By Eugene le Roux, FSAIRAC, and Eamonn Ryan
With the Advanced Development Model (ADM) complete and the client satisfied with functionality, the project enters its most rigorous and costly stage: reliability qualification. This is where many organisations are tempted to cut corners – often with serious long-term consequences.
Retrofitting also damages trust, adds downtime for users, and may introduce safety concerns if done under time pressure. DC Studio | Freepik.com
EDMs prove reliability
Next comes the Engineering Development Model (EDM) phase. Unlike the ADM, which aims to validate concept and functionality, the EDM’s purpose is to prove reliability, often through extensive destructive and non-destructive testing.
Achieving reliable performance cannot be done with one or two test units. In many industries – especially defense, automotive, aerospace and heavy engineering – an EDM phase may require the construction of 20 or more units. These units undergo:
- full compliance testing against the original requirement
- environmental trials
- durability cycles
- accelerated life testing
- failure analysis and redesign
- retesting after modifications
Only when these units collectively meet the specified reliability thresholds can the product be considered technically mature.
Skipping this stage, or minimising its scope, leaves significant risk unresolved – risk that will inevitably surface later as field failures, warranty costs, recalls or reputational damage.
PPMs represent the final gate before production
Even after reliability is proven, the journey is not complete. A Pre-Production Model (PPM) must be built to ensure producibility – the ease and repeatability with which manufacturing teams can assemble the product at scale.
The PPM may still reveal issues such as:
- inefficient assembly sequences
- supplier inconsistencies
- tooling limitations
- manufacturability challenges
- ergonomics or safety issues during production
Minor refinements at this stage are normal and expected. Only after the PPM is signed off can full production begin with reasonable confidence.
What happens if you skip a stage?
Failing to follow the sequence, or attempting to merge stages, creates cascading problems:
- Unpredictable reliability
- Escalating redesign costs
- Production delays and reworks
- Client dissatisfaction and contract penalties
- Operational risk for end users
Some argue that any remaining issues can simply be fixed through later upgrade or retrofit programmes. While possible in theory, this approach is usually far more expensive and disruptive than doing the work correctly upfront. Retrofitting also damages trust, adds downtime for users, and may introduce safety concerns if done under time pressure.
Why, then, might a contractor push for premature production? Common reasons include:
- pressure to secure revenue earlier
- client impatience or political deadlines
- underestimation of development complexity
- internal budget limitations
- competitive pressures
But short-term gains seldom outweigh the long-term costs.
Are there alternative development methods?
Yes: for example, agile hardware development, spiral development or rapid prototyping frameworks. However, even these methods ultimately require formal reliability and producibility qualification. They may change how the prototypes are built, but they do not eliminate the need for staged validation.
So, what should ‘prototype’ mean? Given the structured sequence described here, it becomes clear that the term ‘prototype’ needs qualification to avoid misunderstanding. Saying “it’s just a prototype” is insufficient. Instead, it is far more precise to specify:
- Concept model
- ADM (Advanced Development Model)
- EDM (Engineering Development Model)
- PPM (Pre-Production Model)
Each represents a distinct maturity level, with different implications for risk, cost, testing and readiness.
Clear terminology leads to clear expectations, which is essential for successful engineering.
