Problematic Substances Compatibility Assessment

Maintenance, Repair and Overhaul organizations conduct engineering activities for specific operations of repair, service or inspection of aircraft systems to ensure the safety and continued airworthiness of an air transport vehicle.

Case Study:

Problematic Substances Compatibility Assessment


DMD Solutions was contacted by a CS-23 aircraft integrator to perform a compatibility assessment between the constituent materials of the fuel system of all their aircraft models and fleets and the fuel additives which were approved for use by their engine OEMs, P&WC and Williams International. Output of this assessment was a concise list of additives to be included in the relevant Aircraft Flight Manual (AFM) and a revision control process to be performed periodically.


The client is well-stablished Swiss CS-23 aircraft integrator which designs, manufactures, and maintains turboprop and turbojet business aircraft – to commercial customers, and military trainers – to air forces such as the Spanish Air Force (Ejército del Aire), the Australian Defence Force, the Royal Jordanian Air Force and the French Air Force (Armée de l’Air Française)



Engine and aircraft integrators are solely responsible for the approval of a fuel additive for use in their respective engines or airframes, as highlighted in ASTM D4054. Engine manufacturers provide the list of compatible fuels and fuel additives, and their usage limitations in the Instructions of Installation (IOI) of the engine or in the Engine Maintenance Manual (EMM). Additionally, Service Bulletins (SBs) are raised when operational limitations are updated.

From the list of fuel additives approved by engine OEMs, aircraft manufacturers can decide to approve only a selection of them in the aircraft, which are recorded in the Type Certificate Data Sheet (TCDS) and in the Aircraft Flight Manual (AFM).

The CS-23 aircraft manufacturer aimed to update all their AFMs to include only those additives which were compatible to all the materials of their fuel systems, avoiding use of hazardous chemicals. It was of paramount importance, as required by the aircraft manufacturer, to thoroughly investigate the constituent materials of all their fuel systems and find any potential incompatibility with engine approved fuel additives.


DMD Solutions technical expertise with problematic substances was fundamental to solve the client’s problem in a resource efficient manner, proposing innovative approaches to assess fuel additives compatibility, which prevented the conduction of any chemical compatibility test to be performed on-site. DMD Solutions’ proposed solution provided a comprehensive approach, suggesting the required modifications and updates in official documents from both engine and airframe OEMs.

Zero Testing

Material compatibility was assessed without performing any test, saving important quantities of material resources.

Service Bulletin & Aircraft Flight Manual Update

A campaign was launched to update the Service Bulletins and Aircraft Flight Manuals to account for findings collected in the development of the problematic substances assessment



After reviewing all fuel additives mentioned in ASTM D1655, ASTM D7566, Engine IOIs, EMMs, SBs, and AFMs it was found that there were more than 40 different fuel additives to assess, which were classified into two main categories (Fuel Performance Enhancing Additives and Fuel Handling & Maintenance Additives). Moreover, each category was divided in more subcategories, and it was the objective of the aircraft integrator to include, at least, one fuel additive per subcategory in their AFMs, while reducing as much as possible the quantity of tests or evaluations to be performed.

In addition, the Bill of Materials (BOM) of the fuel system of the 10 different aircraft models of the company was to be exhaustively analysed to identify all the constituent materials. More than 4,500 different components were found, which in combination with the 40 different fuel additives would have implied conducting more than 175,000 compatibility tests, incurring unaffordable costs for the company.


DMD Solutions provided both technical support in engineering as well as process consulting activities. The DMD Solutions consultant engineer integrated in the Materials and Processes team, leading the project and collaborating closely with the client’s team while working remotely. Continuous communication was key to complete the project while working from home due to COVID-19 pandemic

1. Preparation

Retrieval of fuel additive related specifications
  • Research of ASTM specifications including engine/airframe OEMs’ approved fuel additives (D1655 and D7566) and fuel additives approval process (D4054)
Retrieval of latest versions of engine documentation (IOIs, EMMs, SBs)
  • Research of the latest documentation of each engine model. For the newer engine versions there were not any SB yet, so IOI and EMM were the reference documents. On the contrary, for stablished models, updated SBs had been released, thus becoming the document to work with.
Retrieval of latest version of aircraft documents (AFMs, SDD, and BOMs)
  • Research of the latest version of the Aircraft Flight Manual (AFM) of each aircraft model.
  • Research of the latest version of the fuel System Description Document (SDD) of each aircraft model.
  • Research of the Bill of Materials (BOM) of the fuel system of each aircraft model.


  • Clarify regulatory framework to be analysed


  • Recognise engine approved additives and identify common additives with ASTM specs


  • Recognise airframe approved additives and check consistency with engine approved additives.
  • Identification of all components of the fuel system of each model.

2. Identification

Identification and allocation of each fuel additive in its category and subcategory
  • Identification of each of the 40 additives retrieved from documentation and allocation in the corresponding subcategory: Antioxidant, Metal Deactivator, Fuel System Icing Inhibitor, and Thermal Stability for Fuel Performance Enhancing additives, and Electrical Conductivity Improver, Leak Detection, Biocidal, Corrosion Inhibitor / Lubricity Improver, and Anti-Smoke for Fuel Handling and Maintenance additives.
Identification of materials
  • BOM processing and extraction of all constituent materials of the fuel system.
  • Communication with external suppliers to clarify the constituent materials of complex components in case they are not completely identified in the available documentation.
  • Identification of fuel wetted materials.


  • Identify all fuel additives to be assessed and categorise according to its intended function


  • Condensation of large components inventory to a brief list of materials

3. Investigation

Retrieval of Material Safety Data Sheets (MSDSs) and determination of potential incompatibilities
  • Research of Safety Data Sheets (SDS) for both fuel additive’s constituent chemicals and fuel system’s constituent materials, and determination of potential incompatibilities.
Conversations with fuel additive suppliers for compatibility confirmation
  • Contacting fuel additive suppliers to receive direct confirmation of their compatibility with assessed materials.


  • Identify potential reactive substances to fuel system’s constituent materials.


  • Receive explicit confirmation of compatibility between fuel additives and materials.

4. Assessment

Analysis of the fuel additive approval process and determination of compatible materials (according ASTM D4054) to fuel additives included in ASTM D1655 and D7566
  • Deep investigation and analysis of current fuel additives approval process as explained in ASTM D4054 and identification of generic classes of materials tested by airframe and engine manufacturers to evaluate compatibility with fuel additives
Justification of fuel additives compatibility with materials outside D4054

  • Investigation of alternative means to verify compatibility with materials not listed in ASTM D4054


  • Identification of compatible materials and understanding of their approval process


  • Justify compatibility of all materials with at least one additive per each subcategory

5. Conclusion

Development of a concise list of suggested additives for approval and inclusion in AFMs (from 40 to 10)

Reduction of the initial list of 40 candidate additives to a list of 10 compatible additives, preventing the conduction of compatibility tests and including one fuel additive per each subcategory.

Revision control process to be performed annually

Development of a revision control process to establish tasks to be performed each year in order to maintain all AFMs updated

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