runway, runaway, run away

Runway or runway means the paved strip that an airplane uses to land or take off--
They were still waving good-bye as the plane taxied down the runway.
Runway may also mean a narrow platform, ramp, or paved strip--
The photographers crowded around the runway to get a better view of the fashion models.

Runaway or runaway ( one word ) means someone who has left home or fled from parents or  home--
The parents of a runaway have put up notices with his picture on them.
The runaway was found and is now in foster care.

Runaway, historically, might have described a slave, indentured servant, or apprentice--
Here's an 18th century advertisement, placed by someone searching for a runaway apprentice.
In the 1860's, legal authorities in the northern states refused to punish people who helped a runaway slave.

Runaway may describe something that has escaped limits or control--
There's no driver! It's a runaway train!
The children all liked the story about the runaway soup.

Run away or run away ( two words ) means to leave home without permission, as a teenager--
The teenager threatened to run away whenever he became angry.
Run away also means to flee from danger or a problem, literally or figuratively--
He watched them run away after they heard the noise.
His father taught him that it was smarter to run away than to get into a fight.

Now that you know that, you can say--
"They sped down the runway in an attempt to run away from the runaway baggage cart."

Note--"run a way" ( three words) might fit into a sensible sentence, but I can't think of one.