How long can a turbine-engined aircraft be left fuelled?

Question

Presumably, if one is going to be keeping an aircraft on the ground for a long time without running the engines or the APU, the aircraft's fuel tanks will need to be drained and purged...

• ...to prevent potential damage upon return to service due to degradation of the fuel over time...¹
• ...to forestall a potential explosion hazard from fuel vapor in the fuel system and coming out of the tank vents on hot days...
• ...and to protect the local environment, both from the aforementioned venting of fuel vapors and from liquid fuel potentially draining out onto the ground should a leak develop while in storage.

However, on the flip side, as @Bianfable's comment points out, defuelling an aircraft has a significant disadvantage of its own; empty fuel tanks are vulnerable to condensation, which can cause accelerated corrosion and (in colder climates) ice accumulation.

Piston-engined avgas-burners generally have to be defuelled if they're going to be sitting inactive for six months or more; how long, generally, can a turbine-engined aircraft be left on the ground with jet fuel in its tanks?

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¹: Removing the fuel at the end of the storage period would also work for this purpose, but that would a) waste a planeload of fuel and b) involve draining the fuel system of various tarry fuel-degradation byproducts rather than just ordinary fuel.

Answer 1

Turbine-engined aircraft use jet fuel, which is more similar to diesel than gasoline in handling.

It does not produce an explosion hazard, unless heated up in an enclosed space with a lot of headroom. Environmental damage is a concern, but generally a minor one. The fuel is not volatile and remains usable, but might partially degrade from oxidation.

A DTIC study has indicated that for the typical conservative 2-year storage period, jet fuel is stable even without additives. However, an antioxidant is recommended to prevent degradation for 3 years and beyond.

For longer storage terms, some degradation is observed, but generally a 10-year period can be considered safe for properly treated fuel. This is temperature-dependent, in hot climates, the safe storage period is reduced.

Given that corrosion can occur in empty tanks, the more practical solution is to add antioxidant for prolonged fuel stability, rather than defuel an aircraft.

For very long-term storage with a return to service later, the preservation procedure includes a lot of steps. In most cases, fuel is expected to stay in the aircraft. If draining the fuel, usually when return to service is uncertain, the aircraft's parts are treated with preservatives to allow for later restoration or cannibalization.