Definition
A formal list of every part, component, raw material, and sub-assembly required to manufacture, assemble, or repair a specific aircraft, engine, or component. The bill of materials specifies each item by part number, description, quantity, and often the material specification, providing a complete inventory of what goes into the finished product.
Plain English
A complete shopping list of every part needed to build or repair something. It tells you exactly what parts, how many of each, and what they're made of.
Context Anchor
Seen in aircraft maintenance, parts ordering, repair planning, and manufacturing records.
Derivation
From the older commercial use of 'bill' meaning a written itemized list (as in 'bill of sale' or 'bill of fare'). 'Materials' refers to the physical parts and substances. Together it simply means a written list of materials.
Why Pilots Care
Ensures every required part is identified and available before work begins, supporting airworthiness and preventing incomplete repairs.
Analogy
Like a recipe ingredient list: it tells you every item required and how much, but not how to put it together.
Intuition Check
Do not read bill here as an invoice or a charge to be paid. A Bill Of Materials is a required-items list for making or fixing something.
Example Sentence 1
The mechanic checked the bill of materials to confirm every part needed for the landing gear overhaul was on hand before starting the job.
Example Sentence 2
The shop ordered every item on the bill of materials to complete the annual inspection without delays.