Please check my writing.

The graph compares how many people who traveled by three main British airports over a five-year period between 1998 and 2003. The units are measured in millions of travelers per year.

Overal, what can be seen from the graph is that there are upward trends in the numbers of visitors of all three airports over the period in question. General, Gatwick airport was the leader which often had more travelers than others. The only exception was in 2000 that Heathrow airport had 48.2 million visitors and replaced Gatwick's position.

Looking at the details, Heathrow started with 27.2 million visitors in 1998 which doubled dramatically about 48.2 million in 2000 then fluctuated sharply over the next 3 years. By contrast, the Stansted airport had a sustainable rise from 1998 to 2000 and stayed unchanged at 43.3 million from 2001 until 2003. Except for 2000, Gatwick was the most popular airport and reached a peak 69.3 million travelers in 2003