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There are separate procedures for "parking" (short-term storage) and "storage" (long-term storage), as Airbus calls them; this question is about the latter. Assume that close to optimal storage conditions (as specified in the procedures) are used, as would be typical of a commercial airline putting a passenger jet into long-term storage.

According to this article it takes about 200 hours to put a typical passenger jet into long-term storage. Though maintenance is still required, presumably the maintenance costs during storage will be considerably less than if the aircraft were being flown every day.

According to this comment on YouTube, taking an aircraft out of long-term storage is very expensive; considerably more than the biennial C-check that takes up to 6000 man-hours:

It is a lot more, in fact the longer the storage time the more expensive it gets. Eventually it becomes cheaper to buy a new plane of the same type from the manufacturer, though that point takes fifteen or twenty years to reach.

Is this true, assuming that the jet has been stored (and maintained in storage) per the manufacturer's recommended procedures? If so, why is it so expensive? When taking an aircraft out of long-term storage and restoring it to flight condition, what additional procedures are needed that would not be part of a C-check had the aircraft stayed in service? Are there any C-check procedures that could be delayed (because the aircraft was not in use) to offset this cost?

If the return-to-service versus C-check cost ratio varies dramatically amongst passenger jets, I'd like to hear about examples with the highest ratio you know of.

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    $\begingroup$ What authority does the "comment on YouTube" have? $\endgroup$
    – Ralph J
    Oct 4, 2022 at 2:12
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    $\begingroup$ @RalphJ I am not aware of what level of knowledge that commenter has. He sounds very sure of himself, which initially inclined me to believe him, but on further thought I'm starting to have my doubts. Thus my question here. $\endgroup$
    – cjs
    Oct 4, 2022 at 2:20
  • $\begingroup$ This question can only be answered with opinions because it depends on the aircraft, it's age, how long as it been in storage, etc. There isn't one answer for this. Voting to close. $\endgroup$ Oct 6, 2022 at 15:10
  • $\begingroup$ @JuanJimenez Ok, it no longer depends on how long it's been in storage and I'm now asking not about the cost per se, but the ratio between the return-to-service cost and the C-check cost, which also will vary in the same way with the aircraft age/type/etc. (This was my original intent in the first place.) If you can think of other ways to improve this question to make it more easily answerable, please suggest them. $\endgroup$
    – cjs
    Oct 7, 2022 at 9:15
  • $\begingroup$ Suspect not an answer for question as written but this book examiner.com.au/story/3127169/… includes a multi month struggle to get a small commuter turbo prop airworthy again. It seems in that case due storage conditions they had to strip and replace every rubber seal and hose in the entire airframe despite nominally dry conditions, complicated by the remote location from both spares and engineering support. $\endgroup$ Oct 7, 2022 at 11:09

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As a partial answer to 'why is it so expensive' part, based on reading including this and personal experience bringing ground based equipment out of storage.

If everything has been maintained IAW the manufacturers documented processes while parked then returning it to flight things could be straightforward, but parked aircraft are normally not flying because the money ran out and then things get complicated:

  • Maintenance was not in fact in date when parked
  • It was stored because something expensive broke
  • While stored parts were removed/sold/stolen
  • Preparation for storage was done by someone who knew they might not get paid (see stolen/swapped parts above)
  • May have been parked in the lowest cost location (road salt, paint overspray, forklifts or trucks bumping it, or just plausible risk of these)
  • The aircraft was stored because it was worn out/unreliable/cursed.

These mean that a number of hidden risks may exist even if a look at the calendar says it would be fine to service and fly. Even if stored correctly:

  • A parked aircraft will not get freeze dried at high altitude regularly, and tanks/voids will pull moisture in during day/night cycles resulting in corrosion, mold and even live plants. Some fluids can also decay or separate left static for too long.
  • Most connectors are weather resistant when fitted, but removed equipment can leave plugs to corrode if not sealed correctly.
  • Dirt and contamination in fluid and air systems can build up, rather than being regularly flushed into filters during use. They then sit until at some future point they break loose as a solid chunk blocking part of a system. Blockage may blow back out during shutdown so replacing the blocked part may not get rid of it.
  • Rubber weather seals decay for a combination of leaks and glue like residue sticking things in place.
  • In hydraulic systems seals and hoses often change if left to dry out, potentially producing cascades of leaks bringing system back to operation. Leaks may cause further damage to surrounding systems.
  • Bearings and valves left to sit under load can end up stuck due combination of settling and oil/grease displacement for erratic operation.

This means bringing an aircraft back into service can quickly escalate into opening many normally sealed areas of the aircraft to check condition and repair/replace hardware and structure. This work will cause damage to corrosion protection that then needs to be repaired and the debris from that needs to be flushed out. If poorly planned this may need to happen several times.

If the repairs become extensive then original serviceable but imperfect fixtures/covers etc may need replacing/repair because they are now obvious to those assessing the work.

All of this means that costs of a return to service can be arbitrarily high, as many vintage car owners can attest.

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  • $\begingroup$ Thanks. This is helpful, though I was envisioning a situation where a passenger jet was properly stored and maintained during storage per the manufacturer's recommendations, as I'd imagine any major airline or leasing company would do with an aircraft that they're intending to bring back into service rather than dispose of. $\endgroup$
    – cjs
    Oct 15, 2022 at 13:31

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