B737-800
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 50
Troubleshooting
Ground Event / Encounter Other / Unknown
General None Reported / Taken
Airport; Procedure
150;000 pounds at pushback. Pushed straight back off Gate XX. Started both engines. Did checklist and released brakes for taxi. Plane wouldn't move. Added power; no movement. Increased N1 to 40%; plane would not move. Figured we were chocked or brake stuck. Had Ramp Agents come out and check if we were chocked. They believed mains were below the lip of ramp. They suggested to add more power. I shut both motors down and had them go get a Tug. They discovered both mains were in storm drains. We pushed plane back 10 more feet. Started up and taxied out.Suggestion - Have ramp in ZZZ be aware of storm drains.
Air carrier Captain reported that after pushback both main wheels became stuck in storm drains requiring a tug to free the aircraft.