WASHINGTON — A US surveillance plane was forced to make an emergency landing in Russia Wednesday, following an issue with the landing gear.

Pentagon spokeswoman Lt. Col. Michele Baldanza told Defense News that the plane initially took off from a Russian airfield in Ulan Ude to begin an observation flight, but discovered the landing gear would not fully retract.

"The crew, in cooperation with the Russian escort crew on-board, terminated the Ttreaty observation mission and diverted to Khabarovsk to drop off the escort crew and to exit Russia using the most direct route possible to facilitate inspection and repair at a UsS base in Japan," Baldanza said. "Khabarovsk is a frequently utilized Open Skies Airfield, designated by Russia for treaty purposes, but it is not normally a 'Ppoint of Eexit' for Ttreaty missions."

She added that because the mission was terminated, no imagery was collected during the flight. The aircraft has since left Khabarovsk — located in southeastern Russia, about 77 km KM from the Chinese border — and transited to Kadena Air Base in Japan to undergo maintenance, and is expected to return to Offutt Air Force Base in Nebraska once the problem is corrected. 

The aircraft was identified as a Boeing-made OC-135B, in an initial report from the Express newspaper in the UK.

Under the 2002 Open Skies Treaty, 34 countries, including both the US and Russia, agree to allow unarmed surveillance flights over their territory to provide information gathering about military forces. The goal of the treaty, proponents say, is to provide open information that can be used to confirm adherence to arms-control treaties.

Concern over the treaty spiked in February, however, when Russia announced plans to add a new digital electro-optical sensor to its Tupolev Tu-154 aircraft used for Open Skies flights. Pentagon officials and Congressmen lawmakers alike raised the alarm that the new sensors would give Russia an informational edge over what can be gathered by the equipment used by the US.

According to an US Air Force fact sheet, the plane comes equipped with one vertical and two oblique KS-87E framing cameras for low-altitude photography, and one KA-91C panoramic camera, which scans from side to side to provide a wide sweep for each picture at a height of approximately 35,000 feet. It has a crew of up to 35. 

Twitter: @AaronMehta