To protect CRT displays, the maximum permissible time for ground operations with DC power is:

• A. 5 Minutes
• B. 3 Minutes
• C. 7 Minutes
• D. 10 Minutes

Answer: (A)

When CRT displays are powered on from DC on the ground, heat builds up and cooling is less effective than in flight. A five-minute limit is specified to keep temperatures within safe bounds for the tube, its high‑voltage electronics, and associated wiring, protecting the display from thermal stress and accelerated wear. This ensures you can perform essential checks or brief operations without risking damage, while still providing a practical window for ground tasks. If more time is needed, the proper approach is to power down and allow the unit to cool, or follow procedures that use alternate power or modes. Shorter time alone would unnecessarily constrain operations, while longer times would exceed the safe thermal limits and could lead to overheating.