Cross-canning is an aircraft maintenance technique which involves removing parts from one aircraft and placing them in another. As a short-term stopgap, cross-canning can be extremely effective, as it keeps planes in the air rather than grounding them while they wait for parts. However, it is not entirely without controversy, as there may be times when a cross-canned part fails, tempting people to blame the failure on the cross-canning.
Typically, when parts are cross-canned, they are taken from older planes or planes with a maintenance due and placed into newer planes, or planes which have just been repaired. The idea is that it is better to keep the newer, more recently maintained aircraft flying, rather than flying older planes which might need work soon. In this sense, cross-canning can help to keep a fleet of aircraft healthy and flying, by using parts in highly efficient ways.
In some cases, a part may be cross-canned several times, while maintenance crews wait for replacement parts to arrive. When parts are cross-canned, it is usually noted in the maintenance log for the plane, so that maintenance crews are aware that some of the parts in a plane may have been serviced more recently than others. The serial number and model of the part are also noted down, as is the case with all parts installed in aircraft, so that if there is a recall of a series of part, it is easy to identify which planes need service.
Sometimes, a fleet of aircraft has a restricted maintenance budget, or replacement parts are difficult to obtain. Cross-canning can be extremely helpful in these instances, by maximizing the efficiency of the fleet, keeping working parts in active use rather than allowing them to languish on the tarmac. As a result, this practice is common across a range of aviation industries, from militaries to shipping companies, and people who maintain planes are taught when and how to cross-can parts.
There are some instances in which cross-canning can be problematic. Sometimes unethical maintenance crews install parts which should be serviced, rather than being re-used, in the interest of getting planes up in the air quickly. Cross-canning can also sometimes be used to cover up problems, and there have been documented instances of mis-labeled cross-canned parts which have caused issues.