Date: 202107
Local time of day: 1801-2400
Location: ZZZZ.Airport, FO
Flight conditions: VMC
Light: Night
Aircraft: B777-200
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Taxi
Aircraft component: APU
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Communication Breakdown
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew; Person Maintenance
When detected: Aircraft In Service At Gate
Result: Aircraft Aircraft Damaged; Flight Crew Returned To Gate; Flight Crew Overcame Equipment Problem; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: During push with brake set; started the Right Engine. Immediately after the engine started; we received an APU Limit checklist indication. We ran the checklist which stated an exceedance had occurred and directed us to shutdown the APU; which we did. Shortly after shutting down the APU with the overhead switch; the ground mechanic stated on the intercom 'APU fire; shutdown the APU.' I then stated 'no we do NOT have an APU fire indication in the cockpit; but did get an APU limit checklist; which we ran and shut down the APU already.' He acknowledged the radio and I believe at this point went to the back of the airplane for a closer look. I assumed any smoke he had seen was from the limit exceedance and decided not to fire the APU bottle since we did not have an indication of an APU fire. After taking care of the switches in the cockpit; I went outside to investigate what had occurred and found two mechanics at the rear of the airplane with the APU compartment open; as they investigated the APU from a cherry-picker stand. From the ground; I could see no evidence of any fire either inside the APU compartment nor on the exterior of the tail section. When finished with their examination; the mechanics came into the cockpit to explain what they found. I had great difficulty understanding their English and exactly what they were saying; except that they would now MEL the APU. I understood them to say they thought it was from fluid leaking in the APU. I only found out after talking to the operations director on a phone patch on the ramp in ZZZZ; that the mechanics had used a fire extinguisher during their inspection. They did not tell me this or perhaps both my First Officer and I misunderstood them. I did not witness them using a fire extinguisher and it must have occurred prior to me leaving the cockpit to investigate. I made a write-up in the logbook. No emergency was declared because it seemed well under control. Better communication between crew and mechanics over what they did; as they should have told the Captain that a fire extinguisher was used! Now perhaps they did attempt to tell the crew and we did not comprehend what they were stating.




Synopsis: Flight Crew reported an APU exceedance indication in the cockpit was actually an APU fire that was extinguished with portable fire extinguishers by maintenance.