Aviation is the safest form of transport there is, and it is partly thanks to the work of systems engineers who make sure that everything works as intended.
The manufacture of an aircraft is such a complex project that it requires thousands of people working in coordination on a multitude of activities: market analysis, design, manufacturing, testing, maintenance, etc. In order to carry them out efficiently, there are specialised departments. In this article we will discuss one of them, the engineering of ground test systems.
To start with, it is useful to understand what exactly is meant by the term "systems engineeringAccording to the RAE, engineering is ‘the body of knowledge aimed at the invention and use of techniques for the exploitation of natural resources or for industrial activity’; as for “systems”, in our context, I suggest we stick with the second definition: ‘a set of things that, related to each other in an orderly manner, contribute to a specific object’. We can therefore define a systems engineer as the person responsible for know how the different components of the aircraft work and relate to each other.
To build an aircraft, a multitude of different parts and equipment have to be put together. These are usually manufactured by external companies called suppliers. They have their own facilities and may be located in different countries. Before sending their product to the final assembly line, they carry out a series of tests to ensure that it works properly. A supplier's test engineer is only concerned with his own equipment.. On the contrary, the systems engineer has to take into account the other elements of the aircraft. For example, a light supplier will only test that, if the appropriate voltage is received through its power supply cables, it comes on, whereas a systems engineer will test that, when a certain button is pressed in the cockpit, a warning light on the navigation display comes on and, because some inhibition system is not active, it eventually comes on.
The systems engineer dedicated to ground testing is therefore responsible for functionally test the equipment during the installation process on aircraft. The qualifier "on the ground" is used to differentiate it from the phase when the aircraft has started to fly, which is called the "flight line".
The aim of the tests is to ensuring the functioning of the systems, as well as their quality. It is not necessary to test all the functions of all the equipment during final assembly, sometimes it is guaranteed with the supplier's test certificate. In such cases, the systems engineer is limited to checking the minimum, such as that the equipment turns on.
The two main tasks of the systems engineer are:
- Drafting evidence.
- Identify, if any, the cause of the faults found during the execution of the tests. This process is known as "troubleshooting".
The systems engineer does not work alone, but collaborates with other departments in this sequence:
- The designer of a piece of equipment, system, aerostructure or spacecraft establishes the requirements that must be verified once the item has been manufactured in order to demonstrate that it is fit for service.
- The test systems engineer on the ground writes the functional tests that verify the above requirements.
- The test equipment and tooling engineers provide the means for the execution of the tests.
- Finally, production is responsible for running the tests. If something fails and they are unsure of the cause, they report it to engineering for analysis, thus initiating the troubleshooting process.
The systems engineer adapts the tests to the technical means available to the centre responsible for carrying them out, but if necessary, he/she will ask the test means department for their acquisition or manufacture.
Aircraft systems can be classified in many ways: by their typology, their functionality, etc. One of the most important, and which serves as the de facto aviation standardis the one that established the ATA (Air Transport Association, a private US air transport association) in 1956 and is called ATA 100 chapters. It basically numbers aircraft systems from 00 to 100. For example, the autopilot is ATA 22, the landing gear is ATA 32, etc.
On the other hand, systems engineers tend to specialise by technology:
- Avionics / navigation / missionElectronic systems for navigation aids, internal/external communication systems, defensive systems, autopilot, etc.
- Electric: Systems in charge of generating and distributing electrical power, internal/external lights, etc.
- CargoElectronic and mechanical systems responsible for the transport of loads.
- Pneumatics / fuelAir conditioning and refrigeration, oxygen system, anti-icing, fuel, inerting of tanks with nitrogen, etc.
- Hydraulics / flight controlsSystems responsible for moving flight control surfaces or other surfaces such as doors, the loading ramp, etc.
Within the same technology, the type of elements under test can vary: electrical harnesses, pipes, hoses, equipment, valves, etc. This allows functional tests to be grouped into other sub-categories:
- Electrical.
- Mechanics.
- Watertightness
- Functional
- Adjustments and mechanical adjustments.
- Rodaje de motores/APU (Auxiliary Power Unit).
- Outdoors with engines stopped/started.
- Fuel
For example, within the FUEL technology tests, there may be dry tests that are electrical and/or functional and others with fuel itself.
Testing should be carried out as soon as the functionality to be tested is installed to ensure that you have accessibility. For this reason, the testing process must be integrated with the aircraft assembly processcalled Build ProcessThe gaps in the structure are filled with panels and floors as it is being manufactured. This is especially relevant for testing hydraulic and pneumatic systems.
All tests and the results of their execution must be recorded in a document management processThe computerisation of the functional tests helps in the following aspects: - The documentation of the functional tests can be done either on paper or by using a computerised management system. The computerisation of functional testing helps in the following aspects:
- Edition.
- Execution.
- Management.
- Recording and analysis of results.
- Facilitates data collection from complex electrical cabinets that connect to aircraft interfaces to acquire and stimulate signals.
The list of functional tests of an aircraft depends on its equipment.and the latter in turn from the aircraft version. For example, a maritime patrol aircraft is not tested in the same way as a parachute drop version.
It is often not possible to run a test as planned, and it is necessary to write a new one, called a retest, to replace the original test. This can be due to various reasons: delays in executing the planned schedule, problems with the test equipment, defects found during or after the test, etc. Normally, the retest is carried out on tests from the same factory, but sometimes the test to be repeated depends on another production centre or a supplier. In these cases, the factory where the test piece is located must design a retest adapted to its facilities and accesses, but ensuring the same or at least equivalent verification to that of the original test.
Aviation is the safest form of transport there is. And this is partly thanks to the work of the systems engineers who make sure, as we have seen, that everything works as planned.
