Allow "UNK" or "Unknown" entry for aircraft maintenance times
For those aircraft with missing or incomplete maintenance records, the total time and/or time since major overhaul cannot always be accurately determined for the aircraft or its components. It would be helpful to either allow for "Unknown" to be accepted as an entry as the time, or list it as an optional checkbox. Another alternative would be to offer an "Estimate" or "Approximate" option. Any of these will help in the maintenance times being reported more truthfully.