Date: 201808
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Flight conditions: VMC
Aircraft: A319
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class E ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: MCP
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Troubleshooting; Distraction
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Overcame Equipment Problem; Flight Crew FLC Overrode Automation; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: During climb out of ZZZ at 16000 [and] cleared to FL360; altitude control knob on FCU broke off at FL270 as Pilot Monitoring was setting altitude to FL360. [We] notified ATC that we needed to level off initially at FL270 to investigate the problem; aircraft leveled off on autopilot with no issue. [We] could not reattach knob to change altitude on FCU so asked for a block altitude of 270-280 in order to use VS to climb. Aircraft started climb; so [we] requested FL360 and was granted climb. After 200 feet altitude alert warning horn came on and wouldn't silence so [we] requested descent back to FL270 and was approved. At approximately FL280; warning horn ceased so [we] requested FL280 as final and was approved. VS was only mode working to change altitude. Speed and NAV were both working on autopilot. [We] checked with Dispatch for fuel burn and checked weather along route and decided to continue on to destination. No issues enroute with autopilot and VS mode kept altitude at FL280 with no problems. Contacted Fleet Coordination and Maintenance about problem and asked if there was a circuit breaker we could pull to silence the altitude warning during descent. They said no. [We] reviewed [the] flight manual about warning horn and decided on slowing down and dropping gear early to silence the warning during the descent. [We] also asked ATC for direct routing to IAF to minimize level offs on descent and to save fuel. This was granted. [We] started descent and warning horn sounded as predicted. Pilot Monitoring then said 'let's try ECAM emergency cancel' which silenced the warning; so [we] continued descent at 240 knots with speed brakes deployed. [We] started to get high on descent because [we] planned on descending with landing gear deployed; so [we] put gear down early about 12000 feet to help descent. [We] had to avoid some weather on descent and used some S turns to get on profile. VS and autopilot [was] used during descent until on final for visual Runway XXR at ZZZ1.Work load was very high using VS. As not to over speed gear or flaps; [we] monitored glide path [and] clicked off autopilot and auto throttles at approximately 3000 feet when field was in sight. This actually reduced workload and allowed me to get on profile faster. Still; [we] were a little high but stabilized at 500 feet and landed with no further issues. No emergency was declared or limits exceeded; but profile was high on descent and workload was very high especially since we were delayed over 4:30 hours and ended up landing 52 minutes before 12 hour duty day. I did not think the emergency cancel would silence the landing gear warning horn and it is not listed in the landing gear warning section of the flight manual as a way to silence it; but [I] should have known that and it would have helped in descent planning. Also; we could not find any reference to this particular situation in the QRH or flight manual.


Second narrative: [Report narrative contained no additional information.]


Synopsis: A319 flight crew reported the altitude select knob on the Flight Control Unit (FCU) broke entirely off.