B737-800
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 181; Flight Crew Type 181
Situational Awareness; Communication Breakdown
Conflict Airborne Conflict; Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Flight Crew Took Evasive Action; Flight Crew Became Reoriented
Human Factors; Procedure
On the FTHLS3 Departure; just prior to VANZZ; we were given a clearance to 'climb via except maintain FL210'. The FO and I both agreed that we understood that we were cleared to continue our climb to FL210 and this deleted our hold down altitude of 8;000 feet at VANZZ. As we approached VANZZ we received a TCAS TA followed by an RA. We immediately acquired visual contact with other aircraft and the FO properly responded to RA guidance. After we were clear of the conflict we continued our climb to FL210 without further incident. As we discussed what had occurred; we determined that we may have misinterpreted the ATC Controllers instructions and that he intended for us to meet the VANZZ crossing restriction before climbing to FL210. We both felt that we had not actually climbed above 8;000 feet before VANZZ; but we're not certain.
I think the word 'except' in the clearance led us to a bias in interpretation of the restrictions. This is because the most common instances of 'except' altitudes tend to be in PDCs; and the 'except' altitude is almost always the most restrictive. I think this led me to think FL210 was the new restriction; not the 8;000 feet at VANZZ.
B737-800 flight crew reported confusion when cleared to 'climb via' the PHX FTHLS3 departure that may have led to an altitude excursion.