As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE LANDING GEAR WOULD NOT RETRACT AFTER TAKEOFF FROM IAH. THE GEAR HANDLE WOULD NOT MOVE PAST THE OFF TO THE UP POSITION. THE AIRCRAFT WAS RETURNED TO IAH WHERE IT LANDED WITHOUT INCIDENT. MAINTENANCE FOUND THE M991 AIR SENSING SQUAT SWITCH CARD AT FAULT. THE M991 CARD WAS REMOVED AND REPLACED. THE CARD TESTED GOOD IAW MM 32-09-20, PAGE 416.