User Guide
Series III Avionics
Pilot's Guide
Page 10
VNS-41A VHF Navigation System
General Description
The Chelton VNS-41A VHF Navigation System is a lightweight 200-channel microprocessor-based VHF
navigation receiving system that combines VOR/LOC, glideslope, and marker beacon reception in the
same unit. The VNS-41A is compatible with most HSIs, CDIs, and conventional marker beacon displays.
The ARINC 429 serial data bus interface is compatible with EFIS displays, radio management systems
(RMU), and flight management systems (FMS).
The VNS-41A system consists of a remote mounted VN-411B VHF Navigation Receiver and a panel
mounted CD-412B or CD-413B Control Display Unit.
In addition to processing signals for external use (Marker Beacon Lamps and audio, AFCS, CDI, HSI,
EFIS, etc.), the VNS-41A can digitally display BEARING TO or RADIAL FROM any selected VOR station
on the CD-412B/CD-413B with the function selector panel control.
When an ILS frequency is selected by the VNS-41A, the letters LOC appear below the frequency on the
display when RAD or BRG are selected.
Digital circuit design of the VNS-41A incorporates microprocessor technology to achieve performance,
reliability, accuracy, and features not possible in previous systems. These include advanced filtering
techniques, full-time self-diagnostics, non-volatile frequency memory and continuous calibration.
Special filtering circuits virtually eliminate noise, including rotor modulation noise in helicopter
installations. Self-testing begins when the system is turned on, and continues until turnoff. Faults
detected result in a FAIL annunciation.
Non-volatile memory means that the last frequency selected is in system memory if the system is turned
off, if power is interrupted, or even if the system is removed from the aircraft!
The VNS-41A is TSO'd. It is fully compatible with other equipment using ARINC Characteristic 429
Digital Information Transfer. Frequencies may be controlled remotely by a Navigation Management
System (NMS) and interfaced with an Area Navigation (RNAV) System.