ON REACHING CRUISING ALT IN 'DRVSM' AIRSPACE; FA20 PORPOISES DURING ALT CAPTURE MODE ON AUTOPLT. RESULTS IN LOSS OF SEPARATION AND TCASII TA AND RA ALERTS ON OPPOSITE DIRECTION ACFT.

Narrative

A MGMNT PLT/CHK AIRMAN/IOE INSTRUCTOR WAS THE ASSIGNED CAPT AND CHOSE TO FLY FROM THE R SEAT. APPROX 20 MINS AFTER TKOF FROM FYV; THE ACFT WAS WITHIN 2000 FT OF THE PLANNED AND ASSIGNED CRUISE ATTITUDE. THE CAPT ASKED IF THE ALT PRE-SELECT FUNCTION WORKED ON THE AUTOPLT. I RESPONDED YES; BUT NOT AT SLOW INDICATED AIRSPDS AS THE ACFT WOULD PORPOISE DURING LEVELOFF. WHEN 500 FT BELOW THE TARGET ALT; I MADE VISUAL CONTACT WITH AN APCHING ACFT THAT HAD BEEN DISPLAYED ON THE TCAD FOR SEVERAL MI. I CALLED THE TFC OUT TO THE CAPT AND MENTIONED THAT TCAD DATA INDICATED THAT THIS ACFT WOULD BE ONLY +1000 FT ABOVE US AT OUR ASSIGNED CRUISING ALT. I AGAIN CAUTIONED THE CAPT THAT OUR ACFT COLD NOT SMOOTHLY LEVEL OFF WHEN FLYING AT THIS ALT AND AT A SLOW INDICATED AIRSPD. WHEN THE ALT PRESELECT CAPTURED; THE SPD WAS BTWN 210-215 KIAS. INITIALLY; THE ACFT'S NOSE LOWERED FOR THE LEVELOFF; IMMEDIATELY BEGAN TO SINK AND THEN BEGAN TO PORPOISE IN AN ATTEMPT TO HOLD THE TARGET ALT. AFTER 4 OR 5 PORPOISE CYCLES; THE CAPT BEGAN HAND FLYING THE ACFT. THE PITCH ATTITUDE WAS CHANGING BTWN -1 DEG AND +8 DEGS. I ASKED THE CAPT IF HE WANTED ME TO TAKE THE ACFT CTLS (THE APCHING ACFT WAS NOW LESS THAN 1 MI AND ITS PATH WOULD HAVE IT PASSING OFF OF OUR R WING BY MORE THAN 1/4 MI; BUT LESS THAN 3/4 MI). THE CAPT DECLINED. WE CONTINUED TO OSCILLATE BTWN -200 FT AND +300 FT FROM OUR CRUISE ALT FOR APPROX 1 1/2 MINS. WITHIN 10 SECONDS OF THE OTHER ACFT PASSING US; THAT CREW ASKED ATC; 'WAS THE FALCON WE JUST PASSED RVSM'ED...?' ATC PAUSED; AND THEN SAID AFFIRMATIVE. THAT CREW STATED THAT 'WE RECEIVED BOTH A TA AND AN RA FROM THAT FALCON.'