Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 212; Flight Crew Type 246
Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport
Aircraft
Twenty minutes after takeoff; at FL260; we received a call from the cabin that there was a loud snap; followed by sparks and an acrid smoke coming from the ceiling of the lavatory at door 2L. We were told that when the lavatory door was locked the sparks would continue; but stopped with the door lock not locked. The cabin had a good amount of smoke in it. We contacted dispatch and was patched to [maintenance]. [Maintenance] informed us that there were no CBs to pull to isolate the overhead lights of the lav. Concurrently we were running the Smoke Fire Fumes QRC checklist; and diverted back to [departure airport]. An overweight landing was accomplished in accordance with the QRC Overweight Landing Checklists.
B757 Captain reported returning to departure airport after a lavatory overhead light began to spark and smoke.