B737-800
Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Workload; Fatigue
Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Undershoot; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
General None Reported / Taken
Procedure; Human Factors
Descending into BOS via the ROBUC1 out of FL180 BOS Approach told us to cross PROVI at 11;000 feet; 250 kts. VNAV PATH was engaged and we were on the path. I was unable to program the FMC to accept the new clearance due to the multiple variable crossing and speed restrictions preloaded in the FMC Arrival. Noting that I was still on path and PROVI had 11;000 feet on the legs page I assumed that I would cross at 11;000 feet and manually adjust the speed. I failed to notice the 'at or above' part. Work load was high due to checklists and briefings at this time. Approach handed us off to final approach and when the First Officer checked in I saw that we were almost over PROVI and 3;000 feet high. ATC made no comment and there didn't appear to be any traffic conflicts. It should be noted that this occurred on a very high work load day three of a four day sequence. The leg being flown was [under an hour] off to on and we were running late due to departure problems in ZZZ.
I was the Pilot Monitoring (PM). ATC cleared us to cross PROVI at 250 at 11;000. PROVI is already programed with a cross at or above 11;000 restriction (11;000A). I entered this into the box and it would not accept the entry. I figured out the reason was because the RY 27L transition has another fix farther down the STAR named KRANN. The restriction at KRANN is to cross at 270 KTS and between 11;000 and 13;000.I suggested to the Captain (PF) that we delete the 270KTS 11;000A 13;000B restriction at KRANN thus allowing the FMC and VPATH to accept and show the proper VSI into PROVI. The Captain did NOT want me to remove the restriction at KRANN and communicated to me that he would make the proper crossing at PROVI. 11;000 was dialed into the altitude alerter and the FMC remained in its original pre-programed state of PROVI 11;000A and KRANN 270 11;000A/13;000B I then began working on other descent and approach duties. ATC gave us a frequency change to Boston Approach. I checked into Boston and verbalized our current altitude and descent to cross PROVI at 250/11;000. The Captain (PF) then realized we were almost on top of PROVI and 3;000-4;000 feet too high. We continued our flight idle descent to level off at 11;000 on the ENE side of PROVI. ATC never mentioned a word about the missed altitude and we continued to safely land at the field. This event has three odd situations that stand out. 1) The STAR is very cluttered because of the runway transition insert that's stuffed onto the same page. The Runway 27 depiction transition is the most cluttered with Runway 32;33L track and ball notes as well as the Runway 22L/R track that parallels the Runway 27 track. I found reading and reviewing this distracting and irritating.2) The ATC instruction given significantly contradicted the next set of programmed restrictions in both speed and altitude. This required time and thought as to why the FMC wouldn't take the new restriction we wanted to insert at PROVI. Additional time and thought was given cross referencing the lousy plan view of the ROBUC 1 arrival and Runway 27 Transition track on the [tablet]. 3) The Captain (PF) chose to NOT remove the restriction at KRANN. In doing so; the VPATH performed exactly as expected. Cross PROVI 11;000A and KRANN 11;000A/13;000B. The VPATH and VSI were spot on.In summary; the restriction farther down the STAR need to be manually removed from the FMC if ATC instructs a stricter restriction earlier on the arrival. The other option is to disengage VNAV and use Flight Level Change (FLCH). I believe this to be the best option. If ATC wants to use arbitrary restriction that are not part of the current RNAV STARS that are programed into the FMC as well as [the tablet]; it's best to just remove the technology from the equation.
A B737-800 flight crew reported they failed to meet a crossing restriction on arrival into BOS due to high workload and distractions.