There are basically two options for starting the route:
1. Stay in the Chamonix valley and then take the first telepherique up to the Aiguille du Midi in the morning.
2. Stay on the high mountain (e.g. in the Cosmiques Refuge, bivi on the Col du Midi or at the Abri Simond Bivouac) and then walk up to the Aiguille du Midi (or at least to the ridge) in the morning.
Like on any alpine route the snow conditions will be best in the morning in the summer, so an early start is essential. This is especially so if planning to descent via the Envers du Plan Glacier, as the snow conditions can deteriorate rapidly from mid- to late morning onwards due to the glacier's aspect.
The Midi-Plan traverse is a justifiably popular route due to the superb views it offers of the surrounding mountains (Aiguilles Rouge, Aiguille Verte, Droites, Courtes, Grande Jorasses, Dent du Geant, Mont Blanc, etc... ), the Vallée Blanche and Mer de Glace and the Chamonix valley itself.
Gaston Rébuffat rates the route number 21 of 100 in his book "The Mont Blanc Massif. The 100 Finest Routes".
The route starts down a spectacular set of ever narrowing, and sometimes corniced, snow ridges, and then weaves its way on both the north and south sides of the ridge through various mixed rock and snow sections. Route finding is mostly fairly simple and the general direction is along the obvious ridge to the NE of the Aiguille du Midi and towards the jagged row of Aiguilles.
Some of the rock sections are quite exposed (esp. some sections on the N side working your way up to the Rognon du Plan) and a slip would result in an express ride down to Cham, if the climber is not protected. Nothing unreasonable for a route of its grade though.
From the Aiguille du Midi the route is as follows:
- Descend from the tunnel exit at the telepherique station and follow the snow ridge to Point 3626. The ridge steepens and crosses some rock sections to reach the to the Col du Plan at 3475m.
- Continue the traverse along the rock on the north (Chamonix) side and up a colouir to gain the snow field on top of the Rognon du Plan.
- Traverse the rock on the Rognon du Plan and then descend through a series of small rock gullies / diedrals to the abseil point above the Col Supérieur du Plan (3535m). Abseil down and then follow the snow ridge up to the base of the Aiguille du Plan's rocky summit. An easy scramble leads to the top.
Descent / Return:
1. Either return to the Aiguille du Midi
2. For a more interesting day, descend to Refuge du Requin via the Envers du Plan Glacier. This descent should not be left too late in the day, as the snow conditions on the glacier can get very poor and the climber is exposed to seracs and crevasses before reaching the Refuge.
The Refuge should easily be attained by midday, which leaves the option of either staying the night or walking on down the Mer de Glace to the Montenvers cog railway station.
Taking the latter option allows one to enjoy the impressive scenery of the Mer de Glace, but it does make for a long day in the mountains. The task of navigating though the crevasses and moraines on the snout of the Mer de Glace should not be underestimated.
Crampons + 1 axe .
A rope is essential for abseil from the Rognon du Plan to the Col Supérieur du Plan, and is probably also a good idea if intending to descend via the Envers du Plan Glacier to the Refuge du Requin, due to the risk of crevasses. Throw in the bits you'd need for crevasse rescue for good measure.