Singapore – Singapore has moved ahead with plans to order aerial refueling tankers to replace its Boeing KC-135Rs.

Industry sources say Singapore has issued a request for information (RFI) for six tankers. One source says a request for proposals (RFP) may be issued by midyear.

The Southeast Asian nation has four Boeing KC-135R aerial refueling tankers, the first of which the island nation received in late 1999. These aircraft are in fact A-model KC-135s that Boeing upgraded to R-model by re-engining the aircraft with new CFM International CFM-56 power plants.

Industry sources say new aerial refueling tankers are a top priority for the Singapore Air Force, which has been complaining about the cost and difficulty involved in maintaining the KC-135R. This tanker is based on the Boeing 707 commercial platform.

One source says the reason Singapore’s KC-135Rs may be difficult and costly to maintain is because the aircraft are a lower block standard than the U.S. Air Force’s.

At the recent Singapore Airshow, Airbus Military displayed a U.K. Royal Air Force A330MRTT. Israel Aircraft Industries was also at the show promoting its 767 Multi-Mission Tanker Transport, and Boeing was promoting its KC-46 aerial refueling tanker.

Boeing would ordinarily be the front runner in the competition because of Singapore’s close ties with the U.S. But the KC-46 is still in development. Boeing is already committed to deliver 18 KC-46As to the U.S. Air Force by 2017, leaving no early delivery slots for foreign customers. The earliest Boeing can delivery KC-46s to international customers is 2018, and that may be too late for Singapore.