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Air operations, Expert view, Sustainability

Understanding atmospheric aerosols’ impact on engine maintenance

August 23, 2023

A collaboration between Mitiga Solutions, Aireon and Cirium.

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By David White, VP of strategy at Cirium

Commercial jet engines have become ever more efficient, but they are also increasingly sensitive to potential damage from the environments through which they fly. The issue of volcanic ash clouds hit the headlines in April 2010 when the eruption of Iceland’s Eyjafjallajökull volcano resulted in the cancellation of more than half of European flights. But this is just one among many environmental factors that may impact the life of critical engine parts.

To help provide some hard data around these factors, Cirium, with the support of Mitiga Solutions’ Asset Impact™ solution, used Cirium flight data and Aireon’s global satellite-based aircraft tracking data to understand how environmental hazards can be optimally managed and mitigated.

We measured not only the impact of occasionally dramatic volcanic eruptions but also the impact of a wide range of corrosive and abrasive atmospheric aerosols to which engines may be routinely exposed.

These aerosols include:

  • salt air, causing corrosion for engines operating in and out of coastal airports;
  • mineral dust from desert sands that may score and abrade moving parts;
  • sulphates (sulfur dioxide & sulfuric acid) from air pollution that may degrade critical components such as fan blades; and
  • black carbon from wildfire smoke or other sources that can clog key components such as high-pressure valves and nozzles.

Preventive maintenance practices already seek to take into account exposure to such aerosols, varying the Time Between Overhaul (TBO) for engine parts as laid down by international regulations. To address this challenge the industry approach has been to rely on environmental correction factors based on time-averaged aerosol exposures for entire regions or sometimes city-pairs.

However, this approach has significant shortcomings, as aerosol composition and distribution can be highly heterogeneous in both space and time. This results in under-outliers and over-outliers that are not taken into consideration yet have an impact on equipment; even extreme events are discarded, as they are not accounted for (see Figure 1). Incidents or brief periods of unusually high exposures could still result in greatly accelerated deterioration of engine components. Conversely, better-than-average atmospheric conditions might extend the life of components beyond the 5-year mean.

Figure 1. Under-outliers, over-outliers and extreme events for different aircraft routes. (Source: Mitiga Solutions)

What if there was a way to fully resolve an engine’s aerosol exposure, document its likely exposure over time, and make an informed estimate of the cumulative effects of exposure based upon knowledge of its actual flight paths through areas where aerosols were known to be concentrated? The use of Cirium’s and Aireon’s data through Mitiga’s solution makes that a real possibility.

Mitiga’s meteorologists and atmospheric and data scientists used the latest data on aerosol concentration and dispersion models to locate and analyse the composition and depth of areas of aerosol concentrations and forecast their dispersion patterns.

Mitiga’s ability to locate, analyze and track areas of atmospheric aerosols, combined with Cirium’s detailed flight history, aircraft configuration and Aireon positional data, makes it possible to establish much more precisely what an aircraft’s engine has been exposed to, estimate the amount of that exposure, and plot the results over time.

Figure 2 shows results from an analysis of an Airbus A320 with CFM56 engines that flies short- and medium-haul routes primarily in the Middle East. Mitiga’s dashboard shows data over a 1-year period with a summary of aircraft hours and cycles (top left), a map showing the routes it served (middle top), a graph showing exposure to all aerosols for each operation (top right) and a bar graph showing the estimated absorbed accumulation of each type of aerosol by the engines between May 1, 2022, and April 30, 2023 (bottom).  Results for mineral dust and sea salt exposure are divided into separate bars reflecting the size of the particles encountered.

Figure 2. Atmospheric aerosol exposure results from an analysis of an Airbus A320 with CFM56 engines that flies short- and medium-haul routes primarily in the Middle East. (Source: Mitiga Solutions)

Unsurprisingly, this aircraft/engine combination has significant exposure to sand, mostly 2-5 mm in size, but relatively light exposure to sea salt, sulfates and black carbon. Engines with a profile like this, warrant frequent inspections for abrasive damage to moving parts and may require a complete overhaul earlier than the standard TBO time.

Figure 3 shows further analysis that ranks the amount of exposure encountered on each of the aircraft’s cycles between city pairs, the number of cycles on each route and the median dose of aerosols in grams on each cycle.

Figure 3. Ranked atmospheric aerosol exposure of same aircraft/engine as in Figure 1 by city pair. (Source: Mitiga Solutions)

In contrast, and to illustrate how an aircraft/engine combination’s exposure can vary as a function of where it operates, one can see that an aircraft operating in the US Southwest has a very different profile than the one in Figure 2. In the US environment, organic carbon exposure, likely from wildfire smoke and local air pollution, salt air, sulfates and mineral dust all contribute to the engine’s potential damage.

Figure 4. Atmospheric aerosols aircrafts/engines are exposed to in the US Southwest, by aerosol amount. (Source: Mitiga Solutions)

Trials conducted thus far for this environmental analysis demonstrated benefits for:

  • Preventive maintenance: scheduling maintenance on an individual aircraft basis can help avoid mechanical failures and the resulting costs of schedule disruption;
  • Maintenance cost analysis: third-party or in-house MROs can gain a better understanding of maintenance costs by considering expected exposure to aerosols across the engine fleet;
  • Financial risk management: lessors and OEMs providing power-by-the-hour contracts can more accurately model engine maintenance overheads; and
  • Aircraft valuations: improved accuracy in determining engine condition can in turn help determine the likely hours and cycles remaining before the need for an overhaul.

Other use cases will no doubt emerge. Mitiga Asset Impact™ solution, powered by Cirium and Aireon data, is now available for trial and testing.

To learn more, connect with us.

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