Date: 202105
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: IMC
Weather elements / visibility: Rain
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb; Takeoff / Launch
Airspace: Class B ZZZ
Aircraft component: Gear Extend/Retract Mechanism
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Weight And Balance
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Departure Airport; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: While flying flight ZZZ - ZZZ1 the gear did not come up on takeoff when the gear handle was raised. I was flying and immediately recognized that something was wrong. I kept the airspeed at 220 kts. while we climbed out to 4;000 ft. MSL. I put the auto pilot on and checked the Aux Gear Extension Door; it was down. I called for the QRH and the FO ran the checklist for Gear Disagree with the handle in the off position. It did not help. I gave the aircraft to the FO and directed him to inform ATC that we were going to return to ZZZ. I then contacted Dispatch. Maintenance Control and the [Chief Pilot] were brought on the line as well. While all the parties were assembling; I talked with the Flight Attendants and the passengers. Maintenance Control and I ran the Gear Disagree checklist with the gear handle in the up position. This checklist had me lift and reseat the Aux Gear Extension door. As the checklist was completed; the gear was able to be raised. In conference it was decided to land overweight versus burning down fuel to 157.3. Dispatch sent landing data for our weight on Runway XXR. I took the aircraft back from the FO and then flew an approach to Runway XXR in ZZZ. We configured early and got a normal gear extension. We landed normally with max auto brake set. Our landing weight was 168.0; 10.7 overweight. We taxied clear; the fire trucks checked our brakes and we then taxied back to gate.


Second narrative: I was the pilot monitoring on the flight from ZZZ to ZZZ1. The flight departed the gate and taxied to the runway for a normal takeoff from [Runway] XXL. The visibility was slightly reduced due to rain; and there were overcast clouds at 800 ft. After rotation; the Captain called for gear up and I retracted the gear. We started the right turn on the departure; and the flaps were brought up on schedule and the Captain called for the after takeoff checklist. I checked in with Departure and we were given a 270 heading and 6;000 ft. Departure then gave us Direct to XXXXX; which I programmed in the FMC and LNAV was selected. This was a relatively high workload time; in IMC. I completed the after takeoff checklist flow; electing to leave the engine anti-ice on; ensured the flaps/slats were retracted; and placed the gear handle in the off position. I completed the after takeoff checklist and noticed that there were lights illuminated at the gear panel. At this time; the Captain and I both noticed that the plane did not sound right; and we started trying to diagnose the issue. The Captain used speed intervene to set the speed to clean maneuvering speed of 225 kts. I mentioned that it sounded like a gear door was open; and we looked at the gear lights and that the landing gear lights indicated 3 green on the instrument panel as well as the overhead panel. There were also 3 red lights on the gear indication. The Captain called for the QRH; and I completed the QRH for landing gear disagree. The QRH was completed and we determined that the gear was in the down position. At this time; we both looked at the alternate gear door; which was closed. During my preflight; I had confirmed the alternate gear door was closed visually; and then by stepping on it. I had also confirmed the gear pins were present on the flight deck.At this time; we advised ATC that we would like to stop at 6;000 and get some delay vectors for a landing gear issue that we needed to work on. The Captain transferred controls and radios to me; while she contacted Maintenance Control via the radio. Maintenance Control instructed her to place the gear handle in the up position and then open and close the alternate gear door. Then the gear handle was placed in the down position; and back to the up position. At this time the gear retracted and all gear lights went out. From the time we took off; until this moment was approximately 15 minutes. We decided to [advise] ATC and requested that fire rescue meet us at the runway. We decided that a return to ZZZ was our best option. Due to the fact that we tankered an extra 16k [lbs.] of fuel we were overweight for landing. The Captain talked to Maintenance Control and Dispatch to see if they wanted us to burn off fuel or land overweight. Were sent overweight landing data and determined that a safe landing could be made back in ZZZ; and used auto brakes MAX. During this time; the Captain made several announcements to the Passengers explaining the situation and also briefing the FAs on our expected plan of action. We briefed the approach; and discussed our plan in case the gear failed to come down on the approach. A normal landing was made and we exited the runway and stopped to allow our brake temperatures to be read. Fire rescue said everything looked normal and followed us to the gate.


Synopsis: Flight Crew reported gear would not retract on take off and cycled the alternate gear extension door which allowed the gear to retract. The flight crew performed an air turn back to a precautionary landing.