Unplanned downtime

Unplanned downtime is any stoppage that was not in the maintenance plan. It costs more than planned downtime for three compounding reasons: it cannot be timed to a low-wind period, it usually requires a crew or a crane at short notice, and the parts may not be on site. A planned lift booked into a campaign and an emergency lift on the same component are the same work at very different prices.

Its effect on availability is what most contracts measure, but the energy effect is what matters commercially, and the two diverge. Twenty hours of downtime in a strong wind costs several times what the same twenty hours cost in a calm week, which is the argument for energy-based availability over the time-based figure.

Most unplanned stops are preceded by something. Bearing and gearbox failures develop over weeks, generator and converter issues over days, and pitch and yaw system faults often repeat as intermittent trips before they become permanent. That is the window predictive maintenance is trying to open, and it is why the fault code history is worth reading as a trend rather than as a set of individual events.

Not all of it is avoidable, and a program that claims otherwise is overselling. Grid events, extreme weather, and genuinely random component failures will always account for part of the total, and the honest objective is to move the avoidable share into planned work rather than to promise zero.