PU-38

Crew control function of the PU-38 panel

The main purpose of the PU-38 is remote control of the aircraft heading system from the cockpit. Instead of accessing individual equipment blocks directly, the crew uses the panel to switch modes and manage heading system operation. This is important in flight, where the pilot may need to select magnetic heading, gyro-semi-compass mode or a set heading mode depending on navigation task, flight phase and system condition. The panel provides a practical interface between the crew and the heading equipment.

Operating modes selected through PU-38

The front panel of the PU-38 provides mode selection for the main operating regimes of the Greben-1 system. These include MK, GPK and ZK modes. MK is used for magnetic heading operation. GPK is the gyro-semi-compass mode, where the heading system relies on gyro stabilization. ZK is the set heading mode. Depending on aircraft configuration, the panel also supports quick synchronization or heading correction by command from the cockpit. Correct mode selection is essential for proper heading indication and data output.

PU-38 with GA-8, KM-2, ID-6 and BU-12

The PU-38 does not operate as an independent navigation instrument. It is part of a larger heading system chain. The ID-6 induction sensor provides magnetic reference, the KM-2 correction mechanism compensates deviation and supports correction logic, the GA-8 gyro unit stabilizes and memorizes heading, and the BU-12 amplifier unit supports signal processing and amplification. The PU-38 gives the crew access to this system by providing controls for mode selection, synchronization and manual heading-related adjustment.

Latitude correction on the PU-38 panel

The PU-38 includes a control element, such as a potentiometer or circular scale, for manual latitude input from 0° to ±90°. This is used to compensate for heading error related to the Earth’s daily rotation when operating in gyro-semi-compass mode. Latitude correction is an important part of accurate gyro heading operation, especially during longer flights or when maintaining a stable course reference. Incorrect latitude setting may increase heading drift or reduce the accuracy of the system in GPK mode.

Electrical operation of PU-38

The PU-38 is connected to the aircraft electrical system and uses both DC and AC power circuits according to the Greben-1 system layout. The panel operates with 27 V DC and 36 V / 115 V AC at 400 Hz, depending on the circuit. The current draw is relatively low, but stable voltage and reliable connector condition are necessary for correct mode switching and command transmission. During troubleshooting, technicians should check the switch positions, push buttons, wiring, connector, lamp indication if applicable, and interaction with the connected heading system blocks.

Installation of PU-38 in the cockpit

The PU-38 is designed for cockpit installation, typically on the instrument panel or left-side pilot control panel. The front panel dimensions correspond to an aviation panel-mounted unit, while the body extends behind the panel and includes the electrical connector. This placement gives the crew direct access to heading system controls during flight. When replacing the unit, the installer should verify the mounting dimensions, panel cutout, connector type, depth clearance and compatibility with the specific PU-38 or PU-38B version.

Supply and documentation for PU-38

For procurement, the full designation PU-38 or PU-38B should be stated together with the aircraft type, heading system, required condition and documentation. The unit may be supplied from storage, serviceable, repaired or in another agreed condition. Since the PU-38 works as part of the Greben-1 system, compatibility with GA-8, KM-2, ID-6 and BU-12 should be confirmed before installation. Product passport and system documentation should verify designation, version, acceptance and suitability for aircraft use.