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Aviation History
1961
1961 - 0054.PDF
52 FLIGHT, 13 January 1961 JP.4: An Airline Replies . . . In 1955 TCA considered that it had achieved a big gain inreliability and comfort by switching its shorter-range services to turbine power. An investigation led to the belief that the airlinewould have jeopardized its gain in safety and reliability if it used the kerosine available in Canada at that time. This decision wasmade with the full knowledge of the arguments being put forward by the proponents of kerosine in 1954. TCA now believes itsoperating reliability and safety record with its Viscount services over the past six years have demonstrated better than words thesoundness of its decision. The same engineers reviewed the situation when TCA waspurchasing its DC-8s and Vanguards and, after considering all the factors involved in operating an airline, concluded that theyshould again recommend that TCA adopt JP.4 as its standard fuel; but this time they agreed that kerosine could be used ifand when there would be an economic advantage in doing so. It must not be overlooked that kerosine is not subject to taxin Great Britain or the United States, so the use of this fuel when operating in these countries offers a considerable economicadvantage. Because many of the airlines now believe there is little to choose between the two fuels from an overall safety stand-point, they rightly use whichever fuel is the cheaper, since this is to the advantage of their customers. In Canada it does notmatter which fuel is used in an aeroplane—both are taxed equally. It is futile to debate the technical characteristics of kerosineand JP.4, because invariably both sides believe they are right; one side may quote officially figures for fuel characteristics, andthe other side can rightly counter that the laboratory tests on which the figures are based do not resemble conditions actuallyencountered in service. One side can perform a spectacular stunt like throwing a match in pools of the two fuels to demonstratethe difference in flame-spread and appeal to the emotions of the observers; the other side could spill the fuels on a piece of hotmetal from a damaged engine and see one ignite at a much lower temperature than the other. One can see moving pictures of bodi fuels igniting with theirflame spreading at the same speed in an accident, or one can "rig" an accident with just the right amount of impact to demon-strate that one fuel is better than another. One can say that accident X would have been catastrophic had the "wrong" fuelbeen used; and the other side can demonstrate that the "wrong" fuel was used in accident Y, where it spread all over the groundfrom burst tanks and there was no fire. They can also supplement their viewpoint by quoting catastrophic fires that have occurredin accidents in which the "right" fuel was used. These types of arguments and statements can all be considered most questionableand each side can accuse the other of bias. With respect to crash safety, TCA would sooner rely on the conclusions of the extensiveNACA crash-fire programme, which demonstrated scientifically that enhanced crash-safety cannot be achieved through choiceof fuel. Oil Company's Conclusion Telling evidence is provided by a confidential bulletin issuedby one of the world's major oil companies to its marketers. This oil company sells both fuels, so is not interested in either sidebeing right or wrong. The bulletin reviews the whole situation, and its conclusion is well worth quoting, together with some ofthe points leading up to that expression of opinion: — "It appears that there is no evidence that one type of fuel has anyover-all safety advantage. The soundest position to take is to acknow- ledge that all fuels are hazardous and should be treated identically.The final choice is the airlines'." Among the points brought out in this bulletin is the fact thatturbo-fuel quality requirements have become much more stringent with respect to freezing point, smoke point, thermal stability, gumcontent, percentage of aromatics, and other characteristics since kerosine was used in the first turbine engine. It is mentioned thatas fuel volatility increases (i.e., towards JP.4 rather than towards kerosine) reliability of ignition improves, carbon deposits decrease,flame-out tendencies lessen, smoke generation decreases (which can be important at airports during smog conditions), combustionefficiency increases, and temperature of engine pans decreases (which means increased parts-life as the flame radiation decreases).Also cited is better pumpability at low temperatures, improving starting in very cold conditions. It can also be added that the higher BThU/lb of JP.4 givesmore range for the same payload. In this regard it might be remembered that 1 per cent in fuel weight on one of the big jetsis equivalent to seven passengers. This saving in weight is important from a safety standpoint wherever take-off weights arelimited because of runway lengths, altitude, temperature or air- port regulations. The only time kerosine's higher BThU per gallon(i.e., in volume as distinct from weight) is of benefit is when tanks are completely filled; this occurs on a very small percentage oftrips if the correct aircraft has been selected for the route. Because of their higher viscosity, turbine fuels of the kerosinetype can carry more dissolved and entrained water than can the gasoline-type fuels. At low temperatures this can result in ice-blocked fuel filters and engine starvation if a deficiency or an incorrect setting occurs in the pressure or thermostatic controlof the fuel-filter heater. It is easier to control cleanliness in JP.4, because its lowerdensity and viscosity result in faster settling times for dirt and water. The lower boiling range helps exclude some of theemulsion-forming polar compounds which can be present in kerosines. At the present time the degree of hazard from static dischargein commercial operations is not known. But, because of kerosine's greater viscosity and greater tendency to entrain foreign matter,if there is a hazard it could be expected to be more serious in the case of that fuel. If spilled, kerosine is not evaporated as readily and completely.As a result the danger of fire is prolonged; and if the leakage occurs within a wing, it can definitely be more hazardous.It must be remembered that reliability and safety are synonymous. To ensure reliability requires a much moreappreciative study of conditions (such as deficiencies that might occur through the human element) than has apparently been madeby the proponents of "kerosine only." We feel that these few sincere people who are appealing to theemotions of the public in relation to kerosine versus JP.4 are actually doing aviation a disservice; it is a case where a littleknowledge on the part of the public can be a dangerous thing to the industry; and, as has been said, it is an industry that hasachieved a most enviable record in safety through the conscientious and diligent work of the airlines, the manufacturers and regulatorybodies. They have all worked together, with disagreements at times, but always with the objective of making aviation the safestmeans of transportation in the world. MR DYMENT'S VIEWS The following statement, attributed to TCA's chief engineer.Mr Jack Dyment, first appeared in the Montreal Star of December 28 (we reproduce it in slightly abbreviated form): — "In the type of accident that results in fuel being spilled on the ground,JP.4 is more likely to ignite if there is a spark above it than kerosine, and this is all that Lord Brabazon is talking about. Unfortunately, it isfar from the whole picture. "If there is a severe impact—say if a wing strikes the ground and thefuel tanks break open—there is no difference between kerosine and JP.4. You just can't tell them apart if the fuel splashes. In addition,the research agencies of the US Government [NACA] investigated the common causes of fire in aircraft accidents and found that, contrary topopular belief, sparks are not a common cause, because the electrical system goes out in the crash. "They found the most common cause of fire after an accident is fromengine oil or hydraulic fluid coming in contact with hot metal. This is what causes most fires. . . . Kerosine is closer to engine oil thangasoline and they found that it will ignite from contact with hot metal parts as much as 400 degrees lower in temperature than JP.4. . . . "If you get a leak in a fuel tank in a wing, kerosine will crawl andJP.4 will evaporate. The danger of kerosine coming in contact with a hot part as it did in a Vulcan (in a British bomber accident in which theairplane exploded in the air) [actually a Valiant—Ed., Flight] is greater than with JP.4. Engine reliability is synonymous with safety and if youhave a flame-out in the air—and you can still get them from icing—you are far, far more likely to get them restarted with JP.4 than with kerosine.There is just no comparison. "Kerosine burns at a hotter temperature than JP.4 so the engine partsare hotter and this affects reliability. Because of their higher fuel con- sumption, the tolerances in turbine engines have to be much closer thanwith piston engines and dirt has a more serious effect. Anything close to oil, as kerosine is, needs a longer time for the dirt to settle out—dirtstays in suspension longer in kerosine than in JP.4. "In the case of engine fire, with flames coming back over the wing,the vapour from JP.4 will cool the skin of the aircraft faster than kerosine and kerosine becomes explosive for a much longer time. JP.4 will pro-duce an explosive mixture only through a very narrow range of air-fuel mixtures because it quickly becomes too rich to explode. "There is another factor that we don't know very much about yet—static electricity. Kerosine does pick up static more readily. To what extent a hazard is involved is not known. JP.4 should be better. . . . "In spite of what I have said, we don't think there is any reason whyan airline shouldn't use any of the standard fuels. You must look at your own operating conditions and decide which is preferable. When weselected JP.4, we were told it would cost more than kerosine and we still picked it. As it has turned out, you can toss a coin between them asfar as cost is concerned. It depends where you are. And in spite of what Lord Brabazon says, safety has always been the No 1 considerationwith all airlines—it has to be. Brabazon is chairman of the Air Regis- tration Board, and if this fuel were dangerous I would say he had beenextremely remiss not to have banned it long ago. But, you notice, his board approves it. "Brabazon is a very good speaker at a luncheon and he's very enthu-siastic and he convinces himself. But he is a political appointee on the ARB and no one would consider him an expert." de Havilland and JP.4: page 69
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