The history of aviation development, as well as the corresponding regulations, includes the sad experience of aircraft incidents. One of the most prominent air crashes that has resulted in changing safety regulations is the Concorde Air France Flight 4590, F-BTSC of July 25, 2000 (Concorde Air France Flight 4590, F-BTSC, n.d). This flight operated from Charles de Gaulle Airport in Paris to John F. Kennedy International Airport in New York.There were 100 passengers on board, as well as 9 crew members (Concorde Air France Flight 4590, F-BTSC, n.d). The weather on the day of departure was clear with light winds, so Concorde’s takeoff was normal until the aircraft passed through V1. However, one of the tires soon hit a piece of metal that had become detached from the DC-10 engine that had taken off earlier (BEA, 2000; Concorde Air France Flight 4590, F-BTSC, n.d). After this, the tire failed, and its fragments fell into the lower part of the aircraft and into the well of the left wheel. This accident caused a pressure surge inside one of the fuel tanks, resulting in a massive fuel leak.
The fuel leak resulted in the ignition of engines 1 and 2 of the aircraft. The aircraft continued to take off, although it also began to drift to the left of the runway, forcing the pilot to rotate the aircraft. Within a few seconds, a fire alarm went off in engine 2, after which the engine was stopped. However, an aircraft that has already taken off cannot further gain altitude or speed. It soon became impossible to maintain level flight, the aircraft stalled and crashed into the hotel at Gonnesse (Jupp & Britton, 2003). This accident resulted in the death of all 109 aircraft passengers and crew members, as well as 4 people on the ground (Cramoisi, 2010, p. 9). The investigation of the Concorde accident “showed the need for progress in safety in various areas” (BEA, 2000, p. 179). This case also led to changes in regulations that focus on the safety and design of transport aircrafts.
Resulting Safety Initiatives
Revisions in the regulations concerned changes to the airworthiness structure requirements of fuel tanks for the Boeing Model 787, and the Airbus Model A350. Both the Federal Aviation Agency (FFA) and the European Aviation Safety Agency (EASA) decided to change safety requirements “to address the unique fuel tank failure mechanism experienced on flight 4590” (Resulting safety initiatives, n.d). Special condition for the Boeing Model 787 contains a requirement for changes in the structure of fuel tanks as part of the type certification basis to prevent fires due to fuel leaks (FAA, 2007). Special conditions for the Airbus Model A350 were the same but released later (FAA, 2014). In particular, both aircraft used “carbon fiber composite materials for most of the wing fuel tank structure”(FFA, 2007, p. 54529). However, the ability of this material to withstand damage that can be caused by tire debris has not been established. Thus, according to the new FFA requirements, these aircraft models must use aluminum instead of carbon composite to prevent possible penetration and fuel leaks.
Methods of Compliance Details
The FFA clearly sets out the procedures that are required to obtain the airworthiness of the aircraft certification. One of the methods of compliance is to conduct the necessary flight tests by the applicant (FFA, 2018). The document underlines that “flight test demonstrations are the preferred method to show compliance” (FAA, 2018, p. 3-2). The FAA independently determines the number of test flights that are required to demonstrate compliance with the required criteria. For example, for compliance with Wheels—§ 25.731 flight tests, all tests relevant to wheels, tires, and control brakes must be passed (FAA, 2018). Flight tests can be replaced by simulations, but only in certain situations such as extremely high risks, difficulty in attaining environmental of aircraft condition, etc.
Flight Test Plan
The following elements are critical in order to perform the necessary airworthiness substantiation activities to meet the regulation 25.149:
- Verifying the critical engine;
- Testing of static and dynamic condition for the minimum control speed (air);
- Testing the minimum control speed (ground);
- Testing the minimum control speed (approach and landing);
- Testing the minimum control speed (approach and landing with two inoperative engines);
- Testing of autofeather effects.
Safety Considerations
First of all, it should be noted that weight gain increases VMCA. However, this statement may vary depending on the environmental conditions and aircraft design. Thus, for the passage of flight tests, it would be more reasonable to limit the number of people on the plane. Within the framework of safety concerns, this assumption is also relevant as it reduces the risk of an accident. During the first flight test to determine VMCA it is better to have people on the plane in order to keep track of critical indicators. To minimize risks, the applicant must take into account any design features that may involve aerodynamic or propulsive changes. VMCA test poses an increased risk as one engine is deliberately disabled, requiring pilots to be extra vigilant (Lelaie, 2011). Thus, a second person is needed to quickly turn on the engine in case of an emergency and monitor the safety of the test flight.
Prior to tests, it is necessary to check all aircraft systems, including the serviceability of indicators, as well as the readiness of pilots to perform test flights. It is also critical to define V1 speed, check the atmospheric conditions as well as the state of the takeoff surface (Pilot guide to takeoff safety, n.d). These measures will help to avoid potential emergencies during test flights.
References
Concorde Air France Flight 4590, F-BTSC. (n.d). FFA. Web.
Cramoisi, J. (2010). Air crash investigations: The end of the Concorde era, the crash of air France flight 4590. Mabuhay Publishing.
FFA. (2018). Advisory Circular: Flight test guide for certification of transport category airplanes.
FFA. (2014). Special conditions: Airbus, Model A350–900 series airplane; tire failure – debris penetration or rupture of fuel tank structure. Federal Register, 79(9), 2388-2390.
FFA. (2007). Special conditions: Boeing Model 787– 8 airplane; tire debris penetration of fuel tank structure. Federal Register, 72(186), pp. 54529-54530.
Jupp, J. A., & Britton, J. R. (2003). Breaking the chain Returning Concorde to service following the Paris accident – July 2000. The Aeronautical Journal, 107(1073), 447-458.
Lelaie, C. (2011). Minimum control speed tests on A380. Safety First, (11), 1-5.
Pilot guide to takeoff safety. (n.d). FAA. Web.
Resulting safety initiatives. (n.d). FFA. Web.