THE RPTR ALLOWED A PAX TO HANDLE THE FLT CTLS AND THE PAX LOST CTL OF PITCH AND BANK. THE ALTDEV WAS 700 FT.

Narrative

A PAX ON BUSINESS FLT PRESENTED HIMSELF AS AN ENGINEER FOR THE CORPORATION; ADVISED ME THAT HE HAD 5800 HRS FLT TIME AND PUT HIMSELF THROUGH COLLEGE BY CROPDUSTING; PRESENTED HIS CURRENT MEDICAL AND TOLD ME HE WAS CURRENT IFR. THEN ASKED IF HE COULD SIT UP FRONT. SURVEYING THE DATA AVAILABLE I APPROVED HIS REQUEST. WHILE TAXIING OUT; HE ASKED IF HE COULD GET SOME STICK TIME AND I TOLD HIM AS SOON AS WE CLRED THE IMC CONDITIONS AND WERE ESTABLISHED ENRTE I'D BE GLAD TO LET HIM FLY. ARRIVING AT 6000 FT AND INTERCEPTING V97 I TOLD HIM THE ACFT WAS TRIMMED FOR NEUTRAL TRIM AND HE HAD THE AIRPLANE. HE ACKNOWLEDGED CTL OF THE ACFT AND FOCUSED ON THE COPLT'S FLT INSTS. I REACHED DOWN TO CHANGE TO OUTBOARD FUEL TANKS; UPON COMPLETING THE FUEL PRESSURE AND TANK GAUGE CHK; I LOOKED AT MY ADI TO SEE HOW HE WAS DOING (THIS TOOK APPROX 30 SECONDS). MY IMMEDIATE THOUGHT WAS THAT MY ADI HAD TUMBLED; HOWEVER; AFTER A VERY RAPID XCHK OF THE COPLT'S INSTS I DISCOVERED THE AIRPLANE WAS NOSE LOW ACCELERATING RAPIDLY AND ROLLING SLOWLY TO THE R; ENTERING A SPIRAL. I IMMEDIATELY RELIEVED THE COPLT OF THE CTLS; ASSUMED A CLB BACK TO ALT AND LEVELED OFF. TPA NEVER CALLED AN ALT ALERT OR DEV AND I THEN ASKED FOR A MODE C CHK. THE ALT DEV TOOK ALMOST 1 1/2 MINS. ALT LOST WAS APPROX 700 FT.