Refers specifically to the undercarriage of an aircraft, including wheels, struts, and related mechanisms.
パイロットは着陸装置を下ろした。
The pilot lowered the landing gear.
降着装置 is a broader term that can refer to landing gear for spacecraft or other vehicles, while 着陸装置 is almost exclusively used for aircraft.
instrument landing system; ILS
microwave landing system; MLS
Compound of 着陸 (ちゃくりく, 'landing') and 装置 (そうち, 'equipment, device').