## 1 Introduction
### Problem Statement in the Context of Obsolescence  
To enable a reliable test process, the HighLift components are manufactured as a single component or as a small series and tested as a black box at the system level. In the next step, those components are to be integrated and tested with the focus on the software within the slat flap control computer (SFCC). The test process of a SFCC emphasizes the application of two different test means. The first is the hardware in the loop test bench in which the real SFCC is tested within a simulated environment. The second test mean is a real HighLift system rig, depicted in Figure 1, which performs the slap/flap drive sequences and failure cases using real system components [7]. Both test benches (see example in Figure 2) use I/O cards to access the system under test (SuT). Both test means represent large industrial equipment developed for a specific variant of a product. It makes it the **one-of-the-kind** test mean. It has an operation time for the complete product lifecycle of a specific aircraft variant. When the test campaign is completed, the test means are already ca. 5-7 years old. Within this time span, some of the components may already have become obsolete. To be able to guarantee availability over the complete lifespan, the periodical maintenance actions, such as the periodical refurbishment are mandatory [8]. The usage scenario of a test bench is divided in three phases: pre-certification phase, post-certification phase and in-service phase. During the pre-certification phase, the test rig is used daily, and the availability is critical. Once the aircraft variant is certified and the production has already been started, the post-certification phase starts, and the availability is important. In this phase, the design of an aircraft is optimized and tested, regarding minor issues detected during the certification. During this phase, the test rig is used continuously. Once the post-certification phase is finished, the in-service phase of the airplane starts. During this phase, the test rig is only used if it is necessary. Common requests are when the aircraft has serious problems during its operation or in the occurrence of emergencies. During this phase, the test rig has ended its useful life, but its lifespan hasn't ended, and it has to be ready in cases of testing demands. If the company decides to no longer maintain the equipment, the FAA (Federal Aviation Administration) and EASA (European Union Aviation Safety Agency) can decommission the airplane type completely [3] (p. 105). Obsolescence of an I/O card occurs normally within the mentioned periodic maintenance and refurbishment process performed by the supplying companies. The following two situations are responsible for most obsolescence problems in the maintenance of test benches:  
Figure 1: Airbus A350 Test Rig-Image from Airbus Operations GmbH. Figure 2: A380 Test Bench-Image from Airbus Operations GmbH. 1. The card can be found to be defective--the chance of the defect of an I/O card within first four years of the operation is at 50% [4]. Inevitably, the operating company will face a situation where the defective I/O card is no longer maintained, and a simple replacement is no longer possible. Since the I/O card consists of software and hardware (driver and PCI or VME card), the change of hardware requires the change of software and the reimplementation of all of the accessing proprietary components. 2. Following a necessary upgrade of the operating system of the test bench, the new version no longer supports the I/O card. In this case, the I/O card will need a replacement to a variant that supports the new version of the operating system with all the consequences of the first case. The above-mentioned effects are amplified through the fluctuation in engineering teams. Once the test bench is designed and in operation, engineers change departments or companies. The knowledge of the test bench design vanishes. This applies to supplying companies as well. Those can quit the market completely [1] (p. 100).