WASHINGTON, Dec. 8 (Xinhua) -- After U.S. President-elect Donald Trump on Tuesday criticized the new generation of Air Force One too expensive, reports showed that building the U.S. presidential plane seems to hold firm reasons for the cost.

The current Air Force One is actually a modified Boeing 747-200 with a length of 70.6 meters and a wingspan of more than 59.6 meters to satisfy the special needs of the U.S. leader.

Dubbed as the "flying Oval Office," the three-leveled plane has 400 square meters of floor space and boasts a conference room, a dining room, a private quarters for the president, offices for senior staff members, a press area, a medical operating room with a doctor on every flight, two food galleys that can serve 100 guests, and sophisticated communication systems, according to Boeing.

Under a contract with the government, Boeing is building new presidential planes based on the model of 747-8 which is bigger and better, but the budget for the Presidential Aircraft Recapitalization program puts the price tag at 2.9 billion dollars.

Given that the U.S. president needs two official planes to secure his demand in case one is in maintenance, and the new generation expects bigger space and better equipment, the budget is projected around 4 billion dollars.

This is what Trump is unhappy about. He said the costs are out of control and asked to cancel order in his tweets on Tuesday.

However, Mark Cancian, a senior adviser at the Center for Strategic and International Studies who is familiar with U.S. defense acquisition, told The Wired reporter that the figure "looks reasonable."

The replacement of current Air Force One is expected to upgrade all the electrical systems to military grade and have twin backup power systems, military communications equipment and a "self-defense system," according to local reports.

All those are costly and take years to develop and integrate.

The White House expects the updated presidential plane to come into service by 2023, which means it will be the future president to carry forward the program.

Trump himself owns a Boeing 757-200, which is reported to have luxury interior design but is smaller in every dimension than Air Force One.