FLC BEHAVIOR ILLNESS INCAPACITATION.

Narrative

WHILE DEADHEADING AS ON AIRLINES FLT ORD-SFO; FEB/MON/95; THE FO BECAME SICK TO HIS STOMACH APPROX 30 MINS PRIOR TO TOUCHDOWN. HE LEFT THE COCKPIT FOR ABOUT 10-15 MINS AND RETURNED TO THE R SEAT. HE STATED THAT HE HAD EXPERIENCED SEVERE NAUSEA AND DIARRHEA AND STILL DID NOT FEEL WELL. HE THOUGHT HE COULD MAKE IT TO LNDG. APPROX 25 MI FROM TOUCHDOWN; HE FELT BADLY ENOUGH TO LEAVE THE COCKPIT AGAIN. HE RETURNED APPROX 2 MINS PRIOR TO LNDG. THE CAPT ASKED IF I WOULD TAKE THE R SEAT (AN A320 ACFT) TO PROVIDE SCANNING AND CHKLIST ASSISTANCE. I GLADLY DID SO; EVEN THOUGH MY QUALIFICATION IS CAPT BOEING 737-300/500; LINE CHK AIRMAN. I REMAINED IN THE SEAT THROUGHOUT THE APCH AND LNDG EVEN THOUGH THE FO RETURNED TO THE COCKPIT APPROX 2 MINS PRIOR TO TOUCHDOWN. HE OCCUPIED THE JUMPSEAT FOR LNDG. THE COCKPIT DISCUSSION WAS CTRED ON THE FACT THAT 1) WHEN FO LEFT A SECOND TIME; CAPT DID NOT KNOW IF WE WOULD RETURN OR IF HE WOULD BE CAPABLE OF PERFORMING NORMAL DUTIES. 2) IF HE DID RETURN AND THEN BECAME SICK AGAIN; IT WAS FELT HE WOULD BE MORE OF A DISTR TO THE OP OF THE ACFT. THE APCH AND LNDG WERE UNEVENTFUL. I MONITORED COMS; LOWERED GEAR AND FLAPS; READ BEFORE LNDG CHKLIST AND MADE NORMAL 'CALLOUTS' AT 1000 FT AND 5000 FT. FO RETURNED TO HIS SEAT ONCE CLR OF RWY WITH BRAKES SET. CAPT'S DECISIONS WERE SAFE AND SOUND.