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Ayles Fernie Underslung Dispersant Spray System

STRATUS over Moray Firth

Project Title: Successful testing Aerial Underslung Dispersant Spray System

Products/Services: Aerial Dispersant Spray System

Project Undertaken: From 2019

Industry Sector: Dispersant Spray System

What was the problem? 

The Norwegian Coastal Administration (NCA) required a method for dealing with potential oil spills along its extensive coastline, much of which falls within the Arctic Circle. Using aerial dispersants is an effective option for difficult to reach areas, however having an adapted aircraft on standby is a very expensive option. Existing underslung solutions for helicopters were not meeting all the requirements of the NCA. A new solution was needed. 

How was the Darcy Group involved? 

Ayles Fernie, part of the Darcy Group, first met representatives from the NCA at a trade show. The NCA advised us that they would shortly be putting out to tender for the supply of a bespoke underslung helicopter dispersant spray system.  We already had an excellent track record supplying our marine and fixed-wing aircraft dispersant spray systems, the former already having been supplied to the NCA. We applied and were excited to take on the challenge of an underslung system when we won the tender.  

We designed the system from scratch after consulting with the NCA and taking a full brief of their requirements, as well as helicopter pilots and aerodynamics experts, so we could design an effective system that does exactly what you need it to do.  

We called our helicopter underslung spray system, STRATUS. 

There were many factors that we had to take into consideration. Cold conditions affect the viscosity of the dispersant, which makes it harder to spray. So, the design team needed to investigate insulating the tank. They also looked at ways to prevent the spray nozzles from freezing. The materials used to construct the STRATUS were very important due to the location of use – they needed to be robust and lightweight. We chose to use marine-grade materials, due to our experience with marine applications. 

Robert McGivern photo (1)

Meet the expert: Rob McGivern

"I was involved from the very first design sketches. From looking into mass and load calculations to building the first prototype. I even drove the van with the STRATUS on a trailer up to Scotland for flight testing. To say we got some funny looks on the motorway would be an understatement!”  


Read the full interview

The NCA requested that the system be operable from inside the cockpit. One of the reasons for this is that the helicopter might have to travel some distance before reaching the site of the spill. It’s essential that the diesel engine powering the system doesn’t run out of fuel before reaching its destination, so the system can be switched on when required from within the helicopter.  

The most important factor was the safety of the helicopter and ground Crew. Plus ensuring the STRATUS system could be safely loaded and transported via a helicopter. We also needed to ensure the load would be stable and fly in the correct direction.  We spoke with several helicopter operators to ensure all risks were understood and mitigated.  

Once we understood the risks, we engaged with aerodynamic experts to ensure the underslung load would be predictable and behave as the pilot expected. 

So far, we have designed, manufactured and supplied both 2000-litre and 1000-litre variants – both versions have undergone rigorous testing over the Moray Firth in Scotland.

Check out the video below of the STRATUS during testing.  



The system has been tested with several pilots, who have all given excellent feedback, stating the system was very stable up to 90 knots both in the forward direction and during banked turns. 

What was the outcome? 

The final solution delivered to the NCA included: 

  • The STRATUS 2000 Litre Tank with 10m Spray arms 
  • A trailer for easy manoeuvrability 
  • a 20ft liveried container to store the trailer and tank 
  • ground support equipment including pumps and hoses to get dispersant from the storage tanks into the STRATUS tank.  

That first system produced for the NCA is now based in Svalbard, in the Arctic Circle.  

The STRATUS started life as a bespoke project, but it is now available to order. The tank is available with and without insulation, depending on the climate in the location of its intended use, and a tank size of up to 3,000 litres is an option.

Find out more about the STRATUS system.

Ayles Fernie is currently working on the MKII version of STRATUS taking on board the improvements that we wanted to make to the system, plus the feedback from the NCA. It is through use that we can continually improve our products to make sure they work in the most efficient and effective ways.  

Innovation Award - Darcy

Award-winning product

Our innovative new product was recognised at the 2023 UK and Ireland Spill Association annual awards in two categories. 

We won: 

Innovation of the Year 
Manufacturer of the Year 

Congratulations to the whole team involved in this complex project. 




Get in touch

Interested in learning more about the STRATUS? Get in contact with us today.

© Darcy Darcy Spillcare Manufacture 2015 All Rights Reserved all 3rd party trademarks acknowledged.

Darcy Products Limited trading as Darcy Spillcare Manufacture, a company registered in England number 0472058.

The registered office of the company is, Brook House, Larkfield Trading Estate, New Hythe Lane, Larkfield, Kent ME20 6GN.