The Mach Loop is a series of valleys south and east of Machynlleth used by RAF and USAF aircraft for low-level training flights. On flying days — which are unpredictable but more common on weekdays — jet aircraft descend to valley floor level and fly at high speed through the valley system, providing a spectacle unlike anything available elsewhere in the UK at this altitude.
The best-known viewing spot is Cad West, above the A487 south of Machynlleth, where a ridge provides views down into the valley used by aircraft approaching from the south. The spot is accessible on foot from a small car park off the main road. There is no schedule and no guarantee of activity, but aviation enthusiasts willing to wait are frequently rewarded. The surrounding mountain scenery — part of the southern Snowdonia area — makes the walk worthwhile regardless.