Go by train or car to Fiesch (Valais), take the cable car to Eggishorn (2927 m), take a thorough look with binoculars of the
Aletschorn and decide if the conditions are OK. Schuss down to the Märjelensee (2324m), cross the Aletschgletscher and climb along the Mittelaletschgletscher and stay over night at the Mittelaletsch bivouc (3013m, for 13 persons), that is located at the foot on the east side of the glacier on a small rock. 4 hours.
If you do this trip in summer by foot, take the cable car from Mörel to Riederalp (possibly chairlist to 2227 m) and enjoy the beautiful walk to the foot of the Eggishorn.
Next day climb the steep slope of the Mittelaletschgletscher (not many crevasses) and head to the lowest point between the
Dreieckhorn and the Aletschhorn. Keep on the narrow ridge, go pass the popular Haslerrippe, a famous ridge that enters from north at point 3719 m. Sometimes you will notice traces of crazy mountaineers that carry the skis from the Aletschgletscher (3000m) up here.
The ridge gets wider and leads over a steep step to a higher floor just below the summit that is reached easily. 5 hours.
Maybe you have to carry the skis over some narrow stretches or you will leave them altogether below the Haslerrippe depending on the snow condition. March and April may the best time. You have to make sure that there is enough snow on the Aletschglacier, so you can ski down as far as 2000 m in order to reach Riederfurka (2064 m). Then take cable cars down to Mörel and possibly the train back to Fiesch to your car.
If you decide between foot and ski, you must keep in mind that walking down the Oberaletschgletscher to Belalp on the normal route is very long and tiresome. Once I even missed the last cable car so I had to stay at the nice little hotel at the Belalp. On another approach I discovered on the Eggishorn that there was too little snow, so I took the next cable car down without using the skis at all!
Traversing (Oberaletsch -> Mittelaletsch) on skis is not recommended.
Crampons, axe, rope.