Date: 201906
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: B757 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Time Pressure; Training / Qualification; Confusion
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Passenger Electronic Device; Ground Event / Encounter Other / Unknown
Detector: Person Flight Attendant
When detected: Pre-flight
Result: General None Reported / Taken
Contributing factors: Human Factors; Company Policy
Primary problem: Company Policy

Narrative: Upon boarding the aircraft; the FO (First Officer) told me that a phone had been lost through an opening in the sidewall. It had fallen between the inner and outer walls of the airplane at seat XXF; and the mechanics said they would have to dismantle some of the cargo loading system to locate and remove it; and it was going to be deferred. One by one; three flight attendants came up to the flight deck to tell me how upset they were that the airplane would be flying with an inaccessible phone on board. They were worried that it could cause a fire; and thought it unsafe to fly. The FO and I felt that there are many devices on any flight powered by batteries; and that this was not a significant safety issue; so I decided to accept the airplane. I have little basis for making such decisions. I don't know if there are incidents of phones and similar devices causing fires on airplanes; but since [Company] provides us with training on how to handle such fires; there must be some level of risk. Another reason for concern is that the area in which the phone was lost has no fire detection or protection; and a fire caused by a loose cellphone could burn for some time without detection; and when it is detected; we would have no means of fighting the fire.What [is known] about the hazard of electronic devices to aircraft? Should we refuse to fly airplanes with cellphones lost in inaccessible areas?Does the FAA or NTSB track these problems? Are airlines required to report them?Is there some fix to the sidewall areas of the 757 so that this problem no longer occurs? It must be distressing to our customers when they accidentally drop their phone and find it cannot be returned to them for several days.And if loose cellphones aren't a safety problem; why does [Company] devote time to training us how to handle fires in electronic devices? It's partially [Company's] fault when flight attendants are worried about loose phones lost in the interior of the airplane; since their training includes alarming videos of fires caused by such devices.Our flight was delayed because the flight attendants were obviously concerned about the safety of the aircraft and wanted me to refuse to fly it. I had insufficient information to make a good decision; and would like to find out how this situation should be handled in the future. Could you provide me with some reliable information about this problem; the possible consequences of flying over water with a lost cellphone somewhere in the belly or sidewall and whether or not this is a good reason to refuse an airplane?Since filing the above report; I have learned of a [different Company] aircraft that crashed due to lithium ion batteries catching fire; as well as several incidents of fires in cell phones on airplanes. I also know that there are frequent write ups of fluid spills in airplanes and wonder if a dropped cell phone sliding below the cargo pit might be impacted by such fluids. Pilots and flight attendants are taught about battery fires and we now have gloves and thermal containment bags to address the hazards of electronic fires on board.




Synopsis: B757 Captain reported being dispatched with a lost cell phone in the cabin; and expressed concern they did not have enough information to make a decision on whether to accept the aircraft.