The nature of structural refurbishment of an ageing aircraft is such that unknown conditions may be revealed in the process of disassembly. This may result in more extensive refurbishment work becoming necessary and this poses a challenge to the production schedule.
As a further consequence of the disassembly required during structural refurbishment, additional parts may be required to replace those that are found to be unserviceable. Obtaining these parts in time to maintain the production schedule is a major risk confronting the project.