***This is Aviation Accident investigation Class***
Provide a classmate discussion review /comment addition to what they discussed in their topic discussion
Peers discussion :
Aircraft accidents that are attributed to system failure can be hard to analyze or rather straightforward depending on whether the system failure is the sole reason for the crash or if multiple causes exist that turn the scenario into a Swiss cheese model. Acccording to Wood, (Wood, 2014) aircraft accidents were the system failure was the sole reason and the probable cause can be identified with a high degree of certainty are rare since the systems that are powerful enough to cause an accident all by themselves are redundant and designed with a fail-safe design. This means that a simple system failure does not cause a catastrophe since another system can take over. On the other hand, minor systems without redundancy have the power to cause an accident of their errors are not detected by the flight crew and the situation escalates.
When Lauda Air flight 004 crashed in 1991, investigators assumed a system failure since the FDR picked up asymmetrical thrust in the engines. Upon examining the evidence, investigators found that the actuator for the reverse thrust was in the deployed position. Therefore it could easily be concluded that the plane rolled onto its back in flight since the reverse thrust caused this dangerous aerodynamic condition (Rodrigues, 2012).
The so called â€œhysteresisâ€ error occurs when an instrument continues to indicate the last information received before the accident occurs. Some instruments that are known to do that are the airspeed indicator and the VSI (Wood, 2014). Investigators utilize this information to see exactly what the pilot in command saw as the accident occurred. For example, in a Cessna aircraft the magneto switch could be in the off position. That would indicate that the pilot intentionally turned it off to preserve the engine during a forced landing. On the other hand, if this is not the case in an accident with an engine fire, it would suggest that the pilot did not follow protocol. On large commercial airliners the amount of clues received from this procedure are not as abundant as they are in smaller aircraft. First and foremost most jets have irreversible flight controls, meaning that actuators and flight computer modules are placed between the joke and the control surfaces. What a person on the outside sees and what a pilot in the cockpit sees are therefore not necessarily the same. Moreover, large jets have a lot more software automation than smaller GA aircraft. Consequently the errors are not always tangible.
Runway overruns are some of the most common accidents that occur, especially when bad weather conditions, such as snow or rain, increase the required landing distance of an aircraft. During those investigations, the investigating team needs to be very meticulous about the position of the control inputs in the cockpit. Thrust levers should be idle, if they are not it would be indicative of human error or the notion that the crew attempted to go around. Thrust levers should be deployed, if they are not it would be indicative of human error. Spoilers and autobrakes should be armed. If they are not, the crew either forgot or retracted them to slow down the plane manually. These cockpit instrument analytical techniques are a major part of the system failure investigation of an aviation accident.
In the case of Air France 447 the investigators were clueless in the beginning since it took over a year to find the wreckage (Rodrigues, 2012). Upon discovering the debris, investigators quickly realized that the airplane must have stalled into the water since the structural failures and cracks in the skin indicated so. However, it took the investigators several more months to discover the frozen pitot tubes and come to the conclusion that the pilots were unable to detect this situation and recover the self-induced stall afterwards.
When investigating an accident, it is vital to assure that no evidence is dismissed outright (Wood, 2014). By using process of elimination, investigators can dismiss certain scenarios or system failures until they come to the right conclusion. This process gets harder when multiple failures come together and it is the symbiosis of these failures that creates the overall accident. Witness statements and testimonies are often the impetus that pushes the investigation in the right direction (Wood, 2014).
Time is a major factor when investigation aviation accidents as evidence can be altered over time. When MH 17 was shot down in 2014 investigators did not get access to the crash site for weeks. By the time they finally made their way to the warzone in Ukraine, the evidence had been altered substantially. Even though MH17 is not an example of a system failure, it showcases how critical time can be in order to obtain the most neutral and objective overview of an accident site. Without such an overview, it would be much harder to come to a conclusion and determine the probable cause. In 1979 an Air New Zealand DC-10 crashed in Antarctica while performing a scenic tourist tour. The accident site is very remote and hard to reach as it is located in the arctic desert of Antarctica (Campbell, 2002). The search and rescue mission, called â€œOperation Overdueâ€ did not get to the accident site for another 48 hours. Strong winds and snowstorms likely altered some vital evidence as the wreckage was subject to the influence of nature. This did not affect the final report since the accident reason was obvious (Kanki, 2011). However, if a system failure would have caused the Mount Erebus disaster, rather than human failure, it would likely have been much harder to determine the probable cause as time would have been running against the investigators.