Narrative:

During climb out from iad, en route to mco, we were given a further climb from 10000 ft MSL to 17000 ft, while maintaining a visual separation from an inbound (to iad) commuter aircraft. TCASII developed the proper visual on the TCASII/ivsi for both a TA and a later RA as our 2 aircraft approached one another by 1000 ft vertical and 3-4 mi lateral. The audio portion 'clipped' the first word of 'don't climb' as the RA portion of the alert became more rapid in frequency, as the phrase was repeated over and over. It gave the effect of 'climb, climb.' this could lead to serious confusion and a dangerous misinterp of the situation. Since we were on a positive visual separation, it was not a problem. I reported a TCASII that resulted in evasive action of a different flight in feb/98 in an earlier NASA report. Confusion entailed from a 'climb, climb' audio, though the visual displays were correct. The first officer remarked on a similar experience on another flight with another captain. This makes me think that a service problem exists in which the first word is not only clipped, but so low in volume that it may not be perceptible at a critical time to back up the visual display and should be looked into. Callback conversation with reporter revealed the following information: reporter states that he did complete an irregular operation report to the company but it usually takes a few months before any response is forthcoming. The flight crew observed that the 'clipped' aural aspect seems to occur when the speed of the voice and the volume of the alert pick up. In this instance they were VFR and could observe the aircraft as well as follow it on the TCASII. However, during IFR operations one would not know which indication to believe if there was any question from the aural alert and the wrong direction response could cause a major problem. Reporter has had a similar experience when ATC cleared an aircraft through their altitude and TCASII alert indicated 'reduce climb' but the 'reduce' was not clear nor very audible. They followed the visual display on the TCASII. Reporter feels this is a very dangerous situation and there may be a problem that could be handled with servicing the equipment or updating the database.

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Original NASA ASRS Text

Title: DURING CLBOUT THE FLC OF A B737-200 EXPERIENCES A PROB WITH THE TCASII EQUIP. THE FIRST WORD OF THE ALERT SEEMS TO BE CLIPPED OFF GIVING THE IMPRESSION THAT THEY SHOULD CLB RATHER THAN 'DON'T CLB' AS THE TCASII IS ALERTING THEM. THIS IS NOT THE FIRST TIME THIS HAS OCCURRED.

Narrative: DURING CLBOUT FROM IAD, ENRTE TO MCO, WE WERE GIVEN A FURTHER CLB FROM 10000 FT MSL TO 17000 FT, WHILE MAINTAINING A VISUAL SEPARATION FROM AN INBOUND (TO IAD) COMMUTER ACFT. TCASII DEVELOPED THE PROPER VISUAL ON THE TCASII/IVSI FOR BOTH A TA AND A LATER RA AS OUR 2 ACFT APCHED ONE ANOTHER BY 1000 FT VERT AND 3-4 MI LATERAL. THE AUDIO PORTION 'CLIPPED' THE FIRST WORD OF 'DON'T CLB' AS THE RA PORTION OF THE ALERT BECAME MORE RAPID IN FREQUENCY, AS THE PHRASE WAS REPEATED OVER AND OVER. IT GAVE THE EFFECT OF 'CLB, CLB.' THIS COULD LEAD TO SERIOUS CONFUSION AND A DANGEROUS MISINTERP OF THE SIT. SINCE WE WERE ON A POSITIVE VISUAL SEPARATION, IT WAS NOT A PROB. I RPTED A TCASII THAT RESULTED IN EVASIVE ACTION OF A DIFFERENT FLT IN FEB/98 IN AN EARLIER NASA RPT. CONFUSION ENTAILED FROM A 'CLB, CLB' AUDIO, THOUGH THE VISUAL DISPLAYS WERE CORRECT. THE FO REMARKED ON A SIMILAR EXPERIENCE ON ANOTHER FLT WITH ANOTHER CAPT. THIS MAKES ME THINK THAT A SVC PROB EXISTS IN WHICH THE FIRST WORD IS NOT ONLY CLIPPED, BUT SO LOW IN VOLUME THAT IT MAY NOT BE PERCEPTIBLE AT A CRITICAL TIME TO BACK UP THE VISUAL DISPLAY AND SHOULD BE LOOKED INTO. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT HE DID COMPLETE AN IRREGULAR OP RPT TO THE COMPANY BUT IT USUALLY TAKES A FEW MONTHS BEFORE ANY RESPONSE IS FORTHCOMING. THE FLC OBSERVED THAT THE 'CLIPPED' AURAL ASPECT SEEMS TO OCCUR WHEN THE SPD OF THE VOICE AND THE VOLUME OF THE ALERT PICK UP. IN THIS INSTANCE THEY WERE VFR AND COULD OBSERVE THE ACFT AS WELL AS FOLLOW IT ON THE TCASII. HOWEVER, DURING IFR OPS ONE WOULD NOT KNOW WHICH INDICATION TO BELIEVE IF THERE WAS ANY QUESTION FROM THE AURAL ALERT AND THE WRONG DIRECTION RESPONSE COULD CAUSE A MAJOR PROB. RPTR HAS HAD A SIMILAR EXPERIENCE WHEN ATC CLRED AN ACFT THROUGH THEIR ALT AND TCASII ALERT INDICATED 'REDUCE CLB' BUT THE 'REDUCE' WAS NOT CLR NOR VERY AUDIBLE. THEY FOLLOWED THE VISUAL DISPLAY ON THE TCASII. RPTR FEELS THIS IS A VERY DANGEROUS SIT AND THERE MAY BE A PROB THAT COULD BE HANDLED WITH SVCING THE EQUIP OR UPDATING THE DATABASE.

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.