How can I track non-revenue flights?

You may wish to add activities to the schedule that do not generate revenue. By default all Activity Types are set to track billing status. The statuses of Unbilled/Billed/Paid are useful in making sure that you've collected on all completed flights but can cause noise when using the reservation tab to filter for Completed and Unbilled flights. Any activity type can be set up to no include a billing status by going to:

Settings>Scheduling>Activity Types 

Selecting a type to edit, and then clicking Edit on the Billing Section

and setting the Track Billing Status switch to No