There are a number of aviation phenomena that pilots learn about to keep themselves and their passengers safe. Many of these, such as the Dutch role, are not known to the uninitiated. A Dutch roller is named after a maneuver that skaters in the Netherlands are known for: swinging from side to side at the outer edge of the blade, while also moving back and forth from right to left. Dutch rolls in the air are usually caused by high wind speeds. If this happens, it can damage the tail and fuselage of the aircraft.

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Dutch rolls are potentially dangerous and have caused disastrous incidents in the air. Commercial aircraft have a system known as the yaw damper that can soften the effects of Dutch roll. If an aircraft is not equipped with a yaw damper, pilots are trained to reduce the effects of the maneuver, just as they are trained to both fly in and avoid extreme weather.

But what exactly is a Dutch sandwich? Ken Byrnes – assistant dean, associate professor of aeronautical sciences and chairman of the Flight Department at Embry-Riddle Aeronautical University in Daytona Beach, Florida – told USA Today: “Dutch roll is when the aircraft experiences a rolling motion that is primarily driven by the design … of the wings, while simultaneously yawing due to the adverse yaw effect caused by the sideslip angle. This coupled motion results in a dynamic instability where the aircraft oscillates in both the roll and yaw directions.

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Although the Dutch role is not common on commercial aircraft, that does not mean it never happens. Last May, a Boeing 737 MAX on a Southwest Airlines flight from Phoenix to Oakland, California involuntarily performed a Dutch roll. The plane managed to land safely without injuring its 175 passengers and six crew, but a post-flight inspection revealed significant damage to the tail, rudder and a system that drives the rudder.

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However, Newsweek reported in July that the National Transportation Safety Board’s preliminary report blamed bad weather on the ground for most of the damage to the plane. A storm in New Orleans a few days before the plane left Phoenix had winds of 80 miles per hour, and at the time the Southwest plane was parked at the city’s airport. There the rudder could have been whipped back and forth repeatedly until the storm finally passed. John Cox, a safety consultant and former pilot, told the Associated Press that there was no way a Dutch role could have caused such significant damage to the plane.

Boeing’s 737s are generally not sensitive to Dutch roles. If there’s one thing you need to know about the 737, it’s that they are built in such a way that the pilot can’t do anything and the plane will correct itself on its own. Yet this was one of the happiest flights in Dutch rolling history. A few others show it how dangerous this air problem can be.

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On May 3, 2013, three U.S. Air Force airmen from the 92nd Air Refueling Wing were killed in a mid-air explosion after the KC-135 they were on performed an involuntary Dutch roll. During takeoff, the aircraft experienced a system failure that caused the nose to move back and forth. The crew was unable to diagnose the problem due to a lack of information in the on-board manual and insufficient training, causing the pilot to proceed with the planned mid-air refueling mission. When he made a simple left turn, the Dutch roll became heavier.

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No restoration of aircraft stability was possible at this point. Normally using the rudder to make a turn exacerbated the stress on the KC-135’s airframe, causing the tail section to separate from the rest of the aircraft, which exploded. According to the Air Force, Brigadier General. General Steve Arquiette, leader of the Accident Investigation Board, concluded: “The crew was confronted with a condition that they had not realistically experienced during training, and when paired with decisions based on their relatively low recent experience levels, they were facing an unrecognized dangerous and difficult situation to overcome.”

This crash should not have happenedas the aircraft was a KC-135R, which had new systems to prevent Dutch rolls. Researchers at McConnell Air Force Base in Kansas tried to recreate the flight conditions with simulators, but failed. After this tragic event, air force crews received more training in rediscovering Dutch roles.

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In 1978, Boeing performed some maintenance on a Japan Airlines 747 after it landed at Osaka’s Itami Airport and suffered a tail strike, with the tail hitting the runway. The repairs included connecting the lower half of the aft pressure bulkhead to the upper half. Seven years later, Boeing’s work would be deemed flawed after it led to the deadliest crash in history of a single aircraft that had experienced a Dutch role.

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When the 747 reached a cruising altitude of 7,000 meters en route from Tokyo to Osaka, the rear pressure bulkhead – the part of the plane that Boeing had been working on – ruptured, causing the cabin to drop in pressure. This ultimately separated the Auxiliary Power Unit and part of the tail cone from the aircraft, causing extensive damage to the vertical stabilizer. Soon there was no control over the hydraulic systems, causing the aircraft to enter a Dutch roll, coupled with phugoid movements, in which an aircraft alternately rises and descends, up and then down. This took about 32 minutes.

After only more than 40 minutes in the air, JA8119 Flight 123 crashed into Mount Osutaka, northwest of Tokyo. 520 people died in the crash. Only four survived, and they had serious injuries.

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