On Aug. 2, a Boeing 787-8 took off from Seattle. It flew across the US on a flight path in its own shape: wings, fuselage, tail fins, and all. Then it landed back at Seattle 18 hours later.

Without context, this seems like a publicity stunt. The distance covered in the flight is estimated to be about 25,400 km (15,800 miles). By one estimate, the 787-8 dumped more than 300,000 kg of carbon dioxide in the process.

No one person saw the shape it drew. The only record of the flight appears on sites like FlightAware.

The endeavor was not a complete waste. A Boeing spokesperson told Quartz that today’s flight was to test the endurance of new engines and it was required by regulatory agencies. “Rather than fly in random patterns, the test team got creative and flew a route that outlined a 787-8,” he said.

Boeing has traced such unusual flight paths before. In 2012, another 787 traced the Boeing logo. ”This wasn’t a joy ride,” Boeing’s vice president of marketing Randy Tinsmith wrote on the company blog. “It was an 18 hour… flight test for a 787-8 with GE engines. Our team coordinated with the many air traffic control centers, choosing the routing to avoid restricted airspace.”

Earlier this year, Boeing 737 MAX traced “MAX” across the sky to test that it could fly for nine hours straight. “The flight was to be further bounded by a working range within the Seattle and Salt Lake Air Route Traffic Control Centers’ airspaces to minimize administrative workload,” said Boeing’s flight test engineer Andreas Weisweave on the company blog.

This post has been updated with a comment from Boeing. Also, the original story mistakenly said the emissions from the flight were 300,000 metric tons, instead of 300,000 kg. We apologize for what was clearly not a rounding error.