NAVIGATION

The AH-64D primarily navigates by utilizing a pair of Embedded GPS/Inertial Navigation Units (EGI) aided by a Doppler velocity radar and a database of stored points. After the APU is started and generator power is applied to the aircraft, both EGI’s will automatically begin their alignment process. Aircrew intervention is normally not required aside from verifying the EGI’s alignment status and velocity indications prior to engine start.

Unless updated with a new position via the DTC, the EGI alignment process uses the aircraft’s previous position and heading stored in the aircraft memory from when it was last shut down. This stored position, aided by GPS position signals, shortens the alignment process considerably, allowing an AH-64D to takeoff within minutes if necessary.

Navigational Sensors

While in flight, the AH-64D receives continuous position updates from GPS satellites to maintain INU position confidence and aid in precision navigation. As an emergency back-up during operations in low-visibility conditions, the AH-64D is equipped with an AN/ARN-149 Automatic Direction Finder.

The AH-64D uses true airspeed calculations derived from the pitot probe mounted on the leading edge of the left wing and the static ports on each side of the airframe. These, along with the air data sensors, aid in more precise ballistic calculations during weapons delivery and are the primary source of air mass data to the Flight Management Computer (FMC).

A set of backup instruments are installed within the Pilot’s crewstation that provide indicated airspeed and barometric altitude from the second pitot probe mounted on the leading edge of the right wing and each static port. A standby attitude indicator and a backup magnetic compass is also installed within the Pilot’s crewstation.