An explanation of perfect tenses. 
Transcript is here:
https://drive.google.com/file/d/1oyopkBGxwFDrFK5rW4XK_s0eBG6_0FRH/view?usp=drivesdk

Teacher Joseph's Podcast

Perfect Tenses [with transcript for study]

Helicopter without pilots

For the first time, a military helicopter flew without pilots. There were two flights on Saturday and Monday, and they lasted about 30 minutes. There were no passengers on board.

Engineers installed a special technology in the helicopter which made it possible to fly without pilots. The Black Hawk helicopter flew through a simulated city, and then it landed perfectly at Fort Campbell, US.

This technology helps pilots to focus on missions instead of flying helicopters. They fly in many types of weather, at night, and when they can’t see very well. The military hopes that it will make missions more successful.