The government has begun the necessary procedures to retire in fiscal 2018 two government Boeing 747-400s, as maintaining them is expected to become difficult due to changes in the planes used by major airlines, sources said.

The government is believed to be considering replacing the jumbo jets, which were first introduced in 1991, with state-of-the-art midsized Boeing 787s.

Japan Airlines, which performs maintenance on government planes, retired its Boeing 747s last fiscal year. According to government sources, JAL told the government it could only service the government planes until fiscal 2018.

Since All Nippon Airways also plans to retire its Boeing 747s, the government is believed to have judged it would be difficult to continue using the jumbo jets.

In November, ANA started using Boeing 787s in its commercial service, and JAL also plans to introduce the model.

The energy-efficient Boeing 787 can fly as far as large aircraft: about 15,000 kilometers. Maintenance services will be readily available in Japan, and the government is said to regard the model as "semi-Japan-made" as about 35 percent of the airplane's parts are manufactured in Japan.

More than 40 billion yen is expected to be needed to purchase two Boeing 787s.

But to introduce the planes in fiscal 2019, the government needs to make a final decision by the end of this year and appropriate procurement expenses in the fiscal 2013 budget, due to the extra time needed for ordering, delivery and operational training.

Some in the government oppose purchasing the sophisticated Boeing 787s given the tight state finances. Such opponents say used aircraft or chartered planes would be sufficient.

But many in the government strongly believe such ideas are "unrealistic," as a senior government official put it.

It may be difficult to secure maintenance bases for used aircraft, while chartered commercial planes cannot be installed with special communications scramblers.