the Jeppesen aviation database (also known as NavData) every 28 days, and to load software and configuration to the system. The aviation database must be current to use GPS for navigation during IFR instrument approaches. The bottom slot houses the World terrain and Jeppesen obstacle databases. While terrain information rarely changes or needs to be updated, obstacle databases can be updated every 56 days through a subscription service. The top card can be removed from the G1000 system following an update, but the bottom card must stay in both the PFD and MFD to ensure accurate terrain awareness and TAWS-B information. Primary flight display (PFD) The primary flight display shows the basic flight instruments, such as the attitude indicator, airspeed indicator, altimeter, heading indicator, and course deviation indicator. A small map called the "inset map" can be enabled in the corner. The buttons on the PFD are used to set the squawk code on the transponder. The PFD can also be used for entering and activating flight plans. The PFD also has a "reversionary mode" which is capable of displaying all information shown on the MFD (for example, engine gauges and navigational information). This capability is provided in case of an PFD failure. Multi-function display (MFD) The multi-function display typically shows a moving map on the right side, and engine instrumentation on the left. Most of the other screens in the G1000 system are accessed by turning the knob on the lower right corner of the unit. Screens available from the MFD other than the map include the setup menus, information about nearest airports and NAVAIDs, Mode S traffic reports, terrain awareness, XM radio, flight plan programming, and GPS RAIM prediction. Implementation The G1000 system consists of several integrated components which sample and exchange data or display information to the pilot. GDU display The GDU display unit acts as the primary source of flight information for the pilot. Each display can interchangeably serve as a primary flight display (PFD) or multi-function display (MFD). The wiring harness within the aircraft specifies which role each display is in by default. All of the displays within an aircraft are interconnected using a high-speed Ethernet data bus. A G1000 installation may have two GDUs (one PFD and one MFD) or three (one PFD for each pilot and an MFD). There are several different GDU models in service, which have different screen sizes (from 10