Category Archives: Transportation History

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.

The Silver Bridge Collapse: Don’t Blame the Mothman!

 

By Don Karol

Rumor has it that, just before the December 15, 1967, collapse of the US Highway 35 Bridge in Point Pleasant, West Virginia, a 7-foot-tall monster with large, piercing red eyes and huge, mothlike wings was seen lurking nearby, warning of the impending catastrophe. This “Mothman” was soon blamed for the tragedy in which 46 people died and 9 were injured. Of the 37 vehicles on the bridge at the time of the collapse, 31 fell with it, many plunging into the Ohio River. Fifty years after the collapse of what was then known as the Silver Bridge, paranormal speculation still swirls around the event, perpetuated by movies (like the Mothman Prophecies), legends, and myths. As a civil engineer, though, I put my trust in the laws of physics, materials science, and the findings of the NTSB investigation completed five decades ago, which proved without a doubt that the Mothman wasn’t to blame.

Silver Bridge, Point Pleasant, West Virginia
Section of Silver Bridge, Point Pleasant, West Virginia, that collapsed on December 15, 1967 (source: Herald-Dispatch)

The Silver Bridge collapse was the first significant highway accident investigation in NTSB history. Working with experts from the Federal Highway Administration, the states of West Virginia and Ohio, and leading engineering consulting firms, we determined conclusively that the cause of the collapse was an eyebar fracture in one of the bridge’s suspension chains. The fracture resulted from stress corrosion and corrosion fatigue that had developed over the bridge’s 40-year lifespan. Not surprisingly, no evidence was ever found connecting the Mothman to the failure.

This catastrophic event prompted national concern about the safety of bridges across the United States. President Lyndon B. Johnson ordered all US bridges to undergo safety inspections. Congressional hearings resulted in mandates requiring the US Department of Transportation to develop and implement National Bridge Inspection Standards. In December 1970, landmark legislation was enacted that established national requirements for bridge inspection and evaluation. One would think that these rigorous new inspection standards would take care of bridge failures forever. Unfortunately, during the past half century, that’s not been the case.

1983 bridge collapse in Greenwich CT
A 100-foot-long section of the Interstate 95 bridge over the Mianus River in Greenwich, Connecticut, collapsed June 29, 1983 (source: Bob Child, Associated Press)

On June 28, 1983, a 100-foot-long section of Interstate 95 (Mianus River Bridge) collapsed near Greenwich, Connecticut. Two tractor-semitrailers and two passenger vehicles went down with it, resulting in three fatalities and three serious injuries. We determined that corrosion-induced forces led to lateral displacement of the suspension assembly, which went undetected by the state’s bridge inspection and maintenance programs and ultimately led to the collapse.

On April 5, 1987, tragedy struck again when two spans of the New York State Thruway (Interstate 90) fell about 80 feet into the rain-swollen Schoharie Creek. Four passenger cars and one tractor-semitrailer plunged into the creek, and 10 people were killed. We determined that the New York State Thruway Authority failed to maintain adequate support around the bridge piers, leading to severe erosion in the soil beneath the bridge footings. We also determined that the state’s bridge inspection program was inadequate. Not surprisingly, neither the Mothman nor the Loch Ness Monster was seen in advance of this collapse to forewarn of the impending catastrophe.

1987 bridge collapse near Amsterdam, New York
Divers search for victims in the Schoharie Creek after the New York State Thruway bridge collapsed near Amsterdam, New York, on April 5, 1987 (source: Fred McKinney, Times Union)

Other notable bridge failures we investigated in the late 1980s involved localized flooding and water scouring. One collapse occurred on April 1, 1989, near Covington, Tennessee, when two columns supporting three bridge spans collapsed, sending an 85‑foot section of the US Route 51 bridge 20 feet into the Hatchie River. Five vehicles fell with it, killing eight occupants. Again, our investigation identified deficiencies in the state authority’s bridge oversight. In response to our investigations of these events, additional requirements were developed for periodic underwater inspection of bridges.

Probably the most memorable bridge collapse we investigated occurred 10 years ago in Minneapolis, Minnesota, when a catastrophic failure occurred in the main span of the deck truss in the Interstate 35W highway bridge. As a result, 1,000 feet of the deck truss collapsed during rush hour, with about 456 feet of the main span falling into the river. A total of 111 vehicles were on the portion of the bridge that collapsed; 13 people died and 145 were injured. We determined that a design error in the gusset plates compromised the bridge’s load capacity, causing it to fail under substantial weight increases. Our investigation prompted the development of additional bridge quality assurance and improved bridge inspection requirements.

2007 bridge collapse in Minneapolis, Minnesota
Interstate 35W bridge over the Mississippi River collapsed in Minneapolis, Minnesota, on August 1, 2007 (source: Peter Matthews, Polaris)

On December 15, as we mark the 50th anniversary of the Silver Bridge collapse, let’s focus on the infrastructure improvements we need still need to make five decades later rather than try to place the blame on mythical creatures like the Mothman. Throughout the NTSB’s history, we have investigated catastrophic bridge collapses with one goal in mind: preventing future tragedies. Despite efforts to continually enhance the quality of bridge inspections, unforeseen disasters continue to occur, highlighting the need to thoroughly inspect and replace bridges before they collapse. Supernatural forces do not bring down bridges; neglect does.

 

Don Karol is a Senior Highway Accident Investigator and National Resource Specialist in the NTSB Office of Highway Safety.

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.

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.

 

What Can Be Done to Improve Transportation Safety for Migrant Farmworkers?

By Jennifer Morrison                                                                                     

This week marked the 54th anniversary of the deadliest highway crash in US history. On September 17, 1963, a makeshift bus carrying 58 migrant farmworkers collided with a freight train near the city of Chualar, California (See Figure 1), killing 32 people and injuring 25. The workers on the bus were returning to a labor camp after a 10‑hour shift harvesting celery at farms in the Salinas Valley. The passengers were riding on two long board benches that ran the length of a canopy-covered flatbed truck.

LA Times Headline
Headline and image from the September 18, 1963, issue of the Los Angeles Times. At the time only 27 people were thought to have died; the final death toll rose to 32.
Another deadly migrant farmworker crash occurred in the 1970s. On January 15, 1974, we investigated a crash involving 46 migrant farmworkers near Blythe, California. A farm labor bus traveling on a rural road failed to negotiate a curve in the roadway and vaulted into the bottom of a drainage ditch. The bus came to rest on its left side, partially submerged. Nineteen of the bus occupants, including the driver, died.

The last half century has seen many improvements in transportation safety, yet catastrophic crashes still occur, and the safe transportation of migrant farmworkers remains an issue. During the 8-month period from November 2015 through July 2016, we responded to three multifatality crashes in which 16 people were killed and 57 others were injured. Most of those killed and injured were migrant farmworkers being transported to and from farming locations. We investigate these crashes to learn from them and answer the important question:  What can be done to improve transportation safety for migrant farmworkers?

Today, we released more than 1,100 pages of documents related to our ongoing investigation into the July 2, 2016, crash near St. Marks, Florida, involving a farm labor bus and a truck-tractor semitrailer combination vehicle. The bus, which was transporting more than 30 farmworkers from a farm in Georgia to Belle Glade, Florida, failed to stop at the intersection of State Road 363 and US Highway 98—which was marked by a stop sign and flashing red “stop” signal—and was struck by the truck-tractor vehicle. A postcrash fire ensued, and the truck driver and three bus passengers died (See Figure 2).

On November 28, 2017, we will hold a public Board Meeting to discuss the findings of the St. Marks crash investigation, its probable cause, and safety recommendations aimed at preventing future crashes. We will also review the circumstances of crashes in Little Rock, Arkansas, and Ruther Glen, Virginia (see Figure 2).

St Marks Blog
(Top) Bus and truck involved in the St. Marks, Florida, crash at final rest (source: Florida Highway Patrol). (Lower left) Motorcoach involved in the Little Rock, Arkansas, crash showing the damaged, missing rear portion of the roof. (Lower right) 15-passenger van involved in the Ruther Glen, Virginia, crash showing the deformed roof.
The Little Rock crash occurred on November 6, 2015, when a motorcoach transporting 20 farmworkers from Michigan to Texas departed Interstate 40 and collided with a concrete barrier. The collision resulted in the bus climbing up the side of the barrier, its roof impacting a bridge column that supported a freeway overpass. As a result of the crash, six bus passengers were killed.

The Ruther Glen crash occurred on June 18, 2016, when a 15-passenger van transporting 16 occupants, most of whom were migrant farmworkers, departed Interstate 95. The van swerved right across all lanes of travel and impacted another passenger car before overturning multiple times. Six of the van passengers were ejected and died.

By looking at factors such as federal and state oversight of motor carriers engaged in agricultural worker transportation, enforcement of safety regulations, outreach and education in the agricultural community, and individual states’ best practices, we hope to develop safety recommendations that will improve the transportation safety of migrant agricultural workers and prevent future tragedies.

Attend the November 28 meeting in person or watch via webcast as we attempt to determine, based on our findings from the St. Marks accident and similar crashes, what can be done to improve transportation safety for migrant farmworkers.

Jennifer Morrison is an Investigator-in-Charge in the NTSB Office of Highway Safety.

 

 

Inside the NTSB’s General Aviation Investigative Process

Do We See and Avoid or Avoid Seeing?

 By John O’Callaghan

This is the fourth 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.

John O’Callaghan at a runway friction test in Conroe, TX.

As a National Resource Specialist for Aircraft Performance, which is government-speak for a technical expert in the aerodynamics and flight mechanics of aircraft, I work to determine and analyze the motion of aircraft and the physical forces that produce that motion. In particular, following an accident or incident, I attempt to define an aircraft’s position and orientation during the relevant portion of the flight, and determine its response to control inputs, external disturbances, ground forces, and other factors that could affect its trajectory.

I recently reviewed a 2009 cockpit video taken while I was testing a video recording device in a Bellanca Citabria. The footage called to mind recent NTSB cases that highlight the fallacies inherent in one of aviation’s oldest mantras—“see and avoid.”

The video from the camera mounted over my left shoulder reveals a hazy blue sky above and the Potomac River winding lazily below the Citabria’s plexiglass windows. It shows my head dutifully swiveling as I scan the practice area for traffic in preparation for a series of aerobatic maneuvers intended to test a prototype “portable flight data recorder” developed by a friend of mine. I’m flying in the Washington, DC, Special Flight Rules Area so I’m in contact with Potomac Approach, which helpfully keeps a radar’s eye on me and nearby traffic and conveys what I fail to see.

“Citabria 758, traffic about a mile southwest of your position. A Cherokee is in the practice area, altitude indicates . . . I’m not showing an altitude right now.”

On the video, my head moves around a little more as I respond, “758 looking, thank you.”

The controller then alerts the Cherokee. “Cherokee [call sign], traffic seems to be about 1-mile orbiting, altitude indicates 3,600, a Citabria.”

I’m still looking with no success when Potomac advises that the Cherokee is at 2,200 ft. The controller lets me and the Cherokee pilot know that we are getting close to each other.

 “Cherokee [callsign], traffic just southeast of you, about less than 1 mile, Citabria in the practice area, altitude indicates 3,700.”

 “Roger, we’ll keep our eyes open for that Citabria in the practice area.”

“Citabria 758, that traffic is just northwest of you, less than a mile now, and his altitude still indicates 2,300, appears to be eastbound.”

“758 still looking, thank you.”

The video now shows me craning my neck left and right, leaning forward, scanning the entire symmetrical view offered by an airplane with its seats on the centerline. The airplane banks left and right in gentle turns as I maneuver, trying in vain to spot the Cherokee. A little over 3 minutes after Potomac’s initial advisory, I give up.

“Potomac, Citabria 758 still looking for that traffic . . . is he still a factor?”

“758, now he’s about 5 miles north of you, no factor.”

I don’t know if the Cherokee pilot ever saw me, but if he did, he didn’t announce it. I imagine that most general aviation pilots don’t need to accumulate too many hours before they have an experience much like mine, or its more unnerving inverse: suddenly seeing an airplane that you had no clue about whiz by close enough to read the N-number. Both situations point to the inherent limitations of the “see-and-avoid” concept: the foundation of collision avoidance in visual meteorological conditions (VMC) under visual flight rules (VFR).

My flight was a personal one, unrelated to my duties as an aircraft performance engineer at the NTSB. However, my fruitless search for the Cherokee was consistent with conclusions the NTSB has drawn from investigating a number of midair collisions, and which call to mind what can happen when traffic remains unnoticed.

As detailed in the NTSB reports concerning two midair collisions that occurred in 2015, described further below, the see-and-avoid concept relies on a pilot to look through the cockpit windows, identify other aircraft, decide if any aircraft are collision threats, and, if necessary, take the appropriate action to avert a collision. There are inherent limitations of this concept, including limitations of the human visual and information processing systems, pilot tasks that compete with the requirement to scan for traffic, the limited field of view from the cockpit, and environmental factors that could diminish the visibility of other aircraft.

In a collision between an F-16 and a Cessna 150 near Moncks Corner, South Carolina, in July 2015, the F-16 pilot was unable to spot the C150, even though the Charleston Approach controller had alerted him to the presence of the airplane. The F-16, call sign “Death41,” was flying under instrument flight rules and communicating with air traffic control (ATC); the C150 was flying under VFR and not communicating with ATC.

“Death41, traffic 12 o’clock 2 miles opposite direction 1200 indicated type unknown.”

“Death41 looking.”

“41 turn left heading 180 if you don’t have that traffic in sight.”

“Confirm 2 miles?”

“Death41, if you don’t have that traffic in sight turn left heading 180 immediately.”

[unintelligible reply]

Even before the controller finished her last instruction, the F-16 had begun a standard-rate turn to the left. The F-16 was heavy and, at 240 knots, moving relatively slowly—for a fighter jet. Contrary to what one might think, it could not turn much faster in those conditions. Twenty-three seconds after the controller’s last instruction, the F-16 and the C150 collided at about 1,470 ft above the Cooper River. The crippled F-16 flew for another 2.5 minutes before the pilot ejected safely, and the jet subsequently crashed. The C150 crashed almost directly beneath the collision site, and both the pilot and his passenger died.

We determined the probable cause of this accident was the approach controller’s failure to provide an appropriate resolution to the conflict between the F-16 and the Cessna. Contributing to the accident were the inherent limitations of the see-and-avoid concept, resulting in both pilots’ inability to take evasive action in time to avert the collision.

Midair collisions can happen even when both aircraft are in communication with ATC. A month after the Moncks Corner midair collision, a North American Rockwell Sabreliner collided with a Cessna 172 in the busy traffic pattern at Brown Field in San Diego. Both aircraft were under Brown Tower’s control and on a right downwind for runway 26R, with the Sabreliner outside of and overtaking the C172. The tower controller intended to instruct the C172 to perform a right, 360-degree turn to position him behind the Sabreliner; however, he mistakenly instructed a different C172 to perform the maneuver, and immediately after instructed the Sabreliner to turn right base.

The Sabreliner and C172 subsequently collided, and all five people on the two aircraft died. The cockpit voice recorder on the Sabreliner indicated that both Sabreliner pilots were aware of and concerned about the busy traffic pattern, pointing out other aircraft to each other. One of the nonflying crew in the back of the plane is even heard asking, “see him right there?” presumably referring to traffic. Yet the collision still occurred.

We determined the probable cause of the accident was the local controller’s failure to properly identify the aircraft in the pattern and to ensure control instructions provided to the intended Cessna on downwind were being performed before turning [the Sabreliner] into its path for landing. Contributing to the accident were the inherent limitations of the see-and-avoid concept, resulting in the inability of the pilots involved to take evasive action in time to avert the collision.

My role in the investigations of the Moncks Corner and San Diego collisions was to reconstruct the motion of the airplanes based on radar data and other information, and to evaluate the resulting visibility of each aircraft from the cockpit of the other. In addition, it was my job to evaluate how new collision avoidance technology—such as cockpit displays that provide a radar‑like view of surrounding traffic based on automatic dependent surveillance-broadcast (ADS-B) information—could have averted each accident.

One objective of these visibility studies was to determine whether either of the airplanes involved in the collision were obstructed from the other pilot’s field of view by cockpit structures, or whether the pilots had an unobstructed view of each other but simply failed to see one another (because seeing other traffic from the cockpit is hard!). To find out, we measured the geometries of the window and other structures of exemplar airplanes with laser-scanning equipment, and the resulting measurements were used to determine where the windows were in each pilot’s field of view and whether the other airplane appeared within the windows or not. The results were most intuitively presented by creating computer animations of the collision from the point of view of each pilot using flight simulation software (Microsoft Flight Simulator X) to create the outside scenery and airplane models.

Readers can watch the animations we created for the Moncks Corner and San Diego collisions on our YouTube channel and judge the visibility results for themselves. The performance studies for these accidents provide technical details about the reconstructions, and they note that periods when airplanes are obscured from a pilot’s nominal field of view “underscore the importance of moving one’s head (and occasionally lifting and dipping the wings) so as to see around structural obstacles when searching for traffic.”

Readers can also watch animations of cockpit display of traffic information (CDTI) displays for each of the airplanes involved in these midair collisions. The animations depict the information that these radar-like displays, fed by ADS-B, could have presented to the pilots involved. Had the airplanes been equipped with CDTI, the pilots could have been made aware of the presence and relative locations of the conflicting traffic minutes before the collisions.

In general, the timely and information-rich traffic picture offered by a CDTI can greatly improve a pilot’s ability to detect traffic threats and avoid a collision without aggressive maneuvering. We issued a safety alert, titled, “Prevent Midair Collisions: Don’t Depend on Vision Alone,” to encourage pilots to learn about the benefits of flying an aircraft equipped with technologies that aid in collision avoidance.

Much of flying is an exercise in mitigating or engineering out risk. Pilots are trained, examined, and reviewed; aircraft are certified and maintained; checklists are used; flights are planned; weather is studied. Great effort is made to leave little to chance. However, when it comes to collision avoidance in VMC, we wink at risk management (“see-and-avoid!” “Keep your head on a swivel!”), when the reality is that we rely in great measure on luck. It’s a big sky, and it would be hard to hit somebody if you tried. The odds are against a collision, but on occasion, disaster strikes.

Technologies such as CDTI provide rational risk reduction for the VMC collision avoidance problem. Guardian angels will never lack for work, but tools such as CDTI can help us to make their jobs a little easier.

Inside the NTSB’s General Aviation Investigative Process

Addressing Medical Issues

By Dr. Nicholas Webster, NTSB Medical Officer

This is the second 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 NTSB investigates every aviation accident in the United States. In each investigation, we look at the roles of the human, the machine, and the environment. By learning about the factors that cause an accident, we can make recommendations to prevent similar accidents in the future.

I am one of two medical officers (physicians) at the NTSB who work closely with investigators in all modal offices. When an investigator-in-charge (IIC) is concerned that operator medical issues, drugs, or toxins may have affected performance, he or she coordinates with us to study the medical aspects of the event. The medical officers review medical documents, toxicological testing results, and sometimes autopsy reports of those involved in accidents. In conjunction with the investigative team, we help determine if operator impairment or incapacitation contributed to the cause of the accident, then we help craft language to explain to the public the nature and significance of the medical issues and how they affected the operator and contributed to the accident’s cause. We also work closely with the Board’s biodynamics and survival factors experts to help evaluate accident-caused injuries and determine what changes could be made to prevent future injuries.

The resulting information is presented in a medical factual report, which documents all pertinent medical issues and any potential hazards that the medical issues posed. To ensure accuracy, these fact-based scientific reports are peer reviewed by the investigative staff before they are published as part of the public docket. The medical, factual, and operational details of each event are then analyzed by the investigatory team, which determines probable cause by consensus, peer review concurrence, and Board authority. The probable cause represents the most likely explanation for the event given all available evidence.

Two recent cases have garnered some attention in the general aviation (GA) community, both involving fully functional airplanes operating in manageable weather. In these cases, both pilot action (error or impairment) and pilot inaction (incapacitation) can lead to an accident. In these cases, we found that the pilots were operating in a relatively low-workload environment and had the skill and experience necessary to safely complete the flights. On the other hand, medical data showed that both pilots had severe heart issues that could cause sudden incapacitation without leaving a trace.

The first accident occurred on April 11, 2015, when an experimental Quad City Challenger II airplane crashed into terrain near Chippewa Falls, Wisconsin. The 77-year-old pilot died and the airplane was substantially damaged. The pilot had the skill and experience to operate the airplane in visual conditions. According to witnesses, while the airplane was on the downwind leg of the traffic pattern at the pilot’s home airport, it entered a steep dive that continued until it struck the ground in an open field. Investigators found no evidence of preexisting mechanical concerns and, based on the propeller damage, determined that the engine was producing power at impact. Operational evidence also strongly supported pilot incapacitation.

The pilot had a history of coronary artery disease, which was treated by multivessel bypass surgery. He also had high blood pressure, elevated cholesterol, and hypothyroidism, which were controlled with medications. The autopsy showed that the pilot had an enlarged heart; severe multivessel coronary artery disease (greater than 80-percent occlusion of all vessels), with coronary artery bypass grafts and complete occlusion of two bypass vessels; scarring of the ventricular septum, indicating he had had a previous heart attack; and active inflammation of the anterolateral wall of the left ventricle of his heart. These findings, particularly the large scar and active inflammation of the heart muscle, placed the pilot at high risk for an irregular heart rhythm, which can easily cause decreased blood to the brain and result in fainting without leaving further evidence at autopsy.

Additionally, according to the Chippewa County Coroner Death Report, the cause of death was blunt force trauma. However, the examining pathologist further stated, “the most likely scenario to explain [the pilot’s] death is that he suffered an arrhythmia secondary to myocarditis.” These findings are discussed in detail in the medical factual report. Based on the available evidence, we determined the probable cause of the accident to be the pilot’s incapacitation due to a cardiovascular event, which resulted in a loss of control and subsequent impact with terrain.

The second accident of note was the crash into terrain of a homebuilt Europa XL airplane on June 26, 2015. As in the previous case, the pilot died and the airplane was substantially damaged. In this accident, the 72-year-old pilot also had the skill and experience needed to successfully complete the flight, especially given that it was a clear day and he was operating under visual flight rules.

The airplane crashed under power in a steep, nose-down, slightly inverted attitude in an open field about a half mile from the end of the runway, slightly to the right of an extended centerline. According to the IIC, there was no evidence of preexisting mechanical concerns, the engine was operating at impact, and the operational evidence suggested pilot incapacitation.

The pilot had a history of severe coronary artery disease, which was treated with multivessel bypass surgery, stents, and medication. Additionally, he had elevated cholesterol and high blood pressure, which were treated with medications. Since his last medical certification examination, an exercise stress test showed no significant changes, but a cardiac catheterization report documented that his coronary artery disease had progressed, resulting in 90‑percent occlusion of the left anterior descending coronary artery and impaired blood flow to a part of the heart muscle. Additionally, the autopsy identified multivessel coronary artery disease treated with patent coronary artery bypass grafts, and documented up to 70-percent occlusion of the left anterior descending coronary artery.

These findings are discussed in detail in the medical factual report. The pilot’s severe progressive coronary artery disease and the impaired blood flow to an area of his heart muscle placed the pilot at high risk for an acute cardiovascular event such as a heart attack, anginal attack, or acute arrhythmia. Any such event would likely cause a sudden onset of symptoms such as chest pain, severe shortness of breath, palpitations, or fainting, and would leave no evidence visible on autopsy if death occurred in the first few minutes.

The Mahoning County Coroner Autopsy Report cited multiple blunt force injuries as the cause of death, with coronary artery disease and chronic hypertension contributing to the cause of death. Again, although the pilot died of blunt force injuries, the evidence supports our finding that the accident sequence was likely initiated by his incapacitation due to a cardiovascular event.

These cases illustrate how we integrate medical findings into our investigations. We also provide interested parties with links to publicly available, detailed information that supports our findings. In both of the cases described here, the medical factual reports document significant medical issues in pilots who were operating under sport pilot rules; however, we only determined the medically related probable causes after thorough, scientific, peer-reviewed analysis of all the available facts concerning the human, the machine, and the environment.

Our goal is to identify medically related hazards that may be causal to or resultant from the accidents we investigate, and then work with the experts on the investigative team to develop mitigation strategies, which take the form of safety recommendations, that target and eliminate these hazards and improve transportation safety.