A look at the Flight Test Process

All types of commercially manufactured aircraft must undergo the Flight Test Process. This procedure is required in order to ascertain that the engineering and design characteristics of an aircraft meet established structural, controllability and safety parameters. It serves to establish compliance with certification requirements for new aircraft as well as major changes to existing aircraft.

This is a very involved process, especially for new aircraft, and typically involves the following:

A. Structural testing of actual aircraft components that have been built to design specifications for the express purpose of stress testing. These components are placed in steel jigs where measurable pressure is exerted on specific areas by hydraulic rams. The pressure is then measured in different areas of the structure by attaching electronic stress devices which give a digital readout for engineering interpretation. Through these tests it can be determined if the actual structure can handle the stress loading that the actual aircraft will experience during takeoff/landing and in-flight maneuvers. These tests continue with the electronic stress devices during the initial and subsequent actual test flights so airborne operational measurements can be taken and compared to the static test readings taken on the ground.

B. Ground testing of the actual engine/power-plant selected for the aircraft. This testing program determines if the actual power/thrust output is adequate for the operational weight and design characteristics of the aircraft. Reliability, fuel consumption and noise levels of the power-plant are also of concern. Takeoff, landing, climb and cruise performance of the engines are also monitored during the initial and subsequent test flights.

C. Aircraft reaction to flight control input that indicates a high level of controllability is a desirable outcome of the in-flight checks accomplished during the initial and subsequent test flights. Any problems encountered in this area must be solved ASAP. In order to preclude initial flight problems, multiple ground checks and reliability and engineering studies are done prior to flight.

D. Avionics (aviation electronics) encompasses a number of critical systems that are calibrated and tested numerous times prior to and during the initial flight and on subsequent test flights. These systems include communication systems,

navigation systems, various monitoring systems, the auto-functions of flight control systems, collision avoidance systems, weather systems and aircraft management systems. Military aircraft also include mission or tactical avionics such as military communications systems, military radar, sonar, electro-optics and ESM/DAS (electronic defense measures and defensive aids).

E. The safe operation and reliability of all other aircraft systems receives a high degree of attention and is rigorously checked out and inspected prior to and during the first flight and on subsequent flights. These critical systems include the flight control systems mentioned in C. above, the hydraulic system that provides hydraulic pressure to those components that are operated by hydraulic pressure, the electrical power and distribution system that furnishes electrical power to all components powered by electricity, the fuel system – which includes the storage tanks and distribution lines- the pumps and control valves. It also includes the landing gear system which includes the retraction and extention mechanism, the landing gear doors, the wheels, tires, brakes and bogey mechanism (the bogey mechanism serves to allow multiple wheel landing gear to move so that though the back wheels touch down first, the weight on the back wheels allows that weight to rotate the gear longitudially so that the front wheels are also in contact with the runway.) The bogey also comes into play on takeoff as the front of the aircraft rises before the rear does.

On commercial passenger aircraft special attention is paid to emergency egress concerns such as the number and placement of emergency exits. These exits also include inflatable slides which can be used for both land and water emergency landings. Newer aircraft also include a switch that closes off all openings in the lower part of the fuselage in the event of an emergency landing in water. This prevents water from entering thru these openings and allows the plane to float longer. An emergency oxygen system is also provided for emergencies that may occur at high altitude.

In addition to the A. thru E. Flight Test Process items listed above, there are also provisions for Functional Check Flights (FCF’s). These FCF’s are required following certain maintenance and/or component replacement tasks performed on otherwise operational aircraft. All of these tests and checks are to ensure the safe operation of all aircraft and thus the safety of those individuals in the aircraft as well as those on the ground.