Skylift
The Skylift is a very large heavy-lift helicopter featured in Grand Theft Auto IV's episode The Ballad of Gay Tony. It resembles a S-64 Skycrane/Aircrane. It is first seen in the mission Caught with your Pants Down, where it is being used to transport an APC across Algonquin, in which Luis Fernando Lopez must shoot the chains holding it up to send the APC crashing to earth in order to steal it for Yusuf Amir. It is also seen in the mission For the Man Who Has Everything, where Yusuf flys one in order to hijack a traincar from the Liberty City Rail System.
Even though the Skylift is addressed as unobtainable, the helicopter can still be obtained with a minor exploit involving chasing Yusuf Amir and retrieving the Skylift after the mission For the Man Who Has Everything, but this trick is difficult to exploit. When trying to get the Skylift, you will have to do the Sniping Trick.[1] Here's a video to help you get it.