B752 Mx Experience

HAWK21M · Mon Mar 27, 2006 2:37 pm

Anyone out here with B752 Mx Experience.Any tips on the practical working around this Aircraft.
regds
MEL

Molykote · Mon Mar 27, 2006 3:00 pm

I sent you a personal message....

Tristarsteve · Mon Mar 27, 2006 10:13 pm

The thing that I dread is the PRSOV. They are in the strut and seem to be bigger than the access hole. The right PRSOV is worse. If they dont open there is very little you can do. You cannot see the indicator, cant get a spanner on it. Its a nightmare.
One tip. When you shut the engines down the Engine bleed OFF lights come on. This is the PRSOV closing. If the PRSOVs are not both shut, the APU bleed will not open. But if you select engine start, with the APU running, the APU bleed valve opens and then the airflow pushes the PRSOV shut.
Another thing is that components on B757 are in different places. Some aircraft have pack controllers on E6 in the aft freight, and some on E3 in the fwd equip. Remember the equip bay inside the fwd freight also. Cant get ground power on? Check the fuse on the BPCU in the fwd freight.
For checking out the autopilot, get yourself a Remote MCDP Tester. Worth its weight in gold. You can then sit in the cockpit and do all the tests, instaed of running down to the MCDP in the equip bay.

taguilo · Mon Mar 27, 2006 10:39 pm

Quoting TristarSteve (Reply 2):
One tip. When you shut the engines down the Engine bleed OFF lights come on. This is the PRSOV closing. If the PRSOVs are not both shut, the APU bleed will not open. But if you select engine start, with the APU running, the APU bleed valve opens and then the airflow pushes the PRSOV shut.

BTW, which bus powers the Engine Bleed valves? Standby-DC or Battery?
I undestand they remain in the last position when power is removed.
If they keep open, when you add power to run the APU, reseting ENG Bleed switch Off then On wouldn't close them? (without the need to "fake" an engine start)

Tom

A/c train · Tue Mar 28, 2006 12:44 am

Hangar or line work, ?
Remember spacer and tang washer when wheel or brake changing. Take the brake bar pin out before sticking jack under to change a brake unit.
15/16" spanner for tension latch on c-ducts, watch the hinge panel if c-ducts seem tight opening, it may be tight if the hinge panel hasnt lifted. Make sure slats retracted.
EEC not on engine, in elec equip bay.
Power down aircraft if changing BVCU, otherwise you will blow new one, HAS BEEN DONE!
Theres many resets and tests to rid EICAS msgs, but you'll be forever remembering them all, just pull breakers for box relevant to system !!

theres a few !

HAWK21M · Tue Mar 28, 2006 12:45 am

Quoting TristarSteve (Reply 2):
For checking out the autopilot, get yourself a Remote MCDP Tester

Ideal to have the MCDP remote panel fitted on P61.

Quoting Molykote (Reply 1):
I sent you a personal message....

Thanks for the tips.The Engines are RB211-535C.

Quoting Taguilo (Reply 3):
BTW, which bus powers the Engine Bleed valves? Standby-DC or Battery

28vdc Bat Bus ENG HP BLEED VALVE & TEST.

regds
MEL

MX757 · Tue Mar 28, 2006 1:16 am

Quoting HAWK21M (Thread starter):
Anyone out here with B752 Mx Experience.Any tips on the practical working around this Aircraft.
regds

Always have a ladder handy.

I work hangar and line maintenance (avionics) on the 757-2/3. If you have any specific questions feel free to ask.

taguilo · Tue Mar 28, 2006 1:34 am

Quoting HAWK21M (Reply 5):
Quoting Taguilo (Reply 3):
BTW, which bus powers the Engine Bleed valves? Standby-DC or Battery

28vdc Bat Bus ENG HP BLEED VALVE & TEST.

Thank you MEL

Regards,
Tom

HAWK21M · Tue Mar 28, 2006 1:48 am

Quoting MX757 (Reply 6):
Always have a ladder handy

Thats true.Everything seems to be high.
How reliable are the LG Sequencing valves.

Quoting Taguilo (Reply 7):

My pleasure.
regds
MEL

LMP737 · Tue Mar 28, 2006 5:55 am

Quoting TristarSteve (Reply 2):
The thing that I dread is the PRSOV. They are in the strut and seem to be bigger than the access hole. The right PRSOV is worse. If they dont open there is very little you can do. You cannot see the indicator, cant get a spanner on it. Its a nightmare.

On the PW2000 powered 757's the PRSOV is located on the engine at about the 10 o'clock position. Makes the job much easier than what you have to endure on the RR powered 757's.

A/c train · Tue Mar 28, 2006 6:32 am

If your changing a PRSOV in a small amount of time, especially the r/h one, take the start duct out first, also, any self respecting 757 mx company will have the big spanner tool for making that gap in between the ducts close up when it seems almost impossible!
You think the PRSOV is hard!! the pre cooler is worse by far, that pylon is generally a box of tricks with jobs one time being easy another day being a pain in the ass.

MD11Engineer · Tue Mar 28, 2006 6:48 am

When doing a nose gaer lube job, don't forget the grease fitting behind the light box (lower hinge of the drag brace). You'll either need a special (homemade) fitting for your grease gun or you'll have to remove the whole box (landing and taxi lights, ground intercom panel, APU fire shut down) to get at it. I think it is the most neglected grease fitting on the 757.
BTW, PRSOV change on the PW2000 engined version is a piece of cake, the high stage valve and the PRSOV are the same part number.

Jan

MX757 · Thu Mar 30, 2006 5:38 pm

Quoting HAWK21M (Reply 8):
How reliable are the LG Sequencing valves.

I have no idea, never worked them. So I would guess to say that they are pretty reliable. Wink

HAWK21M · Fri Mar 31, 2006 12:28 am

Quoting MX757 (Reply 12):
I have no idea, never worked them. So I would guess to say that they are pretty reliable.

So what Jobs do you normally encounter Unscheduled Maintenancewise.
regds
MEL

Tristarsteve · Fri Mar 31, 2006 2:20 am

I work the B757 on a line station. We only do Daily checks and send it back to base. I find the aircraft very reliable. The FIM is extremely useful and very relevant. I have about 15 a week and in the last year have had 10 delays. Three in two weeks, a slat actuator leaking, and EDP u/s and a MLG Door actuator leaking. All 3 needed changing, and I had to wait for spares from Homebase. Other than that only minor problems.
Make sure you get a ladder the right height in your van so you can get into the E and E bay, and into the Cargo holds. The aircraft is high off the ground and if you are not 1.80m tall you will need a ladder to do the engine oils.
Talking of engine oils on the RB211 the oil cap often needs levering off, and under it is a float valve which often sticks. So pour the first can of oil in slowly. If it overflows, wait 5 mins and the float usually opens.
Hydraulics transfers from L to R system through the brakes. You can send it back by putting the brakes on with R sys and Off with L system pressurised..

fr8mech · Fri Mar 31, 2006 5:24 am

Quoting HAWK21M (Reply 13):
So what Jobs do you normally encounter Unscheduled Maintenancewise

'Battery Charger', 'Warn Elex', 'Stab Trim', 'Pack Bite' messages all come to mind.

Brake leaks, truck positioner leaks, pylon fuel leaks. We've seen a rash of fuel pressure transmitter (PW2000) leaks.

RB211: engine surges (TPU change).

A/c train · Fri Mar 31, 2006 7:12 am

FR8mech is right on the money there, ive had the warn elex and stab trim msgs frequently and plently of brake and truck positioner leaks.
Engine bleed problems go through phases, Hi stage lights and eng bleed lights quite common, you will get to know the 757 bleed system well with RB211 engine, im not experienced with the P+W.
APU surge valve changes are not uncommon and also the 'ovbd exhaust valve ' message, get rid of that one by doing the equip cooling test.

fr8mech · Fri Mar 31, 2006 8:23 am

Quoting A/c train (Reply 16):
APU surge valve

Heck, I forgot all about the surging APU and the inop APU air problems.

The PW2000 is much more troublesome from a chapter 36 point of view than the RR.

MD11Engineer · Fri Mar 31, 2006 12:48 pm

Quoting A/c train (Reply 16):
FR8mech is right on the money there, ive had the warn elex and stab trim msgs frequently and plently of brake and truck positioner leaks.
Engine bleed problems go through phases, Hi stage lights and eng bleed lights quite common, you will get to know the 757 bleed system well with RB211 engine, im not experienced with the P+W.
APU surge valve changes are not uncommon and also the 'ovbd exhaust valve ' message, get rid of that one by doing the equip cooling test.

But most Warn ELEX messages are nuissance messages and you just have to reset Stby Power to clear them. Stab Trim Messages also often clear through shutting down and popwering up the aircraft.
Anti skid and autobrake problems were quite common as well.

We had a bunch of bleed problems on our PW2040 engined aircraft.

Most of the other stuff was, as mentioned above, APU surges, brake and truck positioner leaks, occasionally thrust reverser trouble, once I changed a rudder PCU for some electrical problem (i forgot exactly what, but IIRC it had to do with the position feedback).
I worked about 5 years with the companiy, that operated, among other aircraft types, 757-200.

Jan

[Edited 2006-03-31 04:48:46]

MD11Engineer · Fri Mar 31, 2006 12:49 pm

Quoting Fr8mech (Reply 17):
The PW2000 is much more troublesome from a chapter 36 point of view than the RR.

Yes, but access to the components is easier than on the RR.

Jan

HAWK21M · Fri Mar 31, 2006 3:05 pm

Quoting TristarSteve (Reply 14):
Talking of engine oils on the RB211 the oil cap often needs levering off, and under it is a float valve which often sticks. So pour the first can of oil in slowly. If it overflows, wait 5 mins and the float usually opens.

Interesting tip.

Quoting TristarSteve (Reply 14):
Hydraulics transfers from L to R system through the brakes. You can send it back by putting the brakes on with R sys and Off with L system pressurised..

The Boeing Instructors spoke of that.That was Educational Smile

What about Start valve manual overiding.Precautions.
And APU U/S Bleedvalve.
regds
MEL

A/c train · Fri Mar 31, 2006 3:10 pm

That Warn elex message was apparent one one particular airplane last summer, every time you went to start the APU when selecting BAT power on you would get the stick shaker! then you could start the APU as normal, this was always followed by a WARN ELEX message which you could clear by cycling the 2 warn elex breakers.
regds a/c

MX757 · Fri Mar 31, 2006 3:31 pm

Quoting HAWK21M (Reply 13):
So what Jobs do you normally encounter Unscheduled Maintenancewise

The two most rash problems that come to mind is:

HF-We had alot of pireps along the lines of no comm and no data link with ACARS. Turns out that the problem with ACARS is that the pilots were not pushing the HF transmit overide button. The no comm problem was usally fixed with a coupler R&R.

ATC-We also had alot of pireps about ATC 1 or ATC 2 fail lights on during flight. Sometimes both failing at the same time. It turns out that Honeywell had corrupted software loaded in the transponders causing intermitent faults.

We had done a MOD here in MCO awhile back that installed EHS (Enhanced Mode S) and Honeywell upgaded the ATC transponders to incorporate the new parameters. When they did this it started to cause chronic failures throughout the 757 fleet. It was a real headache because we were doing alot of troubleshooting before it was found out the transponders were coming out of Honeywell bad.

On the A&P side of the house it seems that the line guys do alot of annulus filler changes on the RR engines. (cracks)

SkydrolBoy · Fri Mar 31, 2006 6:07 pm

Quoting A/c train (Reply 4):
watch the hinge panel if c-ducts seem tight opening, it may be tight if the hinge panel hasnt lifted.

Thats for sure, we made it company policy to have someone watch the hinge doors when opening the c-ducts, cause if they aren't rigged properly they will catch and it makes a mess to repair. Also make sure the C-duct latch access doors are closed before operating the T/R....we found out the hard way that door is harder than the Translating sleeve....

fr8mech · Fri Mar 31, 2006 9:39 pm

Quoting HAWK21M (Reply 20):
What about Start valve manual overiding.Precautions.

Communications with the flight deck is a must and clear the engine to the outboard side when done. Stay clear of the the inlet danger zone.

And while we are on engines. RR engine tower shaft leaks. It seems I hear about 1/week leaking.

Warn Elex can a nusiance, but if it doesn't clear 1st time around with the breakers or the IRS alingment, go right for one of the WEU power supplies. Re-seat, beat, pound or replace.

MX757 · Fri Mar 31, 2006 9:52 pm

Quoting Fr8Mech (Reply 24):
And while we are on engines. RR engine tower shaft leaks. It seems I hear about 1/week leaking.

I forgot about that one, we had 2 here in MCO this year alone!

HAWK21M · Fri Mar 31, 2006 11:28 pm

Is the Tiller on both sides an option on the B752.
regds
MEL

Molykote · Sun Apr 02, 2006 2:52 pm

To answer your question from my personal message:

AHAD = automatic hinge access door

When this guy gets out of rig expect some damage to the C-duct and AHAD edges.

See chapter 78-30 of the AMM for aerodynamic smoothness requirements.

HAWK21M · Mon Apr 03, 2006 1:13 am

Quoting Molykote (Reply 27):
To answer your question from my personal message:

AHAD = automatic hinge access door

Thanks.
regds
MEL

dl757md · Mon Apr 03, 2006 4:23 am

Boeing put out a SB about the cargo door switches. Apparently there has been two incidents where the switch stuck in the close position and injured ramp personnel, one fatally. I've found one so far that the door went from full open to full closed (minus being latched with the door handle of course) hands off after an initial push on the switch. It was pretty cold, about 10F, and once the switch warmed up inside the office after I had changed it, it worked fine. Something to watch out for.

DL757Md

HAWK21M · Mon Apr 03, 2006 5:47 pm

Quoting Dl757md (Reply 29):
Something to watch out for.

If it was Low Temperature related,That'll be a problem not encountered out at BOM.

How reliable are the Red Door Safety Lt bulbs.
What about APU Shutdown in Unattended mode.Any Experiences.

regds
MEL

[Edited 2006-04-03 10:49:12]

dl757md · Mon Apr 03, 2006 7:51 pm

Quoting HAWK21M (Reply 30):
If it was Low Temperature related,That'll be a problem not encountered out at BOM.

I don't think the SB said anything about temperature. I just noted that about the switch that I changed. The switches could fail at any temperature I would imagine.

DL757Md

HAWK21M · Tue Apr 04, 2006 5:52 pm

Quoting Dl757md (Reply 31):
The switches could fail at any temperature I would imagine.

Thats Interesting.
Any Experiences with APU Malfunction Fire detectors leading to Unattended mode Shutdown & Extinguishing.
regds
MEL

AvionicMech · Tue Apr 04, 2006 11:48 pm

Quoting HAWK21M (Reply 32):
Thats Interesting.
Any Experiences with APU Malfunction Fire detectors leading to Unattended mode Shutdown & Extinguishing.

We have had a report of one of our aircraft having the cargo door switch stick in the close position aswell, this is definately something to watch out for.

I have not had any experience of the APU shutting down automatically due to a fire detection fault but even if it did it would still not fire the bottles, that has to be done manually from either the flight deck fire handle or from the nose gear.

fr8mech · Wed Apr 05, 2006 1:36 am

Quoting AvionicMech (Reply 33):
that has to be done manually from either the flight deck fire handle or from the nose gear.

Our B757's have an auto-fire agent discharge system.

aogdesk · Wed Apr 05, 2006 2:24 am

Quoting Fr8mech (Reply 34):
Our B757's have an auto-fire agent discharge system.

You certain about that? I know the A300 has auto discharge, but I didn't think that the B757 did....thought you had to hit it from the left NLG panel when the NLG door switch is. I guess I'd better take a look.. Smile

fr8mech · Wed Apr 05, 2006 3:46 am

Quoting Aogdesk (Reply 35):
You certain about that?

Yup. Nowhere near the tech manuals at the moment, but as I recall, you had something like 30 secs to either hit the fire shutdown (pull handle or hit the button on the nose) or the APU fire system would auto-discharge.

AvionicMech · Wed Apr 05, 2006 6:46 am

I guess I had better look that up as well but I was almost certain that it would not auto-discharge. I will look tomorrow if I remember.

atlamt · Wed Apr 05, 2006 7:58 am

It depends on the fire suppresion system. You can have either a dual bottle which I believe dosen't auto-discharge. Or a single bottle auto-discharge system.

HAWK21M · Thu Apr 06, 2006 12:00 am

Quoting AvionicMech (Reply 33):
I have not had any experience of the APU shutting down automatically due to a fire detection fault but even if it did it would still not fire the bottles, that has to be done manually from either the flight deck fire handle or from the nose gear.

In Unattended mode the B752 does have Auto Fire Extinguishing for the APU.

regds
MEL

atlamt · Thu Apr 06, 2006 4:37 pm

From the AMM:

Effective on the following aircraft only: AIRPLANES WITH DUAL APU FIRE EXTINGUISHER BOTTLES;

when the airplane is in flight and a fire is detected, the APU will shut down automatically, and the fire extinguisher bottles will discharge manually.

Effective on the following aircraft only: AIRPLANES WITH SINGLE APU FIRE EXTINGUISHER BOTTLE;

when the airplane is on the ground and a fire is detected, the APU will shut down and the fire extinguisher bottle will discharge automatically. When the airplane is in flight and a fire is detected, the APU will shut down automatically but the extinguisher bottle must be discharged manually.

HAWK21M · Thu Apr 06, 2006 6:31 pm

Quoting Atlamt (Reply 40):
Effective on the following aircraft only: AIRPLANES WITH DUAL APU FIRE EXTINGUISHER BOTTLES;

when the airplane is in flight and a fire is detected, the APU will shut down automatically, and the fire extinguisher bottles will discharge manually.

What about Grd mode with Dual bottles.I presume it should have the capability to discharge the Extinguisher in Unattended mode.
regds
MEL

atlamt · Fri Apr 07, 2006 7:38 am

From what we were told dual bottle a/c will not discharge automatically. Someone has to discharge the system. The apu will shutdown if a fire is detected but that's it.

The single bottle system discharges automatically because you only have one shot at putting out the fire and the sooner the bottle is fired the better the odds of putting out the fire before it can grow any larger.

AvionicMech · Fri Apr 07, 2006 8:15 am

I looked it up in the AMM today and sure enough the bottle will fire automatically on detection of a fire and obviously shut down the APU. But I also looked in the 767 AMM but could not find anything in there about an auto discharge system but I did not have much time to read through it though so might have missed it.

Sorry for the duff info I wrote down earlier in this thread. Yeah sure

HAWK21M · Fri Apr 07, 2006 2:11 pm

Quoting ATLAMT (Reply 42):

It does not make sense then.If Fire is the concern.Then Two bottles or One Bottle.Unattended mode should fire both types.
We were taught on Single APU Fire bottle.As our B752SFs would be equipped with one.So I need to check the AMM.But my instincts say it should be the same.

regds
MEL

cdfmxtech · Fri Apr 07, 2006 2:33 pm

Quoting TristarSteve (Reply 14):
Talking of engine oils on the RB211 the oil cap often needs levering off, and under it is a float valve which often sticks. So pour the first can of oil in slowly. If it overflows, wait 5 mins and the float usually opens.

Put cap on, then try to pull of as quick as possible. Usually clears the air lock.

HAWK21M · Fri Apr 07, 2006 3:04 pm

How quickly can the Primary Heat Exchanger,Secondary Heat Exchanger & Plenum Diffuser unit be Dropped.
regds
MEL

MD11Engineer · Fri Apr 07, 2006 3:43 pm

We had a bit of problem with cold soaked APUs in winter. Often, when trying to start them you will get a "low Oil Pressure Fail" auto shutdown and fault light. Try to start them again and again (in some cases you'll need to reset the ECU, IIRC it locks out after three failed start attempts).

Jan

A/c train · Fri Apr 07, 2006 6:13 pm

You can drop the complete unit using the IDG stand in about 2 hours, both heat exchangers ram air inlet and ACM plenum, easy little job but it looks like you've done loads so it impresses the bosses! not really too much to look out for either, just make sure you clear the ACM plenum on the way down, otherwise you here the grinding of composite!
Waht does IIRC stand, guess its 'if I recall' or something like that?

MD11Engineer · Fri Apr 07, 2006 7:34 pm

IIRC = If I Remember Correctly

Jan

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