Towards the end of the chapter, you'll be pursued by a Combine Hunter-Chopper. This is a fast-paced chase sequence. You'll need to constantly move and use your hovercraft's mounted weapon to damage the chopper. It will drop mines and fire rockets, so stay agile. The chopper has several phases, and you'll need to inflict enough damage to make it retreat. The chase culminates in a large open area where you'll finally defeat the Hunter-Chopper. After this, you'll reach Black Mesa East.
Half-Life 2
Airboat Chase
Survive the Hunter-Chopper airboat chase in Half-Life 2. Evade mines and rockets while damaging the chopper to reach Black Mesa East.