AN A319 CREW DISCUSSES THE ACR'S PROCEDURE OF SETTING THE LOWEST ARR ALT CONSTRAINT IN THE MCP ALLOWING IF ALT DEVS DURING DSCNT.

Narrative

POLICY OF SETTING LOWEST ALT ON ARR REMOVES A SAFETY BACK STOP TO PREVENT DSNDING BELOW PUBLISHED ALTS IF AUTOMATION FAILS. IN THIS EVENT WE FOLLOWED PROCS IN SETTING AND CONFIRMING SETTINGS AND MONITORED THE DSCNT WITH TIME TO VISUALLY ASSESS THE WX AROUND US AND STILL MISSED WHAT SHOULD HAVE BEEN AN AUTO LEVELOFF. PRIOR TO DSCNT INTO LAS ON THE KEPEC 1 ARR ALL NAV FIXES AND ALT CONSTRAINTS WERE VERIFIED BY BOTH PLTS AND FOUND TO BE CORRECT. WE WERE CLRED TO DSND BY KEPEC 1 ARR AND 8000 FT WAS SET INTO THE MCP ALT WINDOW AND VERIFIED PER PROC AND THE DSCNT WAS MANAGED AND VERIFIED PER FMA. DURING THE DSCNT AFTER SKEBER INTXN THE FO NOTICED THAT THE KEPEC INTXN DISPLAY WAS AMBER IN COLOR AND OUR ALT WAS 11500 FT. IT SHOULD HAVE BEEN 12000 FT AT THIS POINT. THE PFD VERT PROFILE DONUT INDICATED ON PROFILE. THE FO IMMEDIATELY DISCONNECTED THE AUTOPLT AND CLBED TO 12000 FT. THE ARR WAS CONTINUED MANUALLY; SETTING ALTS AS NECESSARY AND USING OPEN DSCNT AND SELECTED SPD. ATC NEVER ACKNOWLEDGED A DEV AND WE CONTINUED TO A NORMAL APCH AND LNDG. KEPEC INTXN TURNED AMBER INDICATING THAT THE ALT RESTR HAD BEEN MISSED. DISCONNECTED AUTOMATION AND RETURNED TO PUBLISHED PROC ALT. VERT DONUT WAS AT THE BOTTOM OF SCALE INDICATING THE ACFT THOUGHT THAT WE WERE HIGH. REEVALUATE THE MCP ALT SETTING PROCS.