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Aircraft Maintenance: two strategies, which is better?

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posted on Jun, 10 2007 @ 10:31 AM
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It came to me a few seconds ago that the USA and some other countries have a different style of aircraft maintenance, and I was curious to which one is more effective.

1. Replacing parts as you go, replacing the parts that look like they are about to fail

2. Giving the aircraft a massive overhaul and replacing most of the burdened parts every 10 years or so (note this still includes replacing parts as they break, so a wheel doesnt have to wait 10 years to be fixed)

what is your opinion?



posted on Jun, 10 2007 @ 11:34 AM
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Originally posted by BlackWidow23
It came to me a few seconds ago that the USA and some other countries have a different style of aircraft maintenance, and I was curious to which one is more effective.

1. Replacing parts as you go, replacing the parts that look like they are about to fail

2. Giving the aircraft a massive overhaul and replacing most of the burdened parts every 10 years or so (note this still includes replacing parts as they break, so a wheel doesnt have to wait 10 years to be fixed)

what is your opinion?


Both.

Aircraft undergo a regime of service and maintenance through their life, ranging from line item maintenance brought up by check sheets filled out by the flight crew (ie 'This is broken, if another one breaks we cant fly the aircraft, please fix') which are carried out as and when the airline has the spare capacity to handle such a maintenance.

There are also periodic checks on aircraft:

A Check - done monthly, generally in regular downtime between scheduled flights

B Check - done quarterly, generally done in regular downtime between scheduled flights

C Check - done 18 monthly, requires aircraft removed from schedule for the duration

D Check - done roughly every 5 years, aircraft is practically taken apart and is removed from the schedule for the duration

E Check - rarely done, mainly its done to increase the number of hours or cycles an airframe can fly for

There are reasons why both of your options are done - aircraft parts are not set to one maintenance schedule, some *have* to be replaced after a set number of cycles, some *have* to be replaced after a set number of hours, and some have to replaced as and when required.

A number of these parts cannot be accessed in routine maintenance, and thus the aircraft has to undergo a heavy check (C or D) periodically to replace them, and also C and D checks cover inspection of the airframe etc, which you just cannot get to in enough detail during routine downtime.

A number of airlines break up the B and C checks into parcels which can be carried out during a heavier than normal A check each month (these are typically carried out overnight at the gate, but in the case where you are doing a C check parcel, the aircraft will be removed to a maintenance base for a day or so to complete it, this is why this approach is only really taken by those airlines with large maintenance bases, or have access to large maintenance bases).

Aircraft maintenance is not just about allowing the aircraft to continue to fly based on whether anythings broken, its also about maintaining the aircraft in such a manner that its both safe to fly (no hidden fatigue issues) and its also economical to fly (if you are replacing bearings every 3 months, during a C or D check you can replace the entire part which is causing the bearings to require replacement, regardless of whether it infact needs replacing itself).



posted on Jun, 10 2007 @ 11:51 AM
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Most A/C components have a useful service life as determined by testing done by the manufacturer in order to receive certification. In general aviation, items such as seals, hoses, pumps and the like have a service life and are replaced (irrespective of actual condition) at their predetermined time. In addition, there are regualr inspections (as noted above) to identify abnormally wearing parts and components.



posted on Jun, 10 2007 @ 12:13 PM
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Well Blackwidow23. To be honest both off them.

1: To repair broken parts immediatly to give the planes direct care and to be sure that they will stay flying when ever there is a problem.

2: To update the aircraft to the latest standards and to replace worn out parts who still are good but need to be replaced soon (like engines en so forth).

Yes it is all in the mix with this one. Both needed to be used.




posted on Jun, 10 2007 @ 02:23 PM
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All military aircraft undergo what's called PDM every few years. It can take as long as 12 months or more in some cases. They strip the aircraft down to basic frame and check EVERYTHING. It can only be done at a maintenance depot. That's when they check for corrosion, replace the skin, check for wiring defects, etc. That's on top of a regular Phase inspection that they undergo every so often at their home station. Phase involves removing engine cowling, panels, the interior, and checking things while it undergoes routine maintenance.



posted on Jun, 10 2007 @ 04:14 PM
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One other factor also effects MRO schedules and that is ETOPS. If I recall correctly, the current ETOPS is 240 moinutes, but Boeing may be pushing for a 300+ ETOPS which may require a more intensive inspection cycle.

[edit on 6/10/07 by FredT]



posted on Jun, 10 2007 @ 04:36 PM
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The confusion arises because airliners used to follow manufacturer's MPDs (Maintenance Planning Documents), but gradually a new concept evolved of MSGs (Maintenance Service Guidelines) based upon tested component lives.
An MSG-3 plan permits an airline to perform maintenance on a predictive removal basis.

There have been several evolutions of MSG rules through MSG1, MSG2 and now MSG3. An aircraft needs a heavy C-check before it can commence upon an MSG plan after a lifetime on an MPD plan.

You can't operate an aircraft on both MPD and MSG plans at the same time.



posted on Jun, 10 2007 @ 04:37 PM
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Originally posted by FredT
One other factor also effects MRO schedules and that is ETOPS. If I recall correctly, the current ETOPS is 240 moinutes, but Boeing may be pushing for a 300+ ETOPS which may require a more intensive inspection cycle.

[edit on 6/10/07 by FredT]


ETOPS 330 is the current upper limit, granted in January this year, with a shutdown rate of 1 in 100,000 or less required. ETOPS 207 was the previous highest.

ETOPs also now stands for 'Extended Operations' rather than 'Extended Range Twin-engined Operational Performance Standard' because it covers three and four engined aircraft now (the focus has mainly shifted from engine performance in three and four engined aircraft to cabin emergencies such as medical issues, fire suppression and oxygen supplies).



posted on Jun, 10 2007 @ 04:44 PM
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In answer to the original question airlines prefer MSG plans because it means less down time and being able to better plan removal on condition. There is a lot of experience amassed on MSG-3 and so far it seems to have worked well.

The suggestion therefore is that the old MPD approach was excessively conservative. The MPD approach with A/B/C/D checks also adds quite a bit of extra cost which passengers must bare in the ticket price.

Under an MPD approach an airliner would require 3 hours of scheduled maintenance for every hour in the air. That can almost be halved by MSG plans.



posted on Jun, 11 2007 @ 03:28 PM
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I think that preventative maintenance would be better than an as-needed repair. When a part fails on your automobile, you can generally roll to a stop if you have to. Not the case with a plane that is 36,000ft in the air. Although it would be more costly to do this, it is better than waiting for a failure. I have been in the auto industry for 10 years now. I work for VW and Bentley. When a VW breaks, you fix it. When a Bentley breaks-down, you replace the other dependent components of the vehicle's system during repair, rather than just the one failed piece. This insures that the new part will not be damaged by working in conjunction with other possibly failed components that may have caused the original failure. I would hope they take the same care with aircraft. Truth is, we would probably all be frightened by the shortcomings of quality control in avionics.


[edit on 6/11/2007 by venom79x]



posted on Jun, 11 2007 @ 05:09 PM
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The biggest issue with avionics is not so much the avionics themselves but the Kapton wiring whose plastic sheathing becomes brittle and breaks after as little as 15 years. Airliners have hundreds of miles of inaccessible wiring and breakage of the sheath on Kapton wiring leads to shorting and fires.

There are solutions available but all are costly.

Re preventative maintenance, there is a second layer of quality control if you like. That is that all airlines communicate maintenance issues with manufacturers and regulatory agencies.

When issues come to the attention of either, then ADs or advisory directives are issued to all operators of that aircraft type and these can also be legally enforced through denial of a certificate of airworthiness.

These AD's can direct airlines to address known issues with anything from worn uplock latches on undercarriages to the need to replace thrust bearings or re-rivet whole airframes as on 1992 AD did for the 727.



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