These were 8 of the most audacious helicopter-assisted prison escapes in historry

On July 11, Mexican cartel kingpin Joaquin "El Chapo" Guzman Loera escaped from what was considered to be the most secure prison in all of Mexico using a mile-long tunnel.

Guzman's escape was especially audacious. Tunnels are expensive, conspicuous, and time-consuming; El Chapo's tunnel may have cost as much as $50 million in labor, building material, and bribes. It isn't within everyone's means to obtain aircraft for a prison escape, but it's easier to get out of prison by air than underground: Over the past 40 years in particular, there has been trend of convicts and their partners on the outside busting out from high security facilities in hijacked helicopters.

Not every attempted helicopter escape has been successful, and most convicts were caught within 24 hours even if the helicopter breakout part of the plot ended up working. There are exceptions, though. Here are 8 of the most impressive helicopter escapes in which the convicts were not immediately caught after breaking out of prison.