As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SEA - LANDING GEAR WOULD NOT RETRACT ON TAKEOFF. RAN THE CHECKLIST BUT NO CHANGE. RETURNED TO THE FIELD AND ACCOMPLISHED A UNEVENTFUL LANDING. FERRIED THE AIRCRAFT TO PDX FOR REPAIRS. IN PDX, FOUND LOOSE JAM NUTS AND MISSING SAFETY WIRE AT THE NOSE WHEEL CENTER PROX SENSOR. REPAIRED AND RIGGED SENSOR IAW 32-61-06-830-801. AIRCRAFT RETURNED TO SERVICE. NO PARTS REPLACED.