Date: 201712
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: Marginal
Weather elements / visibility: Icing
Light: Night
Aircraft: Citation X (C750)
Operating under: Part 91
Flight plan: IFR
Mission: Test Flight / Demonstration
Flight phase: Climb
Airspace: Class A ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Nose Gear
Component problem: Malfunctioning
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine
Second reporter function: Captain; Pilot Flying
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Aircraft Aircraft Damaged; Flight Crew Landed in Emergency Condition; General Evacuated
Contributing factors: Aircraft
Primary problem: Aircraft

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.


Second narrative: We were currently performing a confidence flight for a totally different issue and had a normal take-off. Upon reaching approximately FL200 we heard a thump noise and noticed the landing gear red unlock illuminate momentarily. The Captain had experienced this before; and knew what it was. Since we only got three thumps; [the] Captain decided to continue; as there was no issue affecting our flight at this point. Shortly after that; at approximately FL250; the thumping began and we decided to return for landing at which point we asked ATC for a descent and vectors back. During our return; the nose gear thumping continued intermittently and our intent was to get down to FL180 and Slow down to cycle the gear.  Reaching FL180; we continued our descent for our approach and extended landing gear early to make sure it was working properly at which point we got the two main gear green down and lock with no nose gear down and locked indication and a red up-lock indication. We cycled the gear three different times with no resolution. At this point; we ran our QRH checklist with an attempt to blow down the gear; and pulled the D-ring nose gear up-lock release. This was also not successful. At this point; we notified Approach and asked for vectors to try and resolve the issue further. We communicated with Company Operations and Maintenance to try resolving the issue. The technician on board communicated with a maintenance shop; as well; for any ideas they might have. Many attempts were tried with no resolution. Captain and First Officer traded aircraft control with very clear CRM in order to troubleshoot the issue. None of the maneuvers we tried were effective to extend the nose gear at which point we decided to fly a low approach for airport operations to see if our nose gear was extended at which point we were told the nose gear was partially extended. We climbed back to 5000 feet to continue communication with Company Operations; troubleshoot and burn off some fuel for our attempt to land with no nose gear down. We decided that at 2500 lbs. of fuel we would attempt our landing; giving us enough fuel for a second attempt if needed. We then requested vectors for an approach. We both briefed the approach and evacuations procedures as well as briefed our Technician. Weather was good enough for a visual approach but followed the ILS; which gave us 12000 feet of runway. The Pilot flying touched down at Vref and flew the nose down as gently as possible with an extension of the thrust reversers only at a point where I felt I was losing elevator effectiveness and assist with keeping the nose up as long as possible. We came to a full stop and ran the evacuation checklist.We followed the aircraft QRH checklist in order to extend the nose gear. We had many different ideas and techniques to try and extend the nose gear. I really don't know what else we could have done in order to prevent this as I believe that the aircraft experienced some sort of a mechanical failure during the thumping action; maybe having extended the gear earlier could have avoided this mechanical failure but since we were descending fast I didn't want to damage any of the landing gear.


Synopsis: 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.