Date: 201502
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Learjet 31
Operator: Air Taxi
Operating under: Part 135
Flight plan: IFR
Mission: Ambulance
Flight phase: Cruise
Airspace: Class B ZZZ
ATC / advisory: TRACON 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
Human factors: Human-Machine Interface; Troubleshooting
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Speed All Types; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Weight And Balance
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Returned To Departure Airport
Contributing factors: Aircraft; Weather
Primary problem: Weather

Narrative: During preflight I ensured that the main landing struts and components were reasonably clear of ice and slush. Also ensured that squat switches were unobstructed. I taxied at a slow rate en-route to runway to ensure the minimum buildup of slush and ice on the landing gear. Brakes were used extensively to keep the aircraft at a slow taxi speed and to utilize the residual brake heat for preventing contamination of the main landing gear.  A normal takeoff was executed. During our takeoff briefing I stated that we would leave the landing gear down for one minute after takeoff. We followed through with the plan but the landing gear would not retract. Cycled the landing gear one more time with no success. I instructed the First Officer to ask ATC if we could maintain 8;000 since the aircraft would not pressurize in ground mode. ATC granted our request. Next we activated the main wing anti-ice system in an attempt to use the excess bleed air; vented through the main landing gear well; to melt the contamination on the squat switches. After 10 minutes we attempted gear retraction two more times with no success. Also tried disengaging the anti-skid system and pumping the brakes with no effect. At that point we elected to return to Airport ZZZ but recognized we were over max landing weight and would need to burn off fuel for 15 to 20 minutes. ATC vectored us in the southeastern portion of their airspace. While on vectors; still at 8;000 feet; we also tried increasing speed from less than 200 knots to 250 knots hoping it would shed more of the contamination off the landing gear. We may have been underneath the Class Bravo airspace at this time. We executed a normal descent; approach; and landing at ZZZ. After taxi-in and shutdown we observed an abundance of ice had accumulated on the main landing gear. A discrepancy was noted in the aircraft's maintenance log.




Synopsis: Despite efforts to reduce landing gear exposure to the winter elements during preflight and taxi out; following takeoff the flight crew of a LJ-31 was unable to raise the landing gear. Despite a variety of creative efforts to overcome/eliminate the suspected accumulation of frozen material preventing retraction; the landing gear refused to respond. After a period of delay vectors to reduce the landing gross weight they landed the aircraft and; upon inspection; determined that their suspicions were accurate.