Which items are classified as critical defects?

Critical defects are those that pose a significant risk to safety, operational integrity, or reliability of equipment and systems. In the context of the choice that is classified as critical defects—WSU sanders and SIVs—these components play a crucial role in ensuring effective operation and safety in railway vehicles.

WSU sanders are responsible for providing sand to the rail wheels to enhance traction, especially in slippery conditions. If these systems fail, it can severely impact the train's ability to maneuver safely. Similarly, SIVs (Static Inverter Units) are vital for converting energy from the train's supply system to power on-board equipment, including traction and auxiliary systems. A malfunction in SIVs can lead to a total failure of some essential services aboard the train, compromising both safety and passenger comfort.

The items listed in the other options either don't carry the same level of criticality in operational performance or safety. Emergency communication systems are indeed important, but their failure may not immediately compromise the train’s ability to function. Cabin lighting systems, while necessary for a pleasant environment, do not typically affect operational safety. Engine power indicators are significant for monitoring engine performance but are not classified as critical defects when compared to the implications of WSU sanders and S