Musk first signed up for the free “privacy ICAO aircraft address” program, also known as PIA, through the Federal Aviation Administration in 2022, but hadn’t used it since August 20, 2022.

The special program allows private jet owners to fly cloak their travels using a temporary aircraft registration number. In 2022, Musk applied for a new aircraft registration number four times, JetSpy told Business Insider.

The FAA first launched PIA in 2019. Last year, the FAA told BI it had about 390 alternate ID codes since the program began.

A representative for Musk did not immediately respond to a request for comment.

Mark Dombroff, a partner and aviation attorney at Fox Rothschild LLP and a former FAA lawyer, told Business Insider that it’s unclear why Musk would begin using the program again, as the FAA has yet to make any apparent changes to it that could further benefit Musk.

Jet-tracking personality Jack Sweeney was the first to point out Musk’s new PIA. The college student, who gained popularity for his social media accounts that track celebrities, including Musk and Taylor Swift, pointed out that Musk’s team appeared to face some hiccups using the program.

The PIA program is far from perfect. According to the FAA, it allows aircraft owners to switch out their registration numbers every 20 days, but it can be a laborious process.

Christian Renneissen, Collins Aerospace’s manager for flight deck connectivity, previously told the trade publication AV Buyer that while the PIA program is essentially free, it’s a hassle due to a substantial amount of paperwork. What’s more, the entire process would have to start all over again if the new registration number is exposed and tied to the owner.

Planes are also required to ditch the PIA for their permanently assigned ICAO address when they fly internationally.

“The PIA program limits the ability to identify an aircraft in real-time using inexpensive, commercially available receivers,” an FAA spokesperson previously told BI. “This does not prevent parties from using alternative methods (plane spotting, movement correlations, etc.) to identify PIA participants.”

However, growing security concerns from the likes of Musk and Swift prompted the FAA to further its camouflage efforts, thanks to new language in the FAA Reauthorization passed in May. This includes adding PIA protections for international flights, among other privacy enhancements.

But it’s still likely not enough to fully block private planes from the public view. Sweeney previously told BI that celebrity private aircraft can still be spotted using context clues, such as the airports their jets commonly fly from.