Bruce Willis has openly stated he would like to bring back Bonnie Bedelia to the franchise. She originally played the character of Holly Gennaro McClane, the wife of Bruce Willis' character John McClane in Die Hard (1988) and Die Hard 2 (1990) in the film franchise. Her character hasn't been utilized in the franchise since.
Filming of the Mi-24 Hind helicopter firing scenes took place at a military shooting range where Major Peter Simon, Air Operations Commander of Szolnok Helicopter Base, Hungarian Air Force (the pilot of the helicopter in all scenes) operated the gunship's Gryazev-Shipunov GS-30-2k (30 mm) auto-cannons and S-8 (80 mm) rockets with live ammunition to make sure the shooting effects will be as realistic as possible. Background and targets were applied in post-production.
The black Mercedes SUV featured in a chase scene is a Mercedes-Benz G-Class. The line was developed after the Shah of Iran suggested it to the Daimler-Benz management as a possible military vehicle. Shah Mohammad Reza Pahlavi was a major Daimler shareholder at the time.
The Mil Mi-26 transport helicopter seen at the end of the movie was rented from the Ministry of Emergency Situations of the Republic of Belarus. The original color of the helicopter is white. The temporary camouflage paint scheme was applied in Hungary, where the helicopter scenes were shot.
Uranium-235 is a rare isotope of Uranium-238, with atoms that contain the same number of protons but fewer neutrons. "Weapons grade Uranium" is refined Uranium-235 containing less than 15% Uranium-238.
The Cougar HEV armored truck was portrayed by four replica vehicles: three custom vehicles made by the specialists of Team Szalay, built on chassis of military surplus 6-wheeled ZIL 131 trucks, and powered by Ural truck engines. The fourth replica used for jump stunts was made in the US and was powered by a V10 Dodge Viper engine.
In the final action scene, the helicopter pilot says that the controls are at "full forward cyclic." This means that the cyclic stick (the joystick-like control) is pushed all the way forward in an attempt to bring the nose down.
The 6-wheeled Force Protection Cougar HEV truck used in the street chase and car destruction scenes was driven by Zolee Ganxsta (real name: Zoltán Zana), a well-known Hungarian rapper and drummer, also famous for his extensive tattoos, playing a Russian gangster.
Shot with Super 35, and with the series' traditional 2.35:1 scope aspect ratio in mind, director John Moore re-framed the film to 1.85:1 (possible through the Super 35 format) after deciding the opening car chase sequence looked better that way. He also believed the 1.85:1 ratio would better accommodate the hand-held camera work scenes.
Eric Jacobus and his stunt team designed (and filmed a screen test) of a fight scene between Bruce Willis and Radivoje Bukvic. The scene would have featured Alik attacking John McClane with a knife on a rooftop, but their choreography was not utilized.