The Air Force’s plan to replace engines on B-52 Stratofortress bombers before completing developmental flight testing could increase costs and delay the program, the Government Accountability Office said. The $21 billion modernization effort will install commercial‑configured engines, struts, electrical power generation systems and cockpit displays on 76 B-52H aircraft to keep the fleet operational through the 2050s. The GAO report, released Friday, found that engine and radar costs account for about 88 % of the total expense. Engine program costs have risen 38 % since 2018 and development start has slipped by 32 months. Initially scheduled to begin engine development in late 2023, the Air Force now expects to start later this year, with developmental flight testing expected in the first quarter of fiscal year 2029 and initial operational capability in 2033, representing about four to five years of delay. Officials plan to begin production of the engines in late 2028, meaning engines will be built before critical flight testing of fully integrated systems is completed. The GAO warned that this concurrency raises cost, schedule and performance risks and recommended delaying production until a risk analysis accounts for recent cost growth and schedule delays. The report said that delaying production may be less risky than continuing to maintain the current B-52 engines.