A320
Human-Machine Interface; Confusion; Communication Breakdown; Situational Awareness
ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification
Human Factors; Aircraft
Captain was Pilot Monitoring; First Officer was Pilot Flying. We were at cruise altitude FL230. We were cleared from 16;000 ft. to climb to cruise altitude upon check-in with Center. There was poor illumination of flight instrument displays and a high level of glare in the flight-deck due to sun location and time of day. The ATC Controller was experiencing microphone difficulties due to a stuck microphone. ATC queried the crew about our assigned cruise altitude while the Captain was off frequency delivering a passenger PA. The First Officer responded to ATC query and advised the Captain of the ATC inquiry. The flight proceeded normally to destination. The Captain and First Officer discussed the Flight Plan cruise altitude of FL220. High task loading occurred during the climb due to the short duration of the flight. The ATC query created doubt to the flight crew as to whether we had received and responded to the ATC climb clearance properly; particularly with regard to the reduced ability to see the altitude selection window on the FCU and the Airbus altitude window potential for digit 'skipping'.They 'why' of the event is because ATC queried the crew about the assigned cruise altitude; therefore It appears that ATC did know or remember what altitude they cleared the flight too. Improve the illumination of the FCU unit altitude window.
A320 Captain reported that an ATC communication issue combined with glare and visibility issues on the flight deck resulted in an altitude deviation.