Regional Jet 200 ER/LR (CRJ200)
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
On takeoff when First Officer called for 'gear up' I tried to pull gear up but; lock was still in place. At that time First Officer noticed a 'ckpt ovbd' cool status message. A few seconds later we got a 'WOW overboard and inboard' caution messages. At that time got the QRC out and got to the required section. First Officer took over communications while I did the QRH; we climbed out and cruised at 200 KIAS to 10000 ft. Noticed we had a pressurization problem as well but we were already low altitude for this short flight; decided to descend to 8000 ft. First Officer and I agreed with the QRH possible lack of braking on landing; should [advised ATC]; and then First Officer did at that time. While I was in the back briefing the Flight Attendant; First Officer got vectors for Visual XXL. I gave the Flight Attendant her [duties]; I decided it was best to have the passengers brace due to the braking unassured on landing. On short final I dinged the Flight Attendant to let her know landing was imminent; to start calling for brace positions. Landing was normal; complied with QRH on landing and manually extended the GND lift dumping and spoilers. We then came to a complete stop and had the firetrucks do an inspection of the landing gear just in case on any unforeseen malfunctions or parts missing. Everything was normal; we then taxied to the gate as normal. The maintenance personnel suspected there is a problem with a flight computer in the aft equipment bay. In the air I assumed it was a squat switch problem of some sort but Maintenance says it looks like it's a bigger problem than that; nothing official at this time of reporting.
The aircraft departed the airport where gear change maintenance had been done and during climb-out the crew were unable to move the landing gear handle up to retract the gear and a caution message for the gear WOW (Weight-On-Wheels) system. Upon inspection of the aircraft maintenance personal found some Weight-on-Wheels targets installed in the main landing gear Weight-on-Wheel sensors. During the course of work I was tasked with completing the installation of the right main landing gear on the aircraft as well as finishing the close-out of both main landing gear installations. The night shift had installed the LH gear up to the ops checks and close-out portion of the installation task card. The right gear was only partly installed. I installed the remaining components on the RH main landing gear and performed the close-out portion of both gear installs as the close-out portion of the left and right gear installations have inter-related maintenance tasks. During the completion of the close-out portion of both main landing gears we are required to bleed the IB and OB (inboard and outboard) brakes. With aircraft on jack-stands we are able to pressurize hydraulic system #3 but not able to pressurized the IB brakes for bleeding. However; in order to run the #2 hydraulic pump and pressurize the IB and OB brakes for bleeding I needed to install the Weight-On-Wheels targets to simulate the aircraft on the ground. I installed these targets as required and performed the brake bleeding. According to the installation task card the next several maintenance tasks are to perform gear retraction/extension checks and then perform an operational check of the brakes prior to lowering the aircraft to the ground. I opted to use the WOW targets in lieu of lowering and jacking the aircraft several times. The target tools I was using to simulate the WOW sensors on this aircraft were small tools that did not have conspicuity flags or markings installed at the time. And due to the installation orientation and location on the landing gears they are very un-noticeable if left installed. Also the aircraft will not show any faults if the tools remain in place and the aircraft is lowered to the ground and moved. I suspect these tools were not seen or removed from the aircraft prior to aircraft release. Modifying the main landing gear installation task card for clearer workflow for completion of close-out tasks.  Also; installing conspicuity flags or markings on target tools.
Captain reported gear would not retract after takeoff; causing an air turnback and emergency landing.