1. Make sure you are carrying Dr Linda Morales.
2. When you approach the chopper, slow down until you are exactly 3.5m away (it will show you a prompt in-game)
3. Once you are 3.5 meters away, hold square to place the doctor on the ground and once she has been placed down, immediately push forward your left joystick to move forward. It will play the animation of handing her over to the guys inside the chopper.
4. once this is done you will see two Dr Linda’s, one on the ground where you placed her and the other in the chopper. She has been duplicated and at this point onwards you are invincible to all damage (God mode)
5. IMPORTANT STEP: You must not revive anyone after this point, if you do, you will lose your invincibility. However, your teammates can revive each other.
I am not the founder of this glitch, posting it for people who are not aware. This is a near impossible operation to do so jump on it asap. I have done it twice around an hour ago and can confirm it still works.