When is human error, human error? And, when is negligence, negligence? Answer: When someone else's life depends on how you do your job, there is no room for error. That is why we build in redundancies, why we adhere to procedures.

A tragic case in point - this week in New Zealand, a maintenance company owner and a licensed aircraft maintenance engineer, who was  employed by the company, were convicted of manslaughter in the death of a helicopter pilot.

The pilot, Philip Heney, was killed when a tail component failed while he was landing his Robinson R22 southwest of Nelson, NZ, in August 2005. He had picked up the helicopter from the maintenance facility earlier the same day.

The Crown prosecutor successfully argued that the defendants had failed to ensure that the work done on the helicopter had been directly supervised by a licensed aircraft maintenance engineer and inspected twice by qualified engineers.

The jury returned its verdicts after deliberating for about 10 hours over a two-day period. The two will be sentenced in May.

It makes you wonder, what was going through their heads that day, when they saw the pilot take off, knowing that they had not done their jobs?