Airfield Fuel Update UL91/UL94
Effective immediately, UL91 stocked at Blackbushe will now be marked as UL94, and will be purple in colour. This does not affect the specification of the fuel we have always supplied, but brings the fuel inline with new regulations. You may notice the fuel being dispensed into your aircraft is now purple.
Regulatory Change to UL91 and UL94 Fuel Grades.
Suppliers of Unleaded Aviation Gasoline stocked at Blackbushe had previously supplied fuel in line with DEF STAN 91-090 which mandated that the unleaded aviation fuel was colourless. A regulatory change effective Jan 2026 requires that fuel provided under DEF STAN 91-090 must now conform to ASTM D7547-23 fuel specifications, which requires fuel to be dyed. UL91 is to be dyed red, and UL94 is to be dyed purple.
Why is the Fuel Being Dyed?
The ASTM mandate to introduce colour markers is designed to improve safety and give increased clarity in aviation fuel handling. The purpose of the change by ASTM will help to reduce the risk of misfuelling.
What is UL94 Fuel?
This fuel is similar to UL91 but replaces some of the chemical constituents with iso-octane, to increase the MON to a minimum of 94.0. Both UL91 and UL94 conform to the specifications of ASTM D7547-23. UL94 fuel exceeds the knock-rating specifications of UL91 and is therefore approved for use on any aircraft that has previously been approved to use UL91.
What Fuel is Blackbushe Stocking?
Blackbushe has been sourcing our unleaded fuel from Greenergy (previously Puma) for many years. This product was always sold to us as UL94, but we elected to market it as UL91 so as not to cause confusion with products sold elsewhere. We have found the supply from Greenergy to be reliable, whereas other suppliers have been less reliable in the past.
This new change to dye the fuel, requires us to commit to either UL91 or UL94, as whilst the products can be mixed in aircraft tanks, having a mixed product in our overground tank makes fuel testing difficult. We have therefore elected to continue to stock UL94 fuel which will be dyed purple, as we trust the supply and availability will be reliable, and the product is better suited to a wider range of aircraft. This will not affect the pricing of AVGAS (either 100LL or UL91/94), as in practice there is no change of supplier or cost.
The upgraded octane rating to MON 94.0 allows better detonation resistance especially in higher compression engines and covers a wider range of aircraft than the lower octane UL91 equivalent.
What changes will I notice?
The latest delivery of unleaded fuel is dyed purple and meets UL94 specifications. The overground unleaded tank will be rebranded to UL94, and any fuel receipts will also show the change of fuel grade.
Operators of aircraft using unleaded fuel should inform aircraft users of the colour change and upgraded octane rating.
The Light Aircraft Association recommends that users of aircraft operating with UL91/UL94 approvals have suitable placards fitted adjacent to the fuel filler cap identifying that UL91 or UL94 fuel may be used, and that in the case of aircraft with a POH or flight manual, a note be added to the appropriate section referencing an airworthiness approval notice. See https://www.lightaircraftassociation.co.uk/total-avgas-ul91
If you have any questions, please do not hesitate to contact the airport Admin office.