Date: 201707
Local time of day: 1201-1800
Flight conditions: VMC
Aircraft: B787 Dreamliner Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Aircraft component: Exterior Pax/Crew Door
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Returned To Departure Airport; Flight Crew Landed As Precaution
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: I was advised by the inbound captain that the aircraft had a problem with the door sill plate at door IL that had been addressed by maintenance. He indicated to me that on climb out the fix failed and a very loud noise was observed from the area of the repair. They continued and wrote the malfunction up. Maintenance performed the prescribed speed tape repair and released the aircraft for our flight. Passing 28000 feet on departure the repair failed and we experienced an extremely loud noise (imagine a truck horn) coming from the area of door 1L. We contacted dispatch and had Maintenace Control conferenced in. We observed that the sound almost seemed like an electric motor failing. Maintenance Control researched the history and could not find any previous squawks concerning possible motor/fan problems. We received several calls from the Flight Attendants (FA) with concern about our situation and they also indicated that the passengers were also becoming concerned.  I made a PA addressing the noise but I'm not sure anyone could hear it over the noise in the cabin. At that point I sent the [Relief First Officer] back to evaluate the problem. He reported that there was a slight hissing noise coming from the lower part of the door that was reduced when he put blankets against the door but the loud horn-like sound was coming from below the floor and that the floor was vibrating. Based on his report; the concern from our FA's and Passengers and the prospect of flying for another 11 hours over inhospitable territory I felt that a divert was in order. We called dispatch back and along with Maintenance Control decided that a return to [departure airport] was the best option. The First officer (FO) and [Relief First Officer] were in agreement as well. The FO was flying so he advised ATC and initiated a divert. The next issue was to Jettison fuel or land overweight. Dispatch uplinked the landing data for 435000lbs on runway which indicated that runway weight limit was not an issue. We conducted the Overweight Landing checklist and determined that Approach Climb Limit was also not an issue so with concurrence from Dispatch; (Maintenance Control mentioned that an overweight landing inspection would not be a problem as the aircraft would be down for several days with the door sill issue anyway) and the guidance in the Operations Manual we elected to conduct an overweight landing. Weather was VFR with winds under 10kts. We elected to not declare an emergency as all systems were normal and we had no reason to think that the landing would require any assistance. The landing was uneventful and we taxied to a hardstand where the passengers were deplaned and loaded onto waiting busses.




Synopsis: The Captain of a Boeing 787 reported that a very loud noise from door one left resulted in an air turn-back.