Based on the utilitarianism, when it comes to deciding whether to save those five sick people by killing one healthy people or let those five sick people die, the latter decision is better. However, this action is somehow inconsistent with the principle of utilitarianism. One of the basic principles that utilitarian claims are that people's decisions to make should maximize happiness. So, in this case, saving five people instead of keeping one alive seems to bring more happiness, which means instead of choosing to keep one alive, saving those five people seems more consistent with the principle of utilitarianism.
However, if we consider more deeply, we can realize that the decision is consistent with utilitarianism. One reason that I come up with is that maybe keeping healthy people alive will bring more utility. Since those five people need transplantation, they must be seriously sick, meaning that their life quality after they receive the surgery might have limited utility. Whereas, a healthy person will have a higher life quality and tend to have more utility. In this case, keeping the health people alive will bring more happiness, which proves that the original choice that utilitarians make is consistent.