Original Date: 10/20/1997
Revision Date: 01/18/2007

In order to maintain its life cycle cost allocation baseline, Northrop Grumman’s Affordability and Producibility Management has utilized various dimensional management tools within the Integrated Product Definition (IPD) teams and the Assembly Cost Centers. In particular, Geometric Dimensioning and Tolerancing (GD&T) and Key Characteristics were used to transition from the Engineering and Manufacturing Development (EMD) model stage to the Low Rate Initial Production (LRIP) stage for the F/A-18 E/F program. These tools, applied to the aft side panel (fuselage) section of the F/A-18 E/F, were used to address the Production Readiness Review issues concerning potential problems with datum coordination and the validation of product definition initiatives.

As an engineering drawing language, GD&T communicates the engineering, assembly, and inspection specifications based on functional requirements. Functional, coordinated datums are used as references for defining parts and assemblies in a 3-D space, using three mutually-orthogonal planes per ANSI Y14.5. Rotation and translation of a part after assembly are also controlled with datums. Part surfaces, for example, can be used to define the geometric planes. The mating surface that requires the tightest tolerances should be selected as the zero reference plane for the remaining two planes. Inspection and assembly tooling should also be referenced to the same zero reference on the detailed drawing to maintain the required dimensional tolerances. Northrop Grumman found that the Y=679 Outboard Former of the aft side panel section had areas where the inspection datum arrangement and assembly tooling did not match. The company’s recommendation was to have the assembly tooling datum arrangement match the detailed engineering drawing, or for the engineering drawing datums to be changed to match the assembly tooling.

Key Characteristics identify part features or interfaces, whose variation from nominal, directly affects fit, performance, or service life of the product (i.e., product requirements). Flowed down from the top level Cost Centers to the detailed part, Key Characteristics are absolute must-haves and are listed in the IPD data sheets of each detailed part before procurement from internal and external suppliers. Key Characteristics are also monitored by Statistical Process Control (SPC) techniques to minimize variation. Northrop Grumman identified the potential Key Characteristics for the aft side panel section and recommended listing them on the associated IPD data sheet. These included outer moldline mismatches and gaps, spindle position, nozzle interface surfaces, and engine bay door interface surfaces. SPC measurements for these areas are then monitored for variation. Northrop Grumman is currently listing Key Characteristics on its IPD data sheets for the LRIP stage of the F/A-18 E/F program.

Northrop Grumman’s producibility tools have helped the LRIP stage of the F/A-18 E/F program achieve a more consistently producible and cost effective product during LRIP than was realized during the EMD phase. The company is still fine-tuning its Key Characteristics and GD&T development through studies of industry and academic approaches with Boeing, McDonnell Douglas Aerospace, University of Michigan, Massachusetts Institute of Technology, and the automotive industry.

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