Western miltary a/c maintenance requires routine weighing of the plane yearly or during major inspections.Whereas Russian miltary a/c maintenance does not insist on this kind of weighing,so much so that weighing is not part of any maintenance schedule after initial manufacture ! Can some one give any plausible reason for this anomaly ?
Western doctrine is to keep all aircraft of one type in identical conditions. Once you change one thing, you do it for all aircraft of this type at the same time (or create a subtype). Routine weighing makes sure that the individual aircraft conforms to the type certificate.
Russian doctrine sees every airplane as an individual, and if something is changed, it needs to be documented, but not necessarily done on all other planes of that type. To every airplane belongs a (mostly) metal box with all documents, and they should tell you exactly what has been modified since it was produced. Weighing is now part of maintenance, but needs not be done if nothing has been modified.