Learjet 45
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 75; Flight Crew Total 10100; Flight Crew Type 500
Confusion; Distraction; Human-Machine Interface; Situational Awareness; Troubleshooting; Workload
Aircraft Equipment Problem Less Severe; Deviation - Altitude Crossing Restriction Not Met
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors; Chart Or Publication; Aircraft; Procedure
We loaded the GEELA 6 RNAV arrival into PHX and checked all of the fixes and crossings on the flight plan page. Everything looked good. ATC cleared us to cross SCOLE at FL250; so I just let the airplane intercept the usual 2;500 FPM v-path to SCOLE. ATC then cleared us to descend via the GEELA 6. I asked the Captain to set 7;000 FT [the crossing at NIMBY] in the preselect and we monitored the VNAV. However; when we looked at the FMS VNAV page on the FMS the next fix after SCOLE was HYDRR! It had 'skipped' SPINK and SNRRA. You could select the 'FLTPLAN' page and see the altitudes that go with those fixes on the right side of the screen... but if you pushed VNAV they'd disappear. OK; so that was strange; so I programmed a VNAV fix at SNRRA at FL220. When I did that; it kicked out HYDRR and GEELA. The next fix it showed on the VNAV page was MNSTR. Again; all of the appropriate altitudes were displayed on the flight plan page; but the VNAV page was skipping two crossings at a time! After HYDRR; VNAV skipped GEELA and MNSTR and tried to execute a VNAV descent to HENSN. We crossed MNSTR below 15;000 FT contrary to the arrival procedure. ATC queried us. I have notified our flight standards and safety teams and we will check the FMS to determine if there is a discrepancy.
A Lear 45 flight crew descending via the GEELA RNAV STAR to PHX reported their FMC would drop out two subsequent fixes (and their crossing restrictions) each time they attempted to 'repair' a previously lost waypoint. When distracted by doing so they failed to cross MNSTR at or above 15;000 FT as published.