Narrative:

Right landing gear failed to extend. Recycling through the landing gear lever didn't make the gear extend. Manual gear extension didn't work either. The nosewheel and the left gear were apparently locked and down while the right gear was partially extended. The decision was made to execute a gear up landing in hpn. The plane stopped 300-400 ft down the runway. There was no injury to the occupants of the aircraft (myself and the student commercial pilot).

Google
 

Original NASA ASRS Text

Title: C172RG MADE A DELIBERATE GEAR UP LNDG BECAUSE THEY WERE NOT ABLE TO GET THE R MAIN GEAR DOWN AND LOCKED.

Narrative: R LNDG GEAR FAILED TO EXTEND. RECYCLING THROUGH THE LNDG GEAR LEVER DIDN'T MAKE THE GEAR EXTEND. MANUAL GEAR EXTENSION DIDN'T WORK EITHER. THE NOSEWHEEL AND THE L GEAR WERE APPARENTLY LOCKED AND DOWN WHILE THE R GEAR WAS PARTIALLY EXTENDED. THE DECISION WAS MADE TO EXECUTE A GEAR UP LNDG IN HPN. THE PLANE STOPPED 300-400 FT DOWN THE RWY. THERE WAS NO INJURY TO THE OCCUPANTS OF THE ACFT (MYSELF AND THE STUDENT COMMERCIAL PLT).

Data retrieved from NASA's ASRS site as of July 2007 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.