I don't think the 9-sigma is calculated per operation cycle, I think it's per maintenance cycle which are from a few times a year to every 5 years, depending on the type.
There are several types of routine checks, I think Boeing calls them A/B/C/D (with subtypes, depending) Airbus has a different nomenclature but the idea is the same.
I don’t know for these. C-checks for 737NG are performed every 730 days and include corrosion/wear checks for the most stressed parts, but not all parts (which are checked at D checks): https://en.wikipedia.org/wiki/Aircraft_maintenance_checks
Aircraft undergo regular preventative maintenance checks, with letter codes A - D. The D check being the most comprehensive, it occurs every 6-10 years and basically the entire aircraft is taken apart and inspected, looking for among other things anything like stress fractures, corrosion, unusual wear, etc.
A commercial aircraft does not just accumulate wear and tear for 25 years until something breaks. They can basically fly indefinitely, but in reality after two or three D checks they are usually retired because the cost of the D check is more than the value of the aircraft.
There's an existing inspection period of every 6,500 takeoffs and landings[1]. The expectation is that it would take sufficiently long for a detectable flaw to turn into a dangerous fracture that this would be sufficient to notice it. But, given this failure (and presumably also because of the 2018 one), that assumption appears to be untrue. Checking all of them now and comparing any discovered defects to the number of cycles since they were last checked should allow a recalibration of how frequent checks should be (or, if there's an indication that flaw propagation is significantly faster than anyone expected, potentially stronger measures)
[1] My understanding is that it's based on cycles rather than flight time because takeoff is the part of flying that puts the most stress on the blades - spending 10 hours in cruise isn't much worse than spending 2.
Though, if the maintenance schedule items are mostly of the form "W needs to be inspected after X flight hours, Y landings, or Z days since last inspection", there's probably significantly less experience backing up the Z parameter.
That would be interesting to hear how they come up with those maintenance schedules. Even with the uptick in flights, it doesn't seem like they'd have the dearth of reliability data to make that determination with reasonable accuracy. But maybe they have a lot of internal reliability data we're not privy to.
However, since Airbus != Boeing, nobody around here cares. Only stories that are pointing out problems with Boeing are allowed (or upvoted) apparently.
My experience in the military was that phased inspections on fighter aircraft was done every N flight hours, not based on a fixed amount of time, I would assume helicopters are the same, but I was under the impression that helicopters required more maintenance, not less, due to the increased mechanical complexity, but I never got to work on those, so I really have no idea.
It doesn't. They might do that during an IRAN (Inspect and Repair As Necessary) which is essentially a full engine teardown, easily 5 figures. Certainly not done every 200 hours.
Maybe it's a conflation of many piston aircraft engine manufacturers' recommendation for a TBO (time between overhauls), which is often around 2000 hours. This is essentially a full rebuild of the engine. However, in many cases it's not regulatory and more of a suggestion (there are exceptions, like certain commercial use of the aircraft).
Don't you mean >N days? If a maintenance schedule requires maintenance every 60 days but the plane needs to be rebooted every 50 days, that would be cause for concern.
It’s called predictive maintenance and it is the norm in many critical industries. Replacing equipment every fixed number of X years (no matter what the condition of the equipment is) is wasteful, costly disruptive and does not actually guarantee better reliability. (although it makes people feel better).
Most predictive maintenance is done with data — updated sensor data processed through a mathematical model derived from principles from reliability engineering. In a sense it’s actually more realistic than the X years model (which is a once off number derived from some reliability model too but doesn’t have the benefit of being updated with real data — it’s usually an overly conservative number)
That’s pretty incredible. After a heavy maintenance breakdown, what percentage of the plane gets replaced? Or is everything already on a routine maintenance schedule so the intention is to visually identify unexpectedly failing parts?
Note that this test also does not factor in fatigue, maintenance wear and tear, etc. Planes fly for several decades and some will fly with quite a bit of imperfections (i.e. cracks) for a while before it's maintenance day
http://en.wikipedia.org/wiki/Aircraft_maintenance_checks
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