Investigation underway into rare, dangerous Boeing 737 Max rollover – Boston News, Weather, Sports

(CNN) — Federal authorities and Boeing are trying to determine why a rare, unsafe rollover of a 737 Max 8 occurred during flight.

The oscillating motion is known as a “Dutch roll” and a characteristic described by the Federal Aviation Administration (FAA) is the shape of a figure eight through the nose of an aircraft.

There were no injuries on board Southwest Airlines Flight 746 on May 25, according to the airline and a preliminary report from the FAA. The report said the crew “regained control” and the plane landed safely.

However, the aircraft sustained “significant” damage and the FAA classified the incident as an “accident.” The FAA report said an inspection revealed “damage to the standby PCU” (power control unit), which controls the rudder.

It is unclear whether the damaged unit was the cause of the throw or a consequence of it.

The plane has not flown since landing in Oakland, California, following the incident, except to take it to a Boeing facility in Washington state. Boeing did not immediately comment to CNN.

Southwest told CNN that the incident had been referred to the FAA and National Transportation Safety Board and that it was participating in and assisting with the investigation.

The incident occurred nearly three weeks ago and was added to the FAA’s database this week. According to the airline, there were 175 passengers and six crew members on board.

The NTSB confirmed that it has opened an investigation into the incident. Investigators have downloaded data from the flight data recorder that “will help investigators determine the duration and severity of the incident.”

Voice recordings from the Voice Data Recorder – the other of the so-called black boxes – were overwritten.

In February, the FAA required airlines flying 737 Max 8 and similar planes to check the rudder assembly for loose or missing nuts, washers and bolts. It said the deficiency would prevent pilots from controlling the rudder with foot pedals. Authorities have not said whether that condition and the Dutch roll last month are related.

An unusual movement

Most passengers have never felt this movement of an airplane – and most pilots have never experienced it in flight.

“It’s very opaque,” aviation safety analyst and former pilot Kathleen Bangs told CNN. “It’s a very uncomfortable movement and you can feel the tail swinging around.”

During forward motion in flight, aircraft can pivot about three axes: the nose of the aircraft goes up and down (pitch angle), the wings descend or rise (roll angle), and the tail shifts left or right (yaw angle).

Commercial aircraft turn using a usually seamless combination of roll and yaw, coordinated by the aircraft’s computers. These large aircraft also have yaw dampers that make small adjustments during flight.

The Dutch roll is when the plane rolls and yaws excessively. Passengers will feel the plane shifting to one side and then back to the other — moving back and forth, Bangs said.

She said pilots train for scenarios where their yaw dampers fail. They could take a flight simulator to high altitudes and turn off the yaw damper.

“Then you step really hard on a rudder pedal in the simulator to try to initiate (the roll),” Bangs said.

To get out of a Dutch roll, pilots can slow the plane and descend into denser air. Modern commercial aircraft are designed to be naturally stable in the air, she said, so the plane can return to level flight with minimal additional effort.

But the forces can be enormous. In 1959, four of the eight passengers on a Boeing 707 test and training flight died shortly before Washington DC after the aircraft made an extremely steep roll.

“The aircraft immediately spun and rolled violently to the right,” said a report from the Civil Aeronautics Board, which investigated the incident. “Several spins followed and after control of the aircraft was regained, it was discovered that three of the four engines had separated from the aircraft and it was engulfed in flames.”

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