Date: 201604
Local time of day: 0601-1200
Location: PHX.Airport, AZ
Flight conditions: VMC
Weather elements / visibility: Turbulence
Light: Daylight
Aircraft: A320
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class B PHX
ATC / advisory: TRACON P50
Second aircraft: B737 Undifferentiated or Other Model
Aircraft component: Autopilot
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Workload
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Conflict Airborne Conflict; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Automation Aircraft TA; Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Clearance; Flight Crew Became Reoriented; Flight Crew Took Evasive Action
Contributing factors: Aircraft; Human Factors
Primary problem: Ambiguous

Narrative: Received two TAs; reduced range on NAV Display; visually identified first TA off aircraft right side and visually identified aircraft behind and below left side of aircraft. We both noticed that automatic pilot did not honor the 9000 ft restriction at CHAVO intersection; as PF; I intervened at 8700 ft and climbed back to 9000 ft. After landing; we were notified of a possible deviation.The aircraft did not honor the 9000 ft altitude restriction at CHAVO combined with two TAs resulted in my having to intervene at 8700 ft and climb back to 9000 ft.


Second narrative: On arrival to PHX; we were assigned to descend via the HYDRR1 arrival. Prior to CHAVO; ATC instructed us to slow to 210. A few miles prior to CHAVO intersection; we were descending out of 9500ft MSL with an altitude restriction of 9000 at CHAVO; and last I had seen; the aircraft was showing it would make the restriction. Shortly after; I noticed a B737 climbing under us and just to our right and I called out the traffic. At nearly the same time; ATC called out CRJ traffic to our 10-11 o'clock position and I called it in sight as well. At that moment; we received a TCAS Traffic Advisory from the B737 climbing to our right. We reduced our Navigation Display (ND) range per our SOP; and we received another TA from the CRJ climbing at our left. I attempted to reacquire the CRJ and had trouble spotting it again; and was able to make visual contact off our 9 o'clock position. At that point I noted they were 700 feet below us and turning behind us; approximately 3 or so miles passing to our 7-8 o'clock. We called the traffic in sight and PHX approach switched us to the next frequency. As my attention came back into the aircraft; I noted the Captain had engaged the vertical speed mode and was leveling the aircraft; and I saw around 8;640 on the altimeter; and we had not yet crossed CHAVO; which had a 9000 ft altitude restriction. He initiated a gradual climb back up to 9000 ft at that time and we switched over to the other frequency; which then gave us a descent to 7000 ft. After landing; PHX approach notified us that the CRJ received a TCAS Resolution Advisory from us; while we did not receive an RA and were unaware they had received one.This event occurred primarily due to the autopilot vertical navigation mode not honoring the 9000 foot crossing restriction for some unknown reason. It was exacerbated by the fact that at the critical moment of having to ensure the aircraft stopped its descent; we were distracted by two close-proximity traffic callouts by both PHX approach and TCAS. We spent several minutes trying to identify the TA traffic and keep them in sight right as the aircraft failed to stop its descent at 9000 ft. We were able to immediately identify that we had descended through the 9000 ft restriction after the traffic conflicts were resolved and were no factor.The best way to avoid reoccurrence of this event is to continually return back 'inside' the aircraft to ensure it is doing what it should be doing; particularly if approaching a clearance restriction. However; having two near-simultaneous TCAS TAs on opposite sides of the aircraft made it difficult for both pilots to stay focused inside the aircraft.


Synopsis: A320 flight crew reported receiving a TA after the autopilot overshot a crossing restriction on descent into PHX.