Narrative:

I am writing to describe a TCAS resolution advisory which was questionable. While level at FL260 for crossing traffic cleveland advised us of traffic at 2:00 and FL270. We were eastbound going direct carleton. It was a clear night and we quickly idented the traffic visly. Shortly after that the TCAS issued a 'traffic' advisory and we saw him on the scope at plus 24 and descending. As he moved cross the nose to 12:00 he became plus 15 descending and we received a resolution advisory to 'descend'. As we had him in sight we chose not to. As the traffic went to 10:30 he became level at plus 1.0. We received a TCAS advisory to 'monitor vertical speed' in this TCAS test period several things concern me. I don't think descending into descending traffic was the best solution. I think a right turn would have been more appropriate. If we were IMC we would have descended. I don't think the conflict aircraft in this case was using a flight guidance autoplt with a high rate of descent (could have been climb in another case) during the altitude capture. When hand flying west/O F/D most pilots use 1000 FPM for the last 1000'. Indeed our company manual requires it. I feel if flight guidance systems were programmed to use 1000 FPM or less in the last 1000' then a TCAS alert such as this would not occur and perhaps it would reduce the number of altitude deviations as well. Callback conversation with reporter revealed the following information. In a relative short time of using the TCAS equipment widebody transport, he has 3 alerts that were really not a conflict. System is suppose to inhibit at 500', many times it will give a climb resolution. Training has been if an alert is sounded it is mandatory that it be followed. In the incident forwarded he feels the aircraft behind was in such a high rate of descent the TCAS sensed a conflict and called for a descent also. Would like to see the system used on a volunteer basis versus mandatory. Many times the traffic is seen and really no factor. Claims that below a 1000' you should never get a descent resolution. Recommends the system be inhibited below 1000'.

Related reports:

Google
 

Original NASA ASRS Text

Title: TCAS WARNING TO DESCEND. NO ACTION ACCOUNT TRAFFIC IN SIGHT.

Narrative: I AM WRITING TO DESCRIBE A TCAS RESOLUTION ADVISORY WHICH WAS QUESTIONABLE. WHILE LEVEL AT FL260 FOR XING TFC CLEVELAND ADVISED US OF TFC AT 2:00 AND FL270. WE WERE EBND GOING DIRECT CARLETON. IT WAS A CLR NIGHT AND WE QUICKLY IDENTED THE TFC VISLY. SHORTLY AFTER THAT THE TCAS ISSUED A 'TFC' ADVISORY AND WE SAW HIM ON THE SCOPE AT PLUS 24 AND DSNDING. AS HE MOVED CROSS THE NOSE TO 12:00 HE BECAME PLUS 15 DSNDING AND WE RECEIVED A RESOLUTION ADVISORY TO 'DSND'. AS WE HAD HIM IN SIGHT WE CHOSE NOT TO. AS THE TFC WENT TO 10:30 HE BECAME LEVEL AT PLUS 1.0. WE RECEIVED A TCAS ADVISORY TO 'MONITOR VERT SPD' IN THIS TCAS TEST PERIOD SEVERAL THINGS CONCERN ME. I DON'T THINK DSNDING INTO DSNDING TFC WAS THE BEST SOLUTION. I THINK A RIGHT TURN WOULD HAVE BEEN MORE APPROPRIATE. IF WE WERE IMC WE WOULD HAVE DSNDED. I DON'T THINK THE CONFLICT ACFT IN THIS CASE WAS USING A FLT GUIDANCE AUTOPLT WITH A HIGH RATE OF DSNT (COULD HAVE BEEN CLB IN ANOTHER CASE) DURING THE ALT CAPTURE. WHEN HAND FLYING W/O F/D MOST PLTS USE 1000 FPM FOR THE LAST 1000'. INDEED OUR COMPANY MANUAL REQUIRES IT. I FEEL IF FLT GUIDANCE SYSTEMS WERE PROGRAMMED TO USE 1000 FPM OR LESS IN THE LAST 1000' THEN A TCAS ALERT SUCH AS THIS WOULD NOT OCCUR AND PERHAPS IT WOULD REDUCE THE NUMBER OF ALT DEVS AS WELL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO. IN A RELATIVE SHORT TIME OF USING THE TCAS EQUIP WDB, HE HAS 3 ALERTS THAT WERE REALLY NOT A CONFLICT. SYSTEM IS SUPPOSE TO INHIBIT AT 500', MANY TIMES IT WILL GIVE A CLB RESOLUTION. TRNING HAS BEEN IF AN ALERT IS SOUNDED IT IS MANDATORY THAT IT BE FOLLOWED. IN THE INCIDENT FORWARDED HE FEELS THE ACFT BEHIND WAS IN SUCH A HIGH RATE OF DSNT THE TCAS SENSED A CONFLICT AND CALLED FOR A DSNT ALSO. WOULD LIKE TO SEE THE SYSTEM USED ON A VOLUNTEER BASIS VERSUS MANDATORY. MANY TIMES THE TFC IS SEEN AND REALLY NO FACTOR. CLAIMS THAT BELOW A 1000' YOU SHOULD NEVER GET A DSNT RESOLUTION. RECOMMENDS THE SYSTEM BE INHIBITED BELOW 1000'.

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.