Which type of inspections must be performed every 12 calendar months for IFR?

The correct choice is the ELT (Emergency Locator Transmitter) inspection. Under the regulations, ELTs are required to be inspected every 12 calendar months to ensure they are operational in case of an emergency. This inspection typically involves testing the unit to ensure it transmits a signal and checking the overall functionality to confirm it is ready to send distress signals in the event of an accident.

While other inspections, such as transponder and static source inspections, are also necessary for IFR operations, they follow different timelines and conditions for their requirements. Similarly, airworthiness inspections may have varied periodicity based on aircraft type and usage but are not specified on an annual calendar basis like the ELT inspection. Thus, the periodic 12-month inspection requirement specifically pertains to the ELT, making it the correct answer.