COMMUTER SMT CAPT DOES AN EXTREME MANEUVER ON FERRY FLT.

Narrative

WHILE ACTING AS THE PNF (FO) OF A TWIN ENG TURBOPROP COMMUTER ACFT ON A FAR PART 135 FLT FROM MODESTO; CA; TO SAN JOSE; CA; I OBSERVED THE PF (CAPT) EXECUTE AN ABRUPT AND UNUSUAL ROLLING MANEUVER. THE STATED REASON FOR EXECUTING THIS MANEUVER WAS TO AVOID AN ACFT APCHING FROM THE 10 O'CLOCK POS. HE SAID THE ACFT WAS LEVEL AND COMING RIGHT AT US. I DID NOT SEE THIS ACFT UNTIL IT WAS POINTED OUT TO ME BY THE CAPT APPROX 6-8 SECONDS AFTER HE RETURNED THE ACFT TO WINGS LEVEL UPRIGHT FLT. AT THAT TIME THE ACFT WAS 2-3 MI AT OUR 3 O'CLOCK POS AND GOING AWAY. THE ACFT WAS A LOW WING TYPE OR TYPE; WHITE IN COLOR. THE ACFT WAS ALSO ABOUT 500 FT OR MORE BELOW US. IN MY JUDGEMENT THE MANEUVER THE CAPT USED WAS UNNECESSARY TO AVOID THE OTHER ACFT. THERE WERE NO REVENUE PAX ONBOARD THE ACFT BUT THERE WAS A JUMPSEATING PLT (ALSO A CAPT) WHO IS A COMPANY PLT HE WAS SEATED IN ROW 6 AND WAS NOT ON HEADSET INTERCOM. SINCE THE MANEUVER THE CAPT PERFORMED EXCEEDED 60 DEGS OF BANK; AND INCLUDED GOING THROUGH THE INVERTED POS. I REMINDED HIM THAT THIS WAS CONSIDERED AN AEROBATIC MANEUVER AND AS SUCH IS PROHIBITED. I ALSO ASKED THE CAPT IF HE WANTED TO DECLARE A NEAR MISS WITH STOCKTON APCH. HIS RESPONSE WAS NEGATIVE. THE FLT WAS CONTINUED TO SAN JOSE WITHOUT INCIDENT WHERE I CONDUCTED A THOROUGH POST-FLT. ALTHOUGH NO DAMAGE TO THE ACFT WAS OBSERVED I SUGGESTED THE CAPT GND THE ACFT AND ADVISE COMPANY OFFICIALS. THE CAPT DID NOT GND THE ACFT AND DID NOT RPT THE INCIDENT TO COMPANY OFFICIALS. AFTER CONFERRING WITH PLT UNION OFFICIALS; I; THE FO; RPTED THE INCIDENT TO THE CHIEF PLT. THE ACFT WAS SUBSEQUENTLY GNDED. BOTH THE CAPT AND I WERE IMMEDIATELY SUSPENDED. THE CAPT RESIGNED 48 HRS AFTER THE INCIDENT WHILE I AM WAITING THE OUTCOME OF A COMPANY INVESTIGATION. THE CAPT PERFORMED AN UNAUTHORIZED; UNANNOUNCED; PROHIBITED MANEUVER WITH THE ACFT AND DID NOT RPT THE INCIDENT TO COMPANY FLT MGMNT OFFICIALS. THE ACFT IS CURRENTLY GNDED BEING THOROUGHLY INSPECTED BY QUALIFIED MAINT PERSONNEL. THE CAPT IS NO LONGER WITH THE COMPANY. I FEEL I FULFILLED MY RESPONSIBILITIES AS A FO BY RPTING THIS INCIDENT TO COMPANY OFFICIALS.