Aircraft Accidents and Fuel

First, a recognition: Thank you, Mr. Colacino, for the investigation alert.

A Notice to Air Men (NOTAM) was sent out from the Boston Center on Friday, December 1, 2017, concerning fuel contamination problems, allegedly, out of a Fixed Base Operator (FBO) in Omaha, Nebraska’s Eppley Airfield.  The questionable fuel, according to a November 30, 2017, Aviation International News Online article, was instrumental in causing two Air Force aircraft to make emergency landings immediately after take-off.  According to the NOTAM, the fuel concerns were found in both military and general aviation (GA) aircraft.  The article adds that two Learjets also experienced fueling problems after visiting the same FBO.

The possible causes being investigated – and here I note, the FBO is cooperating fully – are flameouts, clogged fuel nozzles, fuel filters and fouled wing fuel tanks.  The article and NOTAM are unclear as to the types of engines used by the GA and military aircraft; I, myself, have had limited dealings with either aircraft, so I asked my colleagues about what may have caused this situation; by ‘this situation’, I mean: Are military aircraft, GA and Learjet aircraft using the same type of fuel called out in the article: Jet-A, or are there two problems?

Since the two news sources are unclear, let’s elaborate; most GA aircraft – and possibly some military trainers – use regular Avgas, a more robust fuel with higher octane than the fuel found in the average family car.  Learjets, military fighters and some other GA aircraft use Jet-A, a more robust version of diesel fuel than found in some trucks.  Why is this confusion a problem?  Because, Jet-A fuel and Avgas fuel are not stored together in the same tanks; they are incompatible, just as regular automobile gas isn’t stored in diesel tanks.

If one were to follow the trail that led to these events to the source(s), one would ask: What was the common link?  If all the aircraft involved used Jet-A, then the source of the problem would be clear: either the fueling truck (if the same truck was used to fuel all the aircraft) or the fuel storage tank (which would most likely be the same tank), were somehow corrupted.  However, if some aircraft used Jet-A and some used Avgas, then the common link would be two tanks or multiple trucks … or both.

For the sake of argument, let’s assume they both used Jet-A; there could be different reasons for the symptoms found in these cases.  For one, there could be a problem with improper care of the trucks, e.g. the fueling hoses being left uncapped; improper service drainage checks of the truck’s tank for water accumulation or dirt; the truck’s tank becoming filled with rust or debris; or the truck’s filters not being replaced on a routine basis.

When I used to conduct regular daily service checks of my alumni airline’s B727s after flight, we would drain about two quarts of fuel out of each fuel tank.  This was accomplished after four hours of ground time to allow any water a chance to settle to the bottom.  The check allowed us to assure there was no water build-up in the tanks or bad fuel from another station wasn’t polluting the B727’s fuel tanks.  We would then use the drained samples in the diesel ground equipment, so it wasn’t wasted.

The second reason would be the storage tanks.  Problems could be found in water leaking into the fuel tanks from the ground; not conducting regular maintenance of the filters; or even microbial build-up in the tank – yes, microbes are a problem for both Avgas and Jet-A fuel tanks.  There are different types of microbes; these organisms have been found to consume anything from fuel to iron from the Titanic’s rusting hull.  Perhaps there are some microbes that would even eat my Mother-in-Law’s cooking.

Is fuel a consideration in accident investigation?  Most certainly; in fact, in GA accidents, fuel is commonly the first mechanical cause checked out (drug testing is the first operator cause looked into).  If possible, the fuel is sampled, assuming there is any to test after a post-crash fire.  In 2001, I investigated a tour helicopter accident beside the Grand Wash Cliffs near Meadview, Arizona.  No eyewitness to the actual disaster was available, so several theories were floated, including fuel starvation.  Unfortunately, the accident helicopter’s fuel tank could not provide an adequate sample, so no defined ‘cause’ or ‘no cause’ was credited to the helicopter’s fuel tank; several contributing fueling stations were tested, but no issues were found.

Any aircraft engine, whether combustion or turbine powered, relies on three things for operation: fuel, air and ignition.  As mentioned, a break in an engine’s fuel supply can cause different accident-causing events.  A flameout is when the fuel is cut off to the engine enough to lose ignition, perhaps by water diluting the fuel; the flame goes out because there isn’t enough fuel to keep the fire burning.  This turns a single-engine aircraft into a glider.  If a multi-engine aircraft, feeding off a single tank with bad fuel, flames out, this could result in complete failure of all engines – again, think glider.

Clogged fuel nozzles, filters or fouled wing tanks also contribute to accident-causing events.  The fuel nozzles (or jets) atomize fuel as it is sprayed into the combustion chamber, whether it’s the cylinder (combustion engine) or the burner cans (turbine engine); the fuel is pushed, under high pressure, through very small holes in the fuel nozzles, that cause the atomization.  If the nozzles are fouled, the fuel won’t exit the nozzle or it will not break down into a mist, instead dribbling out in a way that diminishes the combustion.

Contaminated filters or polluted fuel tanks can also contribute to an accident.  Filters remove the contaminants or microbial impurities introduced into the fuel tank from outside sources; filters do this before the fuel is pumped into the combustion chamber.  However, unlike a car or truck that can pull to the side of the road, an aircraft has to keep the engines running … no matter what damage they incur.  The filter system, if fouled enough it prevents fuel from getting through, will bypass the fuel filter and direct the contaminated fuel straight through to the combustion chamber.

Findings will soon be made known from Omaha’s fuel issues, procedures, inspections and/or maintenance changes adjusted to prevent future events.  Hopefully, the findings will be shared to assure other airport FBOs won’t duplicate those problems.  To point, the fuel issues here must be handled proactively, not reactively; too often these problems can be discovered earlier with no threat to safety.

Leave a Reply

Your email address will not be published. Required fields are marked *