C182 PLTS HAVE AN ALTDEV DURING APCH TO PDK.

Narrative

WE EXPERIENCED A TOTAL DIRECTIONAL GYRO FAILURE WHILE IN IMC ON THE MISSED APCH PROC OFF WINDER ARPT (WDR) NEAR ATHENS; GA. WE RPTED THIS TO ATL APCH CTL. WE WERE IN IMC PROCEEDING BACK TO PDK ARPT; AND WERE GIVEN VECTORS FOR THE ILS RWY 21 APCH AT PDK WITH AN ASSIGNED ALT OF 4000 FT. AS WE WERE TURNING TO INTERCEPT THE LOC; WE NOTICED THAT WE HAD DSNDED TO APPROX 3200 FT. WE DO NOT KNOW FOR SURE HOW LONG WE WERE BELOW 4000 FT; BUT WE WOULD ESTIMATE THAT IT WAS FOR 1 MIN OR SO. AS SOON AS WE NOTICED THE DEV; WE BEGAN A CLB BACK TO 4000 FT. WE CONTACTED THE CTLR TO CONFIRM THAT WE HAD BEEN ASSIGNED 4000 FT AND NOT 3000 FT. THE CTLR SAID WE WERE ASSIGNED 4000 FT; BUT THAT 3400 FT WAS OUR NEW ASSIGNED ALT. THE REST OF THE FLT WAS NORMAL. A CONTRIBUTING FACTOR TO THE ALT LOSS WAS THAT WE WERE LOOKING AT THE WET COMPASS AND THE CDI DURING THE TURN TO INTERCEPT THE ILS. SINCE THE WET COMPASS TAKES TIME TO SETTLE; WE WERE FOCUSING ON THIS TO ASSURE OURSELVES THAT WE HAD TURNED TO THE PROPER HDG FOR THE APCH. ANOTHER CONTRIBUTING FACTOR IS THAT WE WERE IN IMC AT THE TIME WITHOUT REF TO ANY EXTERNAL REFS WHICH WOULD HAVE LET US KNOW THAT WE HAD LOST ALT. ANOTHER CONTRIBUTING FACTOR IS THAT THE PF HAD ONLY APPROX 4 HRS OF FLYING IN THE PAST 90 DAYS.