Category Archives: Aviation Safety

Thank You

SafetyCompassLogoBy Stephanie D. Shaw

We launched Safety Compass in March 2011 to provide you an inside-out view of the investigative and advocacy efforts we’re engaged in and the important safety issues we’re focused on. As we close out 2017, we want to say “thank you” to you, our readers. Thank you for your interest in the work we do and for sharing our safety messages and recommendations for improving transportation safety.

From teens and sleep to drones, autonomous vehicles to our investigative processes, we’ve given you an inside look at the NTSB and highlighted our comprehensive approach to improving transportation safety across all modes and for all people.

To wrap up the year, here’s a list of some of our most popular blogs of 2017:

Last month, we released data revealing that 2,030 more people died in transportation accidents in 2016 than in 2015. Of those fatalities, 95 percent occurred on the nation’s roadways. Many of those deaths were completely preventable! As we approach 2018, we call on each of you to help us reverse the trend of increasing transportation fatalities, especially on our roadways. Continue to read our blog, see the lessons we’ve learned through our investigations, and share the safety recommendations we’ve made to prevent transportation accidents and crashes, deaths, and injuries.

We encourage you to keep up not only with our blogs, but with other NTSB materials. Sign up to be on our Constant Contact list. Follow us on Facebook (@NTSBgov), Instagram (@NTSBgov), LinkedIn (@NTSB), and Twitter (@NTSB). And in case you missed it, we launched a podcast in 2017, too! Check out Behind-the-Scene @NTSB wherever you get your podcasts. If you’d like to suggest a blog topic, e-mail SafetyAdvocacy@ntsb.gov.

As 2017 comes to an end, we again extend our gratitude to you for working with us to improve transportation safety. We wish you safe travels this holiday season and in 2018.

Williston and Beyond

By Member Christopher A. Hart

A car that is fully controlled by a computer doesn’t get drowsy or distracted. It doesn’t get drunk or impaired by other drugs. If it’s instructed not to go above the speed limit, it won’t. Human error, which is at least partly responsible for 94% of today’s highway crashes, can largely be eliminated if the human driver becomes just another passenger. And with the unacceptable carnage of more than 37,000 deaths in motor vehicle crashes in 2016 alone, we can use all the help we can get. There’s no question that the potential benefits of autonomous vehicles are nothing short of phenomenal.

Getting there, however, will not be as easy as many people think. We recently held a Board meeting to consider the crash in 2016 of a partially automated Tesla into a tractor‑trailer near Williston, Florida. The driver wasn’t paying attention to the road as he should’ve been, and the system allowed the driver to use its “Autopilot” feature in places where it wasn’t designed to operate. The automation system used torque on the steering wheel as a proxy for driver engagement and alerted the driver if too much time passed without detectable movement on the wheel, but the driver treated the alerts as nuisances, dutifully applying torque each time the alert sounded before taking his hands off the wheel again. Although the driver was ultimately responsible for the resulting crash in which he tragically lost his life, the automation allowed him to make unsafe choices.

2015 Tesla Model S 70D car involved in the May 7, 2016, Williston, Florida crash
2015 Tesla Model S 70D car involved in the May 7, 2016, Williston, Florida crash

Flash back to 1914. An airplane flies past reviewing stands full of spectators. The pilot holds his hands high in the air to demonstrate that the airplane is flying itself. The plane makes another pass, then another. According to aviation lore, by the third pass, the pilot, Lawrence Sperry, is walking on the wings. Sperry was showing off his entry in an international aviation safety exhibition: the world’s first primitive autopilot, the gyroscopic stabilizer. It allowed a plane to fly straight and level without pilot input for short periods at a time.

In the years since, aircraft automation has become much more sophisticated. In addition, planes now have systems that sense terrain, they use GPS to know where they are, and they employ a vehicle-to-vehicle technology called a traffic collision avoidance system to help them avoid other planes. Thanks, in large measure to these technologies, aviation has become much safer. Yet, in 2013, nearly 100 years after Sperry’s demonstration, Asiana Flight 214, with more than 300 people on board, approached San Francisco International Airport too low and too slow and crashed into a seawall, killing three passengers.

Fire damage to the fuselage of Asiana flight 214
Fire damage to the fuselage of Asiana Flight 214

The Asiana crash demonstrated automation confusion: the pilot thought that the auto‑throttle was maintaining the speed he selected, but he had inadvertently and unknowingly caused the auto‑throttle to become inactive. It also demonstrated that, due to longstanding overreliance on the automation, the pilot’s manual flying skills had degraded so much that he was uneasy about landing the plane manually on a 2‑mile‑long runway (that’s a long runway!) on a beautiful, clear day.

We’ve investigated automation-related accidents in all modes of transportation. In fact, our investigators see accident after accident involving problems with the interface between the automation and the human operator; we also see far too often that humans are not reliable about passively monitoring automation. And in cases like the Asiana crash, we see that humans get rusty when they don’t use their skills.

The Williston crash showed error types that are not surprising with what’s called level 2 automation. The human driver was responsible for monitoring the environment, but the automation allowed him to shirk this responsibility. This result was foreseeable, given the unfortunate use of the moniker “Autopilot,” which may suggest to the ordinary driver that the car can fully control itself (as compared with pilots, who know that they must still be engaged even when their airplane is operating on autopilot). Thus, one lesson learned is that if the automation should only be usable in certain circumstances, it should be “geo-fenced” so that it will work only in those circumstances instead of depending on the driver to decide appropriately.

What can we expect as our cars move beyond level 2? The aviation experience has demonstrated that as automation increases, so do the challenges. As automation becomes more complicated, drivers are less likely to understand it, and as automation becomes more reliable, drivers will become more complacent, less skillful, and less vigilant to potential failures. As a result, if a failure occurs in a more complicated and reliable system, the likelihood increases that most drivers will not be able to recover successfully from the failure.

In the Asiana investigation, we found that the airline used the available automation as fully and as often as possible. After the crash, we recommended that the airline require more manual flying, both in training and in line operations—not because we’re against technology, but because we see what can happen when pilots lose their skills because they’re not using them.

Then there’s the question of removing the driver altogether. Airliners will have pilots for the foreseeable future because aviation experts have not yet developed a “graceful exit” regarding failure of the automation or what to do if it encounters unanticipated circumstances. Similarly, drivers will be in the picture until the industry develops a graceful exit for their automation failing or encountering unanticipated circumstances . . . and unanticipated circumstances are certainly abundant on our streets and highways.

In every one of our investigations, we study the human, the machine, and the environment. Even across modes, humans and their interactions with automation are a common denominator in an accident’s probable cause. For 50 years, we’ve been finding answers to help the transportation industry save lives, and when our recommendations are put into practice, the industry and the public generally realize safety benefits. We are excited about the opportunities to use the lessons we’ve learned over these many years to help the transportation industry move toward safer vehicles, regardless of who (or what) is operating them.

We’ve come a long way since Lawrence Sperry’s gyroscopic stabilizer, but as accidents like Asiana and Williston show, we’ve still got a way to go before automation can significantly reduce fatalities on our streets and highways. We look forward to continuing to work with vehicle manufacturers to help them develop safer and more reliable automated transportation.

Travelers, Put Safety First this Holiday Season

MultiMode_banner

By Chairman Robert L. Sumwalt

At the NTSB, we’ve investigated many tragic transportation accidents that could have been prevented with some planning, forethought, and good decision making. As we mark the beginning of the holiday travel season, we want to encourage all Americans to make it their goal to arrive safely at their destinations, so we’ve boiled down some lessons we’ve learned that the traveling public can use.

By Car

Fatigue, impairment by alcohol and other drugs, and distraction continue to play major roles in highway crashes. Here’s what you can do:

  • If your holiday celebrations involve alcohol, ask a friend or family member to be your designated driver, or call a taxi or ridesharing service.
  • In a crash, seat belts (and proper child restraints) are your best protection. Always make sure that you and all your passengers are buckled up or buckled in!
  • Make sure to use the right restraint for child passengers, and be sure it’s installed correctly. If you have doubts, ask a Certified Child Passenger Safety Technician.
  • Make sure you’re well rested! A fatigued driver is just as dangerous as one impaired by alcohol or other drugs.
  • Avoid distractions. In this newly released video, survivor-advocates share their stories of personal loss—and the changes they’re working for now: https://www.youtube.com/watch?v=7jNYECrlzGU&feature=youtube.
  • Don’t take or make calls while driving, even using a hands-free device. Set your navigation system before you start driving. If you’re traveling with others, ask them to navigate.

By Bus or Train

The NTSB has made recommendations to improve passenger rail and motorcoach operations and vehicle crashworthiness, but travelers should know what to do in an emergency.

  • Pay attention to safety briefings and know where the nearest emergency exit is. If it’s a window or roof hatch, make sure you know how to use it.
  • If you’re unsure of where the exits are or how to use them, or if you didn’t receive a safety briefing, ask your driver or the train conductor to brief you.
  • Always use restraints when they’re available!

 By Air or Sea

Airline and water travel have become incredibly safe, but these tips can help keep you and your loved ones safe in an emergency.

  • When flying, make sure that you and your traveling companions have your own seats—even children under age 2.
  • Don’t forget your child’s car seat. The label will usually tell you whether your child car seat is certified for airplane use; the owner’s manual always has this information.
  • If you don’t know the rules for using a child’s car seat on your flight, call the airline and ask what you need to know.
  • Pay close attention to the safety briefing! Airline and marine accidents have become very rare, but you and your family can be safer by being prepared.
  • Whether you’re on an airplane or a boat, know where to find the nearest flotation device.

No matter how you travel, you deserve the benefits of the lessons we’ve learned through our investigations, but you need to play an active part to take advantage of them. This holiday season, make a commitment to put safety first.

 

International Advocacy to Prepare and Prevent

By Nicholas Worrell

I recently had the privilege of speaking in Manchester, England, at the National Safer Roads Partnerships Conference. The United Kingdom has some of the lowest road-user fatality rates in the world. While our annual vehicle miles traveled vary greatly, on a typical day, about 109 road users are killed on America’s roadways, while only 5 Britons lose their lives the same way. But, as I reminded the conference audience, even one fatality is still too many.

This was a unique opportunity to represent the NTSB because the audience was mainly British law enforcement officers, and the British tradition of “policing by consent” was tailor‑made for a prevention-focused discussion. Policing by consent means that, because most people want law and order, the goal should be to prevent crime rather than focus on punishing perpetrators. Our Safety Advocacy Division operates with much the same philosophy, working to prevent transportation accidents by encouraging stakeholders to implement the agency’s recommendations. We also explain road safety to vulnerable populations, such as young drivers, to bring lifesaving information to the traveling public, and we share our findings with colleagues.

We know that, as we face coming challenges in road safety, prevention opportunities abound. Our recent speeding study noted the value of a “safe system” approach, which depends on layers of safety in a given road environment and recognizes preventive uses of technology, such as automated speed enforcement. Our recent investigation into the fatal crash of a partially automated vehicle allowed us to consider the double-edged sword of automation. Our investigations have shown that, as vehicles rely more and more on automated sensors, they also collect more data, which should be gathered in a standard format and reported when vehicles with enabled control systems crash.

The world is changing, crash factors are changing, and our tools are changing. The data that cars themselves can provide about crashes is expanding. As I told the law enforcement officers in Manchester, the NTSB has learned that everything an accident can tell us is worth our attention. We are conscious that every safety lesson learned is worth retelling, both to spur acceptance of our recommendations and to prepare ourselves, our colleagues, and the public for the challenges of a fast-approaching future. By sharing lessons learned across borders, we improve our chances at reaching zero transportation fatalities worldwide.

 

Nicholas Worrell is Chief of the NTSB Safety Advocacy Division.

 

Lessons from Our Runway Incursion Forum

By Member Christopher Hart

On September 19 and 20, the NTSB held a Runway Incursion Forum featuring some of the industry’s foremost runway safety experts. These experts came from far and wide, and from a variety of aviation associations, companies, research organizations, government agencies, and airports. It was a very thought‑provoking event, and I believe we had the right people at the table to address an increasing trend in the most significant (Levels A and B) runway incursion events.

NTSB Runway Incursion Participants
Member Hart and NTSB staff with Runway Incursion Forum participants.

The aviation industry has proven itself to be adept at tackling challenging safety issues. In the early 1990s, the fatal commercial aviation accident rate that had been declining for several decades began to plateau. Many safety experts concluded that further reduction in the rate was unlikely because the plateaued rate was already exemplary. Nonetheless, concerned that the volume of flying was projected to double in the next 15­–20 years—and with it, if the rate remained flat, the number of airline crashes—the industry began an unprecedented voluntary collaborative safety improvement program to further reduce the accident rate. This program was called the Commercial Aviation Safety Team, or CAST. Amazingly, CAST reduced the flat fatality rate by more than 80 percent in only 10 years.

Perhaps the most difficult challenge that we are currently facing regarding runway incursions is pursuing additional remedies in the absence of an accident. The industry is frequently accused of having a “tombstone” mentality: attempting to improve safety only when there’s a major accident. I applaud the efforts of the FAA, the general aviation community, the commercial aviation industry, and the airports, along with the front-line vigilance of the pilots, air traffic controllers, and airport operators who live and breathe this issue every day, to proactively identify ways of driving down the numbers. It’s a sign of this vigilance that they came together out of our common concern about the apparent turnaround from the previous downward trend in A and B incursions.

So, what did we learn from our forum? First and foremost, the staff who organized this event recognized one of the major lessons learned from the CAST collaboration: that everyone who is involved in a problem should be involved in developing the solution. Hence, we invited pilots, air traffic controllers, airport operators, affected industry organizations, and the regulator (the FAA), as well as those who collect and analyze the data­—in other words, everyone who is involved in the problem—to discuss their perspectives on the runway incursion problem.

Each participant emphasized the need for more and better data: data to help us identify the problems, determine what caused them, develop interventions, and determine whether the interventions are accomplishing the desired result. We need to determine how to collect better data, how to analyze the data more effectively, and, pursuing the collaboration concept, how to share the data more effectively, both with peers and with other participants in the system.

Perhaps the most challenging issues that warrant better data are the human factors issues regarding human limitations and vulnerabilities, and determining how humans can interact most effectively with rapidly advancing technologies. There has been considerable progress in understanding human factors in the cockpit, and it was interesting to hear in the forum about the development of a new program that also aims to enhance our understanding of human factors issues that affect air traffic controllers.

Participants at the forum also discussed several exciting new technologies—in the cockpit, in air traffic control facilities, at airports, and in airport ground vehicles—to help increase the situational awareness of pilots, controllers, and vehicle operators. We heard of many activities by the airport community to address “hot spots,” the places on the airport surface where runway incursions are occurring most frequently. These activities include changing procedures, improving training, adding new technologies, and making major capital improvements to modify airport geometry.

NTSB Runway Incursion Forum
Member Hart leads a roundtable discussion during the Runway Incursion Forum.

Runway incursions are increasing amidst a culture that, in the last 15–20 years, has become more sensitized to their potential danger. What is needed is both site‑specific remedies (due to the uniqueness of every airport) and systemic remedies that address the system’s commonalities. Through their presentations and active participation in our forum, it became clear to me that our forum participants refuse to wait for an accident to begin making improvements.

We heard from multiple participants that about 80 percent of runway incursions involve general aviation aircraft. Although the creation of new collaboration networks, such as the General Aviation Joint Steering Committee (GAJSC), is beginning to bring general aviation stakeholders more consistently into the runway incursion prevention conversation, we learned that the effort to bring all stakeholders to the table must continue, which is a challenge because the general aviation community is very broad and multifaceted.

I am optimistic that government, airlines, airports, and others will follow up on the most important directions that we collaboratively identified in the forum, and that they will continue to develop and deploy new solutions to the complex problem of runway incursions.

The full agenda, speaker biographies and a recording of the forum are available at https://go.usa.gov/xRhpC.

Inside the NTSB’s General Aviation Investigative Process

The Nuts and Bolts

By Aaron Sauer

This is the sixth blog in a new series of posts about the NTSB’s general aviation investigative process. This series, written by NTSB staff, explores how medical, mechanical, and general safety issues are examined in our investigations.

 

The public’s image of our agency is often based on the iconic blue and yellow NTSBNTSB Investigators Onscene jacket they see at accident scenes. What’s less well known is that examining and documenting on-scene evidence is just one step in an exhaustive process to gather all available information, determine a cause, and recommend any changes that can prevent similar accidents.

Since 2014, 12 percent of general aviation accidents—about three accidents every week—have involved a power plant malfunction. These malfunctions may include a fuel issue, component failure, or improper maintenance.  As an NTSB air safety investigator, I investigate such mechanical malfunctions, gather the facts of the investigation, and ultimately help determine the probable causes of accidents.

After the on-scene phase of the investigation is complete, the airplane wreckage is often recovered by professional recovery services and stored in a secure location until we determine if further NTSB investigation is needed. When circumstances, such as a large hole in the engine crankcase or the in-flight loss of a propeller, indicate that further examination is necessary, we work with the airframe, engine, and component manufacturers. These entities serve as parties to our investigation, providing technical expertise on their product. If required, we coordinate a follow-up plan to examine the aircraft wreckage in greater detail. At the accident scene or recovery facility, our investigators examining the machine determine the scope of follow-up based on any anomalies discovered.

In some accidents involving a reported loss of engine power, the initial examination (typically a 100-hour inspection) turns up no obvious anomalies. At this point, one of the best and most telling follow-up activities is to attempt an engine test run. Engine test runs may be performed at a recovery facility or at a manufacturer’s facility. A successful engine test run is a critical piece of information that may lead the investigation down another path.

When, upon initial examination, the investigator observes an engine issue consistent with an internal mechanical failure, it’s typical to disassemble the engine at the manufacturer’s facility or the recovery facility under NTSB supervision. Examining an engine at the manufacturing facility often provides the advantage of having available engineering staff, historical data and drawings, and proper test equipment for the engine components.

Once at the manufacturer’s facility, the investigation team (typically including NTSB, FAA, and airframe, engine, and component manufacturer personnel) determines the plan or approved test procedure for the detailed investigation. The scope of the investigation is determined based on the known facts and circumstances of the accident, the condition of the engine and components, and the work required to confirm the failure. It’s important to note that, although the parties work collaboratively, the NTSB has the final say if there is any disagreement in the investigation process.

Engine functional testing, partial disassembly, and full engine disassembly are the most common investigation techniques used to determine the cause of a failure or malfunction. Disassembly helps us identify fractured or broken parts, which are then documented and set aside for even further examination.

Most manufacturers have their own materials laboratory, metallurgists, and engineers. At this point and with the team present, our investigators may elect to use the manufacturer’s material laboratory for a preliminary examination to obtain a quick analysis of the failure mode, then forward the parts to our materials laboratory in Washington, DC, for a detailed metallurgical examination.

Even observers with a solid understanding of our processes beyond the on-scene images might not understand the many ways that NTSB investigations can improve safety. Even when all signs point to a mechanical malfunction, our investigative process still looks at two other factors: human and environment. When an accident involves reported loss of engine power, we gather information about the pilot and aircraft owner—documentation from the scene, aircraft records, and Federal Aviation Administration (FAA) records. We interview witnesses, visit and examine maintenance facilities, and meet with manufacturers. When necessary, we conduct follow-up examinations and interviews. If FAA inspectors handle the initial on-scene observations, we work hard to guarantee that our two agencies communicate effectively.

When the fact-gathering phase of the investigation is complete, our investigators compile all the relevant factual information, complete a detailed factual report, and create a public accident docket. For an engine failure accident, the docket may include engine reports, materials laboratory reports, aircraft records, and historical engine safety information in the form of service bulletins and airworthiness directives.

Many people understand that we may make recommendations at any point during an investigation, but sometimes our investigations also result in other actions to improve safety. For example, depending on the nature of the material failure, an NTSB investigator may work with the FAA or the manufacturer to issue a manufacturer service bulletin, service letter, safety notice, or a potential airworthiness directive. The safety action taken by the FAA or manufacturer depends on the failure’s cause, fleet exposure, and the potential safety awareness benefit of each product.

Over my 17 years as an NTSB investigator, I’ve investigated numerous engine-failure–related accidents that resulted from human error and material failure. Despite the varied causes and outcomes of these accidents, one fact stands out: proper maintenance is the best way to avoid catastrophic consequences. Following manufacturer-recommended maintenance practices and procedures and adhering to basic maintenance principles can prevent accidents.

Remember: SAFETY is NO ACCIDENT!

All accident reports and public accident dockets are available on the NTSB website:  www.ntsb.gov.

 

Inside the NTSB’s General Aviation Investigative Process

An Aeromedical Mystery Solved

By: Clint Johnson, Chief, Alaska Region, Office of Aviation Safety

This is the fifth blog in a new series of posts about the NTSB’s general aviation investigative process. This series, written by NTSB staff, explores how medical, mechanical, and general safety issues are examined in our investigations.

Clint Johnson
Clint Johnson at industry event

After nearly 20 years of investigating hundreds of aviation accidents, I recently encountered an invisible killer.

I was enjoying a late summer Saturday afternoon with my wife in Anchorage, Alaska, when my phone rang. My wife – a 20-year-veteran NTSB spouse – knew from the look on my face that our quiet weekend at home had just ended.

An Anchorage Fire Department dispatcher was calling. She reported that rescue crews were on the scene of a fatal airplane crash in a residential neighborhood only 20 minutes away.

When I arrived, I was briefed by a small army of Anchorage Police and Fire Department

hillside-plane-crash-ablaze-1024x576
Hefty Polar Cub airplane crash site

crews. Behind the wall of fire trucks, police cars, stunned residents, and TV cameras, I caught a glimpse of the inverted and burned remains of what looked like a float-equipped Piper 11 in the middle of the residential roadway.

We continued to talk as we walked toward the wreckage site. The pungent smell of burned aircraft wreckage filled the air as we proceeded past the yellow police tape. Finally, I was close enough to see that only the welded steel-tube structure and engine remained, with the fuselage and wings barely recognizable. The postcrash fire had incinerated much of the wreckage.

Witnesses had told the police that just before the accident they watched in amazement as the airplane completed two, low-level, high-speed, 360° right turns over the neighborhood – the first 150-200 feet above ground level, and the second much lower. One homeowner stated that the airplane passed over his home about 50 feet above his roof.

Witnesses also reported that the airplane’s bank angle increased significantly on the second 360° right turn; one pilot-rated witness estimated the bank at more than 60°. Witnesses also reported hearing the airplane’s engine operating in a manner consistent with high power settings throughout both 360° turns.

One man was mowing his lawn as the airplane completed the second, steep, 360° right turn. He said that the airplane flew directly over his yard, then the nose of the airplane pitched down and it began to descend rapidly. The engine rpm then increased significantly, and the wings rolled level just before the airplane impacted a stand of tall trees adjacent to his home, severing its floats.

It crashed on a neighborhood road, coming to rest inverted. About 30 seconds after impact, a fire ensued, which engulfed the entire airplane before any of the witnesses made it to the wreckage.

Sadly, after the fire department crews extinguished the fire, they found the remains of the 75‑year-old pilot and his dog still inside the incinerated wreckage.

While we all waited for the medical examiner to arrive, I began interviewing witnesses. Most concluded, or were well on their way to concluding, that the pilot was “just showing off” to someone on the ground. But the NTSB sets a high bar for conclusions. It was way too early for me to go there.

At the scene, I met a family member, along with a close friend of the pilot. Understandably upset, both reported that it was highly unusual and uncharacteristic behavior for the pilot to be flying as the witnesses consistently described to me. They went on to say that to their knowledge, the pilot didn’t know anyone in the area, but that, given the pilot’s anticipated flight route, he would have been flying over the neighborhood while on the return flight home.

Then, as the pair was preparing to leave the scene, the pilot’s friend said something in passing – something about his longtime buddy’s history of cardiac problems, which, in his opinion, caused the pilot’s erratic flight maneuvers.

I pressed him for more information, but it became clear that he wasn’t prepared to provide any additional information on the subject then and there, and I decided that this was neither the time or place to discuss it. As the pair got back into their car and slowly drove away, I knew that the following Monday morning I’d likely be attending the pilot’s autopsy.

For now, I needed to document and examine the wreckage before it was removed. This included determining control cable continuity to the flight control system, engine control continuity, and more.

The engine sustained significate impact damage, but only minimal fire damage. There were no mechanical problems that I could find on-scene that would explain what the witnesses reported. However, a much more detailed wreckage exam would be accomplished later, once the wreckage was moved to a more secure and suitable site.

On Monday morning, I found myself at the State medical examiner’s facility, meeting with the pathologist who would be working my case. I explained to her what I was looking for, and she started the exam.

The entire autopsy took over two hours to complete, and the pathologist found no conclusive evidence for medical incapacitation from an acute cardiac event. However, per standard protocol, the autopsy team took blood and tissue samples to send to the FAA’s Bioaeronautical Sciences Research Laboratory in Oklahoma City for a toxicological exam.

I knew I would not have the tox report for two to three months, but the autopsy yielded at least one more piece of valuable information: the pilot died from trauma, not the postcrash fire. Unbeknownst to me at the time, this would be an extremely important data point that would help solve the case in the end.

Over the next two weeks, I visited the wreckage two separate times at a local aircraft salvage yard. I looked for evidence that would support various theories, but nothing ever panned out. It was one dead end after another.

Then on a cold and snowy autumn afternoon, the FAA’s tox report on the pilot appeared in my e-mail. I opened it and scanned the results, and only then realized just what I had been missing all this time: Carbon Monoxide, an odorless, colorless and tasteless gas – and a silent killer of general aviation pilots.

The pilot’s carboxyhemoglobin (carbon monoxide) level was an extremely high 48%. To put these results in context, nonsmokers may normally have up to 3% carboxyhemoglobin in their blood, and heavy smokers may have levels of 10% to 15%. And according to family members, this pilot did not even smoke.

Since the pilot died of blunt-force trauma prior to the ensuing fire, it was not possible that this CO level was an effect of the fire. But it was possible that it was a cause of the crash.

I realized that over the last few months I had missed an important and somewhat elementary piece of evidence, the airplane’s exhaust system. I quickly reviewed my on-scene photos, and I could clearly see that the entire exhaust system sustained relatively minor damage in the accident.

Within 15 minutes of receiving the toxicology results, I was on my way back to the stored wreckage. I ended up bringing the entire exhaust system back to the office, muffler, heat exchanger/muff and all. Like the autopsy examiners I had met months earlier, I went to work on this simpler machinery, peeling back the heater shroud.

IMG_2192
Accident muffler can assembly

Inside I found a severely degraded muffler with portions missing, which allowed raw exhaust gases to enter the main cabin through the airplane’s heater system.

Unfortunately, neither the family or any of the pilot’s friends could find any maintenance logbooks for the accident airplane, so I was unable to determine just when the last muffler inspection was done (if ever). However, after talking with several friends of the deceased pilot, many said that he did his own maintenance, and he was not an aviation mechanic.

They went on to say that the pilot, with the help of a few other friends, installed the more powerful Lycoming O-320 engine about 5 years earlier, but none could provide any additional information about how the pilot maintained his airplane.

However, I could report directly to the family what circumstances led up to the death of their loved one, and I was able to show them the physical evidence that I found.

The NTSB’s probable cause summed it all up: “The pilot’s severe impairment from carbon monoxide poisoning in flight, which resulted in a loss of control, and a subsequent inflight collision with trees and terrain.”

Often, it takes time, patience, and knowledge of the human operator, the machine, and the environment to solve an accident mystery to provide answers.