1AD/RAD/36 Amdt 1 - Collins ADF Type ADF-650 - Operation From 27.5 Volt Supply

COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 107 CIVIL AVIATION SAFETY AUTHORITY

SCHEDULE OF AIRWORTHINESS DIRECTIVES

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Radio Communication and Navigation Equipment

AD/RAD/36

Amdt 1

Collins ADF Type ADF-650 - Operation From 27.5 Volt Supply

11/82

Applicability: Collins RCR-650 receivers installed in aircraft having 27.5 volt electrical systems.

Requirement: The voltage-dropping resistor originally specified for operation of the RCR-650 receiver from a 27.5 volt supply was an 11 ohm, 15 watt type. This has inadequate power rating, resulting in its overheating.

To overcome this problem either :

Modify the equipment in accordance with Collins RCR-650 receiver Service Information Letter 1-77 and Collins RCR-650 receiver SB No. 3; or

2. Install a dropping resistor and mounting hardware capable of adequate power dissipation; or

3. Modify the system wiring to provide operating power from a 28V/14V converter of an appropriate rating.

Where a resistor is used it should be mounted in a remote location that does not transfer heat to the avionics equipment.

Compliance: Within 100 hours after 30 November, 1982.

Background: The RCR-650 ADF receiver is designed for operation from a 14 volt supply but is sometimes used in aircraft with 27.5 volt electrical systems. The voltage dropping resistors originally specified by the manufacturer are inadequately rated and overheat or burn out.

The problem can be overcome by fitting higher power rated resistors or modifying the electrical wiring to the receiver and using a DC-DC converter.