Manufacturing an aircraft is such a complex project that it requires thousands of people working in coordination on a wide variety of different activities: market research, design, manufacturing, testing, maintenance, etc. In order to perform these tasks efficiently, there are specialised departments. In this article, we will discuss one of these departments: Ground test systems engineering.
Aviation is the safest form of transport. This is partly due to the work carried out by systems engineers, who are responsible for ensuring that everything works as planned.
To begin with, it is useful to understand what exactly is meant by the term “systems engineering”. According to the Real Academia Española dictionary, engineering is “the collection of knowledge oriented toward the invention and use of techniques for the exploitation of natural resources or for industrial activity”; and in this context, the most appropriate definition of “systems” is probably: “A set of things which, in an orderly way, contribute to a certain objective.” A systems engineer is therefore a person in charge of knowing how the different components of the aircraft relate to each other and work together.
To build an aircraft, you have to assemble many different parts and equipment. These individual elements are usually manufactured by external companies called suppliers, which have their own facilities, and which can be located in different countries. Before sending their product to the final assembly line, they carry out a series of tests that guarantee its proper operation. A supplier’s test engineer is only concerned with their own products. Conversely, a systems engineer must also take into account all other elements of the aircraft. For example, a light supplier will only check that the light comes on if the correct voltage is received through the power cables; a systems engineer on the other hand will check that, when a certain button is pressed in the cockpit, a warning light appears on the navigation display and, if there is an inactive inhibiting system, this eventually switches on.
Systems engineers involved in ground testing are therefore responsible for the functional testing of equipment during its installation in the aircraft. The term “ground testing” is used to differentiate it from the phase in which the aircraft has started flying, which is called “flight testing”.
The objective of the tests is to guarantee the proper operation and quality of the various systems. It is not necessary to check all the functions of all the equipment during the final assembly; sometimes these are guaranteed by the test certificate carried out by the supplier. In such cases, the systems engineer simply checks the basics, such as whether the equipment switches on.
The two main tasks of system engineers are:
- Writing up the tests.
- Identifying the cause of any failures found while carrying out the tests. This process is known as troubleshooting.
Systems engineers do not work alone; they must collaborate with other departments in this order:
- The designer of a piece of equipment, system, aerostructure or aircraft, who establishes the requirements that must be checked, once the element is manufactured, to demonstrate that it is fit for service.
- The ground test systems engineer, who designs the functional tests that will verify the above requirements.
- The test means and tooling engineers, who provide the means for carrying out these tests.
- Finally, the production department, which is in charge of carrying out the tests. If something fails a particular test and they are not clear about the cause, they will pass it on to the engineers, who analyse the result and start the troubleshooting process.
A systems engineer will adapt tests to the technical means available at the centre responsible for carrying them out; however, if necessary, they will ask the test means department to purchase or manufacture any equipment that may be required.
Aircraft systems can be classified in many ways: by their typology, their functionality, etc. One of the most important classifications, which serves as a de facto aeronautical standard, is the one established by the ATA (Air Transport Association, a private air transport association in the USA) in 1956, called ATA 100. Basically, it 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 usually specialise by technology:
- Avionics / navigation / mission: Electronic systems for navigation aids, internal / external communication systems, defence systems, autopilots, etc.
- Electrical: Systems in charge of generating and distributing electrical energy, internal / external lights, etc.
- Cargo: Electronic and mechanical systems in charge of the transportation of cargo.
- Pneumatics / fuel: Air conditioning and refrigeration, oxygen system, anti-icing, fuel, nitrogen tank inertisation, etc.
- Hydraulics / flight controls: Systems in charge of moving flight control surfaces or other surfaces such as doors, the loading ramp, etc.
Within one kind of technology, the type of elements tested can be varied: cable harnesses, pipes, hoses, equipment, valves, etc. This allows functional tests to be grouped into other subcategories:
- Mechanical adjustments and settings
- Engine running / APU (auxiliary power unit)
- Exterior with engines off / on
For example, within FUEL technology testing, there may be dry tests that are electrical or functional, and others with the fuel itself.
Tests should be performed as soon as the functionality to be tested is assembled, in order to ensure accessibility. The testing process must therefore be integrated with the aircraft’s assembly process (or build process) since, as the aircraft is constructed, the gaps in the structure are gradually covered with panels and covers. This is especially relevant in hydraulic and pneumatic systems testing.
All tests and the results of their execution must be collected in a document management process, which is either printed or simply recorded in a computer system. Computerising the functional tests helps in the following areas:
- Recording and analysing the results
- Data collection from complex electrical cabinets connected to aircraft interfaces to acquire and stimulate signals
The list of functional tests that must be carried out on an aircraft depends on its equipment, which in turn depends on the particular version of the aircraft. For example, a maritime patrol aircraft will not involve the same tests as a parachute drop version.
Often, it is not possible to carry out a test as planned and it is necessary to design a new test, called a retest, to replace the original test. This may be due to various reasons: delays in the execution of the planned schedule, problems with the testing facilities, defects found during or after carrying out the test, etc. Usually the retest is done at the same factory, but sometimes the test to be repeated depends on another production plant or supplier. In these cases, the factory where the part being tested is located must design a retest adapted to its facilities and means, while guaranteeing the same or at least equivalent verification as the original test.
Aviation is the safest form of transport. This is partly due to the work carried out by systems engineers, who, as we have seen, ensure that everything works as planned.