General Drawing Hierarchy-Cabin Interiors: The drawing system or structure in both large and smaller aerospace companies can sometimes be challenging to understand. There are very well established NASA drawing standards if you want to dig deeper.

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In this post I will try to break down a simple and generic top level drawing structure typical to the aircraft cabin interiors industry.

Note that this is an example only, it could get a lot more complex than this, so think of this is as a highly simplified version. However, this hierarchy is not uncommon.

General Drawing Hierarchy-Cabin Interiors:

Sample Cabin Structure: 123456-001 (Instl.) > 123456-101 (Top Assy.)> 123456-201 (Bonded/Shell Assy.)> 123456-XXX (Other Sub Assy./Details) > Other Detail Parts

Generic Drawing Tree
Figure 1: Generic Drawing Tree

The figure below illustrates a typical composite structure installed in an aircraft, it is a simple closet. This is the top level, the installation. This top most level drawing is usually described by an “Installation Drawing”.

General Drawing Hierarchy-Cabin Interiors
Figure 2: Sample Composite Structure, Aircraft Interiors

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Installation Drawing, P/N  123456-001:

The installation drawing includes the top assembly drawing plus the installation hardware and miscellaneous parts required to install the product in the aircraft. Sometimes the installation hardware can be supplied as a kit part number. So in the closet Figure above, the top assembly drawing, the tie rod assembly, the floor fitting installation hardware and other installation hardware together make up the installation drawing parts list.

So let us give this installation drawing a number, 123456-001. Here, 123456 is the main drawing number. Different companies may use different styles for this number. Sometimes it can be a combination of numbers such as a customer number, project number etc. Sometimes it may also have dashes and other numbers within the main drawing number.

The drawing number and the -001 combined identifies the part, called the Part Identification Number (PIN or P/N). This -001 is the very first installation drawing dash number. It starts at what is called a Revision- or Revision IR (Initial Release). Then as changes are made to this drawing, small changes are documented with special change numbers. After a set of minor change numbers, they are rolled into the next Revision, 'A'. Similarly the revision levels keep progressing with changes like so: A, B...AA, AB...and  so on.

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Depending on the number of unit, the complexity of the changes etc., each change goes through an extensive drawing review and approval process by the MRB (Material Review Board). Sometimes companies may employ internally approved processes that may not require all the designated personnel signatures. For example a simple electrical change may be signed off by certain personnel without needing 'stress' approval and so on.

Then there is rolling the dash number -001 into -003 (skipping -002) Vs producing an entirely new part number. Depending on how significant the changes are, the -001 maybe rolled into -003. But if the change is too large then an entirely new part number may be required. Odd dash numbers may be reserved for one side while even dash numbers may be used for the opposite side (if there is a mirror structure) of the same installation.

Every concerned department (design, stress, production, quality, program etc.) must sign and approve drawing changes as required before they are released into the document control system and then subsequently passed on to production. These procedures fall into a separate department called the 'Document Control' department. These personnel specialize in these document management processes.

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General Drawing Hierarchy-Cabin Interiors

Top Assembly Drawing, P/N  123456-101:

The installation drawing part number typically includes the 'top assembly' part number. Let us give this drawing a number, let us designate it as 123456-101.

Here, 123456 is still the main drawing number, and 101 is the top assembly dash number. In addition to the top assembly drawing P/N, the installation drawing may also include other installations (plumbing, electrical etc.) or other assemblies and detail parts.

The top assembly may also be split into other sub assemblies. These sub assemblies together could make up the entire assembly.

General Drawing Hierarchy-Cabin Interiors

Bonded Structure or Shell Assembly Drawing, P/N  123456-201:

The top assembly drawing part number typically includes the 'bonded structure' or 'shell assembly' part numbers. These drawings define how the overall panel structure and items bonded on or into the panels are joined together. Let us give this drawing a number, let us designate it as 123456-201.

Here, 123456 is still the main drawing number, and 201 may be the bonded structure dash number. The bonded structure drawing may contain bonded panels, doublers, fittings and so on. A shell assembly produced using panel pins will be similar and defines the pin locations on the panels for example.

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If the top assembly is split into other sub assemblies, then each of these sub assemblies will have respective bonded structure or shell assembly drawings. These assemblies together could make up the entire bonded structure or shell assembly. The bonded structure drawing could include the detail panel assembly part numbers. Typically these panel assemblies will include potted inserts and other bonded components needed to be done at the level of that panel assembly before including them in the bonded structure along the production line.

General Drawing Hierarchy-Cabin Interiors

So in summary, various drawings are created to make the production of the structure most efficient, within the least amount of time, and maintaining quality while minimizing errors.

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Surya Batchu
Surya Batchu

Surya Batchu is the founder of Stress Ebook LLC. A senior stress engineer specializing in aerospace stress analysis and finite element analysis, Surya has close to a decade and a half of real world industry experience. He shares his expertise with you on this blog and the website via paid courses, so you can benefit from it and get ahead in your own career.