noun
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.
Compound of 着陸 (ちゃくりく, 'landing') and 装置 (そうち, 'equipment, device').