October 1, 2021, ©. Leeham News: Last week, we described how we produced our Flight Test Articles, FTAs, and how the company flight tests are made.
Now we have finished the Company flight tests and made any modifications required to the FTAs so we can apply for Certification Flight tests with the regulator.
When we apply for the start of Certification Flight tests, we typically must have flown through all the test points that we will have to fly with the regulator on board, and passed the regulatory requirements for all test points.
This is an enormous task and we can calculate that we must fly something like five hundred sorties of about one to two hours each to achieve this for an aircraft of our complexity level, certified to Part 23.
Now that we are convinced we can demonstrate compliance to all Part 23 requirements we make the formal application with the regulator. The regulator’s personnel have followed our flight test and know well our status. By first conducting the tests as a company, we have taken out risks of failure during certification testing and we can resolve design issues we discover prior to the “for score” testing.
We have also proven that the envelope is safe and the FTA is mature so that the regulator can comfortably get on board and make their findings of compliance.
It’s this knowledge and our continuous documentation on achieved certification requirements together with the formal application that forms the basis for a clearance to begin formal Certification Flights. When a company proposes progressing to certification flights without sufficient proof of maturity first the regulator will often refuse in order to not waste their resources on testing that may need to be repeated. The FAA did this quite publicly earlier this year when refusing to grant approval to start flight testing — Type Inspection Authorization — on the Boeing 777-9.
In essence, we go through the same flight test program again but now with the knowledge and confidence of what we can achieve for each parameter. All parameters are logged, evaluated, and documented to form the basis for the information base for the Type Certificate.
The tests we do serve to demonstrate that all systems and protections work correctly (including at the corner points of the envelope), that the handling and control qualities of the aircraft are appropriate to allow operation without inordinate piloting skill, and that the product is reliable enough for practical use.
There are some common exceptions to this repetition philosophy. Particularly high risk testing, such as the testing to find the absolute minimum takeoff speed, is often only run once to reduce risk to the flight test pilots and the aircraft ( https://www.youtube.com/watch?v=4FSm_SL2n9o&t=255s ).
Additionally, some testing that is very expensive or difficult to set up may be run only once with the regulator present — this increases failure risk but reduces program cost if successful. One example of this would be Cold Soak testing for large aircraft, as the temperature extremes that are needed can be very difficult to find ( https://www.youtube.com/watch?v=e3sWVRwofOA ).
Another example would be Water Ingestion testing due to the time and expense of building the water trough, as well as the risk of runway excursions ( https://www.youtube.com/watch?v=VhtUqsDojRM&t=290s ).
During such simultaneous testing, company and regulator pilots may alternate runs at the controls in order to both make their assessments.
In most cases, the certification flights should be run very similarly to our own. However, they require significantly more formality:
These measures ensure the validity of the testing to the final product to be certified, and also serve as records that can be used to support future change approvals and safety investigations. Most of this data must be retained for the life of the type certificate in case there is ever an accident on the aircraft type.
In addition to the control measures, there are also some differences in actual test cases between the programs. In particular, our engineering program will typically involve taking additional measurements to validate our analytical models or gather data for future product development assessment that is not required by the regulator.