Navaid reliability.

[Blenk]

not unreliable at all

As PB said, the instrument is more technical in nature than anything else and is there to make sure that everything is audit-proof in the future. Nothing to do with the reliability of the nav aids at all really.

In terms of maintenance and flight checking, ADF ILSs are checked at the same periodicity and tolerances as the civil ones. Looking at the table in the instrument ADF NDBs have to be flight checked more often than the civil ones.