A fighter jet and a helicopter operating from the aircraft carrier USS Nimitz both went down in the South China Sea within half an hour of each other, according to a statement from the Navy’s Pacific Fleet.

On Sunday afternoon, the MH-60R Sea Hawk helicopter’s three crew members were successfully rescued. Additionally, the two pilots aboard the F/A-18F Super Hornet fighter jet ejected safely and were recovered. The fleet confirmed that all five individuals are in a stable condition.

The statement noted that investigations are underway to determine the causes of the crashes.

President Donald Trump, during a conversation with reporters on Air Force One headed to Tokyo on Monday, suggested “bad fuel” might be to blame for the incidents. He dismissed any notions of foul play, assuring the public that there was “nothing to hide.”

The USS Nimitz is making its way back to its home port at Naval Base Kitsap in Washington state. This follows a deployment to the Middle East throughout most of the summer, part of the U.S. response to the Houthi rebels’ attacks on commercial vessels. This mission marks the final deployment of the Nimitz before it is decommissioned.

In recent months, another aircraft carrier, the USS Harry S. Truman, has faced a series of operational challenges while stationed in the Middle East.

In December, the guided-missile cruiser USS Gettysburg mistakenly shot down an F/A-18 jet from the Truman.

Then, in April, another F/A-18 fighter jet slipped off the Truman’s hangar deck and fell into the Red Sea.

And in May, an F/A fighter jet landing on the carrier in the Red Sea went overboard after apparently failing to catch the steel cables used to stop landing planes and forcing its two pilots to eject.

No sailors were killed in any of those mishaps. The results of investigations into those incidents have yet to be released.