B737-800
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 512
Distraction; Human-Machine Interface; Time Pressure
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Flight Crew Returned To Departure Airport; Flight Crew Overcame Equipment Problem; General Maintenance Action
Human Factors
We departed ZZZ on a flight to ZZZ1. After takeoff; we tried to raise the landing gear; but was unable. We ran the QRH and returned to ZZZ. As we were preparing for the approach; we noticed the gear pins were not onboard. After pulling into the gate; we were informed by Ground that the gear pins were still installed in the gear. I went outside to talk to Maintenance; he said that the ribbons were still rolled up as they would be in the cockpit. The First Officer said he didn't see any ribbons hanging down that would have alerted him. There was no logbook entry stating that the pins were installed. Some Maintenance had been done the night before also. As a Crew; we were a little rushed in getting things ready for flight; i.e.; having trouble getting clearance thru CDLPC. Everything came together at push; ([weight and balance]; Clearance; doing checklist.) I just failed to look for the pins when we were doing the checklist. My mistake. A lot of departments dropped the ball on this one; but ultimately; I should have caught the pins not being there. Nothing more than just slowing down and double checking everything. Try not to get rushed.
Gear did not retract when commanded after takeoff. We ran the appropriate checklists and returned to ZZZ. Upon landing; we were told by Maintenance that the gear pins were still in and that the warning flags attached to the pins were wrapped around the pin rather than free flowing and visible. I failed to notice the landing gear pins were installed; when performing my walk around. I was not expecting to see the landing gear pins as we are no longer responsible for pulling them; and this expectation bias contributed to me not noticing the pins were still in. In addition; our CPDLC was not working correctly; and this compounded with an urgency to get off the gate for an on time departure; resulted in our not verifying that the gear pins were aboard during the Before Start Originating Checklist.  More attention to detail during the walk around. Slowing down on checklists and verifying that the condition matches the response on the checklist.
B737-800 flight crew reported uneventful air return shortly after takeoff due to landing gear not retracting.