Aerospace part costing: buy-to-fly ratio and the cost of the paperwork
Costing a machined aerospace component. The route matches general machining, but expensive billet makes the buy-to-fly ratio decisive, and certification records are a real cost that must be entered.
The process route matches **CNC machining**: billet, fixturing, cutting, inspection. Read that guide first; the machine hour and tool life methods apply unchanged.
Two differences, and both push the cost far above a geometrically similar part in another sector.
Buy-to-fly is the number that decides the sheet
Aerospace parts are frequently machined from solid, so most of the billet leaves as chips. In other sectors that hardly matters because stock is cheap. Here stock is expensive enough that **the metal in the chips can exceed the machining labor**.
Measure it as billet weight issued over finished part weight. Cost by **billet weight**, never finished weight — this is the most common error in the sector, and it understates the part substantially.
Records and certification are real cost
The part is only usable with its documentation, and producing that documentation costs money that appears on no line unless you put it there:
- Time to compile and retain lot records — labor, with the cause noted.
- Required non-destructive testing — outside processing if subcontracted, machine time if in-house.
- Maintaining approvals and periodic audits — overhead.
- Parts rejected for missing traceability rather than for dimensions — still scrap, but note the cause.
The last one is worth separating because no machining improvement can touch it. Recording the cause is what tells you whether you are treating the right problem.
Three changes from the machining guide
| Category | What changes |
|---|---|
| Material | Enter billet weight issued; record the buy-to-fly ratio explicitly |
| Labor | Add a documentation and traceability line, separate from production |
| Overhead | Add approval maintenance and audit costs |
The remaining seven follow the machining guide — including tooling, which is a heavy line here because these alloys wear cutters faster.
Related guides
- CNC machining cost breakdown: all ten cost categories, in process order
How to cost a machined part properly — material, machine hours, labor, tooling, scrap, rework, outside processing, packaging, freight and overhead — and why two engineers costing the same part get two different numbers.
- Tooling cost per part, and three ways to reduce it
Cutting tools are bought by the box and consumed by the part. How to convert one into the other, how to measure tool life without buying anything, and which reductions actually reach the bottom line.
- Six fields almost nobody fills in, and which way each one bends the cost
Material yield, personal and machine allowances, energy, units per pack and fixed cost per lot: six inputs that are usually left empty, and why five of the six make the cost look cheaper than it is.