Date: 201503
Local time of day: 1201-1800
Location: CYVR.TRACON, BC
Flight conditions: VMC
Weather elements / visibility: 30
Light: Daylight
Aircraft: Light Transport; Low Wing; 2 Turbojet Eng
Operator: Air Taxi
Operating under: Part 91
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Descent
ATC / advisory: TRACON CYVR
Reporter organization: Air Taxi
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Human factors: Communication Breakdown; Confusion
Second reporter function: Captain; Pilot Not Flying
Anomaly: ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action; Flight Crew Returned To Clearance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Became Reoriented
Contributing factors: Procedure; ATC Equipment / Nav Facility / Buildings; Human Factors
Primary problem: Human Factors

Narrative: While on the arrival into CYVR; we were instructed to descend and maintain 10;000 and we complied. After a few minutes at 10;000; we thought we were instructed to 'Descend unrestricted and maintain 4;000'. We read back the clearance and followed SOPs and initiated standard 1;500 foot per minute descent to 4;000. We did not hear any objection from ATC concerning the read back. Upon reaching approximately 8;600 ATC queried our descent and informed us our clearance was to maintain 10;000. We quickly arrested the descent and began climbing back to 10;000 while scanning for any potential TCAS conflicts. We told ATC that we thought we were instructed to descend unrestricted and maintain 4;000 and they said negative; that was not for your call sign. We explained that we had read back the clearance to descend unrestricted and maintain 4;000 with our call sign and they did not reply. We continued the flight uneventful and landed. Shortly after leaving the aircraft and briefing the situation as a crew; we determined that we should call Approach Control via telephone and discuss the situation and find out more information concerning the event. The Shift Supervisor informed us that this has occurred multiple times in the past due to their ground communication equipment being digital. He informed us that only one aircraft can transmit and if another is trying to transmit; it will be blocked and not heard at all. This is what he said occurred in our situation. He said the old analog system would transmit with a lot of static when two aircraft would transmit at once and used to help them identify these types of situations. Also their transmissions were very difficult to understand call signs due to accent and fast paced annunciation.


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


Synopsis: After beginning an early descent because of a communications misunderstanding; a flight crew was informed CYVR digital communications systems acknowledges only one radio call at a time; blocking a second caller. Their incorrect descent clearance acknowledgement was not heard.