Ongoing Study: Fuel Filter Monitors

Previously, "A Question With Fuel Monitors" (Nov/Dec '06 AIRPORT BUSINESS), reported on concerns related to the use of water-absorbing filter elements in filter monitors when delivering jet fuel into aircraft. The standard for some 20 years came under question after the American Petroleum Institute pulled its API-1583 standard; the U.K.-based Energy Institute followed with a warning of its own last October.

The main type of filter used for final filtration of jet fuel into aircraft is the water absorbing monitor element. Perhaps 90 percent of all of the final filters in use today are of this type.

Filter monitor manufacturers can qualify their monitor designs in accordance with IP 1583 Laboratory Tests and Minimum Performance Levels for Aviation Fuel Filter Monitors, a standard published by the Energy Institute (formerly the Institute of Petroleum) in the U.K.

Previous editions of IP 1583 were jointly published between the EI and API, but this is not currently the case for the latest (fifth) edition.

Field Conditions
In short, filters in the field see conditions and trace contaminants that no lab test can possibly match.

In recent years it has been identified that the water removal performance of filter monitor elements may degrade when they are in service (compared to their laboratory performance when new). All aviation fuel filter monitor manufacturers that provide monitor elements "qualified to" IP 1583 fourth edition have also stated that unknown quantities (possibly undetectable) of the water absorbent polymer that elements contain, may pass into fuel. (Information on these topics was provided by the Energy Institute in October 2006, visit

Filter monitor manufacturers and the Energy Institute are hard at work on these issues and hopefully progress will be reported later this year. Meanwhile, a very important warning has been circulated by filter monitor manufacturers and the Energy Institute:

  • Do not use any water absorbing filter elements in fuel that contains anti-icing additive, also known as FSII or Prist.
  • On untreated jet fuel, follow the guidance on this subject of the airline being refueled; the oil company/supplier; or individual company management.
  • Watch the differential pressure carefully, at full flow, or corrected to maximum flow. Do not exceed the required limits, which are usually 15 psid, but in some cases may be a bit higher. If differential pressure drops at full flow, or as corrected to full flow, cease fueling and investigate.
  • Sump the tanks, filter sumps, and low points regularly — at least daily.
  • Monitor elements have provided reliable and safe operation for many years, and doubtlessly have prevented cases of water reaching aircraft. But they are not any more fail safe than the filter separators they replaced.
  • If using filter separators as final filters, it is also very important to watch for water in the sumps and watch for any abnormal results in field tests. In addition, test the water sensors in filter separators regularly.

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There is no such thing as a filter that will ensure the fuel is free of contamination. Diligent adherence to all QC procedures coupled with the use of the best filters available, provides the highest level of safety.

Regarding the use of water-absorbing elements in avgas, there is no standard other than the IP-1583, and the same concerns apply.