A Boeing 737 jet owned by Southwest Airlines has been grounded amid a Federal Aviation Administration (FAA) investigation into a rare mid-air manoeuvre called a “Dutch roll” that occurred mid-flight.
The plane was travelling from Phoenix, Ariz., to Oakland, Calif., on May 25 when the yawing movement occurred nearly 32,000 feet (almost 9,750 metres) in the air.
According to a 2022 Boeing safety pamphlet about Dutch rolls, the motion occurs when a plane moves in two axes as it tips from wingtip to wingtip while the tail rocks side to side. A Dutch roll can be caused by both wind and pilot input, but is nauseating for passengers in either circumstance.
Federal officials said the Dutch roll may have been caused by damage to the jet’s backup power-control unit (PCU), which commands the jet’s vertical rudder.
The damage was discovered during a post-flight inspection of the aircraft.
The Boeing 737 has been grounded since the flight. An FAA incident report revealed there were 175 passengers and six crew members onboard Flight N8825Q.
No injuries were reported, and the plane landed safely in Oakland after pilots were able to regain control of the Boeing 737 following the Dutch roll. The FAA has declared the incident an accident, and Boeing has declined to comment about the incident.
Authorities said the damage to the jet is “substantial.”
Federal officials told CBS News there have been no other reports of similar issues at other airlines. Southwest has not experienced the problem among any other aircraft in its fleet.
The Aviation Herald, which was first to report of the Dutch roll, said the affected 737 has been “ferried” to Boeing’s plant in Everett, Wash., for repairs.
It is not clear what caused the loss of control during the Southwest Airlines flight.
News of the Dutch roll is only the latest drama for Boeing, which was subject to FAA probes and mass groundings after one of its 737-9 Max jetliners suffered a blowout of a fuselage panel in January. The incident and subsequent Boeing issues shook public trust in the company.
Boeing remains under several investigations.
In a report from the company in May, Boeing said it is dedicated to safety and is continually innovating safety trends using machine-learning algorithms that are designed to identify problem areas. Boeing reported it is making changes to address recommendations from an FAA panel.
What is a Dutch roll?
Dutch rolls are caused by any asymmetric input that triggers oscillation.
Boeing described a Dutch roll as being similar to ice skating.
“Ice skaters use the outer edge of their skates to propel themselves across the ice, rocking from side to side while also moving to the left, then to the right and back again,” the company wrote.
“Just as skaters avoid swaying too far and losing their balance, airplanes are designed to keep roll (the lateral movement of the plane) and yaw (the directional movement of the plane’s nose) within regulatory requirements to ensure safety — and potentially reduce the risk of air sickness.”
As of this writing, no passenger on the affected flight has publicly spoken out about the incident.