An American Airlines commercial passenger flight to Hawaii from Los Angeles in late August was at about the halfway point when airline officials realized they had sent the wrong plane.

American Airlines spokesman Casey Norton said planes that fly long routes with no suitable landing areas on the way, such as the Los Angeles-Honolulu route over the ocean, require certification known as ETOPS (Extended-range Twin-engine Operational Performance Standards).

The plane headed to Hawaii on Aug. 31 was not ETOPS-certified, although its fuel tanks, engine and range of flight ability were the same as an ETOPS-certified plane, Norton said. “There were a couple of minor differences with the aircraft,” he said.

Norton said ETOPS-certified flights require extra medical oxygen canisters and a fire suppression canister in the cargo hold that can fight fires for an extended duration.

Flight 31 continued to Honolulu after officials assessed the situation, Norton said. “The flight took off and landed safely,” he said.

The airplane returned to Los Angeles without passengers. Norton said passengers scheduled to be on the return flight were accommodated on other airlines and American Airlines flights.

Federal Aviation Administration spokesman Allen Kenitzer said Sunday that the FAA is looking into the matter but declined to discuss the details.

In the aftermath of the mistake, the airline has updated a software program that aims to ensure the correct airplane is operating on the appropriate route.

“We’re going over our policies and procedures with the FAA to see if there is anything else we need to do,” Norton said.

American Airlines has been flying the Airbus A321S for some time on the mainland and began flying the Airbus A321H to Hawaii on Aug. 18, Norton said. Both planes have the same number of life vests and rafts, and the same engine range, he said.

Blogger Brian Sumers, who is credited with breaking the story, said on his website (briansumers.com): “This wasn’t necessarily unsafe — both versions of the A321 are essentially the same aircraft … but this is a major violation of federal guidelines.”