A PVT AC6T FLC DSNDED BELOW THEIR ASSIGNED ALT AND TRIGGERED A LOW ALT WARNING IN THE ROA TWR. THE ATCT LCL CTLR REACTED PROPERLY AND WARNED THE FLC; THROUGH APCH CTL; WHO RECOVERED.

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AFTER PASSING LYNCHBURG VOR WE WERE DSNDED TO 10000 FT AND GIVEN A VECTOR TOWARDS THE FINAL APCH COURSE FOR THE ILS RWY 33 INTO ROA. WE WERE TRAVELING AT APPROX 230 KTS. DURING THIS PROCESS THE DIRECTIONAL GYRO ON MY SIDE OF THE COCKPIT FAILED AND CAPT WAS TRYING TO DIAGNOSE THE PROB. AT ABOUT THIS TIME; WE WERE ADVISED TO DSND AND MAINTAIN 3800 FT; WHICH IS THE MVA FOR THAT SECTOR. OUR DSCNT WAS DELAYED SOMEWHAT SO WE WERE DSNDING FAIRLY RAPIDLY WHILE TRYING TO DIAGNOSE THE DIRECTIONAL GYRO PROB AND JOIN THE LOC. UNFORTUNATELY; I FAILED TO ARREST THE DSCNT AT 3800 FT AND WE WERE CALLED BY THE ROA TWR UPON REACHING APPROX 3300 FT. WE WERE ADVISED THAT THE TWR WAS RECEIVING A LOW ALT ALERT AND WE WERE ADVISED TO CLB IMMEDIATELY; WHICH WE DID. THE REMAINDER OF THE FLT PROCEEDED UNEVENTFULLY. I ATTRIBUTED THIS PROB TO BEING DISTR AND MY INATTENTIVENESS TO MAINTAINING AN ASSIGNED ALT. I AM CONSTANTLY PREACHING TO EVERYONE THAT RULES 1- 10 ARE 'FLY THE AIRPLANE FIRST' AND I SIMPLY FAILED TO FOLLOW MY OWN RULES. I SHOULD HAVE PAID MORE ATTN TO SIMPLY FLYING THE AIRPLANE AND ALLOWING CAPT TO WORK OUT THE PROBS. THIS IS SIMPLY A PLT ERROR SIT DUE TO DISTR. FORTUNATELY; ROA IS AN EXCELLENT ATC FACILITY. THEY QUICKLY CAUGHT OUR ALT AND GAVE US AN IMMEDIATE CLB. I SINCERELY BELIEVE I WOULD HAVE CAUGHT THE ALT WITHIN THE NEXT FEW SECONDS; ONCE MY SCAN WENT BACK TO THE ALTIMETER. UNFORTUNATELY; OUR RATE OF DSCNT WAS GREATER THAN 2500 FPM WHICH ALLOWED FOR VERY LITTLE DEV TIME.