Flight Crew Air Transport Pilot (ATP)
Flight Crew Total 22200
Training / Qualification; Other / Unknown
Aircraft Equipment Problem Less Severe; Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Returned To Clearance
Human Factors; Aircraft; Procedure
We were cleared to descend via the ELDEE 5. Per our procedure we are to set the bottom altitude of the arrival in the altitude window (8;000 FT) when flying in 'VNAV Path Mode.' The aircraft was on target until the Controller issued 2 speed reductions prior to DRUZZ. We asked for and received relief at DRUZZ. The wind at altitude was roughly 280/80. During the second speed reduction the aircraft dropped out of VNAV Path. Simultaneously we had a pack trip off line. The First Officer began the QRH checklist while I continued with the descent; hustling down to at least be close to the crossing altitude at DRUZZ it did not occur to me that there existed a level portion on the descent between DRUZZ and REVUE until it was too late and we descended below 15;000 MSL. Experience with new automation and accepting the lowest form of automation when a problem exists may be the key to preventing such events. Once the aircraft dropped out of VNAV Path I should have immediately selected the next stepdown altitude (15;000 FT) in the altitude window. Being relatively new on the aircraft I am anxious to master its many modes of descent. Choosing the simplest mode when under duress is usually the safest course of action.
However; prior to reaching REVUE we descended through the required 15;000 FT to approximately 14;300 FT.
When their FMC VNAV Path function was unable to comply with both the ELDEE STAR crossing restrictions and ATC speed restrictions the flight crew of a B737NG attempted to manually comply with the crossing at POOCH at 11;000 FT; but while doing so; descended through the required 15;000 FT between DRUZZ and REVUE. Distraction from a tripped pack during the descent was a contributing factor.