Rule number one, don't run. Rule number two, get low. It's easy to get past him even without a tracker if you just wait and listen to what he's doing. There are a few neat tricks too. The first time the alien sees you, take out the flamethrower and just show it to him without pulling the trigger. He'll go into a little reaction, and during that time you can turn and run for just long enough to lock a door or jump into a vent. You can also back up while holding the flamethrower at him for a long time before he finally rushes you.