CF6-80 Thrust reverser deactivation

[ENGG4LIFE]

hi guys
I would really like some info regarding thrust reverser deactivation on the CF6-80C engines. The procedure is fairly straight forward. My question actualy is what happens when you have any of the top or bottom ball screw actuators completely jammed in the fully extended position. Is it legal to completely remove the actutor, retract the thrust reverser and dispatch the aircraft with one actuator missing? If so can any one assiistt me with any reference material with regards to this, and if not also any reference to that. I have been facing this situation too many times and i have not found the refrerence material to support it. The third party ailine we handle keep refering me to MEL 78-31, but no where does it say you can remove an actutor and lock out the reverser.
Any info will be much appreciated
Thanks
Engg4life

[gas path]

I would hazard a guess here but I reckon the sleeve integrity is compromised by removing an actuator.
However someone who is 'up to speed' with the CF6 installation is bound to make things clear!:ok:

[ENGG4LIFE]

Thank you for your response. Hopefully we will get someone to shed more light on the subject.. Im sure its a question that needs more research. Being in a line station we are limited to material. The procedure employed was proposed by the base maintenance station of the affected airline which i also felt was very unsafe. Thanks again
engg4life

[aintsaying]

The screw jack actuators are what hold the T/R halves in place on the slide tracks.
So if you remove one actuator, how would you hold the C-duct half in place?
If one half moved backwards in flight, YOU WILL KILL EVERYONE ONBOARD.

What is the name of this airline you are dealing with?

[Lightning5]

There is no way you are going to remove the screw jack!! The structural integrity of the reverser system will be compromised. The flex drive shafts from the CDU to the upper and lower screwjacks do sometimes get damaged or worn but I am not aware of a screwjack being jammed in the deployed position. I may stand corrected on this however! Change the actuator/drive shafts is the best option.

[ENGG4LIFE]

AINTSAYIN,
im not trying to justify what was done on the aircraft, the airline responsible claims that removing one of either the top or bottom screwjack will not affect the integrity of the sleeve since you still have the cdu and one more actutor.
I am in complete agreement with you guys its just that i need the facts to support my protest against the maintenance action carrried out..

Engg4life

[Perrin]

Good for you, hope your Airline who operate the A/C take on board what you tell them. Simple thing the MEL, if its not in it then there's no sign off. :=

Keep them up boys

[ENGG4LIFE]

:ok:
Thank you all for your input . Much appreciated.
Engg4life

[aintsaying]

The CDU does not hold the T/R half in place. The screw jacks are the mechanical linkage between the movable T/R half and the non-moving T/R inner half.

Who is this airline that carried out the screw jack removal and then dispatched the aircraft?

[Swedish Steve]

Back in around 1990, a BWIA Tristar Thrust reverser was locked out in Frankfurt after disconnecting an actuator. On rotation the whole thrust reverser assembly departed the engine and hit the stabiliser. The aircraft carried on, but diverted to LHR. There is a UK CAA accident report about it.

[N1 Vibes]

On a Boeing 744 RR RB211 application they have the mother of all lock-out brackets that you can install to 'replace' the integrity of a missing screwjack. Which basically bolts the sleeve to the FWD firewall to prevent deployment in flight. Sorry no gen on the CF6-80. Only other bit of advice I can give is, we once tried to ask GE if we could dispatch a CF6-50 powered 747 with 2 screws of one reverser lockout plate missing and they nearly died...

Brgd's

N1 Vibes

[Bumpfoh]

Don't have the MEL or MMEL available to me at this point in time but this engine installation on the B767 requires for MEL 78-31-1 application that the TRAS brake be funtionally checked operative for MEL application which is in addition to the CDU being mechanically baulked by the installation of the hex drive lock. Belts and braces I guess as well as checking the integrity of the flex shafts.

As previosly alluded to removing a ballscrew actuator would seriously compromise the integrity of the deactivation of that particular sleeve.:ok:

Remind me not to travel with these jokers!

[Bus429]

The sentiments of all comments above are correct. Not in the MEL and associated despatch maintenance requirements - no go. Removing the actuator as the operator suggested could alter the design and certification configuration of the aircraft. It's all very well for an operator to stipulate what has to be done but it has to be within rules and regs; the AMO - and maintenance staff - remain responsible for accomplishment of the task.
Stand firm, ENGG4LIFE, I know what it feels like making a stand like this.:D

[MD11Engineer]

im not trying to justify what was done on the aircraft, the airline responsible claims that removing one of either the top or bottom screwjack will not affect the integrity of the sleeve since you still have the cdu and one more actutor.


And are these "airline responsible" willing to sign for the "fix"?

[born1987]

hi mate have u tried to grease the jack screw because i remembered the incident of alaska airline in which they havent bother to grease there elevators jack screw and while on flight its all treads get worn up and elevator is stuck and had an crash.

[Bolty McBolt]

I believe you could safely remove the lower jack screw.
No there is no MEL provision for it so I do not propose to make it standard practice but with a one flight home Engineering Authority from your tech services dept would be enough to cover the paper work legalities

The CF6-80 744 767 and A330 have a pneumatically driven T/R.
The (CDU) Centre Drive Unit provides the drive and the braking to the upper and lower jack screws via flex drive shafts.
A TRAS brake is fitted above the upper drive actuator to add belts and braces to the system.
I believe the T/R system has enough redundancy built in, that it’s stow forward integrity would not be impaired by one of these flex drive shafts shearing.

So if you had the situation where a jack screw had seized I think it would be feasible to send the aircraft home with the lower jack screw missing after checking the integrity of the other to jack screws, the drive shafts and the T/R brakes plus fit all the locking screws thru the forward edge of the sleeve.
This of course is well outside the authority of my LAE license and I would not carry this out without a piece of paper giving authority to do it.

In my time I have spent many hours on these T/R systems and have often found TRAS lock (short) flex drive shaft sheared and occasionally a long flex drive end sheared but what is most common is the CDU failing it's brake torque check with no associated problems written in the incoming tech log

My 2 cents :ok:

I just noticed the original post was made April 1st

[Bus429]

Bolty,
Even if you were to adopt that method, usual process is to obtain an NTO, TV or equivalent form the TC/STC holder but that in itself does not allow despatch.
The AMO does what the operator wants - the operator is responsible for ensuring required maintenance is accomplished - within the limits of the rules of the regulations and the limits of their maintenance approval. The operator would have to issue a concession, if approved, or go to the regulator. Unless an operator or contracted AMO is so approved to authorise such despatch, it can't happen.
We can't make decisons to despatch on our judgement alone; aircraft have to remain within the approved configuration (and that includes despatch in accorance with the MEL; you can't fly commercially outside the MEL).

[Bolty McBolt]

BUS429
Thanks for the lesson in air leg much appreciated.
In my case the AMO and the operator are the same.
I did say the action is out of the scope of my license and would require an approval from a "tech services" dept of the operator for a concession, as would dispatch for an over head bin removed in the cabin.... Any part missing from an aircraft that is not in the CDL = concession BFD
A concession is only a bit of paper it does not make the aircraft any safer.

My point was to add some balance to what had been written in this thread.
With the lower jack screw removed (not advisable) and T/R locked out as I described I don't believe in the very short term the the sleeve security would be compromised as I have found the lower flex drive shaft "square" end sheared during inspections of these T/R assy in my time. The CDU provides the locking and the lower jack screw is held in place by the flex drive shaft via the CDU locking.

Judging by the topic of this thread this event has already happened and we can argue the merits of a jack screw removed all day but it looks to me like its history

Care to fill in some details ENGG4LIFE ?

[lloyd_dsouza]

HEy guys,

I just started my career as a mechanic. Well I wud like to know hw to deactivate the T/R for dispatch.

[Wirelock]

contact Boeing AOG desk..
tell them what you want to do and they will tell you if you can do it or not...
normally if it is not mentioned in the manual as a fix.. then they will not allow it

[muduckace]

Bus429 said it best, no point questioning the functionality of it. If a component that effects airworthiness is removed from the aircraft and it is not covered by the MEL or CDL it is not legal to operate.

Defering the reverser is defering a whole reverser.

[Tinwacker]

ASFKAP,
You will never ever receive that letter

Maybe not all airlines but mine will produce that letter to cover a deviation from the AMM.

After consultation with Tech Services dept., QA and manufacturer if necessary a letter would be produced that contains itemed instructions for the engineer to adhere to for despatch.
Serialised, time limited and named with a copy to be kept within the tech log for the crews reference.

This has deviated from the original post, so I apologise but going back to the reverser I would have a look in the AMM 71 for any possible relief, cable removal was previously included and screw jacks for some engine types. Finally T/R locked out IAW MEL.

Repeating the comment of GE not allowing two bolts on the lock out plates, there are only two bolts fitted per plate.
I asked GE if one bolt out of the four plates could be ommitted as one anchor nut was damaged and I again had a curt NO....

Lloyd, PM me and I will give you details of T/R lockout procedures and where to look...

And happy New Year from TW

[NWT]

Have to dissagree with that statement. Our MEL clearly says only one lock out plate on each half needs to be fitted.

[kingstonboy]

NWT,
i think clarification required ref lock out plates ie CDU lockout or translating sleeve lock plates in which i believe you are correct.For the record i have locked out T/R with one of CDU lock out bolt location helicoils damaged.Along with associated HP valve and relevant CB`s
:ok:

[muduckace]

When someone asks you to do anything that isn't covered by the MEL (or AMM) ask them to fax you a letter signed by the chief engineer and QA manager authorising you to deviate from the approved procedure with step by step instructions detailing exactly what they want you to do......:=


Yeah, I was going to make the same statement, just my experience especially with our current operator would never recieve this kind of relief. Loved your statement about "step by step instructions". I have refused to go with an E.A. as engineers constantly write them vague leaving ambiguous interpretation of the authority EG: refer back to an AMM that conflicts with the true condition. They have to conform as well to process standards but try to leave the liability on myself, no way my friend..

[Tinwacker]

NWT,

Maybe it's time for me to go back to GE as they have softened.
I was always happy with the idea of a single bolt if situation required as it's still locking the sleeve to the engine frame.

These engines have always been a problem with damaged or hard to access anchor nuts for the locking bolts.

Just our MEL didn't allow - sounds like a useful amendment coming....

Cheers TW

[Perrin]

Yes its so easy writing about it here, try getting help from "the company" at 0400 in the p***ing rain on the ramp.
Keep them up boys.
Peter :rolleyes:

[Tinwacker]

Perrin,

Still not a problem as I do get full response - Company is in Sunshine land while I'm singing in the rain...
Response is easier during the early hours while the other side of the world is wide awake.

Dam it's wet here,
I must just be lucky...

TW

[Long Bay Mauler]

I would have to agree with Bolty,as that is the procedure for stepping away from the AMM and MEL books in our company.I also think that it would be possible to dispatch the T/Rev locked out with at least one jackscrew missing,even if it was decreed that a "dummy" rod of that length was manufactured and installed for a one off flight or set period.

If you need to configure the aircraft legally in any other way as to what is directed in the AMM or MEL book,you need the services of a professional degree educated engineer to give you the authority to do what is required.

I think that the more people you involve in the process of configuring the aircraft in a particular way and they have their licence/approval number there,that ultimately if its dodgy,then no one will want to put their name to it.

I know it doesnt always happen in the real world,but even having ashtrays missing from around the aircraft really should be added to the technical log defered items with an approval from technical services,as having them missing is a deviation from the aircrafts legal configuration.

To the original poster of this thread,I would say to you to follow what is your company's/national authority's regulations,and that if you dont feel entirely happy with what is being asked of you,then ask your boss to certify for the work.If he/she wont,then that should tell you that there is something wrong with whats wanted.You may get the sack,but surely thats a lot easier to live with than the lives of dead passengers on your conscience.:ok:

[Bus429]

Here in EASA land, it's the Part 21 DOA, TC/STC holder (which are Part 21 in EU; US, Can and Bra orgs accepted under bi-lateral) that make the determination often with further approval from the Competent Authority or EASA. Flight outside the MEL? Should that happen?
Fact remains that you cannot generally deviate from approved data. (Having said that, Part 145 does have provision for that under certain circumstances but not those we are discussing here).
You cannot unilaterally alter the aircraft's configuration; the whole basis of approved maintenance is to keep the aircraft at its TC/STC status. I know of an operator that has had its hand smacked for taking units out of aircraft for maintenance and flying with holes in panels and other tricks of that sort.

[cwolfe]

Hi everyone,

-I know this is going to be a side topic to this discussion, but does the CDU actuator provide the power to move the T/R or is the CDU actuator only used to indicate to the pilot the relevant position i.e. (STOW/DEPLOY POSITION or IN TRANSIT).

I'm curious; if the CDU actuator were to fail would this prevent the T/R from being used?

Also how many CDU are there per engine?

[cedgz]

cdu = center drive unit or master actuator, so this actuator drives the 2 slave actuators(mechanically linked with flex shafts)
and the cdu also provides stow/deploy indication and also has an internal brake to prevent deployment in air)
2 cdu's per engine( 1 per reverser half)
if cdu fails, rev won't work

[spannersatcx]

if cdu fails, rev won't work rev half won't work.

[cedgz]

"rev half won't work."

yes, but no green rev indication(full indic and not half ;):ugh:

[cwolfe]

Thanks for the info about the CDU, but just to be clear, if the CDU tension rod assembly which is responcible for the stow, stop, in-transit positions. Should this rod break would the T/R still be able to deploy because the pnematic motors inside the CDU can still provide power to operate the flex drive cables attached to the slave actuators. If this is possible, which is the question at hand, then it would be possible to have a deployed thrust referser, but the pilot be unaware of the thrust reverser position.