The Mach Loop (also known as the Machynlleth Loop) is a series of valleys in the United Kingdom in west-central Wales, notable for their use as low-level training areas for fast jet aircraft and propeller-driven aircraft.
The system of valleys lies 13 km (8 mi) east of Barmouth between the towns of Dolgellau to the north and Machynlleth to the south (Snowdonia Nat. Park), from the latter of which it takes its name.
The training area is within the Low Flying Area (LFA) LFA7 , which covers most of Wales.
Aircraft seen in the area (2022) include Royal Air Force Airbus A400M, Typhoon, Hawk jets and C-130J and Beechcraft T-6 Texan II as well as U.S. Air Force F-15 Eagles which are based at RAF Lakenheath and MC-130 and CV-22B Osprey from RAF Mildenhall.