Narrative:

Cruising at FL260; traffic was called out to us at 12-1 O'clock position and 10 mi. We called 'looking' and looked but didn't see traffic. We looked down to adjust our mfd range to locate traffic on TCAS (it showed the other aircraft at 1 O'clock position and +10; don't remember exact range) while ATC called our position to the other aircraft. After a few seconds the other aircraft reported he had us in sight. A few seconds after that; we both looked up to see an aircraft (falcon 20; white with red or maroon markings) at our 2 O'clock position; co-altitude; nose-on; very close (less than 1 mi). At that same instant the other aircraft made a very aggressive maneuver in both roll and pitch and disappeared behind and above our aircraft; missing us by maybe 500 ft. I then informed ATC we had an near midair collision and after a few radio calls with us and the other aircraft it was made apparent that something had indeed happened; although their equipment and our equipment showed everyone was where they should be. ATC gave me a number to call and then handed us off to the next controller. The rest of the flight was uneventful. I called ATC later and they were stumped as to how this could have happened; and informed me that the other pilot told them that they would have their equipment checked. The time between the initial traffic call and the near midair collision felt like 20-30 seconds. We received no TCAS traffic alert or RA command. Our altimeters were all set to 29.92 and were within 50 ft of each other. I also checked them on the ground and they all looked good. I suspect the other aircraft's equipment was faulty. We simply had no time to react; and we both came away with the realization that we should never totally trust the equipment and vowed to be more vigilant in our traffic searches from now on. We are both extremely thankful this did not take place under IMC.

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Original NASA ASRS Text

Title: CL60 AND FA20 EXPERIENCE CLOSE ENCOUNTER AT FL260.

Narrative: CRUISING AT FL260; TFC WAS CALLED OUT TO US AT 12-1 O'CLOCK POS AND 10 MI. WE CALLED 'LOOKING' AND LOOKED BUT DIDN'T SEE TFC. WE LOOKED DOWN TO ADJUST OUR MFD RANGE TO LOCATE TFC ON TCAS (IT SHOWED THE OTHER ACFT AT 1 O'CLOCK POS AND +10; DON'T REMEMBER EXACT RANGE) WHILE ATC CALLED OUR POS TO THE OTHER ACFT. AFTER A FEW SECONDS THE OTHER ACFT RPTED HE HAD US IN SIGHT. A FEW SECONDS AFTER THAT; WE BOTH LOOKED UP TO SEE AN ACFT (FALCON 20; WHITE WITH RED OR MAROON MARKINGS) AT OUR 2 O'CLOCK POS; CO-ALT; NOSE-ON; VERY CLOSE (LESS THAN 1 MI). AT THAT SAME INSTANT THE OTHER ACFT MADE A VERY AGGRESSIVE MANEUVER IN BOTH ROLL AND PITCH AND DISAPPEARED BEHIND AND ABOVE OUR ACFT; MISSING US BY MAYBE 500 FT. I THEN INFORMED ATC WE HAD AN NMAC AND AFTER A FEW RADIO CALLS WITH US AND THE OTHER ACFT IT WAS MADE APPARENT THAT SOMETHING HAD INDEED HAPPENED; ALTHOUGH THEIR EQUIP AND OUR EQUIP SHOWED EVERYONE WAS WHERE THEY SHOULD BE. ATC GAVE ME A NUMBER TO CALL AND THEN HANDED US OFF TO THE NEXT CTLR. THE REST OF THE FLT WAS UNEVENTFUL. I CALLED ATC LATER AND THEY WERE STUMPED AS TO HOW THIS COULD HAVE HAPPENED; AND INFORMED ME THAT THE OTHER PLT TOLD THEM THAT THEY WOULD HAVE THEIR EQUIP CHKED. THE TIME BTWN THE INITIAL TFC CALL AND THE NMAC FELT LIKE 20-30 SECONDS. WE RECEIVED NO TCAS TFC ALERT OR RA COMMAND. OUR ALTIMETERS WERE ALL SET TO 29.92 AND WERE WITHIN 50 FT OF EACH OTHER. I ALSO CHKED THEM ON THE GND AND THEY ALL LOOKED GOOD. I SUSPECT THE OTHER ACFT'S EQUIP WAS FAULTY. WE SIMPLY HAD NO TIME TO REACT; AND WE BOTH CAME AWAY WITH THE REALIZATION THAT WE SHOULD NEVER TOTALLY TRUST THE EQUIP AND VOWED TO BE MORE VIGILANT IN OUR TFC SEARCHES FROM NOW ON. WE ARE BOTH EXTREMELY THANKFUL THIS DID NOT TAKE PLACE UNDER IMC.

Data retrieved from NASA's ASRS site as of January 2009 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.