LONDON — A Royal Air Force C-130J Hercules is set to take to the air in the next few days to recommence trials of a major upgrade to the aircraft that is so late it has already been rolled into a subsequent improvement program.

Fitted out with an extensive suite of software and hardware improvements known as Block 7, the British C-130J kit installation trials aircraft is set to undertake months of operational test and evaluation (OT&E) work ahead of being further modified by prime contractor Lockheed Martin with additional capabilities known as Block 8.1.

A Ministry of Defence spokesman said it is planned to complete the British flight trials on the Block 8.1 improvements are set to be completed in 2019.

The updates are crucial to the British and other C-130J fleet operators around the world as they provide additional operational capabilities for special operations forces and others.

Communications, air traffic management, navigation and surveillance capabilities are among the enhancements.

The modifications will also allow operators to meet the latest civil air traffic management regulations. Without the update, C-130J aircraft will not be able to effectively operate in prescribed airspaces.

Delays to the Block 7 program resulted in members of nations in the C-130J joint users group opting to merge the Block 7 updates into the later Block 8.1 update

Lockheed Martin said the "Block 8.1 development is on schedule."

All seven members of the users group — including Australia, Canada, Denmark, Italy, Norway, the UK and the US — are contributing to the development, evaluation and trial kit installation phases of the program, the contractor said in a statement.

The Hercules about to restart flight tests for the British was first fitted out as a trial kit installation aircraft for Block 7 in 2012. But following a flight to Lockheed Martin facilities in the US, the machine was became marooned for around two years for technical reasons and eventually returned to Britain without undertaking the tests that which would have triggered the production phase of the Block 7 update for the Royal Air Force.

A British MoD spokesman said the aircraft was eventually returned to Britain after "the UK Block 7 trial kit installation aircraft underwent a graduated release to test flight process and subsequently returned to the UK under a Qinetiq airworthiness release."

Since the return of the aircraft last year, the MoD said work has progressed on Block 7 with the "first flight scheduled in early May."

The aircraft is based at the MoD Ministry of Defence aircraft test airfield at Boscombe Down in southwest England.

"The aircraft is about to commence a period of OT&E flying and once this is complete the expectation is that the aircraft will return to Lockheed Martin to become the UK Block 8.1 trials kit installation aircraft before returning to the UK for Block 8.1 OT&E flying. Following this, it is expected that Block 8.1 aircraft will receive a release to service."

The British MoD said that "following trials of the Block 7 capability, we anticipate the aircraft will be modified to Block 8.1 standard by the end of 2017, with flight trials completing in 2019 prior to final acceptance by the customer."

Other C-130J users will be pursuing their own programs to their own timing with their own trial kit installation tests.

Lockheed Martin used a US Air Force aircraft was used by Lockheed Martin for common-core flight trials with the initial flight of a Block 7 machine in 2011.

The British expect the work on the RAF aircraft to be carried out by a partnership of contractors including Lockheed Martin, Marshall Aerospace, Qinetiq, Atkins and Ebini.

Britain operates 24 C-130Js but is currently scheduled to run that fleet down starting next year as the Royal Air Force begins operations of the first of 22 Airbus A400M airlifters it has on order.

Two aircraft have been delivered to the RAF with a third scheduled to be handed over soon. A further six machines are expected to be delivered by the end of this year.

As things stand, the British are scheduled to take the C-130J out of service by 2022, although there is a debate within the military as to whether seven or eight of the fleet are kept on for special forces duties.

Decisions on the future numbers of platforms will be a matter for the upcoming strategic defense and security review, the said the MoD said.