The cold beer test
The FAA has once again issued a legal interpretation explaining that an “on call” pilot can't count as rest all of the time that a call never came. The agency has been restating this principle periodically for years, and each time, many in the FAR Part 135 on-demand charter world angrily reply that this policy cannot function in the real world. Their position: If a pilot hasn't flown or worked in any way for a week, why can't that same, well-rested pilot fly on 2-hr. notice?
Read more here:: FAA: On Call