Structures and materials

This is the parent guide for the physical part of an aircraft: fuselage and wing structures, machined parts, composites, castings and forgings, fasteners, landing gear, seals and bearings, transparencies, surface treatments and the metal itself. The guides beneath it cover the process questions each of those trades turns on. This one covers what they share, which is that a structural purchase is a purchase of responsibility as much as of hardware.

Decide who owns the design before you ask for a price

Build to print and design responsible are different businesses with different insurance, different engineering staff and different prices. Say which one you are buying in the request for quotation, and say who owns the tooling, the model, the fixtures and the inspection programme when the relationship ends. The second question is what route puts the part on an aircraft. A person who knows a replacement or modification article is likely to be installed on a type certificated product may not produce it unless it comes through one of the routes the rule lists: under a type certificate, under an FAA production approval, as a standard part made to a government or industry specification, as a commercial part, produced by an owner or operator for their own product, fabricated by an appropriately rated certificate holder and consumed in a repair, or approved in another manner by the FAA.² The same section stops a producer outside the first two routes from representing the part as suitable for installation on a type certificated product.² A shop can be excellent and still be on the wrong route for what you need, and that conversation costs nothing before the order and a great deal after it.

The prime's quality system reaches into yours

A production certificate holder must run a quality system that controls design data and documents and that controls suppliers, including procedures ensuring supplier-provided articles conform to the holder's requirements and a process by which suppliers report articles that do not.¹ That is the mechanism behind every source approval, every flowdown clause and every audit a tier-two shop complains about. Read your flowdowns before you sign them. Ask which requirements you are expected to pass to your own subcontractors, particularly for the special processes covered in this directory's coatings and composites guides, and ask what your customer's approved processor list allows.

Materials carry rules of their own

Defense work restricts where certain metals may be melted. The specialty metals clause defines the class by chemistry, covering specified steels, nickel and iron-nickel alloys, cobalt alloys, titanium and titanium alloys, and zirconium alloys, and it reaches mill products, forgings and castings, magnets and fasteners, with defined exceptions for commercially available off-the-shelf items.³ Ask how melt source appears in the certification package and who checks it. Drawings also call out specifications by number and revision, and defense standards are searchable in the government's own register, where a document shows as active, inactive or cancelled with its dates.⁴ Quoting against a cancelled revision is a common and expensive mistake.

Questions that sort suppliers

Ask what proportion of the work is done in house and who performs the rest. Ask for a first article package from a comparable part, and read the material certifications back to the mill. Ask what the shop does when a dimension is out of tolerance and the schedule is short. Ask what rate it has actually run on a part like yours, not what the machine list implies.

The companies below are listed on public facts, each with its source linked.