The Mach Loop (also known as the Machynlleth Loop, Welsh: Dolen Mach) is a series of valleys in the United Kingdom in west-central Wales, notable for their use as low-level training areas for fast 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, from the latter of which it takes its name. The training area is part of the United Kingdom Low Flying System and lies within Low Flying Area 7 (LFA7), which covers all of Wales.

Aircraft seen in the area include Royal Air Force Airbus A400M, Typhoon, Hawk, F-35A/B jets and Texan T1s, as well as U.S. Air Force F-15C Eagles and F-15E Strike Eagles which are based at RAF Lakenheath and MC-130 and V-22 Osprey from RAF Mildenhall. Aircraft from other nations have been sighted training in the Mach Loop, such as Royal Canadian Air Force CT 114 Tutor (in Snowbird livery) and CF-18 Hornet, and F-16 Fighting Falcons of the Belgian Air Component.

In December 2018, a recommendation was circulated within the Ministry of Defence (MoD) which resulted in a reduction in the number of aircraft using the Mach Loop. In addition to this, all non-UK based aircraft are also prohibited from using the Loop unless part of a UK exercise.

The Mach Loop is particularly popular with plane spotters and photographers, as it is among the few places in the world where visitors can see combat aircraft flying below them. One popular viewing point is the carpark located on the site of Llyn y Tri Greyenyn.

• Rainbow Canyon (California)

• RAF Low Flying Training Timetables
• MachLoop.co.uk
• Video of several F35 and Hercules C-130 doing the loop

52°42′31″N 3°50′42″W / 52.70861°N 3.84500°W / 52.70861; -3.84500