SOME VHF HEADS ARE ABLE TO CHANGE FREQS BY THEMSELVES.

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HOLDING AT DIFFERENT FIXES ALONG RTE ATL-EWR. LEFT 1 FIX AND HAD A FREQ CHANGE. CHKED IN ON NEW FREQ; THEN LOST CONTACT. 10 MINS LATER GOT BACK IN RADIO CONTACT. AFTER CHKING; I BELIEVE THE RADIO CHANGED FREQ BY ITSELF. THIS TYPE OF HEAD CAN SWITCH SETTING WITHOUT TOUCHING THE DIAL. IT HAS AN LED DISPLAY AND LESS THAN POS DETENT ON THE DIAL FOR FREQS. YOU CAN BE ON THE FREQ AND HAVE THE PROPER LED DISPLAY BUT NOT IN THE DETENT. IT CAN THEN SLIDE INTO THE DETENT OF THE WRONG FREQ. IT SHOULD HAVE A BETTER DESIGN SO THIS IS NOT POSSIBLE. SOME OF OUR NAV RADIO'S ARE THE SAME WAY IE; ILS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR FLIES THE B-767 FOR A MAJOR UNITED STATES ACR. HIS ACFT HAS 2 DIFFERENT TYPE RADIO HEADS. ONE OF THEM HAS A VERY DEFINITE DETENT. THE OTHER IS RATHER 'SOFT' GOING INTO ITS DETENT. THE RPTR HAS HAD THIS HAPPEN AGAIN SINCE HIS RPT; AND HE HAS TALKED TO OTHER PLTS THAT HAVE HAD THE SAME PROB. THE HEAD WITH THE 'SOFT DETENT IS THE ONE THAT GIVES PROBS. THE RPTR HAS GONE BACK TO THE OLD PROC OF WRITING DOWN THE FREQ TO ASSURE THAT HE HAS A RECORD.