What was found
(CAN) ON JANUARY 02, 2005, AFTER TAKE OFF THE LANDING GEAR WERE SELECTED UP (RETRACT). LANDING GEAR REMAINED ON EXTENDED POSITION. AIRCRAFT RETURNED TO DEPARTURE AND LANDED SAFELY WITH NO INCIDENCE. POST FLIGHT INSPECTION REVEALED NO MECHANICAL DAMAGE. LT AND RT PROXIMITY SENSORS WERE FOUND DEFECTIVE. NLG PROX SENSORS AND LANDING GEAR CONTROL UNIT WERE ALSO REPLACED.