The Hidden Threat of Microbial Contamination in Grounded Aircraft
In response to COVID-19, unprecedented numbers of passenger aircraft have been grounded with fuel left standing in aircraft wing tanks. For many airlines, this creates the unfamiliar need to proactively monitor and manage the risk of microbial contamination. Shell expert, Robert Midgley, Global Technical and Quality Manager highlights the problem and response to microbe contamination which, if left unchecked, can lead to defuelling and clean-up, or worse, airframe corrosion and blocked fuel systems.
Webinar: Avoiding Microbial Fuel Contamination for a Safer Return to the Sky
Title: The Hidden Threat of Microbial Contamination in Grounded Aircraft
Duration: 4:10 minutes
Summary video of COVID-Recovery Webinar episode 1: Fuel Management in Grounded Aircraft
The Hidden Threat of Microbial Contamination in Grounded Aircraft Transcript
[Background music plays]
Stylised line animation over recording
At Shell Aviation, we are committed to deploying our resources and our expertise to help our customers in good times and in bad times. 80% of the world's passenger fleet grounded and from our engagement with customers, we know that this is creating some new challenges.
We'll start off by looking at the different types of microbes. And these organisms really require three things to be able to survive. One is a water phase in which to live. So they tend to live not in the fuel itself, but in any water that is present. They tend to consume the fuel. So using the fuel as a food source, and they also need access to oxygen. So if you have those three things in combination, then we can start to see microbial growth.
Long turnaround times on the ground tend to accelerate growth. If we extend that turnaround time on the ground, then we're in the position where we are now with COVID, where we're on the ground all the time. We see low utilization as being a trigger for this increase in microbial growth.
Why do we see it as a problem? Well, it can start to lead on corrosion problems on an aircraft.
Seals may become brittle and they tend to shrink.
Picture here, especially on the left, which is quite dramatic of steel, it's not just pitting. That's a hole right away through a steel plate. That's due to microbial activity.
How do we prevent microbes from forming ?
That really comes down to the challenge of how a wing tank is built.
On the left, we've got a photograph of the inside of a supply tank, a bulk supply tank.
We can design this tank specifically to drain water because it doesn't have to do anything else.
If we look to the right, you see what happens once we get onto the aircraft.
We've got the equivalent to the tank bottom there in the center of the photograph. You can see it's now a flat bottom, so it doesn't have a positive sump on it. To try to deal with that, we try to suck out parts of that low point within the tank using things called scavenge rakes.
That should try and suck out any water that's sitting in the bottom of this tank and deliver it to the engine while the engine is operating.
Of course, that only works if the engine is operating. Whilst your airplane sat on the ground during COVID, there is no scavenging any of that water.
Sampling, more than any other fuel property, it's really critical getting good, accurate sampling for microbial testing.
So drain points, flexible hoses, sample containers, make sure they're sterile before you're using it.
If we start to look at the test kits, then there are a number that are approved through IATA, International Aviation Trade Association, guidelines
My personal view of this is if you're going to do microbial testing, it's useful to have more than one technique at your disposal because tests may provide you with different information
What happens if you get an indication on the test that you have a microbial contamination? Well, it's common to use in the airline industry one of the two approved biocides. One's Biobor JF, produced by Hammonds. And the other one is Kathon FP1.5
When we get the results that come from the test kits, we can get different levels of judgment on them. So we get background, moderate, and severe, or background warning and action. And when we get to that severe or action level, it's really telling you, you need to act. And that action can be one of two things. -
- Either biocide injection, which is the most common reaction to it, or
- if left untreated, it might mean that you're needing to defuel the aircraft and then do some tank entry and cleaning.
And that microbial testing you need to understand the sampling methodology, what it is you’re sampling but also the strengths and weaknesses of what the microbial test kits will tell you.
But, you really need to have a strategy.
This programme was specifically designed to highlight the problem of microbe growth and the options available to airlines. This initiative is outside of Shell's core services but is an area where we have expertise through our own supply chain management and, on a case by case basis, may be able to directly support our airline customers. So, if you identify that you have a microbe problem in a particular location please do engage Shell and we will work with you to understand the extent of the problem, what resources we have available and any treatment options, in the hope that we may be able to help you.
Section subheader, e.g. scene transition/break
[Conversation/ speech Title]
Rob Midgley, Global Quality and Technical Manager
Visual transition/change, e.g. Split screen, video footage, etc.
Presentation PowerPoint and Speaker Fuel Management in Grounded Aicraft
Tiny Organisms, Big Problems
Microbes in the form of bacteria, yeasts and fungi can grow when water finds its way into fuel tanks. The heavier water sinks to the bottom of the tank, and the zone where it meets the fuel provides an ideal environment for microbes, according to Rob Midgley, Global Technical and Quality Manager for Shell Aviation.
“These organisms require three things to be able to survive. One is a water phase in which to live. They tend not to live in the fuel itself but in the water. Secondly, these organisms would need a food source to survive – in the form of fuel. And they also need access to oxygen. If you have those three things in combination then we have the conditions in which we can start to see microbial growth,” Midgley said on a recent Shell Aviation webinar devoted to the issue and its solutions.
The wide variety of environments and microbes means every infestation is different and can cause a wide range of problems, Midgley said. Bacterial films can interfere with sensors. Microbial mats can clog filters and pumps. Microbial growth can extract the plasticiser contained in seals, making them less flexible and leading to leaks. Fungi can spread filaments under the epoxy layer that lines the bottom of some fuel tanks, breaking it apart and creating debris that can block fuel filters.
“All of these (microbes) tend to form by-products of metabolism that are generally acidic. So that water, if you tested it, would be quite acidic. It’s quite common for the water to be somewhere in the pH of about 3-5.5. Those organic acids are capable of attacking aluminium structures, and of course, that is what aircraft are made of,” Midgley said, adding that other microbes can create sulfuric acid and sulphide ions capable of eating away at steel and copper.
COVID Disruption Creates Perfect Conditions
Unlike fuel storage tanks, aircraft fuel tanks are designed principally to function as a wing and then as a fuel tank. The wing structure and design does not permit a single, simple sump but creates lots of undrainable water traps. When an aircraft is in regular operation, a system of “scavenge rakes” -- pipes in the fuel tanks that mix any water back in with the fuel, is designed to ensure that microbes can’t get a foothold.
Over the last couple of months, while over 80% of the world’s fleet is grounded3, conditions have been created where water may be accumulating in the tanks of many planes. As the approach of summer sends temperatures rising across the northern hemisphere, that is creating ideal conditions for microbes to grow.
“With COVID-19, we are on the ground all the time. And so, the fuel system, the fuel, and the water get to ambient temperature, which in most parts of the world in this season is in that 20-35 degrees (Celsius) range. So, we see low utilisation as being a trigger for this increase in microbial growth,” Midgley said.
“Anecdotally, we’ve been seeing that in some fleets that have not been treated with biocide, somewhere around 50% or more of those aircraft are starting to show signs of microbial growth after two to three months of storage,” Midgley said.
Airlines should test their aircraft for signs of microbial contamination in the fuel, Midgley said. That poses its own challenges. Microbe levels are highest at the interface between water and fuel and decline farther away from the water. Microbe populations can fluctuate over time. Sampling and testing equipment must be kept sterile to avoid
Most microbial contaminations can then be treated with one of two biocide chemicals. However, those pose their own unique challenges, such as not being compatible with certain engines or not having approval in all countries. In the most extreme cases, a plane may need to be defuelled, a complicated process that not all airports can handle,
“Ultimately if we get to the point where we need to defuel … especially if it’s for disposal because it’s been contaminated, then we are going to need some warning if we are to have the potential to help with that because disposal of contaminated fuel is not something we routinely do at airports. It may not even be possible,” Midgley said.
“You really need to have a strategy to treat the aircraft that have a high level of contamination and how are you going to do that. It’s the availability of an injection cart, availability of the additive, and also simple things like being able to access to aircraft that are parked nose to tail on taxiways.”
Ask Shell Aviation
At Shell Aviation, we understand that while the industry is facing various challenges as a result of the pandemic, enabling and maintaining efficient and safe operations will be crucial for Aviation’s recovery.
With most of the world’s aircraft fleet grounded, our industry is presented with an unfamiliar challenge: the increased threat of microbial contamination. Shell advises to proactively monitor and test your fleet to manage and prevent the risk of microbial contamination. Airlines without a microbial prevention or removal strategy, are more exposed to develop microbial contamination over the next few months, which, unchecked, can lead to significant cost and operational issues.
If you are concerned about microbe contamination of your aircraft and would like advice from Shell Aviation, please contact us using the contact form. Details of situation and location will dictate the level of support that Shell Aviation may be able to provide. Once your request is received, we will reply as soon as possible. To make it easier for us to assist you, please kindly provide as much information as possible when completing this form.
Like what you just read? There is more in the Flightpath series, sponsored by Shell.
The Aviation industry is facing a different set of challenges consequential from the COVID-19 pandemic. Restoring global aviation is crucial to fueling world economic recovery and progress. In the COVID-Recovery webinar series industry experts are sharing their views on specific topics that could enable a secure path to recovery. Please sign up here to receive this and other series updates.