Monitoring design is one of basic problems during the development of manufacturing execution systems. In this paper we study the monitoring problems for the Aircraft assembly system in manufacturing execution system environment according to the computer integrated manufacturing system architecture of the Aircraft Company in China. We show that the problem of designing monitoring system for manual assembly system is reducible to modeling and synthesizing problem of monitoring system based on Object Petri Nets. Next the problem of implementing the monitoring system results in designing of structure and functions of the monitoring system. In particular, an efficient rapid prototype schema for implementation is presented. An application is demonstrated how to deal with object Petri nets based monitoring for the aircraft vertical fin assembling.