What is a fuel imbalance and why did it force a Delta flight to turn around mid-air?

A Delta flight had to make a U-turn over the Atlantic after the crew realized there was a fuel issue.

The plane took off from John F. Kennedy International Airport.

What is a fuel imbalance? 

A fuel imbalance is when the amount of fuel between the left and right fuel tanks in the wings of an aircraft is not equal.

Variations in the performance of fuel system components, component faults, and fuel leaks are the most frequent causes of these occurrences.

The fuel system can be isolated to the left and right sides of the plane, making it easy to fix. An inspection of the fuel tanks would be required for a four-engine Boeing 747.

What happens when there's a fuel imbalance?

When the imbalance reaches a certain level, the crew on Boeing plans is notified.

The crew will move fuel from one tank to the other if they can confirm there is no leak. The same balancing procedures should be used if the warning sounds again.

The Delta flight was turned around if the fuel tanks weren't balanced.

Some people might find the experience frightening, like this YouTuber who said he was "sobbing" in his seat and thought he was going to die, but pilots can decide to keep flying.

If proper maintenance procedures have failed to identify a cause, but no external fuel leaks, internal fuel leaks from a pressurized line, or other system component failures are indicated, continued operation of the airplane may be acceptable.

This is acceptable until the earliest available opportunity when more detailed repairs can be performed.

According to Boeing, the most recent fuel issues have been on the 757 and 912 models.

The plane that Delta was flying on was an older plane.