What should you do if you observe an unresolved data block discrepancy in an FMS?

• A. Ignore and continue
• B. Rely on manual navigation only
• C. Continue with the FMS as planned
• D. Verify with raw data before proceeding

Answer: (D)

When an unresolved data block discrepancy appears in an FMS, the important idea is to protect data integrity by checking against raw data before trusting the system to proceed. The FMS relies on data blocks that define the route, waypoints, performance limits, and sensor inputs. If these blocks don’t reconcile, you don’t know which source is correct, so you pause and verify.

Verifying with raw data means comparing the unprocessed information—the original navigation inputs, GPS or inertial data, and the authentic flight plan or database entries—to what the FMS is showing. If the raw data match the FMS readout, you can proceed with added confidence and continue to monitor for any further inconsistencies. If they don’t match, you should not continue with the current plan; revert to the last validated data or re-enter the route following proper procedures, and seek guidance as needed.