Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Time Pressure; Situational Awareness
Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Human Factors
Arriving in TUS we had briefed the RNAV RNP Y Rwy 11 approach.  Our clearance was for the ZONNA 1 arrival which took us from SSAND to OTUKE.  Just outside SSAND we were cleared to fly the lateral course for the RNAV Y.  We cleaned up the box and turned on to the course.  The next fix was LUYEG; our clearance was to cross at 11;000 feet cleared for the RNAV Y approach.  We slowed to 240; went flaps 1; did the LAVS procedure.  The FMA went to PATH and looked normal.  We read the Approach checklist.  I checked the FMAs again; it indicated SPD not PATH.  There was no VNAV scale to indicate high or low on the path.  I selected V/S and slowed the rate of descent.  Before I could enter the next stepdown altitude in the MCP; ATC called with a low altitude alert.  There was no EGPWS warning.  I disconnected the A/P and initiated a climb.   We were in VFR conditions.  We reengaged the A/P and selected 9;500 feet for a crossing altitude at HODPU.  We did the LAVS procedure outside of HODPU.  The FMA went to PATH and looked normal until it crossed the fix and then it went to speed.  After that we used the A/P to fly the lateral course put each crossing altitude in the MCP.  On final I disconnected the automation [and] flew a visual approach.  First Officer did an excellent job monitoring; calling out deviations; and analyzing the problem.  We delayed reading the approach checklist until the FMS was correct for the approach that we intended to fly.  I was distracted by the checklist reading and that caused a delay for me to recognize that the FMA for the vertical mode was no longer in PATH.  We had asked the ABQ Center Controller to clear us onto the approach [but] he told us to make our request to Approach Control.  It meant that we were making changes to the FMS just before turning on to the approach.First Officer and I discussed the FMS setup; the approach; our procedures in the debrief.  We were unable to determine what error caused the airplane to not fly the RNAV approach correctly.  It would have been helpful to do everything earlier; complete the changes to the FMS and read the Approach checklist well before we were cleared onto the approach path.  That would free both pilots to monitor the automation and catch deviations sooner.
Wide body transport Captain reported receiving a low altitude alert from ATC on approach to ABQ when the flight crew missed a change in the FMS vertical navigation mode.