LOTAR Initiative Guide for Aerospace CAD Archiving

The LOTAR (Long-Term Archival and Retrieval) initiative represents a major advancement in the field of digital preservation for the aerospace and defense industries. Faced with aircraft lifecycles that can reach 50 years, while digital formats and software become obsolete in just a few years, LOTAR establishes a standardized framework crucial for ensuring the accessibility and integrity of technical data over several decades.

Developed by an international consortium of major industrial players, this standard offers a standardized approach based on neutral formats such as STEP AP242, thereby preserving all critical information - 3D models, PMI (Product Manufacturing Information) and product structures - independently of technological evolution. The stakes are considerable: without a sustainable archiving solution, the entire technical digital heritage risks becoming inaccessible, compromising maintenance, certification, and future evolution of aircraft.

Table of Contents

• Origins and objectives of the LOTAR initiative
• Archiving challenges in the aerospace industry
• LOTAR standards and OAIS model
• CAD formats recommended for long-term archiving
• Validation and certification of CAD data
• Methodology for validating format conversions
• Working groups and LOTAR application domains
• Practical implementation in companies
• Benefits and return on investment
• Future perspectives for LOTAR

Origins and objectives of the LOTAR initiative

The LOTAR initiative was born from an alarming observation in the aerospace industry: with aircraft lifecycles extending over 30 to 50 years, the preservation of technical data faces the rapid obsolescence of computer systems. This international consortium, formed by major aerospace players, has set itself the mission of developing, testing, and implementing robust standards for sustainable digital archiving.

LOTAR represents a strategic collaboration between several international standardization organizations, including the AIA (Aerospace Industries Association), ASD-Stan (European Association of Aerospace and Defense Industries), prostep ivip, and PDES, Inc. This initiative revolves around a fundamental objective: ensuring that critical engineering data remains accessible, usable, and interpretable throughout the complete lifecycle of aerospace products.

The main objectives of LOTAR can be summarized as follows:

• Define neutral and standardized formats for archiving technical data
• Establish standardized processes for data validation and verification
• Ensure long-term interoperability between different PLM systems
• Meet strict regulatory requirements for data retention
• Enable maintenance and technical modifications decades after initial design

Archiving challenges in the aerospace industry

The aerospace industry faces specific challenges in digital archiving, related to the very nature of its products and the regulatory constraints that govern it. The exceptionally long lifespan of aircraft strongly contrasts with the rapid evolution of computer technologies and digital formats.

This dichotomy creates several fundamental problems:

• The planned obsolescence of proprietary formats and CAD software
• The need to maintain access to technical information for certification and maintenance
• The risks of semantic information loss during data migrations
• The traceability constraints imposed by certification bodies
• Preserving the semantic integrity of the data (especially PMI)

A concrete example of this problem occurs during modifications to in-service aircraft. Without access to the original design data in a usable format, maintenance, repair, and modernization operations become considerably more complex and expensive. Industry estimates indicate that one euro invested in structured archiving saves up to ten euros during subsequent technical interventions.

LOTAR standards and OAIS model

The LOTAR initiative is based on the OAIS (Open Archival Information System, ISO 14721) conceptual model, which defines a robust reference framework for long-term archiving systems. This model, initially developed for the space sector, approaches archiving as a complete process, from ingestion to dissemination, including the preservation and long-term sustainability of data.

The EN/NAS 9300 series of standards, resulting from this initiative, constitutes the main documentary corpus of LOTAR. It specifies the technical and organizational requirements for the long-term archiving and retrieval of digital product data. Its modular structure allows addressing different technical domains:

• EN/NAS 9300-001 to 009: General principles and methodology
• EN/NAS 9300-100 to 199: 3D geometric models and PMI
• EN/NAS 9300-200 to 299: Product Data Management (PDM)
• EN/NAS 9300-300 to 399: Composite materials
• EN/NAS 9300-400 to 499: Electronics and electrical harnesses
• EN/NAS 9300-500 to 599: Model-based systems engineering

These standards define not only the archiving formats but also the validation processes, data models, and mechanisms ensuring long-term integrity. The LOTAR methodology also requires comprehensive documentation of the context of archived data, ensuring their correct interpretation several decades later.

CAD formats recommended for long-term archiving

The choice of archiving formats constitutes one of the most critical aspects of the LOTAR initiative. To guarantee access to data over several decades, formats must meet strict criteria for openness, standardization, and ability to preserve the semantic integrity of models.

STEP AP242 (Standard for the Exchange of Product model data, Application Protocol 242) has established itself as the central pivot format of LOTAR. This ISO standard offers several decisive advantages for long-term archiving:

• Open and internationally standardized format (ISO 10303)
• Complete support for 3D geometric data
• Preservation of PMI (Product Manufacturing Information)
• Ability to maintain product structure and assemblies
• Independence from software vendors
• Integrated validation mechanisms via validation properties

However, LOTAR recognizes that other formats can complement STEP AP242 in a robust archiving strategy. Here is a comparative table of the main recommended formats:

The LOTAR approach generally recommends a multi-format strategy, where STEP AP242 serves as the primary archiving format while complementary formats can be used for specific purposes such as visualization or documentation.

Validation and certification of CAD data

Data validation constitutes a fundamental pillar of the LOTAR initiative. To ensure the long-term integrity of digital models, it is essential to identify and correct any defects that could affect their future usability. This crucial step takes place both at the level of native models and after their conversion to archiving formats.

Specialized validation tools allow performing this verification by detecting several categories of potential defects. CADIQ, which will be presented in more detail later, is among these solutions ensuring model quality before archiving.

The validation process generally includes three main phases:

1. Native model validation: detection and correction of defects in the original format
2. Conversion validation: verification of equivalence between the native model and its converted version
3. Validation properties validation: control of metadata accompanying the converted model

The types of defects checked include:

• Integrity defects: free edges, degenerate faces, invalid volumes
• Semantic annotation defects: unassociated PMI, missing references
• Tooling defects: radii too small, insufficient thicknesses
• Structure defects: nested solids, empty assemblies
• Exchange defects: high curvature curves, gaps between segments

Validation properties play a particularly important role in the LOTAR context. These metadata, embedded in STEP files, document key characteristics such as mass properties, geometric centers, or sample points on surfaces. They constitute a form of digital fingerprint allowing verification of model integrity during future retrievals.

Methodology for validating format conversions

The conversion from proprietary formats to neutral formats like STEP AP242 represents a critical step in the archiving process. To ensure technical equivalence between the native model and its archived version, LOTAR defines a rigorous validation methodology based on several levels of control.

The standard process for validating conversions includes the following steps:

1. Generation of validation properties on the native model
2. Export to the archiving format with inclusion of validation properties
3. Geometric and topological comparison between source model and converted model
4. Verification of PMI and annotation equivalence
5. Validation of product structure for assemblies
6. Documentation of results in a certification report

Validation tools identify several types of potential divergences:

• Major shape changes: volume modifications, added/removed surfaces
• Minor shape changes: geometric deviations, position changes
• PMI modifications: added/removed annotations, value changes
• Attribute changes: modifications of names, properties, metadata
• Structure modifications: changes in the product tree

To facilitate validation, LOTAR recommends the systematic use of STEP validation properties. These metadata include:

• Geometric properties (volume, surface area, center of gravity)
• Sampling points on surfaces (for shape validation)
• Topological properties (number of entities, structure)
• Annotation metadata (number of PMI elements, references)
• Product structure properties (number of components, positions)

The validation reports generated at the end of this process are essential for documenting the compliance of archived data. They are generally produced in accessible formats such as 3D PDF, HTML, or WebGL, allowing intuitive visualization of results and complete traceability of the process.

Working groups and LOTAR application domains

The LOTAR initiative is organized into specialized working groups, each focusing on a specific technical domain. This modular structure allows addressing the particularities of each data type while maintaining overall coherence in the archiving approach.

The main LOTAR working groups include:

• Mechanical CAD 3D with PMI: Defines standards for archiving 3D models including manufacturing information
• Product Data Management (PDM): Focuses on product structure, metadata, and relationships between components
• Composite materials: Addresses the specificities of design and manufacturing data for composite structures
• Electrical harnesses: Develops standards for archiving wiring systems and electrical diagrams
• Model-Based Systems Engineering (MBSE): Addresses the archiving of system models and functional architectures
• Engineering Analysis and Simulation (EAS): Focuses on preserving simulation models and results

Each group follows a similar development process, starting from identifying the specific needs of the domain to arrive at technical specifications and validated test cases. This approach ensures that the developed standards meet the practical requirements of industrial users.

The different application domains of LOTAR reflect the evolution of engineering practices toward approaches based on digital models (Model-Based Definition). The following table presents the main use cases addressed by the initiative:

Practical implementation in companies

Implementing LOTAR in an organization represents a multidisciplinary project involving technical, organizational, and procedural aspects. Although the benefits are considerable, implementation requires careful planning and a progressive approach.

The main steps for successful implementation include:

1. Needs and scope assessment: Identification of critical data requiring long-term archiving
2. Archiving strategy definition: Selection of formats, archiving frequency, retention period
3. Tools and technologies selection: Choice of converters, validators, and storage systems
4. Integration with PLM ecosystem: Connection with existing data management systems
5. Operational processes definition: Validation, approval, and archiving workflows
6. Team training: Awareness and skill development for users
7. Pilot implementation: Testing on a limited scope before generalization
8. Progressive deployment: Extension to all concerned programs

Integration with existing PLM systems generally constitutes one of the most complex aspects of implementation. To maximize efficiency, LOTAR processes must be inserted into established workflows, automating validation and conversion steps as much as possible.

Several technical and organizational challenges may arise during implementation:

• Resistance to change: Need to raise awareness among teams about long-term archiving issues
• Conversion complexity: Some advanced CAD features may be difficult to translate into neutral formats
• Data volume: Modern models can reach considerable sizes, requiring adapted infrastructures
• Process continuity: Archiving must integrate naturally into existing processes to ensure adoption
• Conversion validation: Technical expertise needed to evaluate conversion quality may be rare

Benefits and return on investment

Implementing the LOTAR initiative generates substantial benefits, both short and long term. While the initial investment may seem significant, the return on investment manifests at several levels and throughout the entire product lifecycle.

The main benefits can be categorized as follows:

Strategic benefits

• Securing the company's digital heritage over the long term
• Compliance with aerospace sector regulatory requirements
• Reduction of risks related to format and system obsolescence
• Preservation of technical know-how incorporated in digital models
• Maintaining technical intervention capability throughout the product lifespan

Operational benefits

• Acceleration of maintenance and modification processes
• Improvement of data quality through systematic validation
• Early detection of potential problems in models
• Facilitation of technical exchanges with partners and subcontractors
• Simplified reuse of existing designs for new programs

Economic benefits

• Reduction of re-modeling costs during system updates
• Decrease in maintenance delays and costs through immediate access to technical data
• Optimization of IT resources through the use of standardized formats
• Limitation of costly errors during technical interventions
• Amortization of the initial investment over the entire product lifespan

Several industry studies have demonstrated the favorable cost-benefit ratio of LOTAR archiving. For a typical aeronautical program, the return on investment typically materializes within 3 to 5 years following implementation, with a benefit/cost ratio that can reach 1:10 over the complete lifespan of the program.

The following table presents an estimate of potential savings by activity category:

Future perspectives for LOTAR

The LOTAR initiative continues to evolve to address new technological challenges and emerging industry needs. Several development axes are taking shape for the coming years, expanding the scope and effectiveness of long-term archiving standards.

Major trends in the evolution of LOTAR include:

Extension to new technical domains

LOTAR is progressively extending its scope to new types of technical data. Recent developments include:

• Archiving additive manufacturing data
• Preservation of digital twins
• Conservation of artificial intelligence models related to products
• Archiving IoT data and telemetry
• Preservation of virtual/augmented reality environments

Adoption in other industrial sectors

Initially designed for aerospace, the LOTAR methodology is generating growing interest in other sectors facing similar issues:

• Automotive industry (particularly for long-life vehicles)
• Shipbuilding and offshore
• Energy (nuclear power plants, oil installations)
• Railway infrastructure and civil engineering
• Medical equipment with long service life

Technological evolution

Technological advances continue to influence the LOTAR approach, particularly:

• Integration of blockchain technologies to guarantee archive authenticity
• Exploitation of cloud computing for storage and distributed validation
• Use of artificial intelligence to improve automatic validation
• Development of microservice-based archiving approaches
• Improvement of neutral formats to support advanced CAD functionalities

Roadmap of future standards

Several normative developments are ongoing or planned within the LOTAR initiative:

• Finalization of specifications for archiving MBSE models
• Extension of standards to include cybersecurity aspects of digital archives
• Development of advanced validation methods for complex assemblies
• Harmonization with interoperability initiatives such as STEP AP242 Edition 3
• Integration of archiving approaches into systems engineering methodologies

The LOTAR initiative reflects a growing awareness of the long-term value of digital technical data. In a context of Industry 4.0 and digital transformation, the ability to preserve and exploit this digital heritage becomes a major competitive advantage, beyond simple regulatory compliance.

For companies in the aerospace sector and related industries, adopting LOTAR principles represents not only a technical necessity but also a strategic investment in the sustainability of their know-how and mastery of the complete lifecycle of their products.