This research paper presents an improved proportional–integral–derivative (PID) controller for six-degrees-of-freedom (DOF) unmanned aerial vehicle (UAV) flight stability control. Quad tiltrotor hybrid UAV exhibits particular application value because of its distinctive structure of rotors. Variation in the model dynamics and aerodynamics due to the tiltrotor feature is a great technical challenge and critical issue which has fascinated many researchers in this area. The capability of an airplane to cruise at high speed as well as the distinct feature of hovering in helicopters can be merged as a result of tilting the quadruple rotors of the UAV. Transition refers to the altering between hover and cruise flight modes in mid-air. The mathematical model is developed for both horizontal and vertical flight modes using Newton–Euler formulation. The attitude, as well as the altitude of the UAV, is stabilized through a PID control approach. The results of simulation depict that the presented controller succeeds in achieving good adaptability, robust stability, as well as performance in all three flight modes.