Identifying the end of each minor frame period is the synchronization (sync) word, which is a unique sequence of 1's and 0's. The pattern is generally a pseudo-random sequence that is unlikely to occur randomly in the acquired data and usually occupies two words (or more) in the minor frame. The IRIG-106 Standard lists recommended patterns for lengths 16 through 33 bits. The first three bits transmitted in a frame sync pattern are always a "1," regardless of LSB or MSB alignment.

The length of the frame sync is longer than usual data words to reduce the probability of actual data matching it. The frame sync should also be commensurate with the number of words in the minor frame (typically, it occupies 1 to 5 percent of the total minor frame). An identical pattern is repeated for every minor frame on the assumption that random data will not consistently match the defined pattern. The decommutator can then be programmed to lock onto this pattern to begin regenerating the original commutated measurands.