V2500: Sophisticated quality inspections

LPT disk inspections for one of the best-selling engines for short- and medium-haul aircraft

01.2019 | Text: Thorsten Rienth

Thorsten Rienth writes as a freelance journalist for AEROREPORT. In addition to the aerospace industry, his technical writing focuses on rail traffic and the transportation industry.


To date, more V2500 engines have been built than almost any other engine for short- and medium-haul aircraft in avi­ation history. The V2500 powers com­mercial air­craft including the Airbus A319, A320 and A321 as well as the MD-90. It recently acquired a military appli­cation, too, powering the Embraer KC-390 transporter. The engine is manu­factured under the um­brella of Inter­national Aero Engines, a consortium comprising MTU Aero Engines, Pratt & Whitney and Japanese Aero Engines Corporation.

MTU has a program share of 16 per­cent, of which the turbine disks for the low-pressure turbine are a part. To ensure that the turbine disks manu­factured by MTU in Munich are of suffi­cient quality to be deliv­ered to the customer, they undergo elaborate quality inspections that are planned to the last detail. The following is the detailed plan and defined inspec­tion pro­cess for low-pressure turbine disks:

1. Test planning

Even if every V2500-NDT disk undergoes the same testing process, some planning is neces­sary. Before the testing pro­cess begins, a plan is drawn up to specify which tests will be con­ducted at what point in time and where. Should certain steps change—for instance, because of new regu­lations—these changes are incor­po­rated into the testing process.

2. Programming

Prior to geometric testing, the measuring machine has to be pro­grammed. The appro­priate test program for the coordi­nate measuring machine can then be called up and usually runs completely automatically.

3. Broaching test

In the next manufacturing step, the blades are joined to the disk by means of grooves, the out­lines of which look like little Christmas trees. Of course, the only way to achieve a perfect join is when the broaching grooves have precisely the correct meas­ure­ments.

4. Corrosion test

Corrosion testing is a non-destructive test procedure. Such pro­cedures are par­ticu­larly important in aviation, as they examine a part’s inner structure and help ensure its service life. Spot checks would be insufficient.

5. Metallography

Sometimes, even the most sophisticated techno­logy is still no match for the human eye; that’s why in metal­log­raphy, workers make use of a classic tool: the microscope.

6. Crack test

Crack testing aims to detect even the tiniest of fis­sures in the compo­nent. One method involves applying liquids that are fluores­cent under certain wave­lengths of light. Such liquids would collect in a crack and make them visible.

7. Final test

As the name suggests, final testing refers to the big finale of the indi­vid­ual testing steps. A major part of it consists of a visual inspection. Following a prede­ter­mined workflow, the worker inspects various compo­nent char­acte­ristics under a magni­fying glass. The final stage of testing also includes making an impression of the compo­nent so that edges, radii and chamfers—the latter is the tech­ni­cal term for a beveled surface adjoining compo­nent edges—can once again be reliably inspected.

8. Acceptance test

Anytime flying—and extremely safety-relevant—parts are being processed, a certain amount of docu­mentation
is required. In the accept­ance testing phase, employees check to make sure that every work step has been properly documented.

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