Did you know that there are 5 times more aviation accidents caused by water and dirt in the fuel than from misfueling (pumping the wrong fuel into an airplane)? We heard a supposedly responsible representative of an aircraft manufacturer say that this means the industry should concentrate on the water and dirt problem instead of the misfueling problem. What a monkey!

We already do many things to keep fuel clean and dry but what has been done in the past to prevent misfueling? The answer is almost nothing. Oh yes, we do label trucks, tanks, pipes and fill stands, but not always. The aircraft are supposed to have placards stating what fuel to use, but they do not always. Bottom loading equipment can easily be keyed with product selectors that have been on the market for 30 years but they are not always installed. In fact, only a small fraction of the apparatus is so equipped.

Misfueling accidents all have one thing in common — human error.

After an air show, an experienced and highly professional pilot watched his light twin being refueled with a truck marked “jet fuel”. Fortunately, he crash-landed safely.

A very young, untrained line serviceman put jet fuel in a cabin twin because he saw the word TURBO in the name of the airplane. Seven people were killed.

A dealer had a practice of keeping the unmarked jet fuel truck in one location and the unmarked avgas truck in another. Guess what happened. Someone made a mistake in parking the jet truck. The accident was inevitable.

A corporate pilot arrived at one of the world’s largest airports and deliberately specified that he did not want fuel. He got it anyhow, jet fuel in his avgas cabin twin. The dealer caught this error before the pilot departed.

So you see, it is always human error. Fortunately, someone decides to do something positive about this crazy situation. The General Aviation Manufacturers Association promoted a campaign which is summarized below:

1. The word TURBO has been eliminated from airplane names.
2. Decals were designed and distributed for labeling filler caps.
3. Bands were designed for labeling all overwing refueling nozzles.
4. A keying system was devised to prevent a large jet fuel nozzle filler spout from entering a smaller avgas filler opening.

The fourth action is the one that is the most important, because it overcomes human error. Research showed that 74% of avgas aircraft have filler openings that are less than 2.3” in diameter. Therefore, only 26% of the aircraft fleet needed to be modified with smaller openings if all jet fuel spouts on overwing nozzles were made larger. Through some very clever design, Shaw Aero, the largest manufacturer of caps and filler openings, developed an insert to reduce the size of large openings. These kits are offered by the airframe manufacturers, such as Piper, Cessna, Beech, Mooney and Aero Commander. All new avgas aircraft manufactured after early 1984 have a small filler opening.

The spouts on all overwing nozzles prior to 1984 were sized to fit through the smallest filler openings. However, to make the interference system work, every overwing nozzle that dispensed jet fuel had to have a new spout that is large enough so it would not enter an avgas opening. The problem was that some jet fueled aircraft have a “D” shaped opening; they are not round. The solution was a spout that is oval shaped. It measures 2.6” at the largest point so it will not enter a 2.3” opening, but it will enter the “D” shaped opening.

So now you may think that the problem of misfueling is solved. Unfortunately, it is not solved because of several other problems:

1. The FAA has not developed a clear, consistent policy. For example, owners of Cessna 300 and 400 series aircraft received AD’s that mandated installation of restrictor kits but owners of Beechcraft twin engined aircraft only received Service Bulletins; compliance is not mandatory. The Piper AD only applies to Navajo and Aerostars, not to Aztecs! Very Confusing!!
2. There is no law that forces a dealer, FBO or oil company to install the new oval spouts on their jet fuel nozzles.
3. After all of the heavy research that went into the design of the system, some aircraft that use jet fuel have been found to have filler openings that are too small for the oval spout. Fortunately, some of these can be modified to the large size but others remain a problem. More about these cases will be found later in this article.
4. The real “zinger” in the program is people who “bad-mouth” the idea, just because it is different from what they are accustomed to. For Example:
   1. Some line personnel said that the new oval spout causes excessive splash-back in the Cessna Citations and Beech King Airs. To investigate this, tests were run that showed that round spouts also will cause the same splash-back problem at the same flow rate. The difficulty is that the fuel cannot flow down the slope (dihedral) of the wing rapidly because of the small holes in the wing structure.
   2. Some people say absolutely that the shape of the oval spout causes a spray pattern that results in splash-back. This is pure “bunk” – look at these photographs of the fuel flow pattern.
      
   3. Some people have stated that the flow rate is reduced by the new spout, as compared to the 1½” diameter spout it replaces. Tests by Cessna and OPW prove this is simply not true.
   4. An article was printed stating that the flow in a round spout is laminar but not in the oval spout. Fantastic!! Try to find a qualified engineer who will agree that laminar flow can exist at 9 feet per second downstream of a cone strainer. That is the velocity in a 1½” round spout at 50 gpm. Man! — That is turbulent flow, not “laminar”.

“People” problems are an aggravation but hopefully they can be solved by real facts. Big problems? Yes, there are a few. The biggest one is the Hawker Siddley 125. There are 200 of these aircraft in the U.S.A. (through the 600 Series) that have filler necks that are about 1/4” too small for the oval shaped spout to enter. Obviously, these executive jets must be refueled somehow but FBO’s resisted installing the new spout “just in case” a HS125 landed at their airport. This problem was solved by British Aerospace (the manufacturer) when they developed an adapter spout for HS125 operators. The crew simply hands this adapter to the refueler who slips it on to his oval spout.

But what is to be done about the helicopters that have been found to have small filler necks? These are the Wessex, Boelkows, Puma, Dauphin, Gazelle, Twin Star and the extended range mods for the Hiller OV-12 and the Bell Jet Ranger. Eventually, it is hoped they will all be modified with large filler necks. There is an adapter available from Fjord Aviation Fueling Products. Clearly, this is not a solution to the misfueling problem because someone could use the adapter and put jet fuel in an avgas airplane. However, the adapter was purposely planned to be awkward, to encourage operators to remove it unless it is absolutely needed to refuel one of the listed aircraft.

The end of the story is liability!!!

Regardless of aggravations and inefficiencies that can be blamed on the oval spout, do you think that a misfueling law suit can be won by an FBO because the new spout was not installed? The reason “it would not fit in 200 executive jets and helicopters” that represent possibly 1 percent of the jet fleet in the USA would mean nothing to a jury.

All is not lost! Think of it this way. Any jet fuel nozzle that is equipped with the oval spout will not be capable of putting jet fuel in 74% of the avgas aircraft fleet. That is a real accomplishment!

In conclusion, we feel that the new spouts simply must be used regardless of aggravations they create. People who refuel aircraft do make mistakes, like all other people in this world. No FBO can afford not to install the new spouts and no owner of an aircraft with a large filler opening can afford not to have the restrictors installed.

This is a totally revised issue of GamGram No. 28. Rewriting it became essential because during the 12 years since the original issue was published many changes have occurred.

The basic problem has been that the industry requires more exacting information, better test reproducibility and data that relate more closely to the filter separators that are being used in aviation today. This has resulted in the development of better test procedures and refined testing apparatus. The original title was “How to Measure WSIM.”

Most jet fuel supply systems include a piece of equipment known as a filter separator. Monitor filters are also used but they are not the subject of this GamGram. Unfortunately, very few people know the conditions that must exist for the filter separator to do its water removal job properly. If the water could always be expected to lie in the bottom of a tank with the fuel on top, it would be a simple job to drain it away, and most operators do that regularly. But fuel with water in it that goes through a centrifugal pump becomes an emulsion of literally millions of tiny water drops that do not settle to the bottom of the tank for long periods of time. It is this emulsion that the coalescer elements in the filter separator must deal with. They must gather the tiny water drops together so that they will become large drops (coalesce) that can rapidly settle to the bottom and be drained away.

The enemy of a coalescer element is “surfactant” or surface active agents that prevent water drops from gathering together into large drops. They are chemical molecules that seek and influence a surface. The particular surface they “like” is the surface of a water drop in the fuel. The reason they like a water surface is because they have 2 “heads”. One head likes fuel; the other head likes water. So, if the fuel contains surfactants and if water is present, those 2- headed molecules “zoom” to the surface of the water drop just like bees go for honey. The fuel “heads” orient themselves to stay in the fuel and the water heads are captured by the water. Ultimately, the entire water drop is surrounded by a surfactant film making it impossible for 2 water drops to coalesce together because they cannot come into contact.

In the early days of jet fuel handling, it became obvious that a test was necessary to find out if a batch of fuel was contaminated with surfactants to an extent that coalescer performance would be jeopardized. The Water Separometer Index (WSI) test was developed and after modification it became the WSIM test (pronounced “wiz-um”). A reading of 100 was excellent, meaning that coalescers would perform very well. If the reading was as low as 70 the fuel was considered very poor. Extremely contaminated fuel could be “zero”.

The modern instrument that measures the surfactant contamination of the fuel is currently called the Micro-Separometer®. It is a highly refined version of the original equipment. The reading is still 100 for the best fuel but instead of referring to it as the WSIM rating, it is called MSEP (pronounced Em-sep).

Both the WSIM and the MSEP equipment are based on the same idea; an emulsion of water and the fuel sample is forced through a pad of fiberglass coalescing media. An optical device measures the haze in the effluent. The less haze detected, the higher the rating and vice versa. While precision (repeatability) has never been very good for either test, MSEP has proven to be superior to WSIM. Another big problem has been that the test over-reacts to Stadis 450, the additive that improves fuel conductivity. In other words, a low MSEP fuel may perform quite adequately in a real coalescing performance test. Considerable pressure from users has influenced great effort to overcome these problems.

Possibly the most important variable that has been investigated has been the replacement of fiberglass with the same coalescing media that is used in manufacturing modern coalescer elements that have passed the tests that are specified in API 1581, Revision 3. The new material looks somewhat like heavy paper; it contains very, very fine glass fibers. Fiberglass insulation is such an inconsistent material that coalescer manufacturers were forced to find better media several years ago. The device that holds the fiberglass pads in the current version of the Micro Separometer is an aluminum capsule called the Alumicel®. So what we are saying is that in the future new Alumicels are expected to contain a paper-like coalescing material instead of fiberglass. Meanwhile, the currently available Alumicels must be considered valid. As of June 1996, encouraging test results show that the instrument itself will probably not have to be revised. This is very good news for owners of the model known as Mark V Deluxe.

This review of tests that attempt to determine the effect of surfactants on jet fuel would not be complete without a comment on the technical property that is involved. That property is “interfacial tension”, and in our business it means “strength of the interface between the fuel and water.” If the film of molecules at the interface is strong, large water drops can exist. As the interfacial film decreases in strength, the smaller the water drops will be until the mixture of water and fuel becomes an emulsion. The measurement of interface strength is performed in the laboratory by a delicate instrument called a “tensiometer”. It is definitely not a field instrument but a kit has recently entered the market that performs this measurement in the field. It is called “SWIFT KIT” and is marketed by Velcon Filters, Inc. This kit is particularly useful in checking the performance of clay treaters that are used in our industry to capture and remove surfactants that cause the interfacial tension to decrease; clay adsorbs the surfactant molecules as described in GamGram No. 14. Therefore, by checking the interfacial tension (IFT) before and after the fuel has passed through the clay, the operator can quickly assess the performance of the clay. This can also be determined with a Micro-Separometer but that is a more time consuming and expensive test.

In conclusion, the Micro-Separometer has proven to be the most reliable instrument for evaluating the ability of a fuel sample to have its water removed by a filter separator. A program is currently underway to improve repeatability, and we will further revise this GamGram to reflect the results of that investigation when it has been completed.

A hundred years ago, you could buy patent medicines that were claimed by the salesmen to cure everything from sore feet to blindness. People bought them in desperation for a cure. With ever increasing frequency when a jet fuel problem occurs, we are hearing people exclaim desperately, “Maybe we should consider a salt tower.” Somehow, there has developed (mostly in the USA) an idea that salt will do everything, including removing dirt, water, surfactants and micro-organisms.

We thought it would be useful to review this subject and identify just what this equipment can do. First of all, the correct name is “salt drier”, not “salt tower”, in spite of the fact that they are often big and tall, like a tower. A salt drier does exactly what its name implies; it “dries” and it does it by an elementary process of dissolving salt into water to make brine. Everyone knows that brine is heavier than ordinary water – brine settles more rapidly than water.

Basically, all that is needed is to put rock salt in a vessel and pump fuel through the salt. It is an ancient process that has been used by refiners for decades.

Salt does not remove dirt, and it does not remove surfactants or micro-organisms. However, a system that has no water will grow no micro-organisms. The really interesting thing that salt does is to remove more than just the free water — it super-dries the fuel, removing a significant amount of the dissolved water. Actually, it is this capability that makes the process appealing to many people.

Suppose you have a situation where jet fuel is being transported by ship, barge or pipeline. Water is always present. If the fuel also contains surfactants and has a low MSEP rating (formerly called WSIM), the conventional procedure is to clay treat but the water degrades the clay, resulting in short life. We know that surfactants will burn in a turbine engine but if we do not remove them, the filter separators will become disarmed and will not remove water. It is almost like going around in a revolving door.

Those who promote salt driers, use the following rationale:

• Dry the fuel well below saturation in the airport storage tanks.
• Use extreme care to prevent further water contact, but just in case some water does contaminate the system, it will re-dissolve into the fuel.
• Do not worry about disarming the coalescers with surfactant between the storage tanks and the aircraft, because there is no water to remove.

The fear in the minds of many people is that there will be a brine carry-over which might result in catastrophic corrosion of aircraft. Some aircraft did suffer severe salt corrosion several years ago, but it is not clear whether it was salt drier carry-over or simply sea water contamination. Intelligent design of salt driers and careful maintenance and operation on a continuing basis could surely offer complete safety. The maintenance practice of “taking action only if something goes wrong”, currently used at some airports today, is absolutely impossible with a salt drier. It is a chemical process plant and must be operated as such at all times.

Have you now decided that you really need a salt drier? Have you convinced yourself that the design engineers will “think of everything” to prevent salt carry-over? Have you also decided that your superb management skills will insure that the equipment will always be operated “by the book”?

If you answered “yes” to the above 3 question, maybe you should examine the basic premise – that if you super-dry the fuel, you have given yourself enough water re-dissolving capacity so that you do not have to worry that coalescers may be disarmed by surfactants. How much re-dissolving capacity do you have?

Jet fuel can hold roughly 70 ppm of water in solution at average temperatures. If you dry it to 20 ppm, you can afford to have 50 ppm of new water contact before you will have free water. Take a 5000 US gallon batch of jet fuel and calculate the amount of water we are talking about:

(5000 gal. x 50) ÷ 1,000,000 = 0.25 gal.

This means that one quart of water is your factor of safety In other words, if water accidentally gets into a 5000 gallon batch of fuel, one quart will dissolve and the remainder will be free water that the coalescers must remove to protect the aircraft. Is this factor of safety large enough? We don’t think it is because our experience shows that large amounts of water cause incidents. We have never heard of a real incident on a commercial jet airplane caused by a quart of water in 5000 gallons of fuel. An “incident” is usually 20, 60 or 130 gallons.

Can all airports use salt driers? Absolutely not! The cost is prohibitive for small and even the medium sized airports. It is not just the investment, it is the cost of qualified personnel to monitor the equipment.

In conclusion, we believe that salt driers can serve the very useful purpose of removing water before clay treatment to remove surfactants. The effective life of clay can be greatly extended if there is no water present. We simply do not agree that the surfactants should be left in the fuel. The filter separator must be given the capability of removing water in an emergency; surfactant contaminated coalescers cannot be relied upon to protect an airplane.

One thing is certain in this universe, there is no such thing as a perpetual motion machine. In the real world, which means outside of politics, you cannot get anything done without expending energy.

This rule applies in fuel systems: when fuel flows, it takes energy to push fuel through any valve, meter, filter or pipe. This results in a drop in pressure.

A clean filter element in a vessel will have many open passageways for the fuel to take, so it is easy for the fuel to get through. This is why new filters show a low pressure drop indication on your Gammon Gauge (or other differential measuring device), it takes very little energy to push the fuel through.

As a filter removes dirt or as a monitor removes dirt or water (monitors trap water as a gel), some passageways are plugged. This means that more energy has to be used to push the fuel through the remaining passageways. If half of the holes plugged, the fuel has to move through the remaining holes at twice the velocity. We measure that lost energy as pressure drop.

Filter separators add a complication. Dirt causes pressure drop in the same way as in any other filter element, but water acts different than in a monitor. A coalescer element only collects tiny water drops and makes them into larger ones, and if no water is present, the pressure drop is low. If significant amounts of water are present, the pressure drop increases, but if the fuel becomes dry again, the pressure drop can go back down. The difference is not very large, but can observed on the DP gauge.

On the other hand is the “clay treater” vessel, often called a “clay filter”. These are most commonly found in pipeline terminals and ship unloading facilities, but some are located on airports. In reality, they are not filters at all; the “activated clay” (like activated carbon) is designed to remove chemical surfactant contamination, not dirt or water. Increased pressure drop happens only if there are a LOT of big dirt particles or large amounts of water, which blocks off flow in the clay.

Pressure Drop = Differential Pressure = DP

So you don’t get an increase in the pressure drop (differential pressure or DP) between the inlet of a vessel and the outlet without something bad in the fuel, right?

Not true. Velocity is important. At zero flow, there is no pressure drop, even with virtually plugged filters. As the flow rate increases, DP increases, so an increase in the DP can take place simply because the flow rate is higher or decrease because flow rate is lower. For example, some aircraft can accept 850 gpm/3,200 lpm when the fuel tanks are empty, but this may decrease to just 150 gpm/560 lpm when you are flowing into the last small fuel tanks. The same is true in filling an above ground storage tank, the flow rate can vary as much as 50% or more from “head” pressure as the tank fills.

It is simple if you are at full system flow, you don’t need correction. But if you are flowing at a rate below 100%, you need to correct the indicated DP to what it would have been if the flow rate had been at 100%. Then you can keep a chart and see the trend. 100% is not the rated flow of any component, it is actual maximum flow you can achieve.

For manually correcting DP, there are charts, spreadsheet programs and electronics that can do this.

There are different views on monitoring DP and an increase in corrected DP means different things in different places. A gradual increase is expected anywhere. A sudden increase can signal a serious problem, depending on your experience at this facility. A sudden drop in corrected DP is always serious, it means that a filter element has come loose or failed.

Some people watch DP to spot sudden contamination changes. Some watch DP to schedule the next element change. Some watch DP to make sure the system is shut down and elements changed before DP becomes too high, damaging the filter elements and allowing debris downstream.

We have four alternatives:

1. Simply put a shutdown switch onto the Gammon Gauge (or other differential pressure control) and stop flow if DP gets too high.
2. Add a low pressure switch to determine if the DP is too low, indicating a loose element.
3. Add a differential monitoring control that automatically corrects the DP and keeps a record. Such controls have alarms and shutdowns for high corrected DP, notice trends and sense a decrease in corrected DP that could mean an element has come loose.
4. We can manually calculate corrected DP, with a spreadsheet or by using a chart. The weakness is that you have no automatic shutoff if DP suddenly goes up.

Clearly #4 is no longer allowed on into plane monitors by either JIG or ATA-103.

There are arguments, we’d prefer to avoid, as to what is best. We make a DP transmitter that gives the Gammon Gauge an output that can be connected to an electronic DP correction control and we make switches that can be added to a Gammon Gauge to indicate low or high DP. We also make a High DP shutdown control.

On refueler trucks and on other types of filter vessels, it gets more complicated. Refueler vessels with monitors usually have a higher flow rate through the monitor than the meter shows, because of the pressure bypass control, so correcting DP is very difficult. Some refueler trucks have filter separators, which are not as vulnerable to bursting. Some (rare) have filter separators AND monitor elements, either in a separate vessel or inside of the separator elements.

On fuel farm and terminal filters, it depends on experience. If you never see high DP and the flow rate really doesn’t vary, just keeping records and graphing DP may be enough. Any sudden increase, however, could mean much more than just some dirt, it may mean a mixture with other fuels, like diesel, where the mix is more of a problem than the dirt.

On clay, it means you have problems with water or gross dirt, and could also be more serious than you would think, due to mixed fuel. A low DP does NOT mean the clay is working.

REMEMBER: On any filter, a decrease in corrected DP can be as serious a problem and even a more serious problem than high corrected DP, it means you are very likely pumping unfiltered fuel!

This GamGram was originally published as No. 13 but its position has been exchanged with No. 25 because various revisions over the years have made it more of an interpretive discussion of the color rating technique. It would be a good idea to re-read the 1996 version of No. 13 before reading this article. First of all, let’s review the methods:

1. Color method – This is a field method using system pressure to force a measured volume of fuel through a test membrane. You then rate the color of the membrane, when dry, using the ASTM color booklet. “O” is beautiful; 10 is horrible. Use ASTM Method D2276 Appendix X1.
2. Matched weight method – Two factory-matched membranes are placed together, one on top of the other and a measured volume of fuel (in the field) then flows through both. The laboratory then weighs each membrane, subtracts the weight of the lower one from the top one and reports the amount of dirt that was collected on the top one. This method has the advantage of avoiding pre-weighing, coding and record-keeping before testing. Use ASTM Method D-2276.

Both of these methods have the advantage over a laboratory test of a sample collected in a can or bottle, in that the sample passes through the membranes directly from the flowing pipe that carries the fuel. The advantage we are referring to, of course, is that errors caused by unclean sample containers are totally eliminated. If it is not convenient to use the above methods, your last resort is to use ASTM Method D5452, which describes how to collect samples in shipping containers and perform gravimetric tests in the laboratory. This procedure, which was recently revised, recommends that the sample be taken from a flowing pipe and it recommends the matched-weight technique.

An argument against the color rating method is that the color of the fuel itself can stain the membrane, leading you to think the color is dirt. We have heard of jet fuel made from North Slope crude oil that will color a membrane to a B6 with no weight at all. It is rather obvious that a test is needed that will tell you whether it is dirt or color in the fuel. One easy way is to look at the back of the membrane and compare the color of the front to the reverse side. The difference in color is a measure of the filterable dirt in the fuel sample. It really astonishes us why this old, but simple technique has not been used except by a few people.

A refinement of this procedure is to put 2 membranes in the plastic monitor and then compare the topside colors of both. We like this much better, not only because you may disturb the collected dirt on the top when you turn it over on a color chart, but because color on top can show through to the underside of the membrane. Note: Do not use matched-weight refill membranes for this test because they cost four times more than standard membranes.

If we accept the fact that the above techniques are logical, the big problem now is how to decide how many numbers difference in rating between the top membrane and the lower one is acceptable. To our knowledge, no laboratory has published the results of any research on this, but we surely hope they get started.

One of our oil company customers has the following procedure for delivery of fuel to the aircraft:

He uses ASTM Method D-2276 as the test method, collecting 10 liters:

1. 1. If a single membrane shows a 3 or higher reading (rated wet), run a second test with a double membrane.
   2. If the difference is more than 2 numbers, do not use the fuel until a gravimetric test has been completed.
   3. If the top membrane is rated 6 or darker, the fuel must be tested gravimetrically before use, regardless of the color of the lower membrane.

We would modify this procedure by rating the membranes when dry and by specifying that a gravimetric test be performed if the color difference is as great as 2 numbers. In this way, you learn the weight significance of a 2 number color difference for that fuel. Once you know this, we feel the above plan can be used with confidence.

Do not forget that the color rating technique serves its greatest purpose as a way to detect a change. That is why tests must be performed on a regular schedule with absolutely no variation in procedure. We do not propose to go through a step-by-step procedure because you can easily get this from other sources such as our MiniMonitor instruction booklet. However, there are a few special points that bother us:

1. The Sampling Point — Read GamGram No. 6 and Bulletin No. 3. Why do some people expect to obtain accurate results from a sampling connection that generates rust and debris? Don’t laugh! This is one of the worst problems. We often find rusty gate valves with graphite stem packings in a sampling connection where all other components are stainless steel.
2. Technique
• Do not over-tighten the monitor holder. There is no need to apply great force. O-rings do the sealing. If you have leaks, order new o-rings. Over-tightening can cause membrane breakage around the clamped edge.
• Never move a valve or start and stop a pump while a test is in progress. If you must do these things, you must first stop flow through the membrane with the Flush/Test valve. Then after system flow has been re-established, continue the test by opening the Flush/Test valve.
• Never turn a flushing valve rapidly. How many times have you found a broken membrane? We believe that this is caused by rapidly starting the flush cycle in a high pressure system. The fuel bypasses the membrane, but it can enter the plastic monitor from the outlet side, compressing the trapped air in the monitor. A membrane has little strength and fails from this slight reverse flow. Turn the flushing valve very slowly.
• Another cause of broken membranes is the double-acting syringe that a competitor supplies with his test kit. Sometimes the internal check valves stick, allowing fuel to be forced backward through the membrane when you push the handle inward. To avoid this, remove the plastic monitor before you push in the handle.