A federal investigation is underway after a Southwest Airlines flight plunged toward the ocean off the coast of a Hawaiian island.

The incident occurred April 11 aboard Southwest Flight 2786, but only came to light publicly on Friday after Bloomberg reported Southwest sent a memo to pilots about the incident. Bloomberg reported the memo indicated a “newer” first officer was flying at the time and inadvertently pushed forward on the control column.

Flight tracking data from ADS-B Exchange shows the plane dropping at a rate of more than 4,000 feet per minute while only 600 feet above sea level. The Boeing 737 Max 8 flew as low as 400 feet before rapidly climbing.

“Nothing is more important to Southwest than Safety,” the airline said. “Through our robust Safety Management System, the event was addressed appropriately as we always strive for continuous improvement.”