Narrative:

Upon reaching approximately FL200; we experienced several thumps from the nose gear and noticed the red landing gear up-lock illuminated. Captain had experienced this before and when it quit we felt confident the flight could continue. After a short period; the thumps returned and a decision was made to discontinue the flight and return to departure airport as soon as possible. A descent was commenced and a turn back to the airport was started. The thumping at this point became intermittent. Once we had descended below FL180; and slowed below gear speed; a decision was made to cycle the landing gear. At this point; we got two green lights for the main gear and the red up-lock light. We then asked approach for delay vectors to work the issue. The gear was cycled 3 times with no change to the gear light indication. We then referenced the QRH. I continued to fly; while the captain ran the QRH checklist. Following the checklist; we attempted blow the gear down. When that was not successful; we continued with checklist and pulled the d-ring up-lock release. This also was not successful.at that point; we applied part 91.3 PIC authority with approach. We communicated with company contacts several times trying out various possible solutions. Additionally; the maintenance technician we had on board was in communication with several folks and they offered several possible solutions. None of the ideas had the effect of lowering the nose gear. During the brainstorming; we decided to make a low approach to have ground personnel check on the status of the nose gear. They informed us that the nose gear appeared to be partially extended. We climbed back up to continue working the issue and burn off fuel. During this event; [the] captain and I positively exchanged flight controls as we worked different possible solutions. We tried several more suggested solutions and some of our own troubleshooting. Eventually we reached a point where we had fuel remaining to execute a final attempt to land leaving enough to execute a miss should things not feel right. We then requested final vectors for the ILS approach. We thoroughly briefed the approach; and briefed each other and our technician on the possible evacuation procedures. [The] captain then executed a flawless approach and landing right on the centerline. He timed the deployment of the thrust reversers perfectly to lay the nose gently on the runway. We ran the evacuation checklist and quickly exited the aircraft safely. We helped the arff folks secure the aircraft; and then were transported to the maintenance facility.

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Original NASA ASRS Text

Title: A Citation 750 flight crew reported a malfunctioning landing gear; after several attempts to lower the gear; they could only get the two main gear down; they executed an emergency landing in that condition.

Narrative: Upon reaching approximately FL200; we experienced several thumps from the nose gear and noticed the red landing gear up-lock illuminated. Captain had experienced this before and when it quit we felt confident the flight could continue. After a short period; the thumps returned and a decision was made to discontinue the flight and return to Departure Airport as soon as possible. A descent was commenced and a turn back to the airport was started. The thumping at this point became intermittent. Once we had descended below FL180; and slowed below gear speed; a decision was made to cycle the landing gear. At this point; we got two green lights for the main gear and the red up-lock light. We then asked Approach for delay vectors to work the issue. The gear was cycled 3 times with no change to the gear light indication. We then referenced the QRH. I continued to fly; while the Captain ran the QRH checklist. Following the checklist; we attempted blow the gear down. When that was not successful; we continued with checklist and pulled the D-ring up-lock release. This also was not successful.At that point; we applied Part 91.3 PIC authority with Approach. We communicated with company contacts several times trying out various possible solutions. Additionally; the Maintenance Technician we had on board was in communication with several folks and they offered several possible solutions. None of the ideas had the effect of lowering the nose gear. During the brainstorming; we decided to make a low approach to have ground personnel check on the status of the nose gear. They informed us that the nose gear appeared to be partially extended. We climbed back up to continue working the issue and burn off fuel. During this event; [the] Captain and I positively exchanged flight controls as we worked different possible solutions. We tried several more suggested solutions and some of our own troubleshooting. Eventually we reached a point where we had fuel remaining to execute a final attempt to land leaving enough to execute a miss should things not feel right. We then requested final vectors for the ILS Approach. We thoroughly briefed the approach; and briefed each other and our technician on the possible evacuation procedures. [The] Captain then executed a flawless approach and landing right on the centerline. He timed the deployment of the thrust reversers perfectly to lay the nose gently on the runway. We ran the evacuation checklist and quickly exited the aircraft safely. We helped the ARFF folks secure the aircraft; and then were transported to the maintenance facility.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.