Test equipment and instrumentation

This category covers test benches, automatic test equipment, ramp testers, flight test instrumentation and telemetry. The laboratory that calibrates them is in calibration and metrology, and the shop that uses them to repair a unit is in component repair. The buyer here is usually a repair station, a manufacturer or a test organisation, and the purchase has an unusual property: the rules already say what the equipment has to satisfy, so the specification is partly written for you.

The regulation is your requirements document

A certificated repair station must have the equipment, tools and materials needed to perform the work under its certificate and operations specifications, on the premises and under its control when the work is being done.¹ The equipment must be that recommended by the manufacturer of the article, or at least equivalent and acceptable to the FAA, and all test and inspection equipment used to make airworthiness determinations must be calibrated to a standard acceptable to the FAA.¹ The maintenance performance rules say the same thing from the other direction: use the methods, techniques and practices in the manufacturer's maintenance manual or instructions for continued airworthiness, and use the special equipment or test apparatus the manufacturer recommends, or its equivalent acceptable to the Administrator.² Read those two together before you buy. They mean the question is never "is this a good tester". It is "is this the recommended apparatus, or demonstrably equivalent, for the articles on my capability list".

Equivalence has to be argued, not asserted

If you are buying an alternative to the manufacturer's recommended set, ask the supplier for the technical comparison that supports equivalence: parameters measured, accuracy, uncertainty, stimulus and load conditions, and the test program's coverage against the maintenance manual procedure. Ask who has accepted that argument before and in what jurisdiction. Ask what happens when the article's manual is revised: who updates the test program, how quickly, and at what price. Ask whether the test programs are yours or licensed, and what the licence costs annually.

Calibration is a running cost with a paper trail

Ask what the calibration interval is, what it costs, and where the work is done. Ask for traceability: the national metrology institute publishes calibration services precisely so that measurement quality can be traced to national standards, and a supplier should be able to explain the chain from your bench to that level.³ Ask what happens to your throughput while the set is away, and whether a loaner exists. Ask how out-of-tolerance conditions are handled, because a set found out of tolerance raises questions about every unit it released since the last calibration, and the answer to that has to be a documented process, not a shrug. For defense work, check that any standard called out in the requirement is current in the government's standardization register, where documents carry a status and dates.⁴

Questions that sort suppliers

Ask for the accuracy and uncertainty figures, not the resolution. Ask which articles on your capability list the set covers today, by part number. Ask what a software or program update costs, and how often one is issued. Ask what the support looks like in year eight, and what the last discontinued product's customers were offered.