The US government awarded a $4.49 billion interim contract to Lockheed Martin on 7 July for 91 F-35 fighters.

The undefinitized contract action (UCA), which has a $5.57 billion price ceiling, allows Lockheed to continue producing aircraft until a the low-rate initial production Lot 11 contract is finalised.

The figure does not represent the unit price, which will be settled when the deal is completed. But the overall contract value to Lockheed and suppliers should hover around at least $13 billion for 141 airframes and engines.

The contract value for Lot 10 amounted to $8.9 billion for 90 airframes and engines .

“We are confident that the final negotiated Lot 11 aircraft unit prices will be less than Lot 10,” the JPO says in a statement.

The Defense Department is also negotiating a separate contract with F-35 engine supplier Pratt & Whitney. The Joint Programme Office expects to complete both LRIP 11 negotiations by the end of 2017, a JPO spokesman says in a statement.

Lot 11 will ultimately procure a total of 141 F-35 with deliveries slated between 2019 and 2020, according to the JPO.

The contract includes 91 US F-35s, 28 jets for international partners and 22 foreign military sale aircraft. The US buy includes 63 aircraft requested by the Pentagon, with an another 28 added by Congress. At the end of July, the JPO will modify the UCA to obligate $2.28 billion for 50 purchased by foreign governments.