An investigation has been launched after a plane plunged towards the sea before managing to pull back into a climb just 400ft from the sea.
The Boeing 737 MAX 8 plunged at a maximum descent rate of about 4,400ft per minute off the coast of Hawai on April 11.
The Federal Aviation Administration is investigating the incident with the Southwest Airlines flight. It happened after poor weather conditions forced the pilots to bypass a landing attempt.
While circling back to land, the first officer "inadvertently pushed forward on the control column while following thrust lever movement commanded by the autothrottle", according to a memo sent out to pilots.
The memo also described how the plane briefly dropped at "an abnormally high rate of more than 4,000 feet per minute" before pilots managed to pull up to avoid the crash. The flight crew performed a "roller coaster manoeuvre" to avoid a devastating crash, Bloomberg reported.
"We are investigating this incident," the FAA released in a statement.
The memo said that crew received a "DON'T SINK oral warning" followed by a "PULL UP oral warning" but the first officer later said the crew did not hear the warnings. Thankfully there were no reports of injuries.
It comes after Boeing 737 Max suffered damage to parts of the plane’s structure after it went into a “Dutch roll” during a Southwest Airlines flight last month, U.S. investigators said.
The incident happened as the jet cruised at 34,000 feet from Phoenix to Oakland, California, on May 25, but Southwest did not notify the National Transportation Safety Board about the roll or damage to the jetliner until June 7, the NTSB said.
“Following the event, SWA performed maintenance on the airplane and discovered damage to structural components,” the safety board said.
The NTSB comment could suggest that the incident was more serious than previously known, but aviation experts said it was too soon to know for sure.
A Southwest spokesperson said the Dallas-based airline is participating in the investigation. He declined further comment.
A Dutch roll is a combination of yaw, or the tail sliding side to side, and the plane rocking in a way that causes the wings to roll up and down. The name comes from the way the rhythmic, swaying movement resembles a form of ice skating that was popular in the Netherlands.
The pilots later reporting seeing how severe the incident was through animated recreations, "was a significant, emotional event," the Southwest memo said.
“It’s just a part of aerodynamics,” said John Cox, a former airline pilot and now an aviation-safety consultant. “What you feel in the back is that the airplane sort of wallows.”
Pilots train to recover from a Dutch roll, and most modern planes include a device called a yaw damper that can correct the condition by adjusting the rudder. A preliminary report by the Federal Aviation Administration said that after the Southwest plane landed, damage was discovered to a unit that controls backup power to the rudder.
The damage was described as “substantial.”
Cox said the structural damage likely occurred in the plane’s tail fin, where the power units are housed. He was baffled that the backup unit would be damaged because normally it would not be activated during a Dutch roll.