Date: 201403
Local time of day: 0601-1200
Location: LAS.Airport, NV
Flight conditions: VMC
Light: Daylight
Aircraft: A319
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent; Initial Approach
Airspace: Class B LAS
ATC / advisory: TRACON L30
Aircraft component: FMS/FMC
Component problem: Design
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Human factors: Workload; Human-Machine Interface; Confusion; Communication Breakdown; Distraction
Second reporter function: Pilot Flying; Captain
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: This was the first flight of a four day trip. It is ironic that the Captain and I had a lengthy discussion about the threat of complacency just prior to this flight. KEPEC arrival LAS; assigned to cross CLARR at 13;000 FT; 210 KTS. Altitude of 13;000 FT captured before CLARR and all altitude constraints checked prior to the arrival. Assigned to descend via KEPEC arrival; I set 8;000 FT as the lowest altitude on the descent. After passing CLARR the Captain initiated a managed descent; a magenta 11;000 FT altitude constraint was displayed and DESC was boxed as the descent mode. Upon descent mode initiation; the aircraft started descending out of 13;000 FT. All appeared normal. Unfortunately; there is a 13;000 FT altitude constraint at KEPEC; approximately 20 miles or so from CLARR; we should have been in level flight. I didn't determine that we should be in level flight; not descending; until we were already at 11;800 FT or so. I had my range scale in either 10 or 20 NM (to de-clutter the upcoming restraints) and didn't see the 13;000 FT restriction at KEPEC initially; although I should have known having just verified the altitude constraints. It took me a bit to recheck the approach plate; then the map display and verbalize to the pilot flying that we were below our KEPEC altitude. L30 Approach queried us; then gave us direct to IPUMY (which has an 11;000 FT constraint) and we proceeded with the approach and landing. As the pilot not flying; I should have caught the descent much sooner. I was lured into a flight myth versus flight reality by seemingly normal managed descent indications. I didn't cross check fast enough; I took too much time trying to reconcile what looked OK as a managed descent with the approach criteria. I admit I am puzzled by the aircraft's managed descent below a clearly indicated altitude constraint on the map display and with all seemingly normal managed descent indications. We do this procedure many times during any given trip. From a systems perspective; I really have no answers as to why our managed descent deviation occurred; although I'm sure there is a simple explanation.


Second narrative: The First Officer and I had a lengthy preflight briefing concerning complacency. We have flown together over a hundred times over the last decade or more without incident. I was excited to see that I was flying with him because he is an excellent pilot.On the KEPEC arrival into Las Vegas; we were cleared to cross CLARR at 210 KTS and 13;000 FT. At 13;000; we were cleared to descend via the KEPEC arrival. We set 8;000 for the lowest altitude on the arrival. The pilot flying; the Captain; pushed the altitude knob 'in' to enter the DESC mode for the RNAV arrival. Passing 11;700 FT the First Officer noticed we were descending to 11;000 FT with ALT CNST* displayed. KEPEC had an altitude crossing of 13;000 FT. IPUMY was the next fix after KEPEC and the altitude was 11;000. We spoke with ATC and they gave us direct IPUMY. The pilot flying failed to confirm that the aircraft stayed at 13;000 FT after selecting the DESC mode by pushing the altitude knob in.


Synopsis: An A319 crew monitoring the FMGC in the DESC Mode failed to see that the aircraft did not remain level to the KEPEC 13;000 FT constraint even though the system was in the Managed Descent Mode with next constraint illuminated magenta.