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Thursday, 22 September 2016

What is Apple Jelly


What is Apple Jelly?

Photo courtesy Bill Hoagland, Petroleum Product Marketing Consulting
No, it is not something invented by the late Steve Jobs, it is a redish-brown gooey substance often found in the bottom of jet fuel tanks. Apple Jelly is the nickname given to "APPL Jelly" which comes from the abbreviation for Alberta Products Pipeline where the material was first identified. It is an emulsion of anti-icing additive and water, which precipitates out to the bottom of the tank. These additives are known as Prist, DiEGME, Fuel System Icing Inhibitor (FSII). In 2002 the US Air Force published a study of this problem, worth reading, see references below.

Why Use FSII?

For valid cost reasons, many helicopter operators have their own fuel tanks. It seems to be conventional wisdom that it is a good idea to pre-blend FSII to take out any free water in the fuel. However, the purpose of FSII is to prevent the formation of ice at low temperatures. It is not required above -40°F. Almost all helicopters do not require FSII. If it is used the required concentration is between .10% and .15% by volume.
oto courtesy Bill Hoagland, Petroleum Product Marketing & Consulting

In a follow-up phone call to Bill Hougland of PPMC (See below) he said, “By using proper housekeeping to keep the water out of your tanks it is generally not necessary to use FSII (for helicopters in most cases).  But you must follow your aircraft operation guide.
If Apple Jelly forms in the bottom of your tank is likely that your fuel no longer has the approved concentration of additive thus potentially “off-spec.”  Another argument in favor of its use is the prevention of microbiological growth, although it must be said that FSII is not considered a bio-cide, but only a bio-stat. (In other words it doesn’t kill those bugs.)

The Dangers of Apple Jelly

Apple Jelly is highly corrosive and has been reported to have caused the following events:
  • Disarming of fuel filters, which can allow water and sediment to reach the aircraft.
  • Corroding and removing fuel tank linings including paints.
  • Corrosion of aircraft fuel tanks.
  • Causing erroneous readings on aircraft capacitance fuel gauges.
  • The potential to cause engine flameout on an aircraft, although a search of the NTSB database finds no accidents or incidents of this nature.
  • Potential for off-spec fuel after FSII/water emulsion settles in your tank.

The Solutions

It is highly recommended that your director of maintenance, safety officer, and accountable executive examine all references below. As a matter of priority you should at least consider the following recommendations:
  • Sump your tank and filter daily.
  •  Perform a white bucket (clear and bright) test prior to accepting fuel from a transport.
  • Allow your fuel to settle for one hour per foot of delivered fuel.
  • Confirm that your filter is compatible with pre-blended fuel. (See EI 1581 below)
  • Conduct drain test on all aircraft every day without fail.
  • Write your fuel procedures manual and include it as part of your Safety Management System (SMS) so that you can manage fuel risks appropriately. 


Many thanks to Bill Hougland of Petroleum Product Marketingand Consulting, Parker, Colorado


Note: Some documents are not public domain. Therefore it might be advisable to consult with a fuel expert such as Bill Hougland.

Hougland, B. (2004). Securing your own fuel farm. Air Medical Journal, 23(4), 20-23. Retrieved from
AC 150/5230-4B - Aircraft Fuel Storage, Handling, Training, and Dispensing on Airports. (n.d.). Retrieved from
Air Transport Association of America, Inc. (n.d.). Standard for Jet Fuel Quality Control at Airports ATA_103. Retrieved March 31, 2016, from
Revision 2006.1
REF/ISBN: 9780852935750 Edition: 5th
Spec 103: Standard for Jet Fuel Quality Control at Airports. (n.d.). Retrieved April 04, 2016, from (See Note above)
Investigation of "Apple Jelly" Contaminant in Military Jet Fuel. (2002, March). Retrieved April 04, 2016, from

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