A cheeky pilot tasked with testing a new engine has literally spelled out his boredom for all the world to see.

Asked to fly for two hours along the South Australian coastline, the instructor traced "I'M BORED" in kilometre long letters, clearly visible to those watching on flight trackers.

The pilot took off, tasked with running-in a plane's engine for two hours before it was used for training on Tuesday.

And while the flight path didn't attract much attention at the time, it has now.

The tracking image shows the pilot conducted a series of manoeuvres over South Australia's mid north, to first draw two phallic images.

The aircraft is operated by Flight Training Adelaide, based at Parafield Airport north of Adelaide.

It's director says he doesn't condone the pilot's actions.

But one pilot 9News spoke to - from a competing business at Parafield - said it appeared harmless.

He said it was most likely achieved by carefully plotting the flight path using the autopilot.