Definition
A mathematical check applied to a block of digital data to detect whether it has been changed, corrupted, or tampered with. A short value is calculated from the original data and stored or transmitted with it; the receiving system recalculates the value and compares the two. If they match, the data is treated as intact. If they differ, the data is rejected as corrupted.
Plain English
A built-in test that checks whether a file or data block is still exactly as it was made, or whether something in it has been changed or damaged.
Context Anchor
Seen in navigation database and instrument procedure database discussions, especially when data is being packaged, transferred, loaded, or checked by a database provider or avionics system.
Derivation
Cyclic refers to the repeating mathematical operation used in the calculation. Redundancy means the check value is extra information added alongside the data, not part of it. Together: an extra value, produced by a repeating calculation, used to check the data.
Why Pilots Care
It guarantees that critical navigation information has not been corrupted before the data reaches the aircraft's flight management system.
Analogy
It is like writing the total number of items on the outside of a sealed box. When the box arrives, you count again. If the number does not match, you know something may have changed inside.
Intuition Check
A cyclic redundancy check is not a person carefully rereading the data. It is an automatic computer check that detects whether stored or transferred data no longer matches its original calculated value.
Example Sentence 1
Before the navigation database update was accepted by the FMS, the unit ran a cyclic redundancy check to confirm the file had not been corrupted during the transfer.
Example Sentence 2
If the cyclic redundancy check fails during loading, the flight management computer rejects the entire navigation database.