Northrop Grumman and BAE Systems have withdrawn from the US Air Force's (USAF) T-X advanced pilot training programme.
The T-X programme, which seeks to replace the air force's existing fleet of T-38 Talon aircraft, is valued at $16bn, according to media sources.
Both the companies have decided not to submit a proposal for the programme after carefully examining the T-X Trainer requirements and acquisition strategy, Northrop stated.
Northrop and BAE's decision to withdraw from the USAF competition follows Raytheon and Leonardo's exit last week.
Additionally, Northrop said it and BAE will remain "fully committed to performing on current and future US Air Force programmes, to deliver critical capabilities to America’s airmen".
The USAF has previously announced plans to procure 350 T-Xs to replace 431 T-38s by the end of this year, with plans to achieve initial operational capability by the end of 2023.
According to the air force, the T-38 is unable to complete 12 of 18 advanced pilot training tasks, prompting the air force to rely on fighter and bomber formal training units to complete training at a much greater cost.
In addition, the T-38s assigned to the air education and training command (AETC) have failed to meet the command's requirement for 75% availability since 2011.
The USAF is seeking key performance characteristics for the advanced pilot training mission such as sustained G simulator visual acuity and performance, and aircraft sustainment, as well as a focus on embedded training with synthetic sensors and data link.