By Bjorn Fehrm
November 10, 2023, ©. Leeham News: We are discussing the different design phases of an airliner development program. After covering Conceptual, Preliminary, and Detailed design, we now discuss prototype manufacturing and testing.
Today, we look at the different flight test aircraft needed and their roles.
Figure 1. The development plan for a new airliner. Source: Leeham Co.
Flight test aircraft
Last week, we looked at the important first flight test aircraft, which is used to verify the aircraft’s flight envelope and flight characteristics. For the role, it’s heavily instrumented, where test racks and flight test engineer stations replace the cabin, Figure 2.
Figure 2. The interior of the first CSeries test aircraft. Source: Bombardier.
A flight test campaign for a new airliner in the 200 to 250-seat category takes about two years and 2,000 to 2,500 Flight Hours. To cover all the test points to generate the data needed for verification of design data and certification, a fleet of test aircraft is needed.
Figure 3. The flight test fleet with their roles. Click to see better. Source: Leeham Co.
The first flight test aircraft is used for flight envelope clearance, flying characteristics, flight control system testing and verification, and powerplant with fuel system checks.
The second flight test aircraft, which follows some four months after the first, is dedicated to system tests and verification. There are a lot of systems in an aircraft that need checking to ensure that they work as intended, that the systems cooperate with other systems correctly, and can be controlled with the aircraft’s avionics and cockpit systems.
In an airliner, we have an electrical system with power generation, hydraulic system, cabin Environmental Control System (ECS), Bleed air system for ECS, deicing and engine start, Landing gears, and APU.
The third test aircraft is used for avionics development and verification. It’s also a Certification conformant aircraft regarding avionics functions of the aircraft (cockpit pilot instrumentation, communication, navigation, systems control). It is used for certification testing for the avionics systems and the connected aircraft systems.
The fourth test aircraft is the Cabin development and verification test item. It’s then used to certify the cabin equipment and functions.
The fifth and final test aircraft is a cabin-equipped aircraft, which is serial production conform. It’s used for supplementary certification tasks, operational evaluation with different airline customers, training, and finally, a long worldwide route proving tour.
Serial production aircraft
If there are supplementary certification tasks that need to be done in parallel with the above flight tests, the first serial production aircraft are temporarily retained by the OEM to fly such trials.
After completion of the certification and any supplementary tests for extension of the aircraft certificate like ILS ACT III landing and ETOPS (Extended-range Twin Operations approval), several aircraft are sold at a reduced price as business jets and heads of state transport. The OEM keeps a couple of test aircraft for supplementary development and demo flights.
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