This morning in a post to Twitter, President-elect Donald Trump lambasted the ongoing program to build a new presidential aircraft, calling for its cancellation:

Boeing is building a brand new 747 Air Force One for future presidents, but costs are out of control, more than $4 billion. Cancel order! — Donald J. Trump (@realDonaldTrump) December 6, 2016

The Air Force One replacement contract, awarded in February 2016 to Boeing, is for two 747-8 aircraft equipped for the chief executive's travel and communications. The current pair of VC-25A aircraft that serve as Air Force One—two heavily modified Boeing 747-200B jetliners—are the last of their kind and have been in service since 1990. There are no 747-200 aircraft in commercial service anywhere in the world, making logistic support for them expensive. "Parts obsolescence, diminishing manufacturing sources, and increased down times for maintenance are existing challenges that will increase until a new aircraft is fielded,” Secretary of the Air Force Deborah Lee James said of the existing aircraft when the Boeing contract was announced.

The 747-8 has a longer range, greater maximum take-off weight, and higher top airspeed than the 747-200 that it is intended to replace, as well as better fuel efficiency and lower carbon dioxide emissions. Capable of Mach 0.855, according to Boeing, the 747-8 is the fastest commercial jet in the world. However, the modifications required for a presidential aircraft are extensive. The VC-25A version of the 747-200 is capable of in-flight refueling, carries a full communications suite, and is "self-sufficient" at airports (having its own self-deploying "air stairs" and baggage handling equipment).

The initial contract award in February was for $25.8 million, with the total cost estimated by the Air Force to be as much as $1.65 billion over the full development, construction, and testing cycle. But the new Boeing aircraft aren't expected to enter service until 2024—nearly a full two presidential terms from now. The $4 billion figure apparently is an inflation of a GAO figure placing the cost of the Presidential Aircraft Recapitalization (PAR) program—the official name of the Air Force One replacement contract—at $3.2 billion.

Ars contacted Boeing and Air Force officials for comment. An Air Force spokesperson said that the service was gathering numbers on the program for a response, and a Boeing representative said that a response would be forthcoming. This story will be updated as those details become available.

Update, 3:30 PM ET: Trump commented on the contract further today in a brief exchange with press at Trump Tower in New York, saying, "The plane is totally out of control" and that Boeing was "doing a little bit of a number—we want Boeing to make money, but not that much money."

The Washington Post's Philip Bump speculated that Trump may have made the comments out of anger with Boeing CEO Dennis Muilenberg, who shared his concerns about Trump's views on trade policy with the Chicago Tribune in an article published this morning.