Narrative:

Departed msp airport and climbed to FL310. Given a vector direct onl from ZMP. At approximately XA54Z, a TCASII TA was received with aircraft Y at our 3 O'clock position, half off the screen. About 3-8 seconds later, a TCASII RA was given with the commands to 'climb, climb now.' the first officer began a climb while the captain pushed the power levers forward. As we were in a 1500-2000 FPM climb, I saw on the TCASII screen aircraft Y below us and also climbing. 500 ft below us, then 400 ft below as it went under our aircraft. This was confirmed by an observer who saw aircraft Y pass under our aircraft or just slightly down the right side. The first officer reported he saw 2 aircraft on the TCASII screen, 1 below and 1 above. We contacted ATC and reported a climb, then leveled off at FL317. ATC said they only had 1 aircraft on their equipment and it was at FL330 at our 3 O'clock position (aircraft Z). A 'clear of conflict' aural message was given about 3 seconds after aircraft Y went under us. What I believe happened is that aircraft Z at FL330 was heading outbound on the fsd 124 degree radial, and as we crossed the fsd 124 degree radial heading direct to onl, aircraft Z at FL330 was at our 3 O'clock position. A short time after is when we received our TCASII TA and RA. I think aircraft Y, below us, was trying to intercept aircraft Z at FL330 and did not see our aircraft (X). The only thing that does not make sense is that ATC said they did not have the aircraft below us on his screen. Without all the facts, it only seems that possibly a military aircraft could have been on maneuvers to intercept. Supplemental information from acn 397300: ATC was advised of our maneuver and subsequently relayed that 'the only traffic we know of' is a freighter at FL330. We returned to FL310 and resumed normal flight.

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Original NASA ASRS Text

Title: B727 FLC EXECUTES EVASIVE CLB FROM FL310 DUE TO TCASII RA FROM AN ACFT CLBING BELOW THEM. THIS PUTS THE B727 IN CONFLICT WITH A DC8 AT FL330. ATC ADVISES THEY ARE NOT CTLING ANY TFC BENEATH THE B727.

Narrative: DEPARTED MSP ARPT AND CLBED TO FL310. GIVEN A VECTOR DIRECT ONL FROM ZMP. AT APPROX XA54Z, A TCASII TA WAS RECEIVED WITH ACFT Y AT OUR 3 O'CLOCK POS, HALF OFF THE SCREEN. ABOUT 3-8 SECONDS LATER, A TCASII RA WAS GIVEN WITH THE COMMANDS TO 'CLB, CLB NOW.' THE FO BEGAN A CLB WHILE THE CAPT PUSHED THE PWR LEVERS FORWARD. AS WE WERE IN A 1500-2000 FPM CLB, I SAW ON THE TCASII SCREEN ACFT Y BELOW US AND ALSO CLBING. 500 FT BELOW US, THEN 400 FT BELOW AS IT WENT UNDER OUR ACFT. THIS WAS CONFIRMED BY AN OBSERVER WHO SAW ACFT Y PASS UNDER OUR ACFT OR JUST SLIGHTLY DOWN THE R SIDE. THE FO RPTED HE SAW 2 ACFT ON THE TCASII SCREEN, 1 BELOW AND 1 ABOVE. WE CONTACTED ATC AND RPTED A CLB, THEN LEVELED OFF AT FL317. ATC SAID THEY ONLY HAD 1 ACFT ON THEIR EQUIP AND IT WAS AT FL330 AT OUR 3 O'CLOCK POS (ACFT Z). A 'CLR OF CONFLICT' AURAL MESSAGE WAS GIVEN ABOUT 3 SECONDS AFTER ACFT Y WENT UNDER US. WHAT I BELIEVE HAPPENED IS THAT ACFT Z AT FL330 WAS HDG OUTBOUND ON THE FSD 124 DEG RADIAL, AND AS WE CROSSED THE FSD 124 DEG RADIAL HDG DIRECT TO ONL, ACFT Z AT FL330 WAS AT OUR 3 O'CLOCK POS. A SHORT TIME AFTER IS WHEN WE RECEIVED OUR TCASII TA AND RA. I THINK ACFT Y, BELOW US, WAS TRYING TO INTERCEPT ACFT Z AT FL330 AND DID NOT SEE OUR ACFT (X). THE ONLY THING THAT DOES NOT MAKE SENSE IS THAT ATC SAID THEY DID NOT HAVE THE ACFT BELOW US ON HIS SCREEN. WITHOUT ALL THE FACTS, IT ONLY SEEMS THAT POSSIBLY A MIL ACFT COULD HAVE BEEN ON MANEUVERS TO INTERCEPT. SUPPLEMENTAL INFO FROM ACN 397300: ATC WAS ADVISED OF OUR MANEUVER AND SUBSEQUENTLY RELAYED THAT 'THE ONLY TFC WE KNOW OF' IS A FREIGHTER AT FL330. WE RETURNED TO FL310 AND RESUMED NORMAL FLT.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.