This paper deals with a sequencing problem of a mixed-model assembly line in the 'Ibyota production system, It is important to level wark loads on each station of the assembly line. The sequencing problems of Ieveling the work loads have been studied by many researchers and are known as NP-hard problerns. Most researchers assume that the work overload on each station is always completed by utility workers and the assembly line does not stop. That is, the numbeT of utility workers is

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... large and workers are helped by the utility workers at any time. Few researchers have studied models of the assembly line with line stoppages. In fact, line stoppages occur in the assembly line of the 'Ibyota production system. Whenever a worker in the assembly line judges a possible failure to complete operations within the work zonc, a push of an assembly line button summons an auxiliary workeg different from the utility worker, who will assist in the operation. A group, which is a formal organization of the workplace of the assembly line, consists of about 20 workers and is manned by only one auxiliary workct Therefore, the worker calls the specific auxiliaTy worker. If the worker can complete operations with the auxiliary worker within the work zone, thc line does not stop. Otherwise, the line stops at the downstream limit of the worker's station until they complete the operations. Moreover, when the auxiliary woTker helps the other station, the worker can not call the auxiliary worker. That is, the worker can not be helped by the auxiliary worker and the line may stop. Tb our knowledge, no one has studied the sequencing problcrn of minimizing total line stoppage time of the mixed-model assembly line with the avxiliary workers. This paper investigates this sequencing problem. Since this problem is NP-hard and the size of practical problems at Tbyota Motor Corporation is huge, we propose an approximation algorithm that adapts the goal chasing method, which was developed by the first author of this paper, and show its ethciency through numerieal examples.