Boeing OC - 135B Open Skies The OC - 135B Open Skies United States Air Force observation aircraft supports the Treaty on Open Skies . The aircraft , a modified WC - 135B , flies unarmed observation flights over participating parties of the treaty . Three OC - 135B aircraft were modified by the Aeronautical Systems Center ' s 4950th Test Wing at Wright - Patterson Air Force Base in Ohio . The first operationally capable OC - 135B was assigned to the 24th Reconnaissance Squadron at Offutt AFB in October 1993 . It is now fitted with a basic set of navigational and sensor equipment , and placed in inviolate storage at the Aerospace Maintenance and Regeneration Center at Davis - Monthan Air Force Base near Tucson , Arizona . Two fully operational OC - 135B aircraft were delivered in 1996 with the full complement of treaty allowed sensors , which includes an infrared line scanner , synthetic aperture radar and video scanning sensors . Description of aircraft . The interior seats 35 people , including the cockpit crew , aircraft maintenance crew , foreign country representatives and crew members from the U . S . Department of Defense ' s Defense Threat Reduction Agency ( DTRA ) . Cameras installed include one vertical and two oblique KS - 87E framing cameras used for low - altitude photography approximately 3 , 000 feet ( 900 m ) above the ground , and one KA - 91C panoramic camera , which scans from side to side to provide a wide sweep for each picture used for high altitude photography at approximately 35 , 000 feet ( 10 , 000 m ) . The data annotation and recording system ( DARMS ) processes navigational , altitude , time and camera signals to annotate each picture with correct position , altitude , time , roll angle and other information . In addition , this system records every picture taken according to camera , frame and navigational position and downloads these data to a 3 . 5 - inch floppy disk . A keyboard with trackball is the input device for operation of this system . Two Barco VGA color monitors display camera annotation and other camera data on screen for the sensor operator and observer use . Camera control , located in the sensor operator ' s console , operates and adjusts individual cameras for cloud cover , frame overlap and other functions . The sensor operator console seats four and has all the equipment listed above plus camera bay heating control , chronometers , emergency oxygen , interphone and individual lighting . The flight following console also seats four and includes most of the equipment listed above except for DARMS and camera controls . Seven commercial Norcoid Tek II coolers with individual refrigeration units maintain temperature and humidity control to maintain peak film performance . The units can be removed , if necessary , from the aircraft in order to transport film . The coolers are capable of storing 40 , 000 feet ( 12 km ) of film . Flight path . The aircraft flies on its intended flight path throughout the entire mission with no reliance on ground - based navigation devices . A top - of - the - line commercial system , Litton 92 INS / GPS , which is an integrated inertial navigation system ( INS ) with a global positioning system ( GPS ) , provides continuous updates . The GPS updates the INS several times per second to correct any deviations in the flight path . The INS also feeds precise latitude , longitude , time , roll angle and barometric altitude to the DARMS and camera systems . A true airspeed computer feeds true airspeed data to the INS . A combined altitude radar altimeter provides precise height above ground information to the pilot for navigational purposes as well as a signal to DARMS for film annotation . It is accurate from 0 to 50 , 000 feet ( 15 , 000 m ) above the ground level . Plus , a metric altimeter is installed on the pilot ' s instrument panel for altitude reference when flying in countries that use meters for altitude reference . The aircraft are being upgraded with the Block 30 Pacer Crag Navigational System upgrade , a first step in making them compliant with ICAO mandated Global Air Traffic Management and Global Air Navigation Standards guidelines . Modifications . The OC - 135B modifications center around four cameras installed in the rear of the aircraft . Since its primary mission is to take pictures , most of the installed equipment and systems provide direct support to the cameras and the camera operator . Other modifications to the aircraft also included installing an auxiliary power unit , crew luggage compartment , sensor operator console , flight following console and upgraded avionics . Other modifications support the aircrew . A gaseous oxygen system replaced the liquid oxygen system to be more compatible with foreign airfields , and fluorescent lighting system was added throughout the cabin to provide adequate lighting for operation and inspections . Four upgraded seats with a conference table , interphone , lighting and oxygen comprise the mission commanders ' station for both countries ' mission commanders . A four channel interphone system enables segregated communications between various elements on board . The auxiliary power unit enables the aircraft to start engines and provides electrical power and cabin heat independent of ground support equipment . It was manufactured by Allied Signal with the installation and design of the installation by E - Systems and World Auxiliary Power Company . The aircraft are assigned to Air Combat Command at the 55th Wing , 45th Reconnaissance Squadron , Offutt Air Force Base near Omaha , Nebraska , for operations , training and maintenance . When tasked , ACC ' s role is to transport a DTRA observation team to an Open Skies point of entry airport , and conduct the observation flight , then return the team to the continental United States . References . This article includes public domain text from the following United States Government source :