PU-27E

Mode selection through the PU-27E panel

The PU-27E allows the crew to select the operating logic of the heading system. The panel is used for switching between magnetic heading mode, gyro heading mode and correction-off mode. In magnetic mode, the system uses the magnetic channel for correction. In gyro heading mode, the gyro unit holds the course reference with correction logic applied according to the system setup. In correction-off mode, the correction channel is disconnected. These functions are important when the crew needs to adapt the heading system to flight conditions, magnetic reliability or system checks.

Course alignment and manual heading input

The PU-27E is also used for initial course alignment and manual course setting. During system preparation or correction, the panel allows the crew or maintenance personnel to bring the gyro heading into agreement with the required reference. This is part of normal operation for GMK-series heading systems, where the gyro unit, magnetic sensor and correction equipment must work as one system. If the panel contacts, controls or wiring are faulty, the heading system may fail to align correctly even when the gyro unit and magnetic sensor are serviceable.

Latitude correction using the PU-27E

The PU-27E includes controls for latitude correction. This correction is needed because the gyro heading reference is affected by apparent drift related to Earth rotation. The correction value depends on flight latitude and is introduced through the heading system control circuit. When the PU-27E is replaced by a new unit, the latitude correction system must be adjusted according to the GMK-1 technical operation manual. This is a practical maintenance point: the panel is not just a switch box, it participates in the accuracy setup of the whole heading system.

PU-27E in Mi-8 / Mi-17 avionics

On Mi-8-family helicopters, the PU-27E belongs to the pilot-navigation equipment group. It works with heading system units such as the gyro unit, induction magnetic sensor, correction mechanism, matching equipment and cockpit heading indicators. Depending on aircraft configuration, the heading signal may also be used by autopilot and navigation systems. Because of this, a fault in the PU-27E can show up as incorrect mode selection, no correction, failed alignment, unstable heading agreement or disagreement between the cockpit indication and the expected heading system behavior.

Construction and cockpit installation of PU-27E

The PU-27E is a compact cockpit-mounted control panel with electrical switching, control and correction circuits inside. It is connected to the heading system through a rear plug connector and is powered by the aircraft DC and AC networks used by GMK-series equipment. During inspection, technicians usually check switch operation, panel contacts, connector condition, lighting if fitted, command transfer to the heading system and agreement with the connected units. Manufacturer seals should not be removed without proper authorization, as this may affect acceptance and service documentation.

Supply and documentation for PU-27E

When ordering the PU-27E, the full designation and system version should be stated clearly. The unit is associated with the GMK-1GE heading system and documentation reference 6Zh3.624.003-1 / 6K3.624.003 TU, depending on the document set. Similar PU-series panels may differ by mode positions, markings, connector layout and compatibility with a specific aircraft wiring diagram. For aircraft supply, passport, label, acceptance category, storage condition, test status and compatibility with the installed GMK system should be confirmed before installation.