Military Aviation

OC-135B Open Skies

OC-135B Open Skies


The United States of America Open Skies OC-135B Observation Aircraft supports the Open Skies Treaty. The aircraft flies unarmed observation flights over participating parties of the treaty.


The aircraft is a modified WC-135B. 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. Work on the aircraft also included installing an auxiliary power unit, crew luggage compartment, sensor operator console, flight following console and upgraded avionics.

The interior seats 38 people including: the cockpit crew, aircraft maintenance crew, foreign country representatives and crew members from the Department of Defense's On-Site Inspection Agency.

Cameras installed include one vertical and two oblique KS-87 framing cameras used for low altitude photography approximately 3,000 feet above the ground, and one KA-91 pan camera, which pans from side to side to provide a wide sweep for each picture, used for high altitude photography at approximately 35,000 feet.

The Miletus camera annotation system 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 this data to a 3.5-inch floppy disk. A keyboard with trackball is the input device for operation of this system. Two Barco 12-inch 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 boom compartment 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 Miletus and camera controls.

Eight commercial Norcoid Tek II coolers with individual refrigeration units maintain temperature and humidity control for film 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 of film.

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 Miletus 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 Miletus for film annotation. It is accurate from 0 to 50,000 feet 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.

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 onboard.

The auxiliary power unit enables the aircraft to start engines and provides electrical power and cabin hear 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 Open Skies Treaty was first proposed by President Dwight Eisenhower to Soviet Premier Nikita Krushchev at the Geneva Conference of 1955. The Soviets rejected the concept and it lay dormant for a generation. In May 1989, the U.S. reintroduced the idea of Open Skies as an instrument of confidence building.

The Treaty enhances mutual understanding and confidence by giving all participating countries, regardless of size, a direct role in gathering information about military forces and activities of concern to them. It permits short-notice, unrestricted aerial observation flights over the territory of each signatory.

Air Combat Command's role is to transport the OSIA to an Open Skies point of origin airport, and conduct the observation flight.

The first OC-135B was modified by the Aeronautical Systems Center's 4950th Test Wing at Wright-Patterson AFB, Ohio. It was assigned to the 24th Reconnaissance Squadron, at Offutt AFB, Neb. in October 1993. Two more OC-135Bs will be delivered with the full complement of treaty allowed sensors, which includes a infrared line scanner, synthetic aperture radar and video scanning sensors, by the end of 1996.

General Characteristics

Primary Function: Support Open Skies Treaty
Contractor: Boeing Military Airplanes Div.
Power Plant: Four Pratt & Whitney TF33-P-5 Turbofans with thrust reversers
Thrust: 16,050 pounds (7,222.5 kilograms) each engine
Speed: 500+ miles per hour (Mach.66)
Unrefueled Range: 3,900 miles (6,500 kilometers) Length: 135 feet (41.1 meters)
Height: 42 feet (12.8 meters)
Maximum Takeoff Weight: 297,000 pounds (133,633 kilograms)
Wingspan: 131 feet (39.9 meters)
Crew: Flight: Seven (Augmented crew) - three pilots, two navigators, and two flight engineers OSIA mission flight crew: one mission commander, one deputy mission commander, two sensor operators and one flight follower
Date Deployed: June 1993
Inventory: Active force, 1 (3 by 1996); Reserve, 0; Guard, 0<

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