A person (the supervisor ) is supervising the carrying out of maintenance done by another person if the supervisor:
(a) is physically present at the place that the maintenance is being carried out; and
(b) is observing the maintenance being carried out to the extent necessary to enable the supervisor to form an opinion as to whether the maintenance is being carried out properly; and
(c) is available to give advice to, and answer questions about the maintenance from, the person carrying it out.