ADVANCED MATERIALS & PROCESSES | APRIL 2025 14 The United States National Transportation Safety Board (NTSB) is an independent federal agency charged with investigating all civil avia- tion accidents and significant surface transportation events. The NTSB is not a regulatory agency but determines probable causes of accidents and issues safety recommendations to prevent them from recurring. Among the largest numbers of transportation accidents that the agency investigates are those in the general aviation category or those not defined as commercial aviation (Federal Aviation Regulations Part 121). A recurring issue in general aviation that the NTSB Materials Laboratory has investigated involves the hydraulic actuators that extend and retract the main landing gear of Cessna 210 Centurion airplanes. This vehicle is a six-seat, high-performance, retractable- gear, single-engine, high-wing general- aviation light aircraft. Originally produced from 1960 to 1986, the airplane is widely used by private operators, air-taxi and commercial charter, and private companies. A hydraulic fluid leak caused by a rupture of a hydraulic actuator would prevent the pilot from fully extending the landing gear, impacting their ability to land the airplane safely. BACKGROUND The NTSB investigated multiple accidents of hydraulic actuators integral to the 210 Centurion landing gear system, as detailed in Table 1. Many of the events leading up to each accident were similar. For example, the sequence of events for a Cessna 210B (N9674X) accident in Tacoma, Washington, began in flight as the pilot was completing the landing checklist. The pilot noticed the landing gear would not fully extend/retract. After trying to repeat the procedure, the pilot noted that the main landing gear (MLG) would not lock, and other control surfaces, like the flaps, could not be actuated. However, the nose landing gear (NLG) did extend and lock. The pilot circled over a field near the runway, contacting emergency ground personnel to diagnose and remedy the problem. After trying unsuc- cessfully to hand pump the MLG for over an hour, the pilot attempted an emergency belly landing. While the pilot could control the plane to some degree with the NLG during the landing, the aircraft slid to the left and eventually stopped in the grass left of the runway. The initial examination found hydraulic fluid, colored red, leaking from the actuator, as shown in Fig. 1. This actuator was removed and sent to the NTSB Materials Laboratory TABLE 1 — LIST OF RECENT ACCIDENT INVESTIGATIONS OF CESSNA 210 LANDING GEAR FAILURES CAUSED BY FRACTURED HYDRAULIC ACTUATORS NTSB accident number Accident location (United States) Accident date Airplane Registration number Actuator P/N ANC15LA048 Juneau, AK 12/10/2015 Cessna 210 N3607Y 1280501-1 ANC18LA019 Juneau, AK 7/6/2018 Cessna 210C N3607Y 1280501-2 CEN22LA378 Clinton, AR 8/9/2022 Cessna 210B N9637X P/N damaged WPR23LA213 Tacoma, WA 5/30/2023 Cessna 210B N9574X 1280501-1 CEN24LA018 Pueblo, CO 10/18/2023 Cessna 210B N9597X 1280501-2 Fig. 1 — View of hydraulic fluid (red) leaking from a cracked actuator housing from a 210B (N9674X) accident scene in Tacoma, Washington. Fig. 2 — Rotated views of the fractured hydraulic actuator from a 210C (N3607Y) showing (a) the longitudinal and (b) the circumferential aspects of the barrel crack. (b) (a)
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