Narrative:

Our aircraft was cleared (late) by ATC to descend from 43000 ft to a lower flight level. We therefore had a high descent rate of about 2500 FPM. During the process of leveling off; a TCAS traffic alert warning was issued. The crew spotted the traffic at 2 O'clock and below. The TCAS preventive RA monitor vertical speed was heard; with the vsi red arc indicating a 500 FPM restriction; when the two aircraft crossed on top of each other. Our aircraft TCAS showed 1000 ft; air traffic controller reported a minimum separation of 1000 ft. The other aircraft reported minimum vertical separation of 800 feet. In our view this was primarily a controller mistake; giving a late descent clearance from 43000 ft to 31000 ft; with another aircraft opposite direction at 30000 ft. There was; in fact; no way we could make the crossing restriction and avoid the RA. Of course; it would have been better to miss the crossing restriction; but we got the TA only 5-10 seconds before the RA; so we had no way to know the high descent rate would become suddenly problematic.

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Original NASA ASRS Text

Title: LATE DSCNT CLRNC FROM FL430 TO FL310 REQUIRES HIGH RATE OF DSCNT. TFC AT FL310 CAUSES TCAS TA AND RA ALERTS DUE TO CLOSURE RATE.

Narrative: OUR ACFT WAS CLEARED (LATE) BY ATC TO DSND FROM 43000 FT TO A LOWER FLIGHT LEVEL. WE THEREFORE HAD A HIGH DSCNT RATE OF ABOUT 2500 FPM. DURING THE PROCESS OF LEVELING OFF; A TCAS TRAFFIC ALERT WARNING WAS ISSUED. THE CREW SPOTTED THE TRAFFIC AT 2 O'CLOCK AND BELOW. THE TCAS PREVENTIVE RA MONITOR VERT SPD WAS HEARD; WITH THE VSI RED ARC INDICATING A 500 FPM RESTRICTION; WHEN THE TWO ACFT CROSSED ON TOP OF EACH OTHER. OUR ACFT TCAS SHOWED 1000 FT; AIR TRAFFIC CTLR REPORTED A MINIMUM SEPARATION OF 1000 FT. THE OTHER ACFT REPORTED MINIMUM VERT SEPARATION OF 800 FEET. IN OUR VIEW THIS WAS PRIMARILY A CTLR MISTAKE; GIVING A LATE DSCNT CLRNC FROM 43000 FT TO 31000 FT; WITH ANOTHER ACFT OPPOSITE DIRECTION AT 30000 FT. THERE WAS; IN FACT; NO WAY WE COULD MAKE THE CROSSING RESTRICTION AND AVOID THE RA. OF COURSE; IT WOULD HAVE BEEN BETTER TO MISS THE CROSSING RESTRICTION; BUT WE GOT THE TA ONLY 5-10 SECONDS BEFORE THE RA; SO WE HAD NO WAY TO KNOW THE HIGH DSCNT RATE WOULD BECOME SUDDENLY PROBLEMATIC.

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.