A319
Flight Crew Air Transport Pilot (ATP)
Confusion; Communication Breakdown; Situational Awareness
ATC Issue All Types
Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Airspace Structure; Human Factors; Procedure
During descent into Las Vegas on the TYSSN Three arrival; the following communications occurred. LA Center: '[Callsign]; descend now to cross KADDY at 12;000 and descend via the TYSSN 3' (The TYSSN 3 ends at PRINO Intersection at 8;000). We acknowledged the clearance and began the descent with 8;000 FT selected and a crossing restraint of 12;000 (magenta) set on the FMA. At approximately 14;000 FT; we were handed off to Las Vegas Approach.... Approach [stated]: '[Callsign]; radar contact. After KADDY; turn left heading 260; expect the visual for [Runway] 01L.' We acknowledged and read back the clearance. As we were descending through 11;500 FT; Approach Control seemed slightly confused and asked; '[Callsign]; were you cleared to descend via the TYSSN THREE?' We replied; 'Affirmative.' The Controller then said; ' OK;...um....stop your descent at 10; ten thousand.' We acknowledged the clearance and stopped our descent at 10;000 FT.The Captain and I began to wonder if we missed a clearance. This discussion continued after the flight and we came to the conclusion that there is some ambiguity in this scenario that probably occurs with regularity. In this case; one controller gave a descend via clearance and then the next Controller expected something different and the flight crew was in between. The latest ATIS had a change in arrival runway from 25L to 01L. The Center Controller had us descend via...expecting a Runway 25L approach (which the TYSSN THREE arrival leads right into). The Approach Controller; knowing the runways had changed; took us off of the arrival at KADDY for vectors to Runway 01L. The crossing restriction at KADDY was 12;000 FT. The original clearance we received was to descend via the TYSSN THREE with the final altitude of 8;000 FT at PRINO. When we left the arrival at KADDY; our descent altitude was still 8;000 FT; since we did not receive an amended clearance. We continued the descent in VMC conditions. There are three reasons that this is a problem: 1. Two controllers had a breakdown in communications; with each expecting our flight to do two different things. 2. Lack of communications within the flight crew; and 3. We; as the crew; continued descent in VMC conditions. But we were in mountainous terrain. If we were in IMC; things may have become complicated. Even though we; as crew; are responsible for situational awareness; including MSA; we may have descended below MVA for that sector. We would have trusted the descent clearance because we were in radar contact with the local ATC.There are only so many 'descend via' arrivals today; but that number is increasing. If an aircraft is on one of those arrivals; any time the aircraft is vectored off of the arrival (whether it is for traffic; weather; or ATC vectoring) it should be required to issue an amended clearance with a new altitude. If the aircraft then becomes re-established on the arrival; a new clearance must be given with a new altitude restriction; or another 'descend via' clearance. This will leave no ambiguity between a flight crew and ATC. And likewise; when a new frequency is assigned to a flight crew; when check-in on the new frequency occurs; the 'descend via' should be stated with the decent altitude stated clearly; and ATC should verify that clearance and read it back to the flight crew; so all parties have verified the clearance.
A319 flight crew cleared to 'descend via' the Las Vegas TYSSN THREE Arrival by Center and subsequently vectored off the arrival by Approach Control; continued descent in accordance with the arrival restrictions until advised by Approach to stop descent.