In the end of Prometheus,

After the Engineer's disabled spacecraft crashes onto the ground, Shaw goes to the lifeboat but she is soon rejoined by the Engineer.

But:

The air inside of the alien structure and the Engineer's spacecraft is different from the planet's atmosphere, Humans could breath freely in those places while they need suits outside. This indicates that the Engineers have the same atmospheric requirement as humans regarding carbon dioxide.

So :

To get inside the lifeboat, the Engineer had to cross a significant distance outside, then force open the lifeboat's airlock. It seem hard to believe he just held his breath the whole time.

How did he reach this location?

In the end of Prometheus,

After the Engineer's disabled spacecraft crashes onto the ground, Shaw goes to the lifeboat but she is soon rejoined by the Engineer.

But:

The air inside of the alien structure and the Engineer's spacecraft is different from the planet's atmosphere, Humans could breath freely in those places while they need suits outside. This indicates that the Engineers have the same atmospheric requirement as humans regarding carbon dioxide.

So :

To get inside the lifeboat, the Engineer had to cross a significant distance outside, then force open the lifeboat's airlock. It seem hard to believe he just held his breath the whole time.

How did he reach this location?

In the end of Prometheus,

After the Engineer's disabled spacecraft crashes onto the ground, Shaw goes to the lifeboat but she is soon rejoined by the Engineer.

But:

The air inside of the alien structure and the Engineer's spacecraft is different form the planet's atmosphere, Human could breath freely in those places while they need suits outside. This indicate that the Engineers have the same atmospheric requirement than human regarding to carbon dioxide.

So :

To get inside the lifeboat, the Engineer had to cross a significant distance outside, then forces open the lifeboat's airlock. It seem hard to believe he just hold his breath the whole time.

How did he reach this location?

In the end of Prometheus,

After the Engineer's disabled spacecraft crashes onto the ground, Shaw goes to the lifeboat but she is soon rejoined by the Engineer.

But:

The air inside of the alien structure and the Engineer's spacecraft is different from the planet's atmosphere, Humans could breath freely in those places while they need suits outside. This indicates that the Engineers have the same atmospheric requirement as humans regarding carbon dioxide.

So :

To get inside the lifeboat, the Engineer had to cross a significant distance outside, then force open the lifeboat's airlock. It seem hard to believe he just held his breath the whole time.

How did he reach this location?