Why won't the aircraft door open in the 'Dam and Blast' mission in GTA San Andreas?

In order to progress further I need to complete the Dam and Blast mission. In order to initiate the mission, I need to enter the aircraft at the airport, but the problem is that I cant seem to get CJ to enter the plane.

I mean simply I cant get the door open he just keeps on running around in circles around the plane. I’ve reloaded the craft, and blew it up 3 times, still no luck.

I’m playing on my Alienware Aurora ALX R4 PC. Is it a bug?