Narrative:

At around mid-morning my student and I started up the aircraft and taxied out of the ramp. We then proceeded to do normal operations and test. After all the test were complete; and the engine had warmed; we then took off to the south (of course with proper clearance). We then proceeded south over 10 miles and did a series of maneuvers in preparation [for] my students CFI check ride.after we finished up on maneuvers; we then came back into the airport for landing practice. After completion of the first touch and go; we continued in the pattern for another landing. Upon reaching mid-field downwind; as my student placed the gear selector down we realized we didn't have a down and locked gear indication (one green light). My student then asked the tower for an east heading to work on our issue. After running the checklist; 'landing gear fails to extend checklist' this did not fix our issue. We have now realized by looking out the window that the right main is swinging freely in a mid-travel position. At this time; we realized we needed more time and space to analyze our issue. At this point; I have taken over the radios and my student is flying. We then asked the tower for a turn to the south to clear his airspace and further work on the issue. As my student was flying to the south; I gave tower my phone number and asked him to get one of FBO mechanics to call me. After talking to the mechanic; we then confirmed that we could try and slip the plane to get the gear to lock down but the chances were it was not going to swing into position. We then talked about a 'gear up landing' and how that would be a less risky landing then landing with 2 of 3 gear down. Once I was off the phone with the mechanic; I told my student to climb to 5000 feet to get some altitude under us before we tried a series of slips and pitch changes to try and swing the gear into place. All of these techniques did not work. We then asked tower for a low approach over the field and headed back to the airport. We asked for the low approach to see if the mechanic could see anything different from his viewpoint. We wanted to see if he saw anything out of the ordinary besides the gear not fully down and locked (something else blocking the gear from extending fully). After passing him; he said the nose wheel and left main appear down but the right main was not fully extended and locked.we now had all the confirmation we needed that we were going to have to do a gear up landing. We then declared PIC authority under far 91.3 and proceeded to the south once more to wait for emergency crews to arrive. Once established on a south heading; I took control of the aircraft and asked my student to pull out the poh (pilot's operating handbook) and double check the emergency procedures and see if there was anything that differed between our checklist and the poh. After confirming the checklists were identical and there were no other procedures we then discussed how putting the gear up was the safest way to land the aircraft in the situation we were given. The emergency services have now arrived and we headed back in to do a gear up landing. On the downwind leg; we cycled the gear up. The gear all came up but the right main. It dangled in a half travel position. We confirmed this with tower and then told them we would no longer talk to them once we turned final. This being because we were going to turn off the master and all electrical components prior to landing. After turning final we turned all electrical systems off. Once the field was made; we then pulled the mixture to idle/cutoff and cracked the exit doors. I then glided the plane to the runway and held it right above the runway until it got slow enough it couldn't fly anymore. We then impacted the runway with the planes belly. The plane then skidded to a stop and my student and I exit towards the tail as previously briefed.

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Original NASA ASRS Text

Title: A Cessna 172RG instructor pilot reported the failure of the landing gear to extend normally. After a series of unsuccessful maneuvers to extend the gear; a decision was made to land with the landing gear partially retracted.

Narrative: At around mid-morning my student and I started up the aircraft and taxied out of the ramp. We then proceeded to do normal operations and test. After all the test were complete; and the engine had warmed; we then took off to the south (of course with proper clearance). We then proceeded south over 10 miles and did a series of maneuvers in preparation [for] my students CFI check ride.After we finished up on maneuvers; we then came back into the airport for landing practice. After completion of the first touch and go; we continued in the pattern for another landing. Upon reaching mid-field downwind; as my student placed the gear selector down we realized we didn't have a down and locked gear indication (one green light). My student then asked the tower for an east heading to work on our issue. After running the checklist; 'Landing gear fails to extend checklist' This did not fix our issue. We have now realized by looking out the window that the right main is swinging freely in a mid-travel position. At this time; we realized we needed more time and space to analyze our issue. At this point; I have taken over the radios and my student is flying. We then asked the tower for a turn to the south to clear his airspace and further work on the issue. As my student was flying to the south; I gave tower my phone number and asked him to get one of FBO mechanics to call me. After talking to the mechanic; we then confirmed that we could try and slip the plane to get the gear to lock down but the chances were it was not going to swing into position. We then talked about a 'gear up landing' and how that would be a less risky landing then landing with 2 of 3 gear down. Once I was off the phone with the mechanic; I told my student to climb to 5000 feet to get some altitude under us before we tried a series of slips and pitch changes to try and swing the gear into place. All of these techniques did not work. We then asked tower for a low approach over the field and headed back to the airport. We asked for the low approach to see if the mechanic could see anything different from his viewpoint. We wanted to see if he saw anything out of the ordinary besides the gear not fully down and locked (something else blocking the gear from extending fully). After passing him; he said the nose wheel and left main appear down but the right main was not fully extended and locked.We now had all the confirmation we needed that we were going to have to do a gear up landing. We then declared PIC authority under FAR 91.3 and proceeded to the south once more to wait for emergency crews to arrive. Once established on a South heading; I took control of the aircraft and asked my student to pull out the POH (Pilot's Operating Handbook) and double check the emergency procedures and see if there was anything that differed between our checklist and the POH. After confirming the checklists were identical and there were no other procedures we then discussed how putting the gear up was the safest way to land the aircraft in the situation we were given. The emergency services have now arrived and we headed back in to do a gear up landing. On the downwind leg; we cycled the gear up. The gear all came up but the right main. It dangled in a half travel position. We confirmed this with tower and then told them we would no longer talk to them once we turned final. This being because we were going to turn off the master and all electrical components prior to landing. After turning final we turned all electrical systems off. Once the field was made; we then pulled the mixture to idle/cutoff and cracked the exit doors. I then glided the plane to the runway and held it right above the runway until it got slow enough it couldn't fly anymore. We then impacted the runway with the planes belly. The plane then skidded to a stop and my student and I exit towards the tail as previously briefed.

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.