Today’s ETOPS certifications allow US carriers to fly to Hawaii from the mainland United States using narrowbody aircraft. However, these planes must be specifically certified for the operation to be permitted. Unfortunately, a scheduling mistake from American Airlines once resulted in a non-ETOPS-certified Airbus A321 traveling to the Hawaiian Islands from the US West Coast. //

ETOPS stands for Extended-Range Twin-Engine Operations Performance Standards, though some in the industry humorously refer to it as 'engines turn or passengers swim.' Its foundation stretches back to when piston-powered aircraft were widespread in the commercial aviation market. These engines were unreliable, so traveling too far from a diversion airport could have serious and deadly consequences for those onboard.

In response, the Federal Aviation Administration created its 60-minute rule. This regulation stated that any aircraft with two or fewer engines could not fly more than one hour from a diversion airport. //

As a result of modernized airline fleets, the FAA adjusted its standards for long-distance, over-water flying. It started by issuing certifications for individual twinjet aircraft to fly long-haul flights that extended up to 120 minutes from the nearest diversion airport. This regulation became known as ETOPS 120. Among the first to receive these ratings were the Boeing 767-200ER and Airbus A300. //

services to Hawaii were still required to be operated by aircraft with an ETOPS 180 certification, which is slightly higher than the 120-minute rule established for other operations. //

In 1995, the new Boeing 777 became the first twinjet to receive ETOPS 180 certification. In 1999, a major change occurred when the Next Generation Boeing 737 family received an ETOPS 180 rating. The Airbus A320 family followed suit in 2004. //

American operated its Airbus A321 on several routes to the islands from the US West Coast. These A321s were a mixed fleet, as some had the ETOPS 180 certification, while others were not approved to cross vast distances without a nearby diversion airport.

According to ch-aviation, on August 31, 2015, American Airlines flight AA31 was mistakenly operated by a non-ETOPS-certified Airbus A321. The service departed Los Angeles International Airport and was bound for Daniel K. Inouye International Airport in Honolulu, Hawaii. The mistake reportedly occurred 12 days after the A321 was first deployed on the route.

An employee discovered that the aircraft involved, N137AA, was not ETOPS-certified while the aircraft was in flight. They notified American Airlines management, which then informed the FAA of the problem. Despite the mistake, the A321 touched down in Hawaii uneventfully but was ferried back to the mainland without passengers. //

There are minimal differences between a non-ETOPS-certified and ETOPS-certified A321, the latter simply having auxiliary fuel tanks to extend range in the event of a diversion. Additionally, extra medical equipment and fire suppression tools must be onboard and accessible to the crew.