everyone kept a weather eye on how level the engine was hanging. During removal, you have to put some "up" tension on the hoists so you can get the bolts loose.
 
MD11Engineer
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RE: Forklift V. Engine Cradle

Fri Apr 23, 2004 7:06 pm

I got trained to have a look at the truck when a new engine gets shipped to us. If the truck doesn´t have pneumatic suspension I have to reject the engine because it might have been damaged due to shocks during transport.

BTW, I´ve heard (never did one though) that the 727 bootstrp equipment is a nightmare for #1 and #3. Colleagues told me it takes longer to install it than changing the engine.

Jan
Je Suis Charlie et je suis Ahmet aussi
 
FDXmech
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RE: Forklift V. Engine Cradle

Fri Apr 23, 2004 11:31 pm

>>>BTW, I´ve heard (never did one though) that the 727 bootstrp equipment is a nightmare for #1 and #3. Colleagues told me it takes longer to install it than changing the engine.<<<

I did a 727 #3 bootstrap engine change for Peoplexpress. PEX had bought some 727's from Alitalia who gave them lots of equipment including a bootstrap for #1/3 engine.

I remember it being time consuming to hook up. But worse, the bootstrap setup twisted every time the come-a-long was cranked.

---------------------------------------------------------------------------
We had recently done a DC10 #2 engine change with manual hoisting equipment. Talk about a workout, and time consuming.

I'll have to disagree about putting upward tension on the hoists to loosen the mount bolts on the DC10.

The chains should have a little slack and the bolts backed off, this putting a gap between the mount and pylon. At this point the hoists are raised assuming the weight of the engine without actually putting upward tension on the pylon.

[Edited 2004-04-23 16:34:01]
You're only as good as your last departure.
 
MD11Engineer
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RE: Forklift V. Engine Cradle

Sat Apr 24, 2004 4:36 am

FDXMech,

I recently changed an APU on a 757, afterwards my arms felt as if I was practising to become Arnold Schwarzenegger from cranking this SOB 5 meters into the air... Next day I could barely move.

Jan
Je Suis Charlie et je suis Ahmet aussi
 
MD11Engineer
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RE: Forklift V. Engine Cradle

Sat Apr 24, 2004 8:15 am

FDXMEch,

seeing your pictures brings back memories, esp. this JT8D on the 737-200. Those beams on the trolley are f*cking heavy!! We neede three to four guys to lift them into position and another two guys to slip the pins in...

During my apprenticeship we had an engine change once on a 737-200... four experienced mechanics and me, as the youngest. Each of them wanted to be in charge of the operation during the installation and gave conflicting orders, I just shut up and watched. They got the engine up so crooked that one cone bolt got BENT (inboard fwd). One guy looked at it and wanted to continue with the installation, but the others told him to shut up and brought the cone bolt to the NDT shop. It was cracked. They also checked the mount, but it was still ok. Since then, unless it is explicitely stated before, I always ask loudly who is in charge and gives the commands on hoisting and lowering. Only ONE person to give orders.

Jan
Je Suis Charlie et je suis Ahmet aussi
 
Mr Spaceman
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RE: Forklift V. Engine Cradle

Sat Apr 24, 2004 9:07 am

Hi guys.

>> FDXmech, I've hauled around some pretty interesting stuff over the past 10+ years that I"ve been driving transports & straight trucks when I've been delivering general cartage. I carried a couple of huge electric generators once that were on specialized skids and weighed about 20,000 pounds each.

If a day comes when I find myself driving out to YYZ to pick up a brand new one of these ..........  Wow!

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.............. I'll crack right up with excitment and then drive really slow like an old granny!  Laugh out loud

I've driven many tractor trailers that had "Air Ride" suspension on the whole unit (both tractor & trailer) with the large rubber air bags between the wheel axles and the trailer box instead of a leaf spring assembly. There is no comparison.

About 6 years ago, I was carrying 22 skids of BOOZE that weighed about 55,000 pounds in a tractor-trailer with Air Ride when a woman drove her car under my trailer and smashed into my spare tire cage which ripped through her front hood, windshield, and roof! She got stuck to me and I never felt a thing. I dragged her several blocks down the road and into the parking lot of a shopping mall before I noticed her car's trunk sticking out from under my trailer. That's how smooth an "Air Ride" truck can be. Big grin

PS, the woman (about 45) wasn't hurt physically, just emotionally & financially. It was her fault. She wasn't watching where she was driving.


Chris  Smile

[Edited 2004-04-24 02:13:51]
"Just a minute while I re-invent myself"
 
MD11Engineer
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RE: Forklift V. Engine Cradle

Sat Apr 24, 2004 11:42 am

Mr. Spaceman,

Your picture is very nice as a demonstration why NOT to open the C-duct with the slats extended (why not to extend the slats with the C-duct open). It will become expensive.

Your accident:
To prevent accidents like this ( and pedestrians or cyclists getting caught under the trailer and rolled over by the rear wheels when the truck makes a right turn) all trucks and trailers in Europe must have guard bars between the wheels.

Jan
Je Suis Charlie et je suis Ahmet aussi
 
A/c train
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RE: Forklift V. Engine Cradle

Sat Apr 24, 2004 9:29 pm

Through my limited experience admittedly I would have to agree with you MD11engineer, ive done a few 757 eng cx (RB211-535-E4) and one 321 and one 320.
It is great when you have one lower/lift supervisor and 4 men one on each winch obviously. Its happend were weve had a crew chief and a technician giving orders at once, cocks the whole TEAM effort thing up !
I think all people have to be confident to shout when somethings not right or if the cradle is snagging on the c-duct for example, most importantly when the load on the dynanometers gets close to limit or over.
I seem to always get put on the inbd /fwd winch on the RB211, I think thats the hardest on lifting but not to hard  Smile/happy/getting dizzy.
never seen an eng cx done with a forklift though !!, fittted CNA's and nose cowls with fork lift but not the engine itself !
havn't been involved in an engine cx gone wrong yet 'touch wood' and im not looking fwd to it if it does happen !
regards a/c.
 
greasespot
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RE: Forklift V. Engine Cradle

Sun Apr 25, 2004 10:19 pm

We use a bootstrap for the #2 on the 72 and a crane for the 1 and 3. I have seen pictures in my endorsement course of the 1 and 2 bootstrap and have even hear a rumor that we have one but we never use it. Supposedly it is quite a complicated set up. IS This true? The crane and dynamometers are much easier and faster and does the same job. In the 722 we have always used the chain hoisting points under the wing. For the twin otters and beaver we have been very creative at times.

GS
Sometimes all you can do is look them in the eye and ask " how much did your mom drink when she was pregnant with you?"
 
Mr Spaceman
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RE: Forklift V. Engine Cradle

Mon Apr 26, 2004 5:38 am

Hi guys.

>> MD11Engineer, you stated above regarding the 737-8 engine photo .......

"why not to extend the slats with the C-duct open. It will become expensive."

It appears to me that the LE slat has contacted the inboard side of the engine cowling. Is this the case, and does it look like there's damage? Or is the slat just very close?

Also, what is a C-duct?

PS, regarding my truck accident, Tractor-Trailers over here in Canada & the USA don't have guard bars between the wheels. All we have is a large placard (about 1 ft X I.5 ft) on the back right side door of the trailer that warns other drivers that ....."THIS VEHICLE MAKES WIDE RIGHT TURNS!" and there's a diagram of a car smashing into an 18 wheeler while it's turning. Big grin

"Just a minute while I re-invent myself"
 
Mr Spaceman
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RE: Forklift V. Engine Cradle

Mon Apr 26, 2004 5:51 am

Hi guys.

In this photo of a United Airlines Boeing-777 that's waiting for it's new engine to be trucked in, you can see a steel horizontal bar located below the pylon mount that has hooks & chains & levers hanging from it.

Is this equipment a type of engine hoist or bootstap that will be used to raise the new engine into place under the pylon?


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Chris  Smile
"Just a minute while I re-invent myself"
 
MD11Engineer
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RE: Forklift V. Engine Cradle

Mon Apr 26, 2004 6:15 am

Mr. Spaceman,

Yes, this is a bootstrap kit. The beams can be broken down into pieces (some are still bloody heavy!) and are usualy stored and shipped together with the hoists and other accessories in one or several big crates.
The beams attach to special hard points on the pylon or in case of the 727 on the fuselage. The 737-200 bootstrp kit just consists of hoists, which get attached to hard points on the lower side of the wing with a kind of bayonett fittings.

Jan
Je Suis Charlie et je suis Ahmet aussi
 
VC-10
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RE: Forklift V. Engine Cradle

Mon Apr 26, 2004 6:41 am


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DC-10Tech
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RE: Forklift V. Engine Cradle

Mon Apr 26, 2004 3:05 pm

VC-10, those are pictures of the dream #2 bootstrap setup! We had the electric hoist motors in the AF on KC-10's, but when I worked at Omni, we hoistied that sucker using chains, talk about work!

FDXMech is correct, the current procedure on the DC-10/MD-11 is to snug the hoists and loosen the mount bolts until you have a slight gap, then remove readjust the hoists and remove the bolts. Upon raising the engine, you stop with just a small gap between the engine and pylon, then crank the engine up into place using the mount bolts.
Forums.AMTCentral.com
 
Jetfixer75
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RE: Forklift V. Engine Cradle

Wed Jun 02, 2004 2:59 pm

The 727 has bootstrap equipment for #1 & #3 engines? The only thing I've ever used is a crane. I hated hooking up the equipment for #2 as well as humping the engine all the way up there.


 
MD11Engineer
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RE: Forklift V. Engine Cradle

Wed Jun 02, 2004 4:20 pm

Yes, bootstrap equipment exists for #1 and #3 engines on a 727, though I´ve got no experience with it. Some of my colleagues, who used it, told me, installing it takes longer than changing the engine and is generaly a PITA.

Jan
Je Suis Charlie et je suis Ahmet aussi
 
Buzz
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RE: Forklift V. Engine Cradle

Wed Jun 02, 2004 9:37 pm

Hi All, Buzz here. The thing that really caught my attention on that AA DC-10 engine change that caused the crash at ORD was the leak-down of the forklift was damaging the pylon attach points.
A lot of fork lifts leak a bit, this one seems to have requred constant juggling while carrying the engine and pylon. It's hard to line up bolt holes when the parts are moving relative to each other.
And for the rest of the time that UAL had DC-10's, any kind of pylon work was critical and required an Inspection sign off. No deviations from the Douglas manual were permitted - a long time ago we could get an Engineering Variation Authority if we thought something needed changing. But not on DC-10 pylons.

Forklifts still have a place in aeronautical society... changed an engine on a DC-3 lately?
g'day
Buzz Fuselsausage: Line Mechanic by night, DC-3 Crew Chief by choice, taildragger pilot for fun
 
dl757md
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RE: Forklift V. Engine Cradle

Sun Jun 06, 2004 5:36 am

Mr Spaceman
Please allow me to answer your previous questions from reply 27.
It appears to me that the LE slat has contacted the inboard side of the engine cowling. Is this the case, and does it look like there's damage? Or is the slat just very close?

The LE salt is fully extended but is not contacting the cowling. This is a normal situation that occurs when the flaps are fully extended. No damage has occurred in the photo you posted. If the cowl (it is actually the inboard thrust reverser half or C-duct) was opened and the flaps deployed normally the slats would hit the reverser half damaging both. There is a slat lockout procedure in the AMM that allows you to deploy the flaps and have the C-duct open at the same time for MX.

Also, what is a C-duct?

As I said above it is the thrust reverser half of which there are two of per engine.
They are shown beautifully in the pic you posted in reply 28.

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As you can see the air pathway cross section is C shaped hence the name C duct. It's interesting that before I joined this forum I had never heard it referred to as a C duct. The term at Delta and I assume at most US airlines is thrust reverser half. I like C-duct better as they do indeed look like a C and it's shorter to type!

Dl757md


757 Most beautiful airliner in the sky!
 
Jetfixer75
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RE: Forklift V. Engine Cradle

Sun Jun 06, 2004 9:31 am

Is the bootstrap equipment the same for the 737NG as the 737-300/400/500? I've changed many CFM56-3's but never a -7. Anybody have any insight on this?
 
dl757md
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RE: Forklift V. Engine Cradle

Mon Jun 07, 2004 5:04 am

Is the bootstrap equipment the same for the 737NG as the 737-300/400/500?

Yes. The bootstrap kit for a CFM56-3 on a 300 is different from the bootstrap kit for a CFM56-7 on an 800.
757 Most beautiful airliner in the sky!

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