The US Air Force estimates it would cost more than $1.7 billion over 11 years to upgrade 34 Lockheed Martin F-22s from a training configuration to a fully modernised, operational status, according to a USAF report sent to Congress.

The August report, recently obtained by FlightGlobal, outlines the estimated cost and schedule to bring 31 Block 20 Raptors supporting pilot training and another three Block 20 aircraft supporting flight test to the combat-coded Block 30/35 configuration.

Block 20 aircraft would need at least four generations of upgrades -- and perhaps more -- to keep up with the combat-coded fleet if installation kits are funded after 2025.

Since the Block 30/35 F-22 fleet entered service in 2005, the USAF has introduced a fourth generation of the Northrop Grumman APG-77 radar in the Common Configuration programme, new air to ground weapons and radar modes under Increment 3.1, new air-to-air weapons during the ongoing Increment 3.2 and planned communications upgrades called TacLink 16 and Tactical Mandates.

The USAF also plans to introduce a helmet-mounted cueing system for weapons and a "billion dollar" sensor upgrade for the Block 30/35 fleet, the report says.

Though still in development, the service plans to field TACLink 16 and TACMAN on Block 30 and 35 aircraft in fiscal year 2021 and 2022 respectively. The USAF recommends including TACMAN and TACLink 16 in the update to avoid creating a split fleet configuration.

The tactical updates cost almost $8 million more per aircraft, bringing the price per aircraft to $50.5 million.

Some of the cost estimates could change because production has stopped for many of the key components, such as the fourth-generation APG-77 that the USAF introduced with the common configuration upgrade.

Another option could leverage parts from the Lockheed F-35's APG-81 radar, which is also supplied by Northrop, the report says. But the USAF’s analysis did not consider integrating F-35 radar components.

“This will require additional analysis and is an area that would be explored further at the beginning of the upgrade programme,” the report states.