What was found
AFTER GEAR UP/FLAPS UP HAD HYD PRESS, STAB MISCOMPARE ANNUNCIATORS AND UNLOCK GEAR LIGHT. PULL HYD C/B, AND LOUD THUMP HEARD AND FELT IN NOSE GEAR AREA. PUSH HYD C/B IN GET SAME NOISE. ALL LIGHTS OUT AND SYSTEMS WORKED FINE WITH GEAR DOWN AND FLAPS FULL AT LANDING. AFTER T/S VIA CE-560XL MM FOUND HORIZONTAL STAB COMPARE AIRSPEED SWITCH TO FAIL. REPLACED FAILED SWITCH WITH NEW SWITCH IA CE-560XL MM CHAP 27-40-00. CARRIED OUT OPS CHECK STANDBY PITOT/STATIC SYSTEM IAW CE560XL MM CHAP 34-11-08. CARRIED OUT STAB OPS CHECK IAW CE-560XL MM CHAP 27-40-00. ALL CHECK WERE GOOD. JACKED A/C AS REQUIRED. PERFORMED LANDING GEAR FUNCTIONAL TEST. RETRACTED AND EXTENDED LANDING GEAR 30 TIMES, NO DEFECTS NOTED.