View Full Version : be careful with your jet fuel

17th Feb 2006, 06:04
Inaccurate fuel gauges puzzle American officials


FORT WORTH - American Airlines is checking the fuel systems of its entire
fleet of Boeing MD-80 aircraft after a mysterious spate of incidents in
which cockpit gauges showed the wrong amount of fuel on board.

The source of the problem remains a puzzle, airline officials say. It
appears to stem from an increase in tiny microbes growing in fuel tanks.
Those particles can affect the probes that tell pilots how much fuel is on

"Everybody has their theory about why this is coming up right now," said Don
Dillman, an American pilot who also is managing director of flight
operations. "We still don't know for sure."

American officials insist that their airplanes remain safe, and point out
that all flight carry a fuel reserve far in excess of the reported
discrepancies. Still, the problem has been a major headache for the
airline's maintenance department, which, according to one internal report,
has been working "round the clock" on the issue.

It also demonstrates the increasing challenges American faces maintaining
its airplanes as its fleet ages. The airline has deferred or cancelled many
aircraft purchases in recent years to save money, and plans to buy only two
new airplanes before 2013.

"There's always a tradeoff," said Alan Sbarra, an aviation consultant with
Roach and Sbarra Airline Consulting in San Francisco. "You save money when
you don't buy new aircraft, but then you spend a lot more time and money on
maintenance as they get older."

Dillman said the problem has also surfaced at other airlines that operated
MD-80s. "This is an industry issue," he said.

American officials declined to say how much the fuel gauge issue has cost
the airline. Last year, American spent $228 million on maintenance,
materials and repairs.

Unlike most carriers, American still services its aircraft in-house, rather
than outsourcing the job to contractors. The carrier has maintenance bases
in Fort Worth, Tulsa, and Kansas City, Mo.

That's an advantage when it comes to issues such as the fuel problem,
Dillman said.

"We've maintained the MD-80 for years in-house," he said. "At this point, I
think we know more about this aircraft than Boeing does."

American operates the world's largest fleet of MD-80s, with 337 in service.
The aircraft is used heavily at Dallas/Fort Worth Airport.

When it comes to the mysterious microbes in the fuel tanks, one theory is
that the growth of the tiny pests was spurred by excess seawater that was
blown into the jet fuel supply during Hurricane Katrina, Dillman said.

Others say the MD-80 is particularly susceptible to the problem because it
doesn't burn off water in the fuel tanks as well as other aircraft. And one
airline report says a polyurethane coating on the fuel tank probes in some
older airplanes may have lost its effectiveness.

Regardless, American officials have moved aggressively in recent weeks to
investigate the problem and ensure that no flight ends up short on fuel.
This month, mechanics manually inspected every fuel tank on each of
American's MD-80s to make sure none were giving critically inaccurate
readings. They have also beefed up maintenance procedures to focus more
intently on the fuel systems.

Mechanics at American's maintenance base in Tulsa "have been working around
the clock to find a solution to this dilemma," stated a recent message to
pilots from David Johnson, the airline's MD-80 fleet captain.

The work includes:

A one-time, manual check of the fuel level in the tanks of every MD-80 in
the fleet.

More frequent draining of water out of the airplanes' fuel tanks.

Adding a chemical that slows down the growth of the microbes.

Increased inspection of the fuel systems during regular maintenance checks.

Paper fuel reports are given to pilots before every flight so they can
double-check the gauges.

American has also sent a team of workers to inspect fuel stations on the
East Coast that are supplied by Gulf Coast refineries, to test the hurricane
theory, Dillman said.

Airline officials stress that even with the inaccurate readings, no
airplanes have been in danger of running out of fuel during a flight.
Airplanes typically take off with several thousand pounds of extra fuel.

"There is an extremely large cushion of safety out there," said John Hotard,
a spokesman. He added that American's maintenance department spotted the
trends early on and has aggressively worked to solve the problem before it
could become a larger issue.

Still, inaccurate fuel gauge readings are a serious matter for an industry
where safety is crucial. Last summer, an incorrect fuel reading caused an
engine on an MD-80 to flame out as it approached Chicago.

The plane landed safely with the remaining engine. Mechanics later
determined that the problem in that case was due to a mechanical breakdown
in the fuel system rather than microbe growth in the tank, Dillman said.

According to one internal report obtained by the Star-Telegram, American
found 50 instances last year when fuel gauges gave inaccurate readings.

Of those 50, the report stated, 10 were off by 500 or more pounds of fuel.

"We must have complete assurance that our fuel quantity gauges are
accurate," the report stated. "Reasonable assurance is never good enough in
the flying business."

Dillman said that while any fuel gauge error is considered serious, it
should be taken in context with the total number of flights operated by

"Certainly it's significant, but keep in mind we flew 460,000 flights last
year," he said.

The airline has also been communicating regularly with pilots and has
advised them that the airplane is safe to fly. But officials have also
warned that pilots need to remain vigilant and aware of potential problems.

"You are a proud bunch of aviators flying a proud bird," wrote Johnson in
his message to pilots. "I'm glad we are keeping it pointed in the right
direction together."

Trebor Banstetter, (817) 390-7064
[email protected]

17th Feb 2006, 06:42
I was always wondering, how capacitive fuel level senders in large aeroplanes account for the different fuel qualities. In some motorgliders, you have to switch your fuel level indicator according to the type of fuel you filled in (Avgas/Mogas) because the dielectric properties are different.
In large aeroplanes you can often also use different types of fuel (Jet A-1, JP-4, Avtur...) with different additives (anti icing, anti fungi...). Still you donīt have to change any settings on your fuel level indicator system. How does this work ???

Dan Winterland
17th Feb 2006, 08:08
Because most jets have an SG sensor in each tank. On the 747-400, you can acess each tank's sensor via the Central Maintenance Computer - each tank's fuel SG will be given to 3 decimal places.

The microbes mentioned a fungus that loves to live in kerosene. It can be controlled with fuel additives such as Priss.

17th Feb 2006, 08:12
I suppose blocks of strontium chromate have been nixed by the greenies.....:8

17th Feb 2006, 10:15
I was always wondering, how capacitive fuel level senders in large aeroplanes account for the different fuel qualities. In some motorgliders, you have to switch your fuel level indicator according to the type of fuel you filled in (Avgas/Mogas) because the dielectric properties are different.
In large aeroplanes you can often also use different types of fuel (Jet A-1, JP-4, Avtur...) with different additives (anti icing, anti fungi...). Still you donīt have to change any settings on your fuel level indicator system. How does this work ???

There is a compensator probe in the lowest part of each tank to which the other probes are referenced. These are checked along with the other probes in each tank during each routine calibration, which happens every 630 flying hours in the organisation I work for.

Loose rivets
17th Feb 2006, 12:58
Mmm...Gaia works in mysterious ways.

17th Feb 2006, 14:41
Until quite recently we were operating a Falcon corporate Jet out of a tropical country, and it's tanks were regularly befallen with a fungi-like microbe that would coat everything in a reddish goo...

-even draining the water daily, and doing fuel/water checks on EVERY uplift did not stop the growth..

- even going to a once-a-month application of BIOBOR (recommended is 3 times/year) did not kill the little buggers..

- in the end, the C-check took 2 additional weeks, because they actually had to drop the wing (!) and open the fuel tanks to clean the mess out.

After talking to the people who manufacture the anti-bacterial additives like BIOBOR or Pryst, it seems bacterial growth cannot be avoided in tropical countries, only contained...

Ignition Override
18th Feb 2006, 05:17
What about the electronic sensors and summing units on other Douglas predecessors, such as the DC-8 and -9?

At least American Airlines did not provoke its mechanics into a strike, thereby losing invaluable experience on its several fleets.

18th Feb 2006, 17:46
I flew the DC9-30 and everything seemed to work just fine...but two things to remember.

american has been trying to keep fuel a little tight and maybe that is why things got a bit more urgent

also, maybe strange bugs hitherto unknown have been placed in the fuel due to , yes, hurricane katrina... maybe water levels changed allowing microbes to grow.

I think we should call them "whittle bugs" by the way. named after Sir Frank Whittle and I am sure everyone on this forum knows who he is/was.

I do recall an odd occurance once, long ago in a galaxy far far away. A cessna 402 (over wing fueling caps) was left out to be fueled. The caps were left off and the fueler went home. Yes, it rained! didn't even fill the tanks with water, but the WATER was such a different value for capacitance ( electrical that is) it showed full on the gauges.

Well, it all turned out ok as the plane couldn't even start its engines...but lots of water in jet fuel just might make the quantity system show too much when there was not enough.



18th Feb 2006, 19:23
Uuuuuum actually they are called cladosporium resinae, and live on the interface between a hydrocarbon fuel and water....(as taught at all good RAF training schools since metal wings and kerosene came along)..I'm sure Sir Frank, (and Ian) would be horrified to have a bug named after them.....:}

18th Feb 2006, 19:31
perhaps my play on words was missed, whittle rhymes with LITTLE...get it.

God Save the RAF.


18th Feb 2006, 21:10
I have heard that once this goo starts accumulating that the different fuel additives will not get rid of it. The probes must be taken out and power washed or however they are cleaned. I don't know if this problem has been prevalent on the DC-9 or derivative fleet or if this is a result of some change in AA's maintenance procedures.

19th Feb 2006, 01:31
This was rather a huge problem long ago with the first purpose-built executive jet, the Lockheed JetStar, and in many cases, whole lower wing skins needed to be replaced.
Thsis led to the tank and plank inspection, which is still done today, as part of the CPCP program.
Unwanted microbes are nasty, to be sure.:eek:

20th Feb 2006, 17:17
Cladisporum Resinae was certainly the name given to me about the black gunge which caused leaks in the tanks of an aircraft operated in Saudi re-fueled from a little used fuel tanker in Al-Jouf then unflown for a month. Apparently likes tank sealent and after a while will cause corrosion of the tank.
Prist ( anti ice/microbe concentrations were said to be possibly low and or insufficiently dissipated during the re-fuelling allowing the organism to gain a hold in water droplets inside the tank either brought in with the fuel or from condensation with the tanks over the inactive period.
Tank flushing with Biobor another fuel antimicrobiological agent was not an approved cure for this particular make so the alternative cure of flushing the tanks with industrial(methyl) alcohol, not available in Saudi, was carried out at maint base in Switzerland. Crew resorted to a similar treatment with the ethyl varient. Both effacious. Capacitence fuel probes luckily seemingly uneffected.