Date: 201907
Location: ZZZ.Airport, US
Aircraft: B757 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise; Initial Climb
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Main Gear Door
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Other / Unknown
Reporter qualification: Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting; Workload
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Person Flight Crew; Person Passenger
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition; Flight Crew Diverted; General Flight Cancelled / Delayed
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: When I boarded the flight; I introduced myself to the Flight Attendant and let her know I was a 787 instructor and had formally been an instructor on the 757/767 for many years and that I was seated in 7-E if they needed any assistance at any time. I normally try to also introduce myself to the pilots but access to the flight deck at that time was very congested. On initial departure out of ZZZ I noticed a slight vibration/ rumbling of the jet. I didn't pay too much attention to it at the time as I was talking to gentleman seated next to me. I did notice that sometime after departure we didn't seem to be moving over the ground as fast as we normally do but thought maybe ATC had given the crew a speed restriction. There was also weather that the crew was deviating around. At some point in the flight; the FA (Flight Attendant) came back and asked if I could come to the forward galley to discuss something with her. She then told me the crew was having some type of mechanical issue and requested my assistance. Initially; I spoke with the pilots via the intercom. They believed that they had some type of gear/gear door issue. They asked me to walk to the middle of the cabin and see if I noticed any unusual sounds or vibrations. I noticed there was a pronounced vibration which seemed to come from the right side (First Officer's) of the jet and it seemed louder than normal. I was then asked to come up to the flight deck to discuss the situation with the pilots. When I entered; I noticed there was a gear door light. There was a jump-seater that was also assisting the crew. The Captain gave me a quick assessment of the situation and advised me that they felt they had a gear/gear door issue and had just finished discussing the issue with Dispatch and [Technical Support Maintenance Control]. They had also slowed down to a slower airspeed than normal to avoid potentially damaging the gear/door due to increased drag. They had also discussed with Dispatch fuel requirements to continue to ZZZ1 at a lower altitude and slower airspeed. They had also decided to divert to ZZZ prior to my involvement. I suggested they may want to rethink a ZZZ divert as I had heard from another pilot prior to my flight that ZZZ was IROPS (Irregular Operations). I suggested a potential divert to ZZZ2. They said they had discussed that idea with Dispatch and didn't want to fly back through the weather they had just deviated through. To unload the pilots; I offered to communicate the Captain's directions and brief the flight attendants and keep them advised. I then reviewed the 757 QRH with the jump-seater and the pilots and we agreed that checklists were completed properly. I re-briefed the 'TEST' to the flight attendants and emphasized it should be a normal landing but that airport fire rescue was standing by as a precautionary measure. The Captain elected to land the aircraft since [priority handling was requested] and there was some potential of unknown outcome after landing. The Captain also briefed a modified go around to leave the gear down. It was a normal visual approach. At approximately 150 feet ZZZ Tower directed us to go around and stated 'Aircraft X go around your main gear appears abnormal'. As the crew was initiating the go around maneuver; the ARFF (Airport Rescue and Fire Fighting) stationed at the approach end of the runway says to Tower; 'The gear appears normal to me'. We came back around and the Captain made a normal landing.




Synopsis: Off-duty First Officer reported assisting Flight Crew with a landing gear door issue; resulting in a diversion and precautionary landing.