The crash of Pan Am flight 759: Analysis
On the 9th of July 1982, afternoon thunderstorms were building over the working class New Orleans suburb of Kenner, where 66,000 people lived in the shadow of Louisiana’s largest airport. But at exactly 4:09 p.m., disaster struck: a Pan Am Boeing 727 bound for Las Vegas suddenly fell from the sky less than a minute after takeoff, tearing a swathe of destruction through Kenner and killing 153 people. On the plane, there were no survivors; eight residents of Kenner also lost their lives, and 11 houses were severely damaged or destroyed. In seeking the cause of the crash, investigators turned to the weather: the plane appeared to have been caught in a microburst, a sudden downdraft that shoved it into the ground right at its most vulnerable moment. The investigation highlighted the risk of what was then a poorly understood phenomenon, and found that the disaster could have been prevented if the FAA had acted sooner — and even then, change wouldn’t come until microbursts had killed again.
Pan Am flight 759 was a regularly scheduled service from Miami, Florida to San Diego, California with stopovers in New Orleans and Las Vegas. In command of the Boeing 727 operating this flight were Captain Kenneth McCullers, First Officer Donald Pierce, and Flight Engineer Leo Noone. All were very experienced; McCullers had over 11,000 flying hours, Pierce had more than 6,000, and Noone had more than the other two put together.
Operated by the 727 nicknamed “Clipper Defiance,” flight 759 arrived in New Orleans in the early afternoon after an uneventful trip from Miami. While 138 passengers boarded the plane, the pilots monitored the weather, watching carefully as thunderstorms gathered near the airport. They likely were not very concerned: none of the storms they could see on their weather radar looked serious, and there were no significant weather advisories, or SIGMETs, in effect for the New Orleans area.
The intensity of a thunderstorm, for aviation purposes, was measured on a scale of 1–6, with 6 being the most intense. A level 1–2 storm will have light to moderate turbulence and lightning, and does not pose a significant threat to an airliner. In a level 3 storm, severe turbulence is possible; in a level 4 storm, severe turbulence is likely; a level 5 storm will have severe turbulence, powerful wind gusts, and possible hail; and a level 6 storm features large hail, severe turbulence, and extreme wind gusts. Anything above level 3 was to be avoided at all costs. However, the pilots’ weather radar didn’t show any storms above level 2.
The pilots of flight 759 planned to take off on runway 10, angled east southeast, as this was the only runway long enough for a fully loaded 727. Out of an abundance of caution, they decided to make their initial turn to the north instead of to the south to avoid storm cells to the south and southeast of the airport.
At about 4:00 p.m., flight 759 left the gate and began taxiing toward runway 10. During this time, the Low-Level Wind Shear Alert System (LLWSAS) at the airport detected wind shear several times.
Wind shear, on the most basic level, is a significant difference in wind speed and/or direction within a narrow geographical area. For example, if the wind at one end of the runway is blowing north at 15 knots, and at the other end of the runway the wind is blowing south at 5 knots, then a 20-knot wind shear is said to be occurring on the runway. Most commonly associated with thunderstorms, wind shear can be a significant hazard to planes because of its effect on airspeed, or the speed of an aircraft relative to the surrounding air mass. A sudden transition from a headwind to a tailwind can cause a massive drop in airspeed, even though the speed of the plane relative to the ground below might not have changed. This can lead to an unwanted descent close to the ground, or in extreme cases, even a stall. To make sure pilots are aware of wind shear, airports installed wind shear detection systems beginning in the 1970s. A LLWSAS like the one installed at New Orleans International Airport in 1982 relies on several sensors scattered around the airport that detect when the wind speed and direction in one area is different from a nearby area, and send an alert to air traffic controllers that can then be passed on to pilots.
At 4:02, the controller received a wind shear alert. On the general frequency he stated, “Low level wind shear alert at northeast quadrant, 330 degrees at 10 [knots], northwest quadrant 130 degrees at 3 [knots].” This indicated 13 knots of wind shear between the west and east ends of the airport, an amount that was enough to notice but was not particularly dangerous. The pilots of flight 759 heard the report and continued with their takeoff preparations. Over the next several minutes, a cell moved near the end of runway 10, but it appeared to be a minor level 2 cell and posed no threat to the takeoff.
A few seconds before 4:08, Pan Am flight 759 began its takeoff roll on runway 10, heading east against a 16-knot headwind. The controller had not received any wind shear alerts since 4:02, and the pilots of flight 759 likely assumed that there was no significant wind shear at that moment. Nevertheless, Captain McCullers advised First Officer Pierce, who was flying the plane, to build up more speed before lifting off to give them a bigger margin if they encountered wind shear. He also ordered Flight Engineer Noone to turn off the air conditioning so that they would have more engine power. Then, while the 727 sped down the runway, the wind shear returned. The headwind began to decrease rapidly as flight 759 encountered a 38-knot shear on the margin of the nearby storm cell. At 4:08 and 40 seconds, flight 759 lifted off from the runway and began climbing, but it was already in enormous danger. The headwind evaporated utterly and was replaced by a 7-knot downdraft, then an increasing tailwind. The plane’s airspeed fell precipitously. Still inside the airport boundary, the 727 reached a maximum altitude of barely more than 100 feet, then began to descend. Five seconds after liftoff, Captain McCullers said to First Officer Pierce, “Come on back, you’re sinking Don. Come on back!”
Now facing a significant tailwind, the wings struggled to generate enough lift to keep the plane airborne. The pilots applied maximum thrust and pitched the nose up to climb. But directly beyond the end of runway 10 lay the suburb of Kenner, its western boundary marked by Williams Boulevard, a four-lane street with trees growing out of the median. Headed straight for Williams Boulevard, flight 759 dropped below 50 feet above ground level, then entered a slight climb as the pilots’ efforts began to pay off. Unfortunately, it was too late. The 727 passed just 50 feet over the heads of terrified motorists and then plowed into the trees on Williams Boulevard, tearing off pieces of the left wing amid a hail of flying branches. Banking left, the plane struck another set of trees then rolled inverted, its left wingtip slicing into the ground. Flight 759 crashed a couple doors down from the intersection of Fairway Street and 17th Street, destroying a house at 1624 Fairway. Breaking apart as it went, the plane cartwheeled forward and slid for two and a half blocks, tearing diagonally across Hudson Street, 17th Street, and Taylor Street. A fireball curled into the sky over Kenner as the jet fuel ignited, setting the mangled wreckage ablaze.
In mere seconds, the crash turned a quiet residential neighbourhood into a scene of total devastation. Some residents of Kenner never knew what hit them. At the first house to be struck, four members of the Giancorte family were all killed, including three young boys. Farther along, the plane tore through the Schultz household, killing 11-year-old Jennifer Schultz, while her mother Barbara, 7-year-old sister Rachel, and Rachel’s friend Lisa Baye suffered severe burns while trying to escape through a window. Lisa, 6, subsequently died in hospital. The plane also demolished the home of the Trahan family, where Melanie Trahan was at home with her daughters Bridgette, 4, and Melissa, 16 months. Melanie and Bridgette were both killed. And a few got lucky: three members of the Weems family, whose house was completely leveled, had left just minutes earlier to buy bread.
The first rescuers on the scene were faced with total pandemonium. Six houses had been totally destroyed and five others were severely damaged, and there was hardly anything left of the 727, save for the tail. The tangled debris of the plane had been mixed into the shattered wood and cinder blocks from the houses and the entire mess set ablaze, throwing up a cloud of black smoke that could be seen for miles. Shocked residents of Kenner, some of them suffering from severe burns, wandered at the periphery of the devastation. Many couldn’t be sure whether their houses were still standing or whether their loved ones were still alive. Ambulances rushed several people to nearby hospitals while firefighters struggled to bring the blaze under control and look for survivors.
For several hours, the search proved fruitless. All they could find were bodies, from both the plane and from Kenner. There were bodies lying in the streets, crushed under the rubble of homes, even floating in a swimming pool. Of the 138 passengers and 7 crew on board flight 759, none survived; on top of that, the death toll on the ground was beginning to rise. Then, after several hours, a police officer spotted movement in the wreckage. To the complete disbelief of everyone on the scene, he found 16-month-old Melissa Trahan alive in the rubble of her house, pinned underneath the mattress from her crib, which had flipped over on top of her and sheltered her from the flames. The entire recovery operation came to a halt as first responders cried tears of joy at the discovery of just a single survivor amid so much carnage.
All told, eight residents of Kenner lost their lives, six of them children under the age of twelve. With the addition of the 145 people on the plane, this brought the death toll to 153, making Pan Am flight 759 the second deadliest crash on US soil at the time. (The figure is sometimes quoted as 154, due to the inclusion of an unborn baby carried by a passenger who was 7 ½ months pregnant.)
While Kenner tried to pick up the pieces, investigators from the National Transportation Safety Board arrived at the scene to work out the cause of the crash. What they found was that flight 759 unwittingly flew straight into a microburst, a type of downdraft associated with thunderstorms. At the time, microbursts were poorly understood. Their characteristics were simple enough: a powerful downdraft concentrated into a small area strikes the ground, then spreads outward at low altitudes in all directions, dissipating within a few minutes as it expands. This process creates severe wind shear, as the wind on one side of the microburst blows in the opposite direction from the wind on the other side. Therefore, a plane entering the microburst first encounters an intense headwind, then an intense tailwind, accompanied by a downdraft. The headwind increases airspeed and therefore increases lift, making it easy to fly into. Then the headwind abruptly disappears, and the tailwind hits, decreasing airspeed, while the downdraft decreases lift right when it is most needed. In the case of Pan Am flight 759, this sequence of shifting winds prevented the plane from ever climbing much over 100 feet above ground level. Only 20 seconds after lifting off, the 727 struck trees and crashed after the sudden tailwind put it into a descent from which the pilots were unable to recover in time.
The problem with microbursts was that no technology existed that could reliably detect them, and studies had shown no correlation between the intensity of a thunderstorm and the likelihood of a microburst. Furthermore, a microburst’s small size meant that it could be entirely contained between the sensors of the Low Level Wind Shear Alert System, which were spaced 3 kilometers apart. Therefore the LLWSAS wouldn’t detect the wind shear and set off an alarm until the microburst had spread out, by which point the most dangerous part of its brief lifespan was already over. A wind shear alert sounded in the control tower while flight 759 was airborne and was broadcast over the general frequency two seconds after the crash, but this was too late to be useful, considering that wind shear was already severe enough to bring down a plane before the alert ever went off.
This raised an important question: if pilots encounter a microburst — a distinct possibility considering the inadequacy of the detection technology — what should they do to prevent an accident? In 1979, the Federal Aviation Administration published an advisory circular explaining that the best way to deal with wind shear is to sacrifice airspeed for altitude. Because the airflow during a downdraft comes from above, the plane’s angle of attack — the angle of the pitch axis relative to the airflow — decreases. A lower angle of attack means less lift, and the plane descends. By pitching up steeply, pilots can increase the angle of attack to a level that will provide enough lift to maintain altitude. The FAA circular noted that this manoeuvre could require a pitch angle much greater than pilots are used to, and at low altitudes, it could require extremely fast reaction times. All of this information was incorporated into Pan Am’s flight operations manual, but the manual made no mention of the microburst phenomenon or the conditions associated with it.
The NTSB found that the pilots of flight 759 spent 6 seconds identifying the presence of wind shear and choosing a course of action before they attempted the aforementioned manoeuvre, by which time they had already descended 50 feet. The minimum plausible reaction time under those circumstances was assessed to be about 4.25 seconds — probably not enough to prevent the crash. But if the pilots’ reaction time had been a little bit faster even than that, the descent and collision with trees might have been avoided. The next question, then, was how to decrease that reaction time.
There was certainly some room for improvement in pilot training. Although the captain flew wind shear scenarios during recurrent simulator training, these scenarios were not graded; they were meant for practice only. They also did not specifically simulate a microburst, and recovery could be made with a relatively conservative pitch up and thrust increase. Furthermore, the first officer was not required to receive such training, and there is no evidence that he did. Therefore, while the pilots probably knew about the more drastic measures described in the 1979 FAA circular, they most likely never had an opportunity to practice them. Better training for dealing with wind shear could have decreased their reaction times.
Another way to improve reaction times would be to redesign the flight director. The flight director is an overlay on the attitude and airspeed indicators that shows the airspeed and pitch attitude needed to fly the desired flight profile. However, this instrument doesn’t take into account environmental factors, such as wind shear, in its calculations. Therefore, to make a wind shear recovery, pilots had to deviate from the optimal attitude shown on the flight director, a disconnect that increases reaction times. A dynamic flight director that detects wind shear and revises its recommended attitude could prompt pilots to take corrective actions more quickly.
In fact, an extensive FAA study that lasted from 1975 to 1979 explored exactly this possibility. This study found that without any airborne detection technology, pilots were often unable to handle significant wind shear. In fact, the authors of the study wrote, “A major conclusion, over all the tests, was that conventional instrumentation was found inadequate for coping with wind shear during approach and landing. The percentage of acceptable approach outcomes under these conditions was generally less than 50%.” However, when using a modified flight director that could react to changes in wind speed and direction, pilots were almost universally able to land safely despite severe wind shear on approach.
However, the study found that wind shear on takeoff was even more dangerous than wind shear on approach. This is because a landing aircraft is in a stabilized flight profile, while an aircraft just taking off may already be at its performance limits with little room for error. The study found that with standard instrumentation, every simulated takeoff that encountered severe headwind-to-tailwind wind shear ended in a crash. Furthermore, even optimal reactions were not always enough to prevent an accident. “The computer studies indicated that there are realistic wind profiles in which even operation at the limit of airplane capability is not enough to prevent ground contact,” the authors of the study wrote. “The overall picture given by the takeoff outcome data was that individual wind shear effects were dominant and that none of the aiding techniques tested could cope efficiently with the combined effects of a headwind shearout and downdraft during the first 500 feet of the climbout. An attempt to make a normal takeoff in such a situation, even when aided by a minimum-height-loss pitch-steering algorithm, cannot be retrieved by pilot action.” In other words — an encounter with a sufficiently strong microburst on takeoff could be unrecoverable.
After the publication of the study in 1979, the FAA issued a Notice of Proposed Rulemaking floating the possibility of requiring the installation airborne wind shear detection technology. But the aviation industry reacted negatively to the proposal, arguing that it was too expensive and carried little benefit. As a result, the FAA withdrew the notice and no requirement was ever created. Three years later, Pan Am flight 759 was still using the same standard instrumentation that the study found inadequate to help pilots deal with severe wind shear.
Another takeaway from the study was that some wind shear should be avoided at all costs because a successful penetration is impossible. However, this would require advance knowledge of its presence, and as stated earlier, a microburst doesn’t necessarily show up on ground-based wind shear alert systems until it’s too late. One solution would be a device on board the plane that could detect wind shear farther along the projected flight path. But with the technology available in the late 1970s and early 1980s, attempts to create such a device were unsuccessful; the best design was only able to predict wind shear six seconds in advance, which was far too little for pilots to take evasive action. But despite this glaring deficiency, the FAA invested no resources in developing on-board wind shear detection technology.
The NTSB also examined the question of whether Captain McCullers made the right call in deciding to take off in the first place. As it turned out, there was no obvious clue that would have told him it would be unsafe to proceed. The previous wind shear alert had expired and no new one had been issued. There were no level 4 or 5 storms in the area. The storm off the east end of runway 10 was probably a level 3 cell, but attenuation of the radar signal due to heavy rain might have caused it to appear as a level 2 cell on the 727’s weather radar. Neither a level 2 nor level 3 cell was considered to be dangerous; the pilots might not have known or did not consider the fact that a cell of any intensity level could produce a microburst.
On top of all of this, Pan Am operations guidelines, which were broadly similar to those of other US airlines, didn’t designate a particular point at which wind shear became too severe to take off safely, instead leaving it up to the pilot to decide whether takeoff was feasible. The last report at 4:02 indicated wind shear of 13 knots — hardly enough to convince a captain to delay takeoff. (This value may have been an underestimation, as the LLWSAS sensor east of runway 10 was surrounded by trees on three sides, reducing its recorded wind speeds.) In light of all of these factors, it seemed Captain McCullers made a reasonable decision based on the information he had, and he appeared to be aware of and ready for the possibility of wind shear.
Taking all of these findings together, the NTSB painted a stark picture of an aviation system that doomed flight 759 before it ever took off. Despite the known threat of wind shear, no reliable detection technologies existed, and pilots weren’t well trained to handle it. As a result, the Pan Am pilots took off without knowing that they were flying into a deadly microburst, and weren’t able to react until it was too late.
The NTSB issued numerous recommendations to improve the way the industry handled wind shear. These recommendations included that low level wind shear alert systems be reviewed to identify gaps in their coverage; that the locations of LLWSAS sensors be made available to pilots, along with information about the system’s limitations; that a way be found to incorporate meteorological data, radar readouts, and wind shear alerts into a system that would tell pilots whether or not it is safe to take off; that the FAA study more deeply the effects of wind shear on aircraft performance; that pilots be trained in a simulator using realistic microburst scenarios; that advanced doppler radar be developed to help air traffic controllers reliably measure storm intensity and detect wind shear; that the industry develop and adopt enhanced flight director technologies and on-board wind shear detection technologies; and that pilots receive better training on the use of available meteorological information. A further six recommendations were issued regarding improvements to the quality of black box data, because the cockpit voice recording from flight 759 was nearly unintelligible and the data recorder tracked few parameters.
As a result of these safety recommendations, the FAA restarted research into wind shear-related areas that had been stagnant since 1979. However, development of reliable wind shear detection systems and enhanced flight directors dragged on for several years. By 1985, the industry’s approach to dealing with wind shear was not that different from its approach in 1982.
Then on the 2nd of August 1985, Delta Airlines flight 191, a wide body Lockheed L-1011 Tristar, was on final approach to Dallas-Fort Worth International Airport when it encountered a microburst. The pilots were unable to react to the wind shear in time. The downdraft and loss of lift pushed the plane into the ground, causing it to make a forced landing in a field short of the runway. The Tristar crossed a highway, killing a motorist, then crashed into a water tank, destroying the plane. 136 of the 164 people on board were killed. Once again, a microburst had brought down a passenger plane belonging to a major US airline.
With two massive crashes due to wind shear in barely over three years, it was clear that the pace of improvement was not sufficient. Under massive public pressure in the aftermath of the Delta crash, the FAA accelerated its efforts and met most of the original recommendations from flight 759 by the end of 1986, thanks in large part to an ambitious research program that saw test pilots fly a Boeing 737 into real microbursts around the country. Airborne wind shear detection technology was finally mandated by 1993, and today advanced systems can reliably detect microbursts and divert planes away from them. No US airliner has crashed due to wind shear since 1994, and it is likely that the United States will never see such a crash again.
It is doubly tragic that the 153 lives lost in the crash of Pan Am flight 759 did not spur action that was sufficiently aggressive to prevent the Delta crash three years later. And of the two crashes, Delta flight 191 is better known today by a wide margin, even though more people died on flight 759.
Today, the neighbourhood in Kenner where the plane went down bears few outward signs of the tragedy that took place there. Most of the eleven houses destroyed in the crash have been rebuilt, although several lots remain empty to this day. Nevertheless, as a community, Kenner has done much to preserve the legacy of the disaster, in the form of memorials, documentaries, annual remembrance services, and more — little of it organized on an official level. The pain of loss lingers, especially among those who knew the many young children who lost their lives. And people still fondly remember Melissa Trahan as the “miracle baby,” although she is now an adult with kids of her own.
Unlike some crashes in urban areas, flight 759 is a widely known aspect of the local lore, and still represents a raw moment the area’s history. And unlike many crashes where those responsible try to dodge blame, Pan Am and the US government accepted responsibility and paid out millions in settlements to relatives of the victims, even though it could have been argued that no one was directly at fault.
Pan Am flight 759 is part of a category of accidents that can be said to have slipped through the cracks of aviation history. These accidents often had large death tolls and drew considerable attention at the time, but failed to produce safety improvements that prevented similar crashes from happening again. Because Delta 191 tends to get all the credit for the program to combat wind shear, Pan Am 759 has descended into relative obscurity, even though it was the catalyst that started the program in the first place. By putting it at the focal point of this article, I hope to provide an alternative perspective to the story of wind shear that gives this tragedy something more than a line or two at the bottom of the page.
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