Commercial aircraft maintenance schedules

[Ogre]

Dear forum

A question was raised in the office the other day regarding whether commercial or military aircraft were better maintained. Thinking back to my days in uniform, the fast jets I worked on were maintained on both calendar and flying hour schedules, for example minor servicings at 1000 flying hours and major servicings at 2000 FH (with other lesser servicings between)

I guess the question is, what are the servicing schedules for commercial passenger aircraft in comparison? Obviously the number of hours a 737/747/A200/A300 fly per month would be considerably greater than a military aircraft in the same calendar period, so if the servicing schedules are of the same fh then the servicings would be more frequent

Comments?

[Bus429]

It depends on:


TC holders' recommendations and MPD/MRBR (for the aircraft you mention)
Annual utilisation
Manner in which aircraft is operated
Operational experience


Maintenance programmes may have tasks based on calendar and/or hours & cycles.

[Rigga]

Military aircraft are maintained to a lesser standard because the use of the aircraft is ignored (i.e. the aircraft gets the same maintenance whatever it does or wherever it goes or however much it is used - refer to Hawaian Airways B737)

There is no independant MRB as the MOD is the regulator, the type certificate holder, the operator, the owner and the maintainer. So there is also no regulatory independant view of what could or should be maintained.

There are no safety critical maintenance task methods employed to ensure correct practices on duplicated systems on anything other than the BAe146 - even though the RAF had the problem to begin with!? (No lessons learned there then?)

...but what do I know....

[Karl Bamforth]

Really Rigga ?

U must have worked on different aircraft/sqdns to me then.

[Rigga]

Karl,

...it would be really interesting to read what you think I mean and perhaps could you please describe how you do it?

[muduckace]

Time and cycle regulated based on manufacturer specs and regulatory input developed as aircraft have progressed over the years. Military operators get away from these recommendations as the civil authorities are a lesser than authority. Makes me think of a military operator as a less than regulated entity. Having said this crashing an aircraft as a result of a mechanical regulates all.

[muduckace]

If I remember this one correctly it was a result of sealant removal on the lap seams (one skin over another) that had been removed with metallic objects that had scored the aluminum fuselage (big lesson). None involved realized the serious implications of this process, we have learned a lesson and evolved.

[Mr @ Spotty M]

If that was the case we would have had the lap joint inspections now becoming ADs a lot earlier.
I think it was more corrosion and fatigue in this case, as we all ended up with CPCP programmes after the incident.

[muduckace]

I had received training on this matter, maybe it was suspect but not proven? I do not buy into the the corrosion aspect (other than a result of above mentioned root cause). Thousands of 727's and 737's (early models"s) were developed with lap seam fuselages. It may be a combination of corrosion and this unknown dangerous maintenance practice.

What I do know is that sealant removal in all AMM's I have read stress the usage of non metallic tools. These warnings do not come W/O a costly liability that the manufacturer has learned from.

CPCP programs are cost saving measures in most cases and elective but smart. Commonly in my experience they are pushed harder by airlines who actually own their aircraft. Belly skin and wet area sheet metal replacement can get quite costly.

[Bus429]

It was Aloha 243 in 1988 and one of the causal factors was degradation of the crown skin joints as a result of the method of bonding used (hot or cold, can't remember which but it was changed thereafter).
AMPhad not adequately considered high-cycle but low hours (89000 vs 36000) incurred through "island-hopping".
Other factors:

Little or no NDI training for experienced inspector
He had done many of the same inspections on other aircraft with no findings
Pressure to reduce "D" check downtime meant a lot of maintenance from B & C checks was spread across night-stops
Inspection of this area shortly before it failed was done on an overnight layover.
Many other factors like FAA failing to mandate fully the requirements of a related Boeing SB


Read this (http://www.ntsb.gov/publictn/1989/aAR8903.htm) but a full report could be found.

[HAWK21M]

Considering the Harsher environment & severe usage....Military Aircraft would be mantained at a less interval compared to commercial aircraft.

[Rigga]

My apologies - it was the Aloha Jet (737 Cabriolet) I meant to refer to.

Thanks to BUS429 for remembering it correctly.


To illustrate the difference in operating environments - Tornadoes are today used in both the Deserts of Afganistan and the mists of Scotland on the same maintenance programme - there may be slight differences but that would mainly be for the differing role equipments carried in each arena. Though the Afganistan aircraft are utilised much more they will essentially get the same levels of maintenance as those less used in scotland.

As stated earlier, the RAF relies on supervisor signatures and Independant checks to cover maintenance safety but does not conduct any safety critical maintenance task processes to avoid a single worker doing the same mistake on similar systems on one aircraft (except on their BAe146's).

Also, no-one in the RAF certifies that the whole aircraft is airworthy, they only sign for the completion of each task done whether that is a bulb replacement or a Major maintenance check. There is also no method of conducting anything like an independant airworthiness review to expose any gaps in maintenance or records...etc. A sort of review is normally done on the operating unit who may brush past errors to expedite more flying, be it for training in UK or for "real" operational uses.

I'm not saying that all the military are an unsafe bunch, but they haven't generally kept up to date with modern techniques, an area where they once led everyone, and some may have even slipped off-the-tracks a little with the needs of a war in mind.

[Bus429]

Rigga,
Some military organisations - through their IPTs - are adopting/adapting Part M and Part 145 (I think they refer to the latter as MAOS).