An Illusion of Normalcy: The crash of USAir flight 1016
On the 2nd of July 1994, a USAir DC-9 bound for Charlotte, North Carolina encountered a powerful thunderstorm on final approach. As a massive downdraft struck the plane, the pilots attempted to go around, but the jet lost height and crashed to earth in a residential neighborhood, striking trees, streets, and a house before breaking into three pieces and bursting into flames. Of the 57 people on board, 37 died in the crash and its fiery aftermath, while 20, including all five crewmembers, escaped with their lives.
The investigation into the crash immediately focused on the weather. The plane appeared to have flown through a thunderstorm that produced a powerful downdraft known as a microburst, pushing it straight into the ground. But as the inquiry proceeded, it became clear that the cause was more complicated than a freak weather event. How was it that in 1994, after years of scientific progress, a microburst could still bring down an American airliner? Why did the pilots fly into such a dangerous storm in the first place? And why did their training, specifically designed to help them penetrate a microburst, fail to save the plane? As it turned out, the crash of USAir flight 1016 actually sat at the intersection of weather and human factors — a situation where natural dangers and insidious human failings came together with disastrous results.
USAir flight 1016 was a short, scheduled flight from Columbia, South Carolina to Charlotte, North Carolina. The 35-minute hop between the two Carolinas was the fourth leg of a five-leg trip that began that morning in Pittsburgh, followed by stops in New York City, Charlotte, and Columbia. Now, Captain Mike Greenlee, First Officer Phil Hayes, and the three flight attendants prepared to turn around and head back to Charlotte before continuing on to Memphis, Tennessee. Joining them on board the 21-year-old McDonnell Douglas DC-9 were 52 passengers, including two infants, making for a total of 57 occupants.
Flight 1016 departed Columbia on time, and within a few minutes, the pilots made contact with controllers in Charlotte to prepare for the approach to the airport. The plan was to conduct a visual approach to runway 18R, looping around to come in from the north. At that time, weather conditions were mostly clear with scattered clouds, and there was certainly nothing that would hinder their ability to see the airport.
At 6:33 p.m., about 10 minutes from landing, the pilots observed a small storm cell on their weather radar. Summer thunderstorms in the Southern United States are an almost daily occurrence, so its presence was not particularly notable. Nevertheless, Captain Greenlee, who was the pilot working the radio and monitoring the instruments, told the Charlotte approach controller, “We’re showing a little buildup here at, uh, looks like it’s sitting on the radial,” he said, referring to the extended centerline of the runway. “Like to go about five degrees to the left, to the west.”
“How far ahead are you looking?” the controller asked.
“About fifteen miles,” said Greenlee.
“I’m going to turn you before you get there,” said the controller. Essentially, he planned to have flight 1016 execute a U-turn to line up with the runway prior to reaching the storm cell off the north end of the airport. At this point, the pilots believed that the problem had been taken care of.
As flight 1016 lined up with the runway, however, another storm cell moved in rapidly from the south-southeast, accompanied by precipitation that showed up on the approach controller’s radar screen. “I’ll tell you what, USAir 1016,” said the controller, “[we] may get some rain just south of the field, might be a little bit coming off north, just expect the ILS now. Amend your altitude, maintain three thousand.” In light of the possible presence of rain over the airport, the controller had told the pilots that they should expect to approach using the instrument landing system, or ILS, the ground-based device that helps guide the plane down to the runway in low visibility conditions.
As the cell slowly moved over the airport, Captain Greenlee remarked, “Looks like it’s sitting right on the…” Although the rest of his sentence was cut off by an air traffic control transmission, he appeared to be acknowledging the presence of the storm over the airport. “If we have to bail out, we bail out to the right,” he continued, deciding that if they abandoned the approach they would turn right to try to avoid the worst of the storm.
About 15 seconds later, Greenlee commented, “Chance of shear,” encouraging First Officer Hayes to prepare for possible wind shear. Wind shear, a significant change in wind speed and/or direction over a short distance, is often associated with thunderstorms and can be hazardous to aircraft, so it was no surprise that Greenlee wanted Hayes to watch out for it as they approached the runway.
The approach controller now handed flight 1016 over to the tower controller, who would remain with them until touchdown. At 6:39, the tower controller cleared flight 1016 to land and informed them that another USAir flight that had just landed on runway 18R had reported a “smooth ride all the way down.” At around this time, the pilots observed the storm moving off the northern end of the airport and into their approach path, but the report from the other USAir crew seemed to indicate that it was nothing to worry about.
At 6:41, Charlotte International Airport’s Low-Level Wind Shear Alerting System (LLWAS) detected differing wind speeds and directions in three different quadrants, triggering a wind shear alarm in the control tower. “Wind shear alert, northeast boundary, winds 190 [degrees] at 13 [knots],” said the controller, passing on just one of the three areas where wind shear had been detected.
At around this time, the rain increased from light to heavy, a downpour that witnesses described as a “wall of water” and “some of the heaviest rain [they had] ever seen.” Two USAir flights, caught in the deluge while at the gate, elected to delay departure until the storm had passed. On board flight 1016, the rain suddenly slammed into the plane without warning, taking them straight from a dry sky to a biblical downpour in a matter of seconds.
“Here come the wipers,” said Greenlee.
What no one yet knew was that the thunderstorm was producing a powerful microburst. Near the end of a thunderstorm’s lifespan, its internal updrafts may become too weak to hold up cold air masses located high in the storm. The cold, dense air plunges down to earth, creating a powerful downdraft that then spreads out horizontally in all directions upon striking the ground. Microbursts can bring heavy rain and extreme winds to a localized area for a period of several minutes, but for aircraft, the most dangerous part of a microburst is the wind shear. A low-flying aircraft entering a microburst will first encounter a headwind, which increases performance, followed by a downdraft which pushes it toward the ground, then a tailwind which decreases performance right when the crew is trying to escape the downdraft.
As flight 1016 strayed into the outer edge of the microburst, it first encountered the headwind, causing the plane’s airspeed to increase. “Ooh, there’s ten knots right there,” said Hayes.
“Okay, you’re plus twenty,” said Greenlee. Eight seconds later, Greenlee determined that the rain would be too heavy to see the runway and the approach must be abandoned. “Take it around, go to the right,” he said to Hayes.
As Hayes began to pitch the plane up to climb, Greenlee contacted the tower controller and announced, “USAir 1016’s on the go!” Turning back to Hayes, he ordered, “Max power!”
“Yeah, max power,” said Hayes, jamming the throttles forward.
“USAir 1016, understand you’re on the go sir,” said the controller. “Fly runway heading, climb and maintain three thousand.” But the pilots had no intention of flying the runway heading, and in fact by this point they had already begun a right turn to try to peel out of the storm.
With the engines spooling up to max power and First Officer Hayes holding the plane at 15 degrees nose up, flight 1016 was on track to successfully escape the microburst. But just when it seemed like everything was under control, Captain Greenlee began to suffer from a subtle form of disorientation. When Hayes simultaneously pulled up to climb, turned to the right, and pushed the engines up to max power, everyone on the plane was subjected to significant angular forces rarely experienced in normal flight. However, in the absence of a visual reference outside the plane, the human body has difficulty translating physical cues into a mental model of the aircraft’s motion. In such a situation, a sudden acceleration that presses one back into one’s chair is sometimes indistinguishable from a gravitational force caused by a very high pitch angle, leading one to believe that the plane is pitched steeply upward when it is not. This phenomenon is known as somatogravic illusion. Although pilots are trained to recognize and ignore the somatogravic illusion, it is thought that in this moment of extreme stress, Greenlee was thinking too quickly to process whether the “pitch up” sensation that he was experiencing was actually real. In response to the illusion of a dangerously high pitch angle, Greenlee called out, “Down, pitch it down!”
Although Hayes was not suffering from a somatogravic illusion — the effect is much stronger when one is not at the controls — he too acted on instinct, responding to his captain’s command with an immediate nose down elevator input. The DC-9 pitched over from 15 degrees nose up to 5 degrees nose down, right in the heart of the microburst. A 35-knot headwind suddenly gave way to a 26-knot tailwind, causing a massive decrease in airspeed right at the most critical moment. Normally, pilots must pitch up to temporarily increase lift and counter this loss of airspeed, but by pitching down, Hayes actively assisted the microburst in pushing the plane toward the ground. Flight 1016 dropped like a rock from an altitude of just 350 feet as the pilots struggled to figure out what was going on. The ground proximity warning activated, calling out, “WHOOP WHOOP, TERRAIN.” Captain Greenlee called for “firewall power,” and Hayes pushed the throttles as far forward as they would go, but it was too late.
Flight 1016 touched down in an overgrown field just inside the airport perimeter fence, shearing off the landing gear and sending the plane sliding into a nearby forest. Trees battered the plane, tearing off the left wing and spraying jet fuel down the side of the fuselage. Still in possession of considerable momentum, the DC-9 slammed into a grove of large oak trees, sending a tree trunk slicing like a knife through the forward cabin. The tree ripped off the cockpit with a large trailing section of the left cabin wall and instantly killed everyone in rows three through eight, while another oak smashed into the back of the plane, severing the tail. The disintegrating wreckage slid out onto Wallace Neal Road, where the cockpit ground to a halt, while the center and tail sections continued across the street and onto a residential property. The rear fuselage with many of the passengers still inside crashed into the carport of a private house while the center section and right wing came to rest on the lawn, surrounded by flames.
When the wreckage came to a halt, flight attendant Richard DeMary was one of the first to come to his senses. Seated in the aft-facing flight attendant jumpseat just behind the cockpit, he found himself exposed to the rain as the roof and one wall had been torn away around him. In the adjacent seat, flight attendant Shelley Markwith had also survived with a broken kneecap, and First Officer Hayes could be seen climbing out through a window. Looking back toward where the tail used to be, all he could see were three unoccupied rows of seats and a long trail of twisted fuselage skin, complete with several windows but missing much of the floor. It wasn’t immediately clear what had happened to the rest of the plane, and for a moment DeMary wondered if they — the crew — were the only survivors.
More desperate struggles to survive soon kicked into high gear just a few meters away. On the front lawn of the house, the center section comprising rows 9–14 caught fire and burned over very quickly, killing all but two of the occupants who had survived the initial impact. Rows 3–8 and 15–16 were completely pulverized, the seats and their occupants strewn for dozens of meters back along the wreckage path. But in rows 17–21, the rearmost part of the cabin, almost everyone was still alive. The tail section had come to rest partially inside the house, and some passengers jumped down from the break in the fuselage to find themselves inside the poor family’s garage. Near the engines at the rear, a fire had erupted, threatening to overcome those who could not escape, and while struggling to get out through breaks in the fuselage, several people suffered serious burns, including the third flight attendant.
After carrying the crippled Markwith out of the plane and into the street, DeMary ran over to the tail section, where he found several passengers struggling to escape. Climbing up next to the fuselage, he helped pull a mother and her baby to safety, followed by another passenger some moments later. Another woman cried out for her infant daughter, who had been ripped from her arms during the crash, but no one could find her.
When emergency services arrived, they found surviving passengers as well as the flight attendants and both pilots sitting near the wreckage, trying to take stock of the situation. Firefighters immediately took over the rescue process, gathering together more scattered survivors, including one man who had become trapped inside the house. But by the time the fires were out and the situation assessed, it was clear that many people had not survived the crash. Of the 57 people on board, 37 passengers died in the crash and the fire that followed, while all five crewmembers and 15 passengers escaped with their lives. Among the dead was the 9-month-old infant, torn from her mother’s arms and killed during the impact.
Some hours later, representatives of the National Transportation Safety Board arrived on the scene and launched their investigation. The first thing recalled by everyone involved in the crash was the weather, and this was where the NTSB first turned its attention. An initial analysis of the evidence from the plane’s black boxes in combination with recorded data from the LLWAS at the airport pointed conclusively to the presence of a microburst at the time of the crash. Microbursts had caused major crashes before: 154 people died in 1982 when a Pan Am Boeing 727 crashed into a New Orleans neighborhood due to a microburst, and a further 137 died in 1985 when a microburst brought down a Delta Lockheed L-1011 Tristar on approach to Dallas. In both of these cases, the microburst had simply overpowered the crew, striking too quickly and too close to the ground for the human pilots to react in time. Had the same thing happened again in Charlotte?
First, investigators had to understand why flight 1016 flew into the microburst in the first place. Pilots are trained not to fly into active thunderstorms, and although studies had shown some do anyway, Greenlee and Hayes were not under any significant time pressure and seemed entirely prepared to go around if they needed to. So why didn’t they do so until after they were already in the microburst?
It soon became apparent that the pilots were missing key information about the storm that passed over the airport while they were on final approach. First of all, upon entry to the Charlotte area, the pilots had obtained the weather report prepared by the National Weather Service and broadcast by the Automated Terminal Information Service, or ATIS; however, this report did not contain any mention of thunderstorms at Charlotte International Airport. At that time, the thunderstorms had yet to materialize, and the report was in fact accurate. But just a few minutes later, several thunderstorms started to form, which was consistent with the forecast. The next ATIS report, prepared at 6:36 and broadcast at 6:42, did mention thunderstorms and heavy rain over the field, but at this time flight 1016 was on final approach just two minutes from touchdown and was not expected to tune in to the ATIS frequency to obtain the report. Therefore the pilots never heard an ATIS broadcast that contained any mention of potentially dangerous weather.
Furthermore, the controller did not provide any information to the crew about the magnitude of the storm. A thunderstorm’s intensity is measured on a scale of 1 to 6, with 6 being the most extreme, and anything higher than 2 is considered dangerous to aircraft. The storm that flight 1016 flew into was retroactively determined to be somewhere between level 3 and level 5, but the controller would not have been able to determine this on his own. A National Weather Service meteorologist in Atlanta, Georgia was responsible for monitoring storms throughout the region and informing airports of any dangerous weather, but he didn’t inform Charlotte of the storm until after the accident. In fact, this one person was responsible for 260,000 square kilometers of airspace over one of the most meteorologically active areas of the United States, far more than he could properly handle by himself. He had been unable to inform Charlotte of the intensity of the storm earlier because he was busy informing a different airport of a different storm that he believed posed a greater danger.
However, the controller did have radar that was capable of determining the level of precipitation produced by the storm, which could serve as an indicator of its intensity. This information was also not passed on, and in fact flight 1016 never even heard the words “heavy rain.” Instead, the controller had told them that they “might get some rain just south of the field” and that there “might be a little bit coming off north,” which would have indicated to the pilots that the rain was light and that they would only catch the edge of it. This was not standard phraseology, and in fact controllers were not trained to interpret data from their weather radar and inform pilots of the actual measured precipitation level.
Additionally, during the minutes before the crash, lightning was observed near the airport, wind shear alarms sounded in three quadrants, and visibility dropped as low as 730 meters, near the minimum for the approach that flight 1016 was flying. Out of all this information, only the wind shear alarm in a single quadrant was passed to the pilots, and it was not the quadrant they would be landing in. In fact, controllers tended to disregard the low-level wind shear alerting system because they perceived it to be unreliable, and only broadcast the alerts they were highly confident were genuine. The controller also could not have informed the pilots of the low visibility because the instruments that displayed this information in the control tower were not turned on. The tower supervisor was supposed to have activated the equipment when he observed that visibility dropped below 1 mile (~1,600m), but he never did.
Each of these pieces of information might have seemed small on its own, but together they could have painted a stark picture of the storm. Had the pilots known that the storm’s intensity was level 3 or higher, that there was lightning, heavy rain, and wind shear alerts in three quadrants, they almost certainly would have abandoned the approach sooner and avoided the microburst. Instead, all they had was whatever they saw with their own eyes, a mention of “some rain,” and a report from another USAir pilot that the ride down was “smooth.” Until they flew into the storm and saw its power firsthand, there was no indication that it was unsafe to proceed.
After entering the storm, Captain Greenlee decided to go around not because of wind shear, but because he had lost sight of the runway. He therefore ordered a regular go-around instead of the specialized wind shear escape maneuver, which was optimized for microburst penetration. In fact, the pilots had no direct cue that they were encountering wind shear at all. The plane had an alarm that was supposed to sound when the plane was in a wind shear condition, but it never went off. In fact, its preconditions were not met until approximately 9 seconds before impact, and its programming logic inhibited it from activating while the flaps were in motion in order to prevent nuisance alarms, so it would not have actually sounded until 4 seconds before impact, when the flaps finished retracting. Even then it still did not go off, for unknown reasons.
Compounding this problem was the nature of the wind shear training received by the pilots. The training consisted of several very specific scenarios that pilots had come to associate with wind shear. Prior to encountering the shear, the simulations always included turbulence, but no turbulence was present before flight 1016 entered the microburst. The training also tended to cause overreliance on the wind shear alarm, which in this case never activated. This rote memorization of the simulator scenarios and reliance on cues that are not always present left the pilots unprepared for the wind shear that they actually encountered. All of these factors explained why Greenlee and Hayes never used the specialized techniques that they had been taught to employ when trying to penetrate wind shear.
But an analysis of the microburst dynamics and of the airplane’s performance showed that it could have been penetrated safely even without using the wind shear escape maneuver, as long as the pilots maintained maximum thrust and a 15-degree nose up attitude, as First Officer Hayes had initially commanded. Instead, after several seconds Captain Greenlee said, “Down, push it down,” and First Officer Hayes pushed the plane to 5 degrees nose down. Investigators were baffled. Why would anyone do this? Interviews with the pilots revealed nothing, as Greenlee didn’t remember giving the order and Hayes didn’t remember hearing it.
Eventually, investigators concluded that Greenlee suffered from a somatogravic illusion, when the body mistakes forward acceleration for high vertical pitch in the absence of outside references. But Greenlee was a highly experienced pilot who was in the air force reserves and flew F-4s and F-16s. Surely if anyone was resistant to the somatogravic illusion, it would be him! In reality, however, no one — no matter how well trained — is completely immune, and several factors actually made him more likely to encounter the illusion. Firstly, he was not at the controls, so he did not have control feedback that would correlate with the motion of the plane. And secondly, his situational awareness may have been compromised. The Cockpit voice recording revealed that procedural discipline was poor, with both pilots engaging in non-pertinent conversation throughout the approach, in violation of rules banning off-topic discussion below 10,000 feet. Greenlee also missed required altitude and airspeed callouts, suggesting that he was not adequately monitoring the instruments. It is therefore entirely possible that Greenlee was not aware of how close they were to the ground or what their airspeed was, removing key indicators that would help him contextualize what he was feeling and decide on a course of action. Even after suffering from the somatogravic illusion, he might not have ordered Hayes to push the nose down if he knew they were only 200 feet above the ground, far too low to attempt such a maneuver.
The full causes of the crash were now apparent. Flight 1016 flew into a dangerous thunderstorm due to misleading information about its intensity, and the pilots were unprepared for the microburst that it produced. During the microburst penetration, a lack of situational awareness caused Captain Greenlee to suffer from a somatogravic illusion, and he ordered Hayes to pitch down right when he needed to pitch up, allowing the microburst to push the plane into the ground. Now, the NTSB had to ask: could the crash have been prevented?
One line of inquiry connected to the failed wind shear warning. If the warning had sounded 9 seconds before impact when the conditions for activation were first met, the NTSB calculated that it would still have been possible to save the plane if the pilots had immediately applied the wind shear escape maneuver — maximum power, maximum safe pitch up, and flaps extended. However, given the crew’s apparent lack of situational awareness before and during the wind shear encounter, the NTSB expressed doubt that the pilots would have had the necessary reaction times to apply the wind shear escape maneuver in time to avoid ground impact.
The crash also could have been prevented if advanced doppler radar, capable of detecting wind shear directly, had been installed at the airport. Doppler radar measures changes in the frequency of returning radio waves to determine the speed of airborne particles in a storm, giving a detailed three-dimensional picture of wind speed and direction. A program to roll out doppler radar at all major US airports had been launched after the two microburst-related crashes in the 1980s, and Charlotte was supposed to be one of the first airports to receive the new equipment. But the Federal Aviation Administration had been locked in a bitter pricing dispute with the owner of the land on which the doppler radar was to be installed, and by 1994, Charlotte had slipped from 5th in line to receive the equipment all the way down to 38th. At the time of the crash, the land dispute remained unresolved. The FAA and NASA were also in the process of developing on-board doppler radar that could detect wind shear ahead of the plane and warn the pilots — another initiative that came out of the accidents in the 1980s — but in 1994, it was still not quite finished. Therefore, despite the existence of microburst detection technology and a recognized need to deploy it, flight 1016 was still operating in much the same technological environment as Delta flight 191 and Pan Am flight 759 were when they encountered microbursts and crashed 9 and 12 years earlier, respectively. Tragically, USAir flight 1016 was brought down by a known problem that authorities were already working hard to eliminate. Shortly after the crash, both ground-based and airborne doppler radar at last entered widespread use, and flight 1016 was the last US airliner to be lost due to wind shear.
Nevertheless, there were important safety lessons to be learned. After concluding its investigation, the NTSB recommended that controllers be required to update pilots about thunderstorm conditions, including such features as lightning, wind shear, and rain; that controllers be required to inform pilots of the highest precipitation level near the airport as indicated on their radar; that airlines re-emphasize the importance of strict adherence to standard procedures; that NWS meteorologists like the one in Atlanta be given the tools or staff to adequately disseminate information about rapidly developing thunderstorms; that wind shear training be diversified to prevent rote memorization of particular scenarios; that USAir ensure its instructors were providing wind shear training correctly; that USAir improve training to help pilots detect microbursts based on indirect cues; that the wind shear warning activate even when the flaps are in transition; and that all infants be restrained in a seat on takeoff and landing. All of these recommendations led to tangible improvements in safety.
When the NTSB issued its determination of the probable cause of the crash, the Air Line Pilots Association protested vociferously, claiming that the NTSB was putting too much blame on the pilots. It argued that the microburst was strong enough to bring down the plane regardless of whether the pilots pitched down or not, a claim that the NTSB ultimately dismissed because ALPA’s study was not sufficiently rigorous. Of course, ALPA was just doing its job — defending the pilots. In the end it was easy enough to recognize that while Greenlee and Hayes made mistakes, they were also victims of circumstance. Both pilots soon recovered from their injuries and went back to flying for USAir, now armed with a level of firsthand knowledge that most pilots will never acquire — and a newfound appreciation for dangers that to other pilots might seem abstract. As of 2017, they were still flying for American Airlines, which bought USAir in 2013. Flight attendant Richard DeMary, who pulled several survivors out of the burning plane, also got his due. In the year after the crash, he received numerous awards for his heroism, which he graciously accepted. “While I was the individual in the event,” he said in an interview for Mayday, “the awards really represent a recognition of the flight attendant profession, and that flight attendants play a role of extreme importance on each and every flight.”
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