To solve the high-cost of frequent maintenance of public reference points which are widely used to build global coordinate system in the digital aircraft level adjustment recently

a novel level adjustment method for aircraft without public reference points was proposed. The mathematical model of horizontal coordinate system without public reference points is established

and the horizontal coordinate system is built with the moveable dual-axis inclinometer of high precision and the mounting base of inclinometer. Based on the horizontal coordinate system

the horizontal posture of aircraft is calculated

and numerical control positioners are driven to move coordinately to achieve aircraft level adjustment. Then the test system for the level adjustment of aircraft is developed. Besides that

an application experiment on a certain type aircraft has been conducted in the assembly plant

which demonstrates that the level adjustment precision of test system is better than 0.4 mm

and the horizontal coordinate system can provide an accurate adjustment datum for the whole adjustment process. The method can complete the level adjustment process ideally

and also improve the efficiency and precision of measurement and adjustment.