This papers presents a phase locking loop (PLL) suitable for use in aerospace and aircraft applications in additiontomanyother fields. The concept is novel in that it makes use of the state variables of two hydraulic servo loops, x and ic in order to achieve detection of the phase error. The PLL consists of a phase detector and voltage controlled regulator (VCO). No need for a loop filter was necessary. Phase locking was tested in a simula-tion condition where two first order hydraulic servos were used as master and follower servos. Results were very satisfactory as shown by simulation results, Figs. 5, 6 and 7.