What is triggered lightning? North Sea helicopters grounded due to ‘atmospheric’ phenomenon

Triggered lightning has only ever been recorded in the North Sea and The Sea of Japan.

By Jamie Sinclair

January 7 2025, 6:04 pm

Helicopter operators can face a triggered lightning threat during winter months. Image: Shutterstock.

Helicopter flights transporting off-shore workers across the North Sea have been grounded due to triggered lightning.

The severe weather causes disruption for all major helicopter operators as it has done today.

Flights from Aberdeen Airport were not permitted to take off as a result of the risk.

Triggered lightning is only known to happen in the North Sea and The Sea of Japan.

And the unique phenomenon only occurs in winter, with as few as one or two strikes happening between November and April every year.

Bristow was one of the companies affected today.

What is triggered lightning?

Ice crystals form and move within the base of a cloud, creating a positively-charged area, a key component of triggered lightning.
The other component is the helicopters themselves. They naturally generate a negative charge through static electricity, created by friction of the rotor blades with the air.
In normal conditions, this will be discharged to the ground on landing.
However, if a negatively-charged helicopter flies through or close to a positively charged area the two will interact and equalize. And that can create a lightning strike.

A Bristow helicopter. Image: Ronnie Robertson/Flickr.

Operators take necessary measures to prevent lightning strikes

Bristow’s Head of UK Flight Operations, Tim Glasspool, explains: “To a passenger sitting in the Aberdeen terminal, or on an offshore platform, the weather might look pretty decent.

“On a cold but cloudy day, perhaps with hardly any wind, calm seas and no fog, things might seem good for an on-time departure.

“But in the flight planning room our Met Office weather forecasting system can tell a very different story.

“Conditions might be calm, but if the forecast shows patches of red on the route, then those areas are an absolute no-go.

“Unless we can chart a safe course well away from these areas, we don’t fly.

“Our aircraft are designed to withstand lightning strikes, but they can seriously damage important instruments and navigation systems.”

A spokesperson for Bristow said: “Our teams will work hard to make up the flights as soon as they can but safety will always take priority.

“Weather is a key issue for all operators at this time of year.