When Nancy Pelosi uses "military aircraft" to travel, is it done according to regular military schedule? Or do they provide the service at her beck and call?

I always hear criticisms of House Speaker Nancy Pelosi using military aircraft instead of civilian airlines when traveling.

My grandparents (retired government) use military aircraft as well. But it’s not like they can call the Army or Air Force up and demand a plane. They just use military planes that are already traveling for other purposes.

Is Nancy Pelosi merely using the same service my grandparents use?

Or do they arrange private jets for her?