B737 Next Generation Undifferentiated
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 269
Situational Awareness; Communication Breakdown; Confusion
Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Undershoot; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors; Procedure
As we descended into LAX on the OLAAA 1 Arrival; SoCal Approach reissued the descent clearance several times in the format 'Descend via the OLAAA 1 except maintain Flight Level XXX.' Approximately 15 miles east of CYNDE; SoCal asked if we could make CYNDE at or below 13;000 ft instead of the published 14;000 ft. We replied that we could and SoCal issued the following clearance: 'descend to cross CYNDE at or below 13;000 ft then descend via the OLAAA1 except maintain 12;000 ft.' We complied with the clearance; crossing CYNDEE and then maintaining 13;000 ft as we didn't need to leave 13;000 ft until approximately 18 miles after OLAAA. At about OLAAA we were transferred to a new SoCal sector and I checked in with 'Call sign at 13;000 ft descending via the OLAAA 1 except to maintain 12;000 ft.' A few minutes later; SoCal asked if we were going to be descending further as he reissued a clearance to descend via the OLAAA 1 except maintain 8000 ft. At this point I noticed co-altitude traffic about 5 miles to our 9 o'clock slowly converging and wondered if SoCal intended for us to continue our descent immediately to deconflict from that traffic. When I queried the Controller; he stated that he thought we were previously cleared to 'descend and maintain 12;000 ft.' I stated that our actual clearance was descend via except maintain 12;000 ft. We were then cleared to descend via the OLAAA1. A few miles prior to MADOW; as the Captain and I discussed this event; SoCal unexpectedly changed our landing runway and issued a 210 knot speed restriction. The Captain asked me to reprogram the new approach in the FMC as he selected Speed Intervention to comply with the speed restriction. As I reprogrammed the approach I failed to notice that we were going above the FMC-computed vertical path due to the early deceleration. Immediately prior to MADOW we got an 'Unable 8000 ft at MADOW' FMC message and I then realized what was happening. At that point it was too late to recover and we crossed MADOW at approximately 8500 ft. The Captain then attempted to get back on profile with speed brakes but we also crossed TOZEK slightly high at approximately 7200 ft. For the first part; I think Pilots and Controllers alike are still getting used to the 'descend via' phraseology; particularly when combined with other crossing restrictions that aren't published on the procedure. I will make every effort to ensure ATC is clear on what our clearance is in the future on check-in.For the subsequent altitude deviations; it was yet another case of distractions getting the better of me. Distraction from the previous misunderstanding with ATC as well as distraction from the runway change/FMC reprogramming both led to a lapse in my monitoring such that I didn't realize we weren't going to make the upcoming published altitude restrictions until it was too late. I need to continue working on managing distractions so that I can be a more effective PM.
B737 First Officer reported being cleared to descend via the OLAAA 1 Arrival to LAX except with several altitude adjustments. After a runway change and a speed adjustment; two crossing restrictions were missed.