B737-800
Flight Crew Air Transport Pilot (ATP)
Flight Crew Total 15000
Situational Awareness; Human-Machine Interface
Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Flight Crew Requested ATC Assistance / Clarification
Chart Or Publication; Human Factors; Aircraft
We were cleared for the YWT4 [WATERLOO FOUR] RNAV STAR; descend to 11;000 MSL. The FMC was programmed and on VNAV PATH. When it became clear we would not make the intermediate crossing restrictions we contacted ATC.
When a B737-800 flight crew became aware they would be unable to comply with a crossing restriction on the YWT RNAV STAR to CYYZ they advised ATC.