MD80 CREW RPTED COCKPIT AND CABIN FILLED WITH CONTAMINATED AIR.

Narrative

MD80 ACFT AT ANC AT THE GATE; PRIOR TO RUNNING ENG START CHKLIST; APU WAS PREVIOUSLY MEL'ED. A GATE START WITH EXTERNAL AIR WOULD BE REQUIRED. ACFT PNEUMATIC SYS WAS CONFIGURED FOR VENTILATION WHEN MAINT REQUESTED THAT WE MOTOR THE L ENG TO CONDUCT A HYD LEAK CHK. SINCE WE WERE ONLY MOTORING THE ENG; WE DID NOT RUN THE START CHKLIST. THE CAPT OPENED THE XFEEDS AND STARTED MOTORING THE L ENG WHEN THE CABIN FILLED WITH A FOUL ODOR. THE CAPT IMMEDIATELY STOPPED MOTORING; CLOSED THE VENTILATION SWITCH AND SHUT OFF THE R PACK SWITCH. INITIALLY; WE THOUGHT THE FUMES MAY BE ASSOCIATED WITH THE POTENTIAL HYD LEAK THAT MAINT WAS LOOKING AT ON THE L ENG. THE CAPT DECIDED TO DEPLANE THE PAX. WE THEN FOUND OUT THAT A COMPRESSED AIR BOTTLE WAS BEING USED AS THE GND AIR SOURCE. AS SOON AS THE FUMES ENTERED THE ACFT WE REALIZED THAT WE INAPPROPRIATELY CONTINUED TO VENTILATE WHILE MOTORING THE ENG. THIS ALLOWED CONTAMINATED AIR TO ENTER THE ACFT FROM THE COMPRESSED AIR BOTTLE. WE OBVIOUSLY MADE THE MISTAKE OF CONTINUING TO VENTILATE DURING THE ENG MOTORING. SOME CONTRIBUTING FACTORS INCLUDE AN MEL'ED APU; POTENTIAL HYD LEAK; NO KNOWLEDGE OF USE OF COMPRESSED AIR BOTTLE PRIOR TO MOTORING; NO SPECIFIC PROC FOR FLC TO DO ENG MOTORING FOR MAINT PURPOSES. SUPPLEMENTAL INFO FROM ACN 409557: I WAS UNAWARE THAT WE WERE GOING TO BE STARTING WITH A PRESSURIZED AIR BOTTLE THAT HAD A HISTORY OF BAD AIR QUALITY. WHEN THE 'MOTOR' SEQUENCE STARTED; A FOUL ODOR ENTERED THE CABIN AND COCKPIT. I DISCONTINUED THE 'MOTOR' AND SHUT OFF THE AIR CONDITIONING PACK. THIS STOPPED THE BAD AIR FLOW. THE PAX WERE DEPLANED IN ORDER TO VENTILATE THE CABIN. SUBSEQUENT INVESTIGATION DETERMINED THAT THE SOURCE WAS A CONTAMINATED START BOTTLE.