Less Common Tenses
The past perfect progressive and future perfect progressive are not commonly used in English. They indicate action which occurs continuously over a period of time, when another action or event intervenes. Some examples are included here for your reference.
Past Perfect Progressive
We had been playing baseball for two hours yesterday when it started to rain.
I had been sending out applications for months. Finally, I got a phone call.
Future Perfect Progressive
We will have been flying for two hours when we cross the Mississippi River.
In August, I will have been studying here for three years.
Often the past perfect progressive and future perfect progressive can be replaced by their counterparts: past perfect or future perfect.
I had been driving for hours when I stopped to rest.
I had driven for hours when I stopped to rest.
By the time I get to Tempe, I will have been traveling all day.
By the time I get to Tempe, I will have traveled all day.