Narrative:

This small transport is equipped with the factory arc radios that feature 3 frequency memories per communication transceiver. This allows 3 preset frequencys, a great convenience except for the following flaw. During the above mentioned sequence usually under IMC in controled airspace, #2 communication had the incredible facility to change channels by itself! For example, we would set in a bur frequency of 135.20 on #2 memory and 132.90 on #3 of communication #2. When handed off from the former frequency to the latter, my partner and I would watch the rig change back to the former frequency all by itself within a minute or so. My partner and I are/were both aerospace engineers, and his specialty is electrical engineering (mine aeronautical). We believe this fault to be caused by dirty and loose contact in the navcom plus aeroelasticity aggravated by moderate turbulence. We became suspicious when the monitored frequency became very quiet. I don't believe we violated any far's during this experience, but certainly this condition warrants attention. (Other factors: 2 xponders dead, 75% of flight was IMC, #1 communication behaved itself.)

Google
 

Original NASA ASRS Text

Title: GA SMT HAD PROBLEM WITH RADIO MEMORY.

Narrative: THIS SMT IS EQUIPPED WITH THE FACTORY ARC RADIOS THAT FEATURE 3 FREQ MEMORIES PER COM TRANSCEIVER. THIS ALLOWS 3 PRESET FREQS, A GREAT CONVENIENCE EXCEPT FOR THE FOLLOWING FLAW. DURING THE ABOVE MENTIONED SEQUENCE USUALLY UNDER IMC IN CTLED AIRSPACE, #2 COM HAD THE INCREDIBLE FAC TO CHANGE CHANNELS BY ITSELF! FOR EXAMPLE, WE WOULD SET IN A BUR FREQ OF 135.20 ON #2 MEMORY AND 132.90 ON #3 OF COM #2. WHEN HANDED OFF FROM THE FORMER FREQ TO THE LATTER, MY PARTNER AND I WOULD WATCH THE RIG CHANGE BACK TO THE FORMER FREQ ALL BY ITSELF WITHIN A MINUTE OR SO. MY PARTNER AND I ARE/WERE BOTH AEROSPACE ENGINEERS, AND HIS SPECIALTY IS ELECTRICAL ENGINEERING (MINE AERONAUTICAL). WE BELIEVE THIS FAULT TO BE CAUSED BY DIRTY AND LOOSE CONTACT IN THE NAVCOM PLUS AEROELASTICITY AGGRAVATED BY MODERATE TURB. WE BECAME SUSPICIOUS WHEN THE MONITORED FREQ BECAME VERY QUIET. I DON'T BELIEVE WE VIOLATED ANY FAR'S DURING THIS EXPERIENCE, BUT CERTAINLY THIS CONDITION WARRANTS ATTN. (OTHER FACTORS: 2 XPONDERS DEAD, 75% OF FLT WAS IMC, #1 COM BEHAVED ITSELF.)

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.