What type of RNAV is based on Inertial Reference Units/Systems?

The correct answer is based on the fact that Inertial Reference Units (IRUs) or Inertial Reference Systems (IRS) utilize sensor technology to track an aircraft's position, velocity, and orientation without reliance on external references. This system uses accelerometers and gyroscopes to provide real-time navigation data, allowing for highly accurate and autonomous navigation through the calculation of position over time.

IRU/IRS RNAV systems are particularly advantageous in environments where other navigation aids may be unreliable or non-existent, ensuring that the aircraft can maintain its course even in adverse conditions.

On the other hand, the other options refer to different types of navigation systems that rely on various external signals or reference points, making them distinct from the inertial-based approach of the IRU/IRS systems. For example, Global Navigation Satellite Systems (GNSS) utilize satellite signals, LORAN is dependent on terrestrial radio navigation systems, and DME/DME RNAV relies on Distance Measuring Equipment for position calculations. These approaches do not inherently use the inertial principles that characterize IRU/IRS navigation.