What type of updates does an Inertial Reference Unit (IRU) require?

An Inertial Reference Unit (IRU) primarily relies on data that helps it determine aircraft orientation and position using internal sensors, which are not dependent on external sources. However, to maintain accurate navigation, the IRU needs to be aware of any changes in magnetic variation over time. Magnetic variation refers to the angle difference between true north and magnetic north, which can change due to various factors such as geographic location and changes in Earth's magnetic field.

As the aircraft moves and travels through different areas, the magnetic variation relevant to its specific route can vary. Consequently, the IRU requires updates from a magnetic variation table to ensure that the navigation information it provides is accurate. This enables the aircraft to properly align its inertial navigation system with the Earth's magnetic field and enhances overall navigation precision.

The other options, while relevant to overall navigation systems, do not pertain specifically to what the IRU requires to operate correctly. For instance, geographic location updates, while important for GPS systems, are not necessary for the IRU, as it operates independently of GPS. Weather condition updates and aerodynamic performance updates might be valuable for flight planning and safety but are not specific needs of the IRU itself.