Narrative:

[We were] dispatched with APU inoperative; necessitating starting an engine at the gate. Ground pneumatic start procedures call for closing the isolation valve on the opposite side of the engine being started. Plan was to start number 4; thus we attempted to close the left isolation valve. Pushing the switch generated a 'bld isol left' EICAS alert message and the ecs schematic showed the left isolation valve open; though we had selected it off. However; the duct pressure on the left side did drop to zero when we closed the isolation valve. Maintenance advised us to go ahead and start the number 4 engine in the hope that engine bleed pressure would cause the left isolation valve to close. We started number 4. The 'isol valve disagree' light did not go out and so we shut the engine down so maintenance could work on the valve. In the meantime; flight attendants were advising us that it was extremely hot in the aft cabin. The ground air conditioning had been pulled from the time we commenced our attempts to start the engine at the gate; the hoses being attached to the jetway which had been retracted. The ground pneumatic cart was extremely weak. In fact we aborted our first start attempt because the duct pressure dropped to zero. There was not even enough output from the ground cart to operate a pack. Normally; once the start valve is opened we can hear the ground cart rev up as it takes on the pneumatic load. This did not happen. On our second start attempt the mechanic did something to increase the cart's output and we got a successful start; but then as stated earlier had to shut the engine down to address the valve issue. At this point; knowing that the cart was weak and could not support pack operation; we asked for the air conditioning hoses to be connected back up; but that was not possible because the mechanic was now accessing the isolation valve to wire it open. The temperature reached 90 degrees plus in zones D and east. Maintenance completed wiring the isolation valve open; but at this point we had lost our tow bar and delayed 10 more minutes waiting to get that back. Passengers [were] very uncomfortable. [There were] numerous calls from the flight attendants expressing their concern. We made pas and explained the best we could. After maintenance wired the left isolation valve open we went ahead and started number 4 engine at the gate even though the irregular procedure directed us to close the left isolation valve; which was now not possible.in hindsight; it would have been possible to start the number 1 engine at the gate instead because the right isolation valve was operating normally. We learned that the ground pneumatic cart did not belong to our company; it was borrowed. We were told that the company used to have its own cart but no longer; due to cost cutting. Clearly; dispatching with the APU inoperative is only a sound decision if there is adequate ground support equipment at our international stations. In this instance; a more robust ground pneumatic cart would have allowed us to operate air conditioning packs while we figured out how to address the isolation valve issue. Our passengers would still have been slightly delayed; but least they would have been comfortable. The station personnel were doing the best they could with the equipment they had; no complaints about them. They were very responsive to our requests; but limited in what they could do for us; given the poor operation of the borrowed cart and the need to wait for the return of the tow bar.

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Original NASA ASRS Text

Title: B747 First Officers report being dispatched with an inoperative APU; requiring engine start at the gate with an external air cart that is inadequate. In addition; a bleed air isolation valve will not close; requiring maintenance action. The flight is delayed and the passenger cabin overheats.

Narrative: [We were] dispatched with APU inoperative; necessitating starting an engine at the gate. Ground pneumatic start procedures call for closing the isolation valve on the opposite side of the engine being started. Plan was to start number 4; thus we attempted to close the left isolation valve. Pushing the switch generated a 'Bld Isol L' EICAS alert message and the ECS schematic showed the left isolation valve open; though we had selected it off. However; the duct pressure on the left side did drop to zero when we closed the isolation valve. Maintenance advised us to go ahead and start the number 4 engine in the hope that engine bleed pressure would cause the left isolation valve to close. We started number 4. The 'Isol Valve Disagree' light did not go out and so we shut the engine down so Maintenance could work on the valve. In the meantime; flight attendants were advising us that it was extremely hot in the aft cabin. The ground air conditioning had been pulled from the time we commenced our attempts to start the engine at the gate; the hoses being attached to the jetway which had been retracted. The ground pneumatic cart was extremely weak. In fact we aborted our first start attempt because the duct pressure dropped to zero. There was not even enough output from the ground cart to operate a pack. Normally; once the start valve is opened we can hear the ground cart rev up as it takes on the pneumatic load. This did not happen. On our second start attempt the Mechanic did something to increase the cart's output and we got a successful start; but then as stated earlier had to shut the engine down to address the valve issue. At this point; knowing that the cart was weak and could not support pack operation; we asked for the air conditioning hoses to be connected back up; but that was not possible because the Mechanic was now accessing the isolation valve to wire it open. The temperature reached 90 degrees plus in zones D and E. Maintenance completed wiring the isolation valve open; but at this point we had lost our tow bar and delayed 10 more minutes waiting to get that back. Passengers [were] very uncomfortable. [There were] numerous calls from the flight attendants expressing their concern. We made PAs and explained the best we could. After Maintenance wired the left isolation valve open we went ahead and started number 4 engine at the gate even though the irregular procedure directed us to close the left isolation valve; which was now not possible.In hindsight; it would have been possible to start the number 1 engine at the gate instead because the right isolation valve was operating normally. We learned that the ground pneumatic cart did not belong to our company; it was borrowed. We were told that the Company used to have its own cart but no longer; due to cost cutting. Clearly; dispatching with the APU inoperative is only a sound decision if there is adequate ground support equipment at our international stations. In this instance; a more robust ground pneumatic cart would have allowed us to operate air conditioning packs while we figured out how to address the isolation valve issue. Our passengers would still have been slightly delayed; but least they would have been comfortable. The station personnel were doing the best they could with the equipment they had; no complaints about them. They were very responsive to our requests; but limited in what they could do for us; given the poor operation of the borrowed cart and the need to wait for the return of the tow bar.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.