Cockpit voice recorders and flight data recorders in U.S. aircraft accident investigation

U.S. Aircraft Accident Investigation Standards and Case Study

The accident investigation standards of the U.S. follow the regulations mandated by government agencies such as the NTSB (National Transportation Safety Board) and the FAA (Federal Aviation Administration). These two agencies act as governing bodies that spell out the exact requirements and regulations concerning the investigation of any U.S. crash. They also help to dictate exactly how investigations are carried out, and report on the findings of the investigations after they are concluded. There have been many technological advancements in the field of crash investigation, many of which allow investigators and regulators to better understand the exact circumstances and scenarios involved in the crash as well as the minutes and hours leading up to the crash itself. These technologies have been incorporated into both the aircraft and the investigations in order to more fully understand why planes crash and how these crashes can be prevented in the future. These government agencies along with many U.S. And international air carriers also study the investigation results in order to learn to train their pilots and staff more effectively using real world examples from previous crash investigations.

One of the most commonly-used investigation tools that have become commonplace in U.S. aircraft are the cockpit voice recorders and the flight data recorders. These tools allow investigators to see the last few minutes before the crash from the perspective of the flight crews and also see how the aircraft behaved during this time frame. Each of these devices is mandatory on U.S. aircraft currently, and each offers their own unique advantages for crash investigators (Office of Technology Assessment, United States Congress, 1988). Following an accident, these devices are removed and sent to NTSB headquarters in Washington D.C. For professional analysis.

Cockpit Voice Recorders

Often, these are referred to as the "black box." After a crash occurs, investigators typically find these recorders using signals that are sent out through a "pinger" that is activated by specific g-force sensors (Office of Technology Assessment, United States Congress, 1988). These sensors give investigators an advantage in certain types of crashes which occur over water or in very inaccessible terrain. They allow investigators to home in on the exact location of these recorders. The cockpit voice recorders themselves are complicated pieces of equipment that record certain parameters within the voice interactions of an aircraft. Typically they record the last 30 minutes of cockpit voice conversations, radio transmissions, and internal communications that come from the aircraft (NTSB, 2010). These allow investigators to listen to the digital records that have been saved on the recorders like radio and microphone transmissions as well as engine sounds as they are heard from the cockpit.

Often times these records contain valuable information that can help solve cases where pilot error is involved. It can also help investigators understand the exact human reactions to the circumstances and situations involved just before and during a crash. This technology also allows air carriers and simulator trainers to help recreate the exact conditions before the crash in order to help train future crews in how to handle specific scenarios that may have led to a crash in the past (Wells and Rodrigues, 2004). This is one of the ways in which crash investigation technology is aiding in helping to reduce the prevalence of crashes through training and preparation.

Flight Data Recorders

The flight data recorder is another extremely valuable tool in crash investigations. This device records more than 1000 in flight characteristics and parameters within the aircraft and its behavior shortly before a crash (NTSB, 2010). These parameters include warnings, alarms, sensor information and actual in-flight aircraft behavior. Often, the information provided by these devices is unobtainable by any other means, and can help corroborate information given by crash witnesses or survivors (Kane, 2003). It can also be used as a training aid for future air carrier training programs and simulations as the exact parameters and aircraft behavior can be mimicked in a simulator for these purposes. The flight data recorder also allows NTSB officials to piece together a timeline of events immediately before a crash and to build computer models to help illustrate the parameters and flight characteristics that occurred before and during an accident (NTSB, 2010). This information is often the most important in helping to understand how an accident occurred and how to prevent similar accidents in the future. These recorders are housed in a nearly indestructible box that alerts investigators of its whereabouts using a "pinger" system similar to that of the cockpit voice recorder's. According to NTSB specifications, the flight data recorders and cockpit voice recorders can provide up to 25 hours, or 30 minutes, respectively, of continuous information about the flight. They can also each withstand water pressure of up to 20,000 feet, temperatures of up to 1100 C. For up to 30 minutes, and 3400 G's for up to 6.5 milliseconds (NTSB, 2010).

Other Technology

Besides the direct data and voice recorders contained within the aircraft, the NTSB also has many other technologies that aid in helping to understand the underlying causes of a crash and recreate the specific scenario that occurred before and during the crash itself. Another major tool that the NTSB uses in nearly every crash investigation is computer modeling (Learmount, 2009). This allows investigators to not only visually understand how the aircraft behaved but to predict, using computer models, exactly how an accident may have occurred and how the aircraft structures and technologies would have behaved during this time period (Faith, 1997). This is important in understanding how certain materials behave under stress and in accident situations. Often times, by using these computer models, NTSB investigators can relay pertinent and valuable information to aircraft designers and engineers to help in making aircraft safer in the future.

Through the use of flight simulators, the NTSB can gain valuable insight into how humans react to specific situations and flight characteristics, whether trained or warned for them or not. This allows NTSB investigators to help build probable cause by showing how similarly trained and experienced pilots react to scenarios played out as they happened during an accident (Faith, 1997). Through the use of flight simulator technology, the NTSB can also help air carriers emphasize certain training regulations and changes that need to be made in the post-investigation stages of the accident (Kane, 2003). These changes often come as a result of a crash or investigation and help the carriers to train safer, more effective flight crews for future flights.

The NTSB has exclusive access to many of the nation's more technologically advanced laboratories for expert analysis of crash investigation evidence (Office of Technology Assessment, United States Congress, 1988). This can often include analysis of metal fatigue as well as composite materials and their abilities to withstand certain stresses in the aircraft. Any sort of material analysis is done at these labs, which the NTSB has around the nation. Depending on the specific needs of the crash investigators, labs and experts are available at any time for analysis. Much of the results from these analyses are incorporated into future aircraft design and manufacturing as well.

Recent Crash Investigation and Analysis

The recent air crash in Alaska involving former U.S. Senator Ted Stevens was investigated by the NTSB, just as any air crash involving U.S. aircraft would be. But since the aircraft on which Mr. Stevens and other passengers were flying on was a privately-operated aircraft, it was not carrying either a flight data recorder or a cockpit voice recorder (Voice of America, 2010). This crash, like many other small aircraft crashes in the U.S., represent a challenge to investigators in that they are not able to use such tools to help determine probable cause and reconstruct the moments leading up to the crash itself. This is a major disadvantage in the investigation, but since this crash, like so many others, involved a celebrity, the NTSB was careful to conduct a thorough and discreet investigation.

The aircraft involved in the crash came down in a fairly remote section of Alaska, so access to the crash was very limited (Voice of America, 2010). This hampered NTSB efforts to create a headquarters of operation near the crash itself. Instead, investigators moved much of the crash from the point of impact to a hangar where they could more accurately understand the dynamics and specific circumstances that fed into the crash. Another major help to investigators was the fact that there were survivors who could help to relay the last moments of the crash in order for the NTSB staff to gain insight into exactly what happened, and to help establish probable cause (Voice of America, 2010). The NTSB was able to use reports from other pilots as well as official weather records and reports to help reconstruct the circumstances that could have potentially led up to the crash. They also interviewed other Alaska bush pilots and people who knew more about the experience levels of the pilots involved in the Stevens crash to help understand the human limitations associated with the incident (Voice of America, 2010).

After nearly a month of investigation and analysis, the NTSB was able to establish probable cause for the crash as a combination of pilot error and bad weather (Voice of America, 2010). Establishing this was not done through the typical methods of analysis like many other air crashes, but the NTSB was able to use its discretion in investigating, just as its own field manual spells out, and help to mold the investigation to the specifics of the crash itself, which was somewhat unique because of the area it occurred in and the type and size of the aircraft that crashed.

The NTSB and other regulatory agencies within the U.S. government have an established protocol for accident investigations (Faith, 1997). These protocols involve the discretion of these agencies in trying to understand probable cause as well as the use of some very specific and useful technologies. These technologies are mandatory in many U.S. aircraft, but as was seen with the crash involving former U.S. Senator Ted Stevens, these technologies are not always employed (Wells and Rodrigues, 2004). Aircraft accident investigators have to rely on expert knowledge in laboratories for analyzing crash evidence as well as computer models which can use the same evidence collected at the scene of the crash to develop a comprehensive computer model for investigators to analyze. Many times, these computer models include permutations and possibilities that go on for further analysis as part of the investigation itself. Also, investigators are keen to pass along any knowledge or specific understanding that is gleaned from the crash investigations to U.S. pilot training facilities (Learmount, 2009). This can help to prevent future crashes under similar circumstances and conditions by giving pilots training experience.

The NTSB, as a government agency, performs a very specific and useful function in its investigations of air crashes. Without a governing body to help analyze and relay crash information to the industry, nothing could be learned from the disasters of the past. Certainly there has been marked improvement in the design, manufacturing, and operation of aircraft that has come specifically from past air accident investigations. These investigations not only answer the underlying questions surrounding the crashes but also give future pilots and engineers better tools and understandings to help keep them from repeating the mistakes of the past.