Narrative:

The flight originated at int (winston-salem), nc. There were 4 people aboard. I have my multi-engine instrument instructor's certificate and roughly 1000 hours of flying experience. The other pilot had a private certificate. The airplane was a cessna 175. After departing int, the double a batteries which were purchased just before the flight were completely drained in our hand-held GPS unit. This was not a problem since it was used as a backup navigation unit. However, over the appalachian mountains the panel-mounted LORAN began to wander and became unreliable. This was not a problem for it was also a backup navigation unit. With the great distances between the vors, our CDI was showing centered, although I knew that as the radials expanded with distance, we could actually be several mi off course. So our only navigation was now 1 VOR head. This compounded with the challenge of our directional gyro which was the old style made navigating interesting. Our directional gyro began precessing more than 20 degrees in a 5 min period. It would also lock on a heading even after a turn was made. So I began relying solely on our magnetic compass for heading information. This equipment was checked prior to the flight and it was working and met IFR instrument and equipment standards. With this in mind we were approaching a cold front which produced level 3 and 4 thunderstorms. The line was visible at 10000 ft. It stretched from eastern kentucky to mussle shoals, al. Approaching knoxville after crossing the foothills of the 'smokies,' we descended from 10000 ft to 6000 ft to decrease our headwind. This was requested and approved by our controling agency. At 6000 ft we were in the haze and were approaching a wall of clouds. Knowing there were widely scattered thunderstorms around knoxville, I requested a switch of frequencys to the FSS. They informed me of several thunderstorms in my vicinity. I was unable to monitor the approach frequency while listening to the FSS with our radio package. I made the decision to amend our altitude 1000 ft lower considering our situation with equipment and the thunderstorms. The other pilot had changed our frequency for approach so I had to look through our approach plates to find our frequency. I reported back as quickly as I could and reported our altitude change. I made this change being fully aware of consequences. However, I felt it was necessary for the safety of our aircraft. We flew for several mins at 5000 ft. I was able to see and avoid thunderstorms at this altitude. After this time, approach called back and questioned our altitude. I told them I had descended from 6000 ft to 5000 ft and reported this to them. However, we were on the eastern sector frequency of knoxville. We were told to change frequencys and basically got the tower number to call at arrival. I had intended to fly to mcgee tyson in knoxville to wait out the thunderstorms, however, we proceeded to crossville, tn. Upon looking at the situation with 20/20 hindsight, I would have done the same thing. Going to crossville, I encountered a few thunderstorms. I would not have wanted to be on the gauges during this time in that aircraft. Our destination, rnc (warren county memorial), tn, got pounded. The controller in knoxville, I found out, is not a pilot. I used to fly freight in BE58 barns at night through thunderstorms. However, I had a professional pilot with me with good instrument and airborne radar. If that controller had ever been through one of these with me, she would have given me a little more latitude. The flight standards person I spoke with was a pilot and was more understanding. I have never made an altitude deviation before without permission. However, I think this situation warranted it.

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Original NASA ASRS Text

Title: ALTDEV. WHILE ON IFR CLRNC, RPTR PLT, BEING CONCERNED ABOUT LINE OF WX, DSNDED 1000 FT WITHOUT CLRNC. FLT STANDARDS REVIEWED THE INCIDENT WITH THE RPTR.

Narrative: THE FLT ORIGINATED AT INT (WINSTON-SALEM), NC. THERE WERE 4 PEOPLE ABOARD. I HAVE MY MULTI-ENG INST INSTRUCTOR'S CERTIFICATE AND ROUGHLY 1000 HRS OF FLYING EXPERIENCE. THE OTHER PLT HAD A PVT CERTIFICATE. THE AIRPLANE WAS A CESSNA 175. AFTER DEPARTING INT, THE DOUBLE A BATTERIES WHICH WERE PURCHASED JUST BEFORE THE FLT WERE COMPLETELY DRAINED IN OUR HAND-HELD GPS UNIT. THIS WAS NOT A PROB SINCE IT WAS USED AS A BACKUP NAV UNIT. HOWEVER, OVER THE APPALACHIAN MOUNTAINS THE PANEL-MOUNTED LORAN BEGAN TO WANDER AND BECAME UNRELIABLE. THIS WAS NOT A PROB FOR IT WAS ALSO A BACKUP NAV UNIT. WITH THE GREAT DISTANCES BTWN THE VORS, OUR CDI WAS SHOWING CTRED, ALTHOUGH I KNEW THAT AS THE RADIALS EXPANDED WITH DISTANCE, WE COULD ACTUALLY BE SEVERAL MI OFF COURSE. SO OUR ONLY NAV WAS NOW 1 VOR HEAD. THIS COMPOUNDED WITH THE CHALLENGE OF OUR DIRECTIONAL GYRO WHICH WAS THE OLD STYLE MADE NAVING INTERESTING. OUR DIRECTIONAL GYRO BEGAN PRECESSING MORE THAN 20 DEGS IN A 5 MIN PERIOD. IT WOULD ALSO LOCK ON A HDG EVEN AFTER A TURN WAS MADE. SO I BEGAN RELYING SOLELY ON OUR MAGNETIC COMPASS FOR HDG INFO. THIS EQUIP WAS CHKED PRIOR TO THE FLT AND IT WAS WORKING AND MET IFR INST AND EQUIP STANDARDS. WITH THIS IN MIND WE WERE APCHING A COLD FRONT WHICH PRODUCED LEVEL 3 AND 4 TSTMS. THE LINE WAS VISIBLE AT 10000 FT. IT STRETCHED FROM EASTERN KENTUCKY TO MUSSLE SHOALS, AL. APCHING KNOXVILLE AFTER XING THE FOOTHILLS OF THE 'SMOKIES,' WE DSNDED FROM 10000 FT TO 6000 FT TO DECREASE OUR HEADWIND. THIS WAS REQUESTED AND APPROVED BY OUR CTLING AGENCY. AT 6000 FT WE WERE IN THE HAZE AND WERE APCHING A WALL OF CLOUDS. KNOWING THERE WERE WIDELY SCATTERED TSTMS AROUND KNOXVILLE, I REQUESTED A SWITCH OF FREQS TO THE FSS. THEY INFORMED ME OF SEVERAL TSTMS IN MY VICINITY. I WAS UNABLE TO MONITOR THE APCH FREQ WHILE LISTENING TO THE FSS WITH OUR RADIO PACKAGE. I MADE THE DECISION TO AMEND OUR ALT 1000 FT LOWER CONSIDERING OUR SIT WITH EQUIP AND THE TSTMS. THE OTHER PLT HAD CHANGED OUR FREQ FOR APCH SO I HAD TO LOOK THROUGH OUR APCH PLATES TO FIND OUR FREQ. I RPTED BACK AS QUICKLY AS I COULD AND RPTED OUR ALT CHANGE. I MADE THIS CHANGE BEING FULLY AWARE OF CONSEQUENCES. HOWEVER, I FELT IT WAS NECESSARY FOR THE SAFETY OF OUR ACFT. WE FLEW FOR SEVERAL MINS AT 5000 FT. I WAS ABLE TO SEE AND AVOID TSTMS AT THIS ALT. AFTER THIS TIME, APCH CALLED BACK AND QUESTIONED OUR ALT. I TOLD THEM I HAD DSNDED FROM 6000 FT TO 5000 FT AND RPTED THIS TO THEM. HOWEVER, WE WERE ON THE EASTERN SECTOR FREQ OF KNOXVILLE. WE WERE TOLD TO CHANGE FREQS AND BASICALLY GOT THE TWR NUMBER TO CALL AT ARR. I HAD INTENDED TO FLY TO MCGEE TYSON IN KNOXVILLE TO WAIT OUT THE TSTMS, HOWEVER, WE PROCEEDED TO CROSSVILLE, TN. UPON LOOKING AT THE SIT WITH 20/20 HINDSIGHT, I WOULD HAVE DONE THE SAME THING. GOING TO CROSSVILLE, I ENCOUNTERED A FEW TSTMS. I WOULD NOT HAVE WANTED TO BE ON THE GAUGES DURING THIS TIME IN THAT ACFT. OUR DEST, RNC (WARREN COUNTY MEMORIAL), TN, GOT POUNDED. THE CTLR IN KNOXVILLE, I FOUND OUT, IS NOT A PLT. I USED TO FLY FREIGHT IN BE58 BARNS AT NIGHT THROUGH TSTMS. HOWEVER, I HAD A PROFESSIONAL PLT WITH ME WITH GOOD INST AND AIRBORNE RADAR. IF THAT CTLR HAD EVER BEEN THROUGH ONE OF THESE WITH ME, SHE WOULD HAVE GIVEN ME A LITTLE MORE LATITUDE. THE FLT STANDARDS PERSON I SPOKE WITH WAS A PLT AND WAS MORE UNDERSTANDING. I HAVE NEVER MADE AN ALTDEV BEFORE WITHOUT PERMISSION. HOWEVER, I THINK THIS SIT WARRANTED IT.

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.