About the EGI
The EGI is a small inertial navigation system with an embedded GPS system. It has three modes of navigation:
- Inertial: Uses the aircraft's movement to update it's location
- GPS only: Uses the embedded GPS system to update the aircraft's location
- Blended: which uses a combination of both systems.
The EGI is needed for many sub systems of the A-10C. It provides function for the Enhanced Attitude Control(EAC), the radar altimeter, Stability augmentation system (SAS), and
Before the EGI becomes functional it needs to align itself. It begins the process as soon as it receives power. The EGI aligns itself using a combination of the Earth's gravity to align itself vertically and the rotation of of the Earth to find north.
When either the EGI or the HARS finishes alignment, the aircraft will be able to report heading on the HUD. A full alignment for the EGI takes 4 minutes.
The GPS component of the EGI is completely automatic. It is equipped with anti-jamming and anti-spoofing technology. When it acquires a satellite it will report time information to the CDU. It provides assistance to the inertial guidance system, making the EGI very accurate, and very responsive when used in blended mode.
- The EAC cannot be armed until the EGI has at least marginally aligned. A full 4 minutes is needed for a complete ground alignment.
- Without an EGI alignment you will not have the ability to arm the EAC. This will prevent you from using the autopilot, the PAC system, and the SAS. This will make flying difficult, and your gun very inaccurate in bursts. A partial EGI alignment will allow for CCIP and CCRP pippers however they will be less accurate than with a full alignment. Note you must activate the EGI via the NMSP panel regardless of alignment or you will not receive any additional services.
- After your EGI aligns don't forget to switch to EGI navigation mode by pressing the EGI button beneath the HSI.