Date: 201706
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: Mixed
Light: Daylight
Aircraft: A319
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Tower ZZZ
Aircraft component: APU
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting
Anomaly: Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Other / Unknown
Detector: Person Flight Crew
When detected: Taxi
Result: Flight Crew Returned To Gate; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft; Weather
Primary problem: Aircraft

Narrative: We started both engines on the APU after push and expected a quick taxi to XXR. We then were directed to XXL and told to expect a reroute due to weather in 10 minutes. I elected to keep both engines running at this point as it would be a short delay. A few moments later tower informed us that Center was very busy and to expect an indefinite delay. I asked for and received permission to shut down. I pulled up the AOM (Aircraft Operations Manual) Engine Shutdown during ground delay checklist. Considering the length of delay and that we had successfully started engines on the APU only minutes earlier; I elected to shutdown both engines. I talked to the lead FA and shutoff the seatbelt sign so passengers could use the lavatory. I then sent a message to dispatch to inform them of our delay. A few minutes later a FA in the aft galley called to ask if the APU air was on as is was quickly getting very hot. I informed her that it was on and that we would cool the cabin. I discussed with my FO that the APU was weak and that we would have to start an engine. We discussed that we would simply return to the gate if fuel became a problem. About this time tower informed us that a reroute was not required and to contact them when ready to taxi. We attempted a normal start on engine 1. The bleed pressure dropped to 10 psi after selecting the start master and the FADEC aborted the start. I called Maintenance Control and told them about the aborted start and very low bleed pressure. They told us to go ahead with a manual start. The manual start was unsuccessful even after performing the load shedding recommended in the procedure. I called Maintenance Control again. I informed them that we would try to start engine 2 so we could return to the gate or at least cool the cabin and cross bleed start engine 1.  The start on engine 2 was unsuccessful. They walked us through a function under the CFDS (Central Fault Display System) menu to do a 'bleed boost'. The engine still would not start. At this point the FAs had called to inform us that passengers were in distress due to the high heat. The FO and I fully opened the cockpit windows and opened the cockpit door to attempt to start airflow through the cabin. I directed the FO to call ops for a tow to the gate while I called the Chief Pilot. Ops indicated that it would take 25 minutes to tow us to the gate. I told the Chief Pilot that I only had 2 options at this point; as we had elderly passengers and children on board; and soon would be facing a medical emergency.  We could evacuate the aircraft; which I believe almost always causes passenger injuries; or open a few doors in the cabin to lower the temperature. He agreed that it was a safer course of action to open doors and directed us to open the forward right (R1) door and aft left (L2) door. We discussed that in the event of an evacuation we would close and arm the doors and perform a normal evacuation via the slides. The temperature was showing 96 in the cockpit and in the 90s in both aft zones. At this time the FAs were serving ice water to the passengers to aid in cooling. I stood with the lead FA as he opened the forward door and we discussed what to do in an evacuation. I directed him to stay at the door so a passenger could not fall from the aircraft. I then walked to the aft galley and did the same.I returned to the cockpit and made another PA (I did several during this process). The temperatures immediately began to cool. Within a few minutes the tug arrived. We closed and armed the doors; the FAs secured the cabin; and we were towed to a gate. The tow took several minutes and we were relieved that the cabin had cooled somewhat before having to close the doors again. At the gate I directed all passengers to deplane so they could cool off in the terminal and so the aircraft could cool as well. Maintenance Control deferred the APU. I called dispatch and obtained a completely new release with increased fuel to run both engines during along taxi out. I talked with the crew and everyone indicated that they were fit to continue. We delayed at the gate until cabin temperatures reached 80F.  We then quickly boarded and were able to successfully complete the flight.In the future I will only shutdown both engines if it is absolutely necessary and that we have a very strong APU. [Company] offered all passengers on our flight free non-alcoholic drinks and a voucher for future travel. This made everyone very happy and we had numerous passengers come to the cockpit after landing to thank us.




Synopsis: A319 Captain reported a delayed situation in hot weather and a malfunctioning APU with engines shutdown resulted in excessive cabin heat for the passengers.