After beginning an early descent because of a communications misunderstanding; a flight crew was inf...

Attributes
ACN	1247889
Time
Date	201503
Local Time Of Day	1201-1800
Place
Locale Reference	CYVR.TRACON
State Reference	BC
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Light Transport Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 91
Flight Phase	Descent
Route In Use	STAR GRIZZ4
Flight Plan	IFR
Person 1
Function	Pilot Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Flight Instructor Flight Crew Instrument Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 135 Flight Crew Total 6800 Flight Crew Type 1410
Person 2
Function	Captain Pilot Not Flying
Qualification	Flight Crew Instrument Flight Crew Multiengine Flight Crew Flight Instructor Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 111 Flight Crew Total 7971 Flight Crew Type 1938
Events
Anomaly	ATC Issue All Types Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance

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.

Original NASA ASRS Text

Title: 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.

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.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

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.