Moerdijk, South Holland, Netherlands Tornado – October 6, 1981

Introduction

Most of the summaries we have created at Tornado Talk follow a given tornado track from start to finish, documenting the people and places affected along the way. This story, however, is not centered around the evolution of a twister. Rather, it is the story of a Dutch airliner in 1981 that, by incredible misfortune, encountered a dissipating tornado and suffered an unsurvivable outcome. Four crew, 13 passengers, and one person on the ground lost their lives. As of September 2023, this is the only proven, direct instance in aviation history that such a thing has happened.

Disclaimer

None of the writers at Tornado Talk are fluent in either the Dutch language or knowledgeable about the culture and societal norms of the Netherlands. For some materials, online translators were necessary to convey the full stories. This includes any information found in newspapers. Please note that we cannot personally verify that all translations are fully accurate.

Summary

4:20 pm Central European Time (CET), October 6, 1981: At Rotterdam airport in Rotterdam, South Holland, the Netherlands (NLD), the two pilots of NLM Flight 431 were being informed about weather conditions ahead of their scheduled flight. Air traffic control notified them of thunderstorms with only light precipitation, generally southwest of Rotterdam. This was not unusual or of concern; such showers could be easily avoided, and in any case, they did not appear capable of causing any flight issues. Preparations for takeoff continued as normal. They were scheduled for a routine 5:00 pm CET flight from Rotterdam to Hamburg in West Germany, with a stopover in Eindhoven, NLD.

The atmosphere, however, was far from calm. Much of the meteorological information for this incident is derived from Volume 112 of The Meteorological Magazine, published in February 1983. It contained a piece by W.T. Roach and J. Findlater titled “An aircraft encounter with a tornado.”

A sprawling, low pressure system was drifting over the south-central United Kingdom, embedded in a trough with a strong upper-level jet streak flowing to the northeast. Weather observations noted warm and moist winds coming from the south ahead of a northwest-southeast oriented cold front, moving toward the northeast, situated over the English Channel. This, combined with an east-west oriented warm front moving slowly north across the central Netherlands, created a dangerous combination of shear and instability for strong thunderstorms.

The Fokker F-28 aircraft pulled up from the runway at 5:04 pm CET. The thunderstorms were dramatically strengthening, causing wind damage in a few towns not far to the southwest. Neither the pilots nor air traffic control knew this. Back in 1981, up-to-date weather information took time to be received. In this case, a radar operator at a site in the town of Schipol sketched on a map what the radar screen was showing them. They then had to transmit copies of their sketch to other airports in the country, where air traffic controllers could radio pilots what the drawing looked like. This process was performed at regular intervals but took over 20 minutes. At 5:00 pm that day, the radar actually depicted a well-developed cluster of thunderstorms over the southwestern Netherlands. In fact, a different radar at De Bilt that updated hourly showed a hook echo on a storm approaching the flight path. Back then, the significance of this feature was not as commonly known, so it was not included in the regular sketch. Even if it had been, though, none of that information could have reached the flight in time.

Flight 431 quickly reached a cruising altitude of 3,000 feet and an airspeed of roughly 270 mph. Here, they began using their primitive onboard weather avoidance radar. A crude, online translation from Dutch to English was made of the final report by the Netherlands Aviation Safety Board. It included, “After detecting intensive shower activity in the storm front on the weather avoidance radar, the crew changed course southwards with the permission of air traffic control in order to avoid the heavy cores, straight through the storm front to fly over an area that appeared on the onboard radar as a relatively less active area between two heavy showers.”

At 5:09 pm CET, air traffic control granted them permission to change course. The plane sped due south into the murky clouds. Little did they know that a tornado was already looming within this system.

We can only make guesses from this information on the storm’s structure relative to the track of the plane and the vortex. Based on the fact that the pilots were following their training to skirt around the edge of the storm, the most plausible explanation is that there were indeed two storm cells. The northern one was producing a tornado. The mesocyclone spawning the twister would have naturally been located along the southern or southwestern side of the thunderstorm. Since there was an extending hook on radar, there likely was a rain-free area of inflow that the pilots could have tried to pass through.

Tornadic storms are constantly morphing, and an occluding and weakening circulation like this is especially dynamic. Perhaps the still clouded but mostly rain-free cyclone just wasn’t visible on their instruments. A less likely but still plausible alternative is that there was a radar return, but the mesocyclone aloft curled back into the storm during the occlusion, colliding with the jet. Photos that will be discussed shortly revealed the tornado itself was in the final stages of dissipation and gone before the plane even hit the ground.

We do not know anything about the beginning evolution of the twister, nor of the damage on the ground it caused. It is almost entirely thanks to a report in Volume 112 of The Meteorological Magazine that anything can be said about the tornado.

We believe that this was a relatively short and weak track. The vortex moved northeast during its life, with a rough forward speed of 35-45 mph. The ground circulation was over 300 yards wide, and the condensation funnel was less than 100 yards across. The cloud base at the time was just under 450 yards above ground level. It moved across the Moerdijk industrial park, and a map in the Meteorological Magazine explicitly shows the path encompassing a marked building complex.

Local newspapers in the Netherlands reported substantial wind damage and funnel cloud sightings 7-12 miles north, but these came from one or more separate probable tornadoes that are not documented. Since there was no mention of such issues near Moerdijk and the industrial park, the twister was likely too weak to cause substantial effects. A crucial part of the report’s analysis was a set of photographs. A police launch boat had deployed from a harbor on the northern side of the Hollands Diep and spotted the tornado. The officer traveled east to pursue the twister, snapping a total of 16 photos. These showed the rope out of the funnel and a subsequent explosion moments after dissipation. A second bystander, Bert Eestermans, also captured two color images. Both the police launch and a color photo are shown below.

A final note on the twister is that an air pollution station just a few hundred yards away recorded some interesting data on the airflow in its vicinity, which is shown in the image below.

While we don’t know many meteorological specifics about the storm, the flight data recorder (also called the black box) preserved the final minutes of NLM Flight 431 in great detail. The aircraft powered at about 280 mph into the lower part of the tornadic mesocyclone above the cloud base. What happened next is illustrated in the graphs below.

In just a few short seconds, the plane experienced wildly opposing forces far beyond its structural limits. The flight data recorder showed incredibly rapid and constant vertical changes in g-forces in both directions. The values plummeted to –2.5 g as it entered the circulation, then reversed almost instantaneously to +6.8 g. There was a second spike down and up again to +6.8 g, then back down to –3.2 g. These forces well exceeded what the passenger plane could withstand.

The graphs show an unnatural and brief spike in altitude of nearly a thousand feet. However, like most aircraft, the altimeter onboard relied on changes in air pressure to determine the altitude of the plane. As noted in the Meteorological Magazine, it’s likely that the rapid decrease of 29 mb is due to the low pressure of the tornado. The damage suffered and rapid vertical changes in wind speed and direction could have also influenced the data.

The final report from the Netherlands Aviation Safety Board stated (in translation), “the aircraft’s right wing was raised sharply at first bent and then, at the end of that acceleration, swung to…. Because this sweeping motion downward was accompanied by an extreme acceleration in the downward direction (- 3.2 g), the lower skin of the wing was buckled up. As a result, the structural integrity of the wing was lost, whereupon a large part of the wing broke off backwards in the upward direction.” The wing that was sheared off landed a little northeast of where it was torn away, in the water near the southern bank of the Hollands Diep.

The plane only took a few seconds to traverse the mesocyclone, but the damage was done. The aircraft inverted upside down and rapidly accelerated in excess of 400 mph. Eighteen seconds after losing its wing, NLM Flight 431 impacted the ground 1.5 miles SSW of Moerdijk in a field right next to a highway and raised railroad. It was utterly pulverized on impact, spraying shrapnel across the area and digging a crater in the soil. The explosive result sent a cloud of smoke into the air, which was seen in the final images from the police launch.

The crash site was at the edge of the Moerdijk industrial park, well under a mile from the heart of a sprawling Shell chemical facility. In the years since, operations have greatly expanded to within 170 yards of the impact point, as well as underneath the path of uncontrolled descent. Were this incident to happen in the present day, there would be a greater risk of harm on the ground. Below is a news report about the crash.

"Not a week goes by that I don't think about it. You don't realize it at the moment, but afterwards the accident made a big impression on me."

Bert Eestermans

In 1981, Bert Eestermans was a 23-year-old amateur photographer and a volunteer with the Moerdijk fire station. He was interviewed by Omroep Brabant, a Dutch public broadcaster, on the 40th anniversary of the tragic crash of Flight 431.

Storms had been brewing near Bert’s family home at Roodevaart. He had taken a position by the window on the upper wing of the house to take photographs. In a matter of a few clicks, he would wind up taking a picture of the “windhoos” that ultimately was to blame for the downing of The Fokker F28 Fellowship.

Not only did Bert see the tornado, he saw the impact. “The sky was green and black. I heard the sound of the jet engine and saw the plane spinning around. About four hundred meters away, the plane crashed. A little later, there was a huge explosion of ten thousand liters of kerosene. It caused such a mushroom, which you also see with an atomic bomb. I heard squeaking tires from motorists on the highway and after that it was quiet.”

Bert rushed to the fire station and joined his fellow comrades. They were the first at the scene. “We were able to put out some large pieces of wreckage, but we immediately saw that no one had survived the crash. Because of the huge blow, there were no recognizable human remains.”

Eestermans reflected back on a letter he had received from Germany. It was from the mother of one of the victims. She asked in the note if Bert would send her pictures of the crash site. And he did. “She was very happy with it, because she understood very well that her son’s grave was actually also here.” You can see his full 40th anniversary interview in the video below.

Numerous Dutch newspapers reported the details of the devastating accident days and weeks after it occurred. Bert was one of many eyewitnesses to the crash. Cor Scheffers, owner of the Roodevaart marina, was interviewed within an hour of the incident and his story is told in the October 7, 1981 edition of Limburgsch dagblad.

Scheffers was working in the marina’s canteen when he heard “a whistling sound.” He peered out the window and saw the aircraft’s broken wing spiraling out of control. “At first I thought the plane would end up on the canteen and ran away to the exit of the yard. When the aircraft landed on the ground, it exploded. A blowtorch of up to 150 m high could be seen. I was terribly scared.”

The newspaper expressed how shaken up Mr. Scheffers was while describing what he had witnessed. He said he returned to his office to report the crash to emergency services and then walked back outside. “When I came off the embankment and saw the wreckage, I knew it. No one could have come out of this alive. Between the splinters of the plane I saw pieces of human. A jaw, a piece of head, a hand. And also items of clothing, pants and a passport. And the most terrible thing was that I didn’t hear a voice. Just the crackle of fire. I kept looking for her people who had survived. I couldn’t understand it, something terrible had happened and no one could tell me anything about it. It was a graveyard.”

Chris Melissant from Klundert relayed what he saw on this fateful day in the October 7, 1981 edition of Algemeen Dagblad. “It was horrible, all the bangs and the noise. You could hear the lightning and at the same time, I think the plane exploded.” The paper reported that Melissant’s home was hit by parts of the jet. “A piece of metal from the plane ended up in our dog’s pen. I’ve never seen the animal so wild.”

The same news source quoted Jaco Bijl from Strijensas, who saw the crash from his house. “Suddenly I saw the plane coming down from the black wild storm clouds, spinning and spinning, with a plume of smoke behind it. When the plane hit the ground near Moerdijk, a huge explosion occurred, followed by a conflagration. Seconds after the plane crashed, another piece of the plane came down. It was a pretty big piece, I think it was the wing. “

The October 7, 1981 edition of Het Parool told the eyewitness story of antique dealer A. van der Meer. He had been standing outside watching the storms. “Actually it was a fantastic sight. I used to be a sailor and have seen a lot, but never anything like it. The sky above Moerdijk was inky black. You could see it raining in the distance and behind that shower was a kind of typhoon, which went with the rain. You could see the wind spinning in circles like a whirlwind. I was watching that with my daughter, when suddenly that plane emerged from the cloud cover. There was a piece of a wing off. Whether it was the left wing or the right wing, I don’t remember. For me, the plane was not struck by lightning, but ended up in the whirlwind. Over the radio I heard that the device was already exploding in the air, but that is definitely not the case. Only when it hit the ground were there two explosions.” After seeing the crash, Van der Meer drove to the accident scene. “What I found there was awful. I could see at a glance that no was helping with that anymore. Much of the wreckage was still burning. I drove back home because I thought: this is work for specialists. For an ordinary man like me, there was no more help to offer.”

Police, fire, and other emergency services arrived at the crash site within minutes. It was immediately apparent that there were no survivors. The main debris field was spread out over an area of 500 square meters. Several newspapers reported that relief efforts were hindered due to bad weather and darkness setting in. Hours after the crash, the plane’s black box was recovered in a field. Any documents that could be salvaged were saved for investigators.

The October 7, 1981 edition of NRC Handelsblad stated that the police had a “disaster identification team” of over 100 people. This team had the horrifying task of recovering portions of the plane and the victim’s remains, which were sent to Woensdreeht for identification.

There was immediate concern from the community about air traffic above the industrial park and specifically over chemical plants. “A flight path over an area with chemical industry significantly increases the risk of a major disaster. You have now seen again what can happen,” said Mayor Van Wouwe to NRC Handelsblad.

A few weeks later, a memorial was held at Koningskerk, a church in Amsterdam. The director of the NLM, Drs. A. Leyer, spoke, and the congregation’s male choir sang hymns. At a nearby cemetery, relatives of the victims paid their last respects. We list the names of the 18 deaths in the In Loving Memory section below. There were four crew members and 13 passengers representing four countries. The last fatality was a volunteer with the local fire department. He witnessed the crash, ran to get help, and then suffered a heart attack.

It is worth emphasizing again how astronomically unusual this disaster is. Tornadoes are small and short-lived, and the cruising altitude of passenger jets is far above their level. There have been other close calls between aircraft and twisters, but this is the only direct encounter that has been factually proven. Such events in modernized nations are even less likely now due to advancements in radar technology and early warning systems. Still, this tragedy serves as a reminder that weather should never be underestimated as a threat, and tornadoes, even at their very weakest, such as this, can kill if people are in the wrong place at the wrong time.