Narrative:

I was in cruise at 10000 MSL in a single engine. WX was clear with a visibility of 15 mi. My location was 30 NM northwest of gillette VOR (gcc) heading 283 toward sheridan VOR (shr) via V-536. An IFR flight plan had been filed for safety reasons and unfamiliarity with the area. I was talking to ZDV and requested lower to avoid high headwinds and to increase my ground speed. I was cleared to 8000 MSL and was requested to report reaching 8000 MSL because radar contact had been lost early in the flight due to mountainous terrain and insufficient radar coverage. Leaving 10000 MSL I began a 500 FPM descent to my approved altitude. Upon descending through 9300 MSL I began receiving navigational and communication interferences. Upon further descent a growing squeal blocked all communication frequencys getting louder as I descended. I made 2 attempts to contact ZDV without success before leveling off at 8000 MSL. After 2 more unsuccessful attempts, still not receiving navaids, and flying at night over unfamiliar mountainous terrain I made the decision to make a VFR climb to reestablish communication. In my opinion and judgement the interference was attributed to ground related obstacles or high terrain. To resolve the problem and ensure the safety of the flight I decided to climb (based on such good VFR conditions). Just as I had anticipated, the problem got better as I climbed. I began a best rate of climb and as I climbed through 9400 MSL the squealing died out and my radios appeared to be receiving normal. I was then able to contact ZDV on the current frequency and advise them of my situation. By this time I had leveled off at 10000 MSL. Since my route of flight took me away from high terrain I decided to continue rather than try and land at an unfamiliar airport in mountainous terrain at night. ZDV asked me to confirm a deviation from an ATC clearance and I advised them of my encounter. I was then instructed to telephone them at a given number upon reaching my destination. I was then handed off to ZLC and continued the flight uneventfully. Upon reaching my destination I telephoned denver ATC and talked to the acting supervisor. I explained the event and he advised me of the potential problems that exist when deviating from an assigned altitude if other traffic had been present.

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Original NASA ASRS Text

Title: PLT OF SMA IN MOUNTAINOUS TERRAIN RECEIVED CLRNC TO DSND TO 8000 MSL BUT LOST COM AND NAV FROM STATIC, CLBED VFR BACK TO 10000. REGAINED COM AND NAV CAPABILITY.

Narrative: I WAS IN CRUISE AT 10000 MSL IN A SINGLE ENG. WX WAS CLR WITH A VISIBILITY OF 15 MI. MY LOCATION WAS 30 NM NW OF GILLETTE VOR (GCC) HDG 283 TOWARD SHERIDAN VOR (SHR) VIA V-536. AN IFR FLT PLAN HAD BEEN FILED FOR SAFETY REASONS AND UNFAMILIARITY WITH THE AREA. I WAS TALKING TO ZDV AND REQUESTED LOWER TO AVOID HIGH HEADWINDS AND TO INCREASE MY GND SPD. I WAS CLRED TO 8000 MSL AND WAS REQUESTED TO RPT REACHING 8000 MSL BECAUSE RADAR CONTACT HAD BEEN LOST EARLY IN THE FLT DUE TO MOUNTAINOUS TERRAIN AND INSUFFICIENT RADAR COVERAGE. LEAVING 10000 MSL I BEGAN A 500 FPM DSCNT TO MY APPROVED ALT. UPON DSNDING THROUGH 9300 MSL I BEGAN RECEIVING NAVIGATIONAL AND COM INTERFERENCES. UPON FURTHER DSCNT A GROWING SQUEAL BLOCKED ALL COM FREQS GETTING LOUDER AS I DSNDED. I MADE 2 ATTEMPTS TO CONTACT ZDV WITHOUT SUCCESS BEFORE LEVELING OFF AT 8000 MSL. AFTER 2 MORE UNSUCCESSFUL ATTEMPTS, STILL NOT RECEIVING NAVAIDS, AND FLYING AT NIGHT OVER UNFAMILIAR MOUNTAINOUS TERRAIN I MADE THE DECISION TO MAKE A VFR CLB TO REESTABLISH COM. IN MY OPINION AND JUDGEMENT THE INTERFERENCE WAS ATTRIBUTED TO GND RELATED OBSTACLES OR HIGH TERRAIN. TO RESOLVE THE PROBLEM AND ENSURE THE SAFETY OF THE FLT I DECIDED TO CLB (BASED ON SUCH GOOD VFR CONDITIONS). JUST AS I HAD ANTICIPATED, THE PROBLEM GOT BETTER AS I CLBED. I BEGAN A BEST RATE OF CLB AND AS I CLBED THROUGH 9400 MSL THE SQUEALING DIED OUT AND MY RADIOS APPEARED TO BE RECEIVING NORMAL. I WAS THEN ABLE TO CONTACT ZDV ON THE CURRENT FREQ AND ADVISE THEM OF MY SITUATION. BY THIS TIME I HAD LEVELED OFF AT 10000 MSL. SINCE MY RTE OF FLT TOOK ME AWAY FROM HIGH TERRAIN I DECIDED TO CONTINUE RATHER THAN TRY AND LAND AT AN UNFAMILIAR ARPT IN MOUNTAINOUS TERRAIN AT NIGHT. ZDV ASKED ME TO CONFIRM A DEV FROM AN ATC CLRNC AND I ADVISED THEM OF MY ENCOUNTER. I WAS THEN INSTRUCTED TO TELEPHONE THEM AT A GIVEN NUMBER UPON REACHING MY DEST. I WAS THEN HANDED OFF TO ZLC AND CONTINUED THE FLT UNEVENTFULLY. UPON REACHING MY DEST I TELEPHONED DENVER ATC AND TALKED TO THE ACTING SUPVR. I EXPLAINED THE EVENT AND HE ADVISED ME OF THE POTENTIAL PROBLEMS THAT EXIST WHEN DEVIATING FROM AN ASSIGNED ALT IF OTHER TFC HAD BEEN PRESENT.

Data retrieved from NASA's ASRS site as of July 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.