What is a block hour?
What is a block hour? (aviation) Time from the moment the aircraft door closes at departure of a revenue flight until the moment the aircraft door opens at the arrival gate following its landing. Block hours are the industry standard measure of aircraft utilization.
Why do you need 1500 flight hours?
The so-called 1,500 hour rule was passed after the fatal Colgan Air crash in February 2009 in America. The crash also led to new requirements for a minimum rest period for pilots before a flight. The official National Transportation Safety Board (NTSB) website report can be read here.