B737 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 190; Flight Crew Total 10500; Flight Crew Type 4000
Confusion; Communication Breakdown; Distraction
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance
Flight Crew Returned To Gate; General Maintenance Action
Human Factors; Aircraft; Procedure
Our APU was placarded inoperative; so we planned the usual supplemental procedures for starting an engine at the gate with external electric power and pneumatic source. That was done satisfactorily using the supplemental procedures. The power shift from external electric to the engine generator seemed to cause a spike which disturbed the flight displays; but they appeared to have recovered. Per the procedure; we deferred the After Start Checklist until pushback was complete; which involved a long tow out. During the After Start Checklist; we noted that the red HDG alert was shown on the standby horizon; the Captain's PFD and ND had lost their attitude and position displays; and the left IRS had placed itself in align mode. Also; the ELEC light was illuminated on the overhead panel. Reporting these events to Maintenance Control; we followed their instructions and identified a failure of the Static Inverter I (this had also been written up and cleared the previous day); and we cleared the failure as instructed by Maintenance Control. We requested an ACARS message authorizing us to continue with the open write-up for this failure. In response we received a Maintenance message advising the Static Inverter Fault is a repeat write-up. Fault clear per AMM; OK to continue to next station.  Without an operating APU; we were unable to start the second engine because local ramp procedures prohibited a crossbleed start until on a taxiway beyond the ramp. Passengers were getting overheated and we were blocking some other flights from pushing back as we realigned the IRS. This realignment was successful after the required time holding in position. We intended to continue the flight; however; on reviewing the MEL (which applied to our situation as we were off the gate; but not off the ground) we learned that for an ELEC light indication we were required to ensure that Maintenance had performed a Standby Power Check.We were unable to accomplish this on an NG airplane; on the taxiway; with no APU; so we returned to the gate. Maintenance came aboard to perform the check. They used a belt loader to enter Door R1 because the jetway could not be repositioned while we were drawing external power; according to the ramp personnel. After Maintenance finished their work we believed we were good to go; and only needed to replenish the fuel we had used during the gate return events. We were prepared to fuel with passengers aboard and the L1 door closed. I ascertained that no exits were blocked externally and that flight attendants were manning their doors in the cabin. However; operations informed us that fueling in this manner was prohibited by local rules at [the airport]. So the only alternative we were given was to de-power the aircraft by deselecting external AC power; which would allow the jetway to be brought up to the aircraft. I explained this to our sweltering passengers. However; when I deselected AC power I immediately noted that the aircraft did not properly transfer to standby power. My displays once again blanked and the standby horizon red HDG flag was on. Also; the siren for the First Officer's IRS on battery power was not sounding. I placed the Standby Power switch to BAT; but it had no effect. We recalled local Maintenance to the aircraft and deplaned the passengers. Maintenance replaced the standby inverter as well as another part of the standby power system; and we operated the flight to destination. Note: these events from gate departure to gate return were observed from the jumpseat by an FAA Aviation Safety Inspector.
After being dispatched with an inoperative APU a B737-NG flight crew was confronted with multiple system anomalies while attempting to start engines; resulting in returns to the gate for Maintenance and sweltering and unhappy passengers who were required to get off the airplane in order to add fuel burned while away from the gate because local rules would not allow fueling with them on board.