FLC OF LGT DSNDING TO FL230 RECEIVED TCASII RA TO DSND. RA CLRED AT 22200 AND TFC WAS VISUALLY ACQUIRED 5 MI APPEARING TO BE AT FL220.

Date: 1991-09 · Aircraft: Large Transport; Low Wing; 3 Turbojet Eng

Anomalies: deviation-altitude-excursion-from-assigned-altitude|deviation-discrepancy-procedural-clearance

Synopsis

FLC OF LGT DSNDING TO FL230 RECEIVED TCASII RA TO DSND. RA CLRED AT 22200 AND TFC WAS VISUALLY ACQUIRED 5 MI APPEARING TO BE AT FL220.

Narrative

WE RECEIVED A TCASII TA AS WE WERE DSNDING AND LEVELING AT FL230 ON ARR INTO CLE. THE TA WAS FOLLOWED SHORTLY BY AN RA WITH A RED ARC ON THE VERT SPD INDICATOR FROM 0- 2000 FPM DSCNT; AND A GREEN ARC FROM 2000 FPM TO 2500 FPM. THE CAPT DISCONNECTED THE AUTOPLT (BLOCK V WITH ALT CAPTURE) AND INITIATED A DSCNT TO COMPLY WITH THE RA. THE FO TRANSITIONED OUTSIDE TO GET A VISUAL ON THE TFC; WHILE AT THE SAME TIME; ATTEMPTING TO INFORM ATC OF THE DEV. BOTH PLTS THEN GOT A VISUAL ON THE TFC WHICH WAS AT FL220 AND LOOKED TO BE AT 3 O'CLOCK AND 5 MI. AFTER SOME INITIAL FREQ CONGESTION; WE INFORMED ATC OF THE DEV. BY NOW WE WERE AT FL222 AND HAD LEVELED. THE RA CLRED AND ATC INSTRUCTED US TO JUST CONTINUE TO FL220. AFTER SOME DISCUSSION ON THE GND; THE CREW FELT THAT THE TCASII HAD NOT REALIZED THAT WE WERE LEVELING AT FL230 AND SENSED A CONFLICT. ITS SOLUTION WAS TO INSTRUCT US TO DSND RAPIDLY (2500 FPM) TO CLR TFC. WE WERE PRACTICALLY LEVEL WHEN THE RA OCCURRED; AND FEEL THERE SHOULD NEVER HAVE BEEN AN RA ISSUED. PERHAPS TCASII IS NOT CAPABLE OF UPDATING DSCNT RATES QUICKLY ENOUGH TO RECOGNIZE THAT A LEVEL OFF IS IN PROGRESS AND NO CONFLICT WILL OCCUR. AS IT WAS; WE WERE PRESENTED WITH A COMMAND TO DSND RAPIDLY TO AVOID CONVERGING TFC BELOW US; AT THE TIME WE WERE LEVELING OFF. WE CHOSE TO INITIALLY GO WITH THE TCASII GUIDANCE AND SORT OUT THE DETAILS LATER.

Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.