VOR receiver against the radial designated on the sign.  Listed below are the steps to use at a VOR checkpoint:  the two VORs indicates that one of the receivers may be  out of tolerance.  V fl r t o OR equipment can also be checked for accuracy while in  ight by flying over a fix or landmark located on a published  adial and noting the indicated radial. Variances of more  han 6° from the published radial should be considered out  f tolerance and not be used for IFR navigation.  T n f i s he pilot must identify an NDB before using it for  avigation, and continuously monitor it while using it  or an instrument approach. The lack of an IDENT may  ndicate that the NDB is out of service, even though it may  till be transmitting (for instance for maintenance or test  purposes). If an incorrect IDENT is heard, then the NDB  should not be used.  RNAV accuracy checks may differ depending on the  different type of equipment and manufacturer. When  available, all written procedures should be followed.  If a VOT or VOR checkpoint is not available and the aircraft is  equipped with dual VORs, the equipment may be checked  against one another by tuning both sets to the VOR facility  at the same time and noting the indicated bearings to that  station. [Figure 2-52] A difference greater than 4° between  Dual VOR Check  RNAV Accuracy Check  NDB Accuracy Check  Airborne VOR Check  1. Tune the proper VOR frequency.  2. Identify the VOR frequency.  3. Set the published radial on the course deviation indicator (CDI).  4. Confirm that the TB is centered.  5. Check the needle sensitivity by changing the omnibearing select (OBS) 10° each way.  6. Set the reciprocal of the radial and check the TO FROM flag change.  7. The maximum permissible difference between aircraft equipment and the designated radial is 4°  and 0.5 NM of the posted distance.  Figure 2-52. Instrument panel with dual VORs.  2-31 