Narrative:

On approach to landing we were following the normal before landing checklist when I instructed the first officer to place the landing gear handle in the down position. After doing so; both crew members observed a green indication for the nose and right main gear; and a yellow X for the left main gear accompanied by a gear disagree left amber cas and master caution annunciator. At this time I instructed the tower that we needed to cancel our landing clearance and proceed to an area where we could troubleshoot a gear issue. Tower instructed us to fly over the field and then to fly a westerly heading. The tower informed us over the radio that our main gear looked down and nose gear appeared angled towards the back. The pm ran the appropriate emergency/abnormal checklist up to the point of step 2 of the ce-680s pilot checklist. Step 2 requires the pm to pull the landing gear blowdown handle. At this time I handed over positive control of the aircraft to the pm while I retraced the checklist items to the same conclusion as the pm. I then placed a call to our flight ops department to inform management of our situation and planned action to follow the checklist to conclusion and land. Management confirmed that they wanted us to land and after the phone call ended I took back positive control of the aircraft and instructed the first officer to act on the checklist item step 2 and pull the landing gear blowdown handle. The pm followed my instruction and no change was made in the left main gear indication and the amber cas remained. During this time we were on radar vectors and had worked our way back to a good position to make a pass near the tower to receive another ground observation and the tower advised that they would have more eyes available to 'take a better look'. I instructed the pm to configure the flaps for landing and I maneuvered the aircraft to a position for optimal viewing from the tower at a normal approach speed to allow for the most time to observe the landing gear. With selection of full flaps; the yellow X over the left main gear indication turned red and the landing gear warning horn sounded and continued for the duration of the time with the flaps in the full down position. The tower advised that all gear appeared down. I directed the pm to clean the flaps up as I maneuvered the aircraft out to the west again and then instructed the pm to finish the 'if gear fails to extend' checklist for the main gear which involved pulling the main gear uplock handle located in the rear of the cabin. At this point the yellow X over the left main gear remained accompanied still by the amber cas gear disagree left. The pm returned to the cockpit and I yawed the aircraft in an unsuccessful attempt to get a positive green indication. The pm and I then addressed that the gear could be down and locked while invalid indications could remain. This completed the landing gear will not extend checklist. Both pilots; the PF and pm; agreed that the gear was most likely in the down and locked position and that there must be a sensor mis-compare or other form of indicating malfunction. I briefed the passengers on our situation and our intentions to proceed with landing as well as that we may need to evacuate the aircraft in the event the gear was not down and locked. I instructed the pm to advise ATC that we intended to land and requested assistance after landing. ATC advised that arff was dispatched and would arrange a tug to take us to the FBO. We aligned for landing and upon selection of full flaps the left main gear indication went again to a red X accompanied by the landing gear warning horn. The pm and I observed the arff team in position on the north side of the runway and on short final heard a ground ops vehicle report over the frequency that all gear appeared down. I continued the approach and made a normal landing without incident. We elected to clear the runway and brought the aircraft to a stop. Both engines were shut down as we waited for a tug to take us to [the FBO]. I decided to open the cabin door to get out to inspect the area around the wheel well. A passenger who I believed to be an a&P mechanic inspected the wheel well and tapped on the left main gear unlock sensor with his hand causing the unlock sensor pin to become unstuck and protrude back out to its normal position with the gear extended. This immediately caused the landing gear warning horn to cease and the red X indication to change to a positive gear down and locked green indication; making all three green gear indications match. I made personal contact with the responding arff crew and tug driver and informed them that an emergency no longer existed and that we would restart our engines and taxi under our own power to the FBO. The pm advised ATC that we no longer required assistance and requested taxi clearance to the FBO. We proceeded to the FBO and off-loaded our passengers without incident.

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Original NASA ASRS Text

Title: CE-680 Captain reported landing safely with an abnormal landing gear indication that was later found to be a sensor malfunction.

Narrative: On approach to landing we were following the normal Before Landing checklist when I instructed the FO to place the Landing Gear Handle in the down position. After doing so; both crew members observed a green indication for the nose and right main gear; and a yellow X for the left main gear accompanied by a GEAR DISAGREE L amber CAS and Master Caution annunciator. At this time I instructed the Tower that we needed to cancel our landing clearance and proceed to an area where we could troubleshoot a gear issue. Tower instructed us to fly over the field and then to fly a westerly heading. The Tower informed us over the radio that our main gear looked down and nose gear appeared angled towards the back. The PM ran the appropriate emergency/abnormal checklist up to the point of step 2 of the CE-680s pilot checklist. Step 2 requires the PM to pull the LANDING GEAR BLOWDOWN Handle. At this time I handed over positive control of the aircraft to the PM while I retraced the checklist items to the same conclusion as the PM. I then placed a call to our Flight Ops department to inform management of our situation and planned action to follow the checklist to conclusion and land. Management confirmed that they wanted us to land and after the phone call ended I took back positive control of the aircraft and instructed the FO to act on the checklist item step 2 and Pull the LANDING GEAR BLOWDOWN Handle. The PM followed my instruction and no change was made in the Left Main gear indication and the amber CAS remained. During this time we were on radar vectors and had worked our way back to a good position to make a pass near the Tower to receive another ground observation and the Tower advised that they would have more eyes available to 'take a better look'. I instructed the PM to configure the flaps for landing and I maneuvered the aircraft to a position for optimal viewing from the tower at a normal approach speed to allow for the most time to observe the landing gear. With selection of full flaps; the yellow X over the left main gear indication turned red and the landing gear warning horn sounded and continued for the duration of the time with the flaps in the full down position. The tower advised that all gear appeared down. I directed the PM to clean the flaps up as I maneuvered the aircraft out to the west again and then instructed the PM to finish the 'If gear fails to extend' checklist for the main gear which involved pulling the Main Gear Uplock Handle located in the rear of the cabin. At this point the yellow X over the left main gear remained accompanied still by the amber CAS Gear Disagree L. The PM returned to the cockpit and I yawed the aircraft in an unsuccessful attempt to get a positive green indication. The PM and I then addressed that the gear could be down and locked while invalid indications could remain. This completed the Landing Gear Will Not Extend Checklist. Both pilots; the PF and PM; agreed that the gear was most likely in the down and locked position and that there must be a sensor mis-compare or other form of indicating malfunction. I briefed the passengers on our situation and our intentions to proceed with landing as well as that we may need to evacuate the aircraft in the event the gear was not down and locked. I instructed the PM to advise ATC that we intended to land and requested assistance after landing. ATC advised that ARFF was dispatched and would arrange a tug to take us to the FBO. We aligned for landing and upon selection of full flaps the left main gear indication went again to a red X accompanied by the Landing Gear Warning Horn. The PM and I observed the ARFF team in position on the north side of the runway and on short final heard a ground ops vehicle report over the frequency that all gear appeared down. I continued the approach and made a normal landing without incident. We elected to clear the runway and brought the aircraft to a stop. Both engines were shut down as we waited for a tug to take us to [the FBO]. I decided to open the cabin door to get out to inspect the area around the wheel well. A passenger who I believed to be an A&P Mechanic inspected the wheel well and tapped on the Left Main Gear unlock sensor with his hand causing the unlock sensor pin to become unstuck and protrude back out to its normal position with the gear extended. This immediately caused the Landing Gear Warning Horn to cease and the red X indication to change to a positive gear down and locked green indication; making all three green gear indications match. I made personal contact with the responding ARFF crew and tug driver and informed them that an emergency no longer existed and that we would restart our engines and taxi under our own power to the FBO. The PM advised ATC that we no longer required assistance and requested taxi clearance to the FBO. We proceeded to the FBO and off-loaded our passengers without incident.

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.