The Nigerian Airspace Management Agency (NAMA) has explained why United Airlines chose to make an air return to Nigeria.

In a statement on Wednesday, Abdullahi Musa, NAMA’s director of public affairs and consumer protection, said the decision to return to Nigeria was made by the pilot based on his assessment of the situation and the perceived safety of landing at the departure airport.

The US National Transportation Safety Board is investigating a United Airlines Holdings Inc. flight that turned back to Nigeria after a “sudden aircraft movement” occurred, injuring passengers and crew.

The U.S. National Transportation Safety Board said on Monday it is investigating a United Airlines flight on Friday from Lagos, Nigeria to Washington D.C., in which a sudden aircraft movement led to injuries of passengers and cabin crew.

The authorities in Nigeria said that the United Airlines plane had to return to Lagos after the episode. Six people were treated at a hospital, officials said.

United Airlines said it was cooperating with U.S. and Nigerian investigators to determine what exactly happened on the flight.

Six people were taken to hospital, and many more were injured after a United Airlines flight from Lagos heading to Washington D.C. experienced a sudden in-flight movement. The United States has opened a probe into the unexpected movement, as the cause is still unknown.

A United Airlines flight was traveling from Lagos to Washington, D.C. when it experienced "sudden aircraft movement."