PIPER COMANCHE SERVICE MANUAL
04/01/09 XII - ELECTRONICS
3H9
12-10. EMI and RFI Check. (PIR-PPS65119, Rev A.)
A. Background
ElectroMagnetic Interference (EMI) and Radio Frequency Interference (RFI) are a growing concern
with the installation of advanced digital avionics. The following test procedure is recommended
before return-to-service each time any electrical / avionics work is performed.
B. Procedure
1. Position the aircraft at least 50 yards from buildings or any other large structures.
2. Ensure all aircraft closeout panels (excluding interior trim panels) and engine cowling are
installed on the aircraft being tested.
3. With the aircraft running and all avionics, exterior lights and equipment ON, verify that:
(a) There are no unusual needle or display fluctuations on any display or gauge;
(b) There is no objectionable background noise in the headsets.
(c) For troubleshooting purposes, if either is present, systematically turn OFF equipment until
the offending system is identified.
4. RFI interference is typically generated by energy from the aircraft communication radios
bouncing around the airframe. Verify that transmitting on the communication system does not
cause RFI interference by performing the following test on each communication system.
(a) On each of the following frequencies key the microphone for 3 to 5 seconds:
121.150 MHZ 127.000 MHZ
131.250 MHZ 121.175 MHZ
121.200 MHZ 131.275 MHZ
123.000 MHZ 131.300 MHZ
(b) Verify that this does not cause any unusual needle or display fluctuations on any display
or gauge.
12-11. Radio Shelf Capacities.
The aft radio shelves in the following installations are limited to the maximum weights shown in Table XII-I.
Shelf Installation Maximum Approved
Drawing Number Weight (Lbs.)
21770 35
22430 30
Table XII-I. Radio Shelf Capacities
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