Aspen, CO, USA
N615RG
CESSNA 560XL
The pilots were on approach to the destination airport. They reported that the approach was stabilized and normal and that the landing gear indications were normal with three green landing gear indicator lights illuminated. During landing and after speed brake deployment, an aural landing gear warning sounded, the right wing gradually dropped and scraped on the runway, and the airplane veered to the right and subsequently came to rest on the right side of the runway, which resulted in substantial damage to the right wing. After the accident, the right main landing gear was found retracted, and the left main landing gear and nose gear were found extended and locked in place. The landing gear handle was found in the UP (retracted) position. The copilot did not recall manipulating the landing gear handle after the initial landing gear extension during flight. Further, cockpit audio captured the crew verifying the gear extension twice, and recorded data showed that the landing gear were extended. Functional testing of the landing gear handle revealed that the unit passed all manufacturer acceptance test procedure requirements except for the test that required the landing gear handle return to either the UP or DOWN position when released from any position. During the testing, the handle exhibited a tendency (multiple times) to stick in place when released. When the landing gear handle was stuck in a position outside of the extend and retract detents, the handle would move if vibration was applied to the case or if the handle was moved manually. After the handle moved out of the retract detent, it sent an “extend” command throughout the remaining travel to the extend position. This allowed the handle to send an “extend command” while the handle was stuck in a mid-travel position and, with some vibration on the case, it would slowly transition towards the retract position and would eventually move into the retract detent position and provide a “retract command.” The results of the testing as well as the postaccident examination of the landing gear handle did not reveal the reason that the handle would stick in a mid travel position. However, the results of the testing showed that a malfunction of the landing gear handle occurred, which likely caused the right main landing gear to collapse during the landing roll. The reason why only the right main landing retracted could not be determined. Postaccident examination and functional testing of the rest of landing gear system revealed no mechanical malfunctions or anomalies that would have precluded normal operation.
HISTORY OF FLIGHTOn June 4, 2021, about 0954 mountain daylight time, a Cessna 560XL airplane, N615RG, was substantially damaged when it was involved in an accident near Aspen-Pitkin County Airport (ASE), Aspen, Colorado. The two pilots and three passengers were uninjured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the cockpit voice recorder (CVR) transcript, at 0933:17, as the flight neared ASE, the crew obtained the current weather information via automatic terminal information service (ATIS) information, which indicated that the wind was calm at ASE. At 0948:05, the crew contacted the ASE tower controller, who reported that the wind was from 030° at 3 knots. The CVR recorded an increase in ambient noise at this time, consistent with the landing gear extension. At 0948:48, the crew confirmed that landing gear was extended. At 0952:52, the crew completed the before-landing checklist, including a confirmation that the landing gear was down. Shortly after touchdown, the CVR recorded the aural landing gear warning, which sounded for the remainder of the recording. At 0954:05, the airplane stopped, and the crewmembers commented that the gear had failed and that they had previously confirmed the illumination of three green landing gear indicator lights. In postaccident statements, the flight crewmembers reported that the pilot flying was in the left seat and that the copilot was in the right seat. The approach was stabilized and normal, and the three green landing gear indicator lights were illuminated. The aural landing gear warning annunciated during landing and after speed brake deployment. The right wing gradually dropped and scraped the runway, and the airplane veered to the right and then came to rest on the right side of the runway. Airport surveillance video showed the airplane landing and all three landing gear were visible. After the airplane touched down, the right wing contacted the runway surface, and sparks emanated from the lower side until the airplane came to rest. AIRCRAFT INFORMATIONThe airplane’s landing gear system was electrically controlled and hydraulically actuated. The landing gear actuators incorporated an internal lock to hold the gear in the extended position. The actuators were held in the retracted position by mechanical uplocks that are normally released hydraulically. In the cockpit, the landing gear control panel contained the landing gear handle, an audible warning system, three gear safe lights, and a red gear unlock indicator (see figure 1). Each green light corresponded to one gear and indicated that it was in the down-and-locked position. The red light indicated an unsafe gear position (in transit or not locked). The landing gear handle had two positions, full up (RETRACT) and full down (EXTEND). The gear handle had to be pulled out to clear a detent before the handle could be repositioned. Operation of the gear and gear doors began after the handle was positioned in one of the two detents. A gear handle locking solenoid, which was activated by the left main gear squat switch, would physically prevent inadvertent movement of the gear handle while an airplane was on the ground. Figure 1. Landing gear control panel (Source: Cessna 560XL Operators Manual). The landing gear warning system sounded an audible warning when one of the following three conditions existed: 1. Gear not down and locked, both throttles retarded below approximately 70% N2 [high pressure rotor rpm] and flaps greater than 15°. 2. Gear not down and locked, both throttles retarded below approximately 70% N2, and valid radio altimeter signal indicates less than 500 feet AGL [above ground level]. 3. Gear not down and locked, both throttles retarded below approximately 70% N2, and a non-valid radio altimeter signal and airspeed below 150 KIAS [knots indicated airspeed]. The audible warning would cease only if the conditions that initiated the activation of the warning were corrected. AIRPORT INFORMATIONThe airplane’s landing gear system was electrically controlled and hydraulically actuated. The landing gear actuators incorporated an internal lock to hold the gear in the extended position. The actuators were held in the retracted position by mechanical uplocks that are normally released hydraulically. In the cockpit, the landing gear control panel contained the landing gear handle, an audible warning system, three gear safe lights, and a red gear unlock indicator (see figure 1). Each green light corresponded to one gear and indicated that it was in the down-and-locked position. The red light indicated an unsafe gear position (in transit or not locked). The landing gear handle had two positions, full up (RETRACT) and full down (EXTEND). The gear handle had to be pulled out to clear a detent before the handle could be repositioned. Operation of the gear and gear doors began after the handle was positioned in one of the two detents. A gear handle locking solenoid, which was activated by the left main gear squat switch, would physically prevent inadvertent movement of the gear handle while an airplane was on the ground. Figure 1. Landing gear control panel (Source: Cessna 560XL Operators Manual). The landing gear warning system sounded an audible warning when one of the following three conditions existed: 1. Gear not down and locked, both throttles retarded below approximately 70% N2 [high pressure rotor rpm] and flaps greater than 15°. 2. Gear not down and locked, both throttles retarded below approximately 70% N2, and valid radio altimeter signal indicates less than 500 feet AGL [above ground level]. 3. Gear not down and locked, both throttles retarded below approximately 70% N2, and a non-valid radio altimeter signal and airspeed below 150 KIAS [knots indicated airspeed]. The audible warning would cease only if the conditions that initiated the activation of the warning were corrected. WRECKAGE AND IMPACT INFORMATIONThe right main landing gear was found retracted, and the left main landing gear and nose gear were found extended and locked in place. The landing gear handle was found in the UP (retracted) position. (The copilot did not recall manipulating the landing gear handle after the accident.) Figure 2 shows a postaccident view of the cockpit, throttle quadrant, and landing gear handle. Figure 2. Postaccident configuration of the cockpit with the landing gear handle (circled in red) in the retracted (UP) position. Postaccident examination of the airplane revealed substantial damage to the right wing. During the examination, the landing gear handle was removed from the airplane for further testing, and an exemplar landing gear handle was installed. The on-site electrical, mechanical, and hydraulic system functional tests with the exemplar landing gear handle revealed no failures or malfunctions that would have preclude normal operation. The landing gear actuators, uplock actuators, and printed circuit boards were removed for functional testing, which found that they met the requirements of the component maintenance manuals or acceptance test procedures (ATP). The internal configuration of the airplane’s landing gear handle was documented using radiographic images. A review of the scanned images determined that the landing gear handle was in the extended (down) position and that there were no indications that the internal components of the landing gear handle had malfunctioned. At the airplane manufacturer’s facility, a visual inspection of the landing gear handle found that the handle was in the retracted (UP) position, as shown in figure 3. No abnormal wear or damage was noted. Figure 3. Left-side view of the accident landing gear handle. Functional testing of the landing gear handle was accomplished per the airplane manufacturer’s ATP. The unit passed all ATP requirements except for the test that required the landing gear handle return to either the UP or DOWN position when released from any position. During testing, the handle exhibited (multiple times) a tendency to stick in place when released. The handle was released anywhere between mid-travel and within about 0.25 inches of the retract detent, and the handle remained in the released position on the retract half of the travel. When the handle was released on the extend side of travel, the handle would snap completely to the extend detent. When the landing gear handle was stuck in a position outside of the extend or retract detents, the handle would only move if vibration was applied to the outer cover, or the handle was moved manually. After the handle moved less than 0.25 inches out of the retract position, an extend command was provided, which was sustained throughout the remaining travel between the extend and retract detents. This allowed the handle to provide an extend command while the handle was stuck in a mid-travel position, as shown in figure 4. With some vibration applied to the case, the handle would slowly move toward the retract position and would eventually move into the retract detent position and provide a retract command. Figure 4. Landing gear handle stuck in a mid-travel position during testing. Engine Data Collection Units (DCU) The airplane’s engine DCUs were successfully downloaded, and the data files were provided to the engine manufacturer for conversion and assessment. According to the manufacturer, the DCUs contained the engine running time, which was the time recorded from selection of the engine electronic control power ON to power OFF and not the time from engine start to engine stop; thus, the engine running time does not typically match the engine logbook times. The engine manufacturer also stated that the DCUs contained a flight number, which was based on the weight on wheels (WOW) switch changing from WOW OFF to WOW ON to identify a single flight. Although the DCU files could not be directly correlated to specific dates and times, the manufacturer was able to reasonably match the recorded data to the accident landing based on the DCU faults. The final two trace recordings on the right engine DCU show that an event occurred immediately after the airplane completed an approach and a landing at an elevation similar to that of the accident airport. The trace recording showed the following sequence of events: o “Gear-down” was “true” for the 3 minutes before the event. o As the airplane touched down, the WOW switch was “true”; a few seconds later, the “gear-down” switch was “false.” o About 8 seconds later, the WOW switch changed to “false,” which triggered an impending thrust reverser fault and a WOW cross-check fault.
The malfunction of the landing gear handle for reasons that could not be determined, which caused the right main landing gear to collapse during the landing roll.
Source: NTSB Aviation Accident Database
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