Date: 202103
Local time of day: 0601-1200
Location: ZZZZ.Airport, FO
Flight conditions: VMC
Light: Dawn
Aircraft: B737 MAX 8
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked; Taxi
Airspace: Class C ZZZ
Aircraft component: Powerplant Fuel Distribution
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Flight Attendant (On Duty)
Reporter qualification: Flight Attendant Current
Human factors: Communication Breakdown
Second reporter function: Pilot Flying; Captain
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Fuel Issue
Detector: Person Flight Attendant; Person Passenger; Person Ground Personnel
When detected: Aircraft In Service At Gate; Taxi
Result: Flight Crew Returned To Gate; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Human Factors; Aircraft; Procedure; Staffing
Primary problem: Procedure

Narrative: Captain advised we had a maintenance issue to have checked out before boarding our return flight to ZZZ. I believe pilots saw something had leaked under the engine; observed by FO walk around. Mechanic looked for AC left engine fuel leak suspected by pilots; after a period of time (I do not recall) mechanic could not find leak; he signed off on logbook. Pax began boarding; entry door was closed; on push back; FA's were doing safety demo when FA 4 was called over by passenger sitting in right window seat a few rows aft of the wing. Passenger stated something was dripping from wing. Demo was almost complete; FA 4 continued with demo then looked out to see pax concern. Upon seeing fluid dripping from several places along the underside of the wing; she went to get another FA to see the issue. FA 4 took FA 3 to see the dripping. FA 4 and 3 went to the forward entry area to inform FA 1; I was working FA 4 and standing next to FA 1 so I was also informed at this time. FA 1 called Captain (CA) to advise. Several minutes later we were notified by CA that we were going back to gate and need to disarm doors. Same mechanic (only one I saw) returned. Passengers remained onboard while he checked the issue further. It is my understanding he reported he still found no leak. Sometime later CA advised crew and passengers via PA that we would be starting engines at the gate to further troubleshoot the problem; he advised passengers to remain seated. I was told this test was done at the Captain's request; not the instruction of this mechanic. Engine test was completed; seat belt sign turned off; more time passed and it was decided to deplane passengers. While crew waited on the AC for info from the company as to our schedule and whether this plane was going to be able to be repaired; our FO showed CA a video of the fuel leak while the engine test was running. I saw this video; fuel was pouring from the engine like a running garden hose. CA stated he had no confidence in this mechanics ability to perform his job as he appeared that he had no idea how to handle it. While I was discussing this with CA he told me he asked the mechanic earlier to call Company Maintenance base for instruction. The mechanic told CA yes he did call Company. CA told me he was angry with this mechanic because he himself called Company and was told mechanic did not contact them.  Aircraft was taken out of service hours later.


Second narrative: Upon arrival at Gate 1 in ZZZ; ground personnel connected to headset after engine shutdown to report a fluid leaking from number 1 (left) engine. He smelled his fingers; reported that it smelled like fuel; and asked me to investigate the fluid. The First Officer and I both investigated; and felt; to the best of our knowledge; that the fluid smelled like fuel. At that point; there was a puddle under the #1 engine; 3 feet in diameter; and fuel was dripping at a rate of 2-3 drips per second. As we stood there discussing; the dripping reduced to 1 drip every 4-5 seconds. The FO and I agreed that we were unfamiliar with any allowable drips on the 737 MAX LEAP engines; and I proceeded to the cockpit to make an entry in the aircraft logbook; dispatch a code in ACARS; and call the Maintenance Control to coordinate for a maintenance technician. The technician arrived and we conferred on the above information; and he proceeded to investigate and coordinate with the maintenance team in Company (my assumptions; although I did hear his telephone conversation at one point). After his investigation; he returned to the cockpit to inform me that he had opened the engine cowl; performed his checks; and found all valves ready for service. He signed off the write up and dispatched the aircraft for service. We boarded the passengers and pushed from the gate at XA:40. Push back was normal; engine start on engine #2 was normal. After push back was complete; we started engine #1. After engine start; and after the push crew had disconnected and given me a salute; ground personnel came back; pointing to the #1 engine. At the same time; the Cabin Crew called to alert me to a passenger that was reporting fluid leaking from the RIGHT side of the aircraft; and a Flight Attendant confirmed that we were leaking fluid. The report that fluid was leaking from the right was incongruous; and caused the FO and I a couple minutes to confer and investigate what that could be. We later found out the leak was in fact from the LEFT side; and was from the #1 engine. I did note in my investigation; that the #1 main tank fuel quantity differed from the #2 main tank fuel quantity by nearly 400 lbs; a discrepancy that didn't exist before pushback as I had noted the fuel during the Before Start checklist. By this time; the same ground coordinator who had reported the previous leak connected to headset and reported that we were again leaking fuel from the #1 engine. His report was that fuel was gushing out from under the engine cowl. The FO and I coordinated and elected to taxi back to the gate to expedite arrival and engine shutdown. The ground crew quickly assembled and we returned to the gate at approximately XA:48; and shut down both engines. I made another logbook entry and called Maintenance Control to inform them that we had returned to the gate and required the maintenance technician to perform more checks before we could depart. The maintenance technician returned; and we performed an engine run at the gate on the #1 engine; which resulted in identifying a large fuel leak; with the technician recording video. At this point the aircraft was taken out of service; and I began coordinating with station personnel and Crew Scheduling for subsequent actions.


Synopsis: Flight Attendant reported to Flight Crew that a passenger noticed liquid streaming from wing and Captain elected to return to the gate. The liquid was later determined to be fuel and the aircraft was taken out of service.