The Mach Loop is a set of valleys, situated between Dolgellau in the north, and Machynlleth in the south (and from which the Mach Loop gets its name), which are regularly used for low level flight training, with flying as low as 250 feet (76 metres) from the nearest terrain.
To the south of the Mach Loop there is an area called Tactical Training Area 7T, in which, at specified times, the aircraft may fly as low as 100 feet (30.5 Metres). The Royal Air Force publish a timetable of when the Tactical Training Areas may be in use, however experience shows this to be of little use in determining whether low level flying will take place on a particular day or time.
Low flying is an vital skill for military aircrew, and the Royal Air Force uses various areas of the United Kingdom for low level flight training. The United Kingdom is split into 18 low flying areas, (or “LFAs”), the LFA’s being numbered 1-19 (strangley there is no LFA15). The Ministry of Defence website has a map showing the location of the low fly areas. The Mach Loop is located within LFA7, which covers the whole of Wales, except for a small section in the north-east of Powys, which is within LFA9.
Some question the purpose and value in Miltary aircrew undergoing Low Level training, yet it is an essential skill for any pilot or navigator.
Some snippets from the MOD outlining the value and reasoning behind Low Level training sorties.
Low flying remains an essential skill for military aircrew.
Whatever missions we ask our Armed Forces to undertake the aircrew must be able to fulfil the task as effectively as possible, often without time for “work-up” training. Current Operations around the world see aircrew of both fixed and rotary wing aircraft undertaking operations at low level. They are only able to do this through specialist training gained through the use of the UK Low Flying System.
The UK Military Low Flying System covers the open airspace of the whole of the UK and surrounding overseas areas from the surface to 2,000 feet above the ground or mean sea level.
Military fixed wing aircraft are judged to be low flying when they are less than 2000 feet minimum separation distance from the ground.
View the full document here: http://www.mod.uk/DefenceInternet/AboutDefence/WhatWeDo/AirSafetyandAviation/LowFlying/