This paper deals with the order sequencing problem in a man-on-board storage and retrieval warehousing system which is suitable for storing items of small size and light weight. Considering the operating characteristics of the man-on-board system, a heuristic procedure is presented for the problem of sequencing a given set of retrieval requests. The validity of the procedure is investigated through computer simulation. The results show that the procedure performs better than those from previous studies. We also develop the expected travel time models based on the probabilitic analysis for single and dual commands assuming randomized storage assignment policy.