Learning how to operate one machine makes it easier to operate a similar new machine. For example, learning how to operate navigation equipment on one aircraft makes it easier to operate similar navigation equipment on a new aircraft. The learning and practice gained on the old equipment transfers to operating the new equipment. Positive transfer occurs when a previously learned behaviour increases some aspect of performance on a similar new behaviour. Positive transfer is more common than negative transfer which occurs when an old behaviour interferes with the performance of a similar new behaviour.
Although positive transfer is more likely than negative transfer, error rates can be much higher when negative transfer occurs than when no previously learned behaviour exists. For example, if a pilot already knows how to operate navigation equipment and if negative transfer occurs, he or she may make more errors while learning to operate new equipment than a pilot who has never operated navigation equipment.
Combinations of negative and positive transfer can also occur while learning a new behaviour. For example, a previously learned behaviour can improve reaction time on a new behaviour while also increasing error rates. Consider this, if a pilot has already learned how to quickly react to an alarm, the same pilot may react to the same alarm on new equipment even more quickly (positive transfer on reaction time) than without already knowing how to react. Although the reaction may happen very quickly, it may be to push the wrong alarm switch located in the same position as the old alarm switch (negative transfer on error rate). In essence, the old behaviour contributes to making errors at a faster rate on the new behaviour.
Now add fatigue into the mix…if a pilot is learning new equipment and he or she is fatigued, negative transfer and error rates increase even more. This means that if you want to perform at a high level while you are in a learning phase, it’s best to ensure that you sleep well before you practice the learning and that you are alert during the practice.
 Singley, M. K., & Anderson, J. R. (1989). The Transfer of Cognitive Skill. Cambridge, MA: Harvard University Press, as cited in Woltz & Gardner (2000).
 Woltz, D. J., Gardner, M. K., & Bell, B. G. (2000). Negative transfer errors in sequential cognitive skills: Strong-but-wrong sequence application. Journal of Experimental Psychology: Learning, Memory, and Cognition, 26(3), 601-635.