The plane flight covers 400 miles in the first hour. as you approach the landing site, it takes you an hour to cover the last 200 miles. this is an example of

Negative acceleration

Explanation:

According to the described situation we have two velocities:

-An initial velocity during the first hour:

-A final velocity during the last 200 miles:

As we can see, the final velocity is less than the initial velocity, this means the plane's velocity decreased.

On the other hand, acceleration is defined as the variation of velocity in time:

Since the plane's velocity decreases, the acceleration is negative.

Hence, this situation is an example of negative acceleration.