On 20 July 1935 a Douglas DC-2 aircraft, registration PH-AKG, operated by KLM, flying from Milano, Italy to Schiphol, Amsterdam, in the Netherlands crashed at Pian San Giacomo, Switzerland, killing all thirteen people on board, in the deadliest KLM accident at that time.
The Douglas DC-2 PH-AKG (named: "Gaai") operated by KLM departed on 20 July 1935 at 11:56am local time for a scheduled international flight from Milano, Italy to Frankfurt, Germany.
While flying over the pass, the plane encountered severe weather with heavy thunderstorms, torrential rain and drop in temperature.
[11] Also, because the pilot had flown the route already ten times, and knew it was important to fly at a high altitude over the Alps.
[3] Aviation "Het Vliegveld" published a review article with comments made in journals worldwide about the accident of the Gaai.
[5] In the wreck the notebook was found of Jos van Langen, foreign editor of the daily newspaper De Tijd.
[11] On five pages he wrote initially very clearly and in full sentences, but the notes became shorter and scribbled shortly before the accident.
Een wees gegroet en schietgebedje tot Sint Christoforus geven vertrouwen Al gauw boven de wolken; vrij regelmatig Dwars door de wolken; alles wit stijgen 3000 M. Regen tegen de ramen 4000 4500 boven de wolken hemelblauw zichtbaar 4600 4700 bijna 5000 regen klettert geen blauw meer regen half één knal dalen snel 4000 3800 3200 sneeuw 3000 2800 2500 2400 vlak boven toppen bliksem 2100 Milan 20/7 it's 12 o’clock in the Gaai with around 10 passengers, most Dutch De Tijd informs us of the accident of the "Maraboe", after a fellow passenger informed us of the disaster of last Sunday A say goodbye and quick prayer to Saint Christopher give confidence Soon above the clouds; quite regular Straight through the clouds; all regular rise 3000 M. Rain against the windows 4000 4500 above the clouds blue sky visible 4600 4700 almost 5000 rain patters no more blue rain half past twelve boom quickly descend 4000 3800 3200 snow 3000 2800 2500 2400 just above (tree)tops lightning 2100 The course of the flight can almost be followed minute-by-minute.
[14] Van Langen's notes were found to contain important information, and were used in the investigation to answer why the plane flew between the mountains and not above them.
[11] The investigation was done by the Dutch Government Study Service for Aviation (Rijksstudiedienst voor de Luchtvaart) and led by Dr. Ir.
Due to the irregular detachment of ice from the propeller blades, strong vibrations of the aircraft occurred and the pilots were forced to turn down the engines.
The icing disappeared not above 3000 meters, and at that altitude the plane was surrounded by mountain tops, in very poor visibility due to the bad weather.
With the skills of the pilot, he succeeded in obtaining ground visibility at an altitude of around 1600 meters and tried to find a way out of the San Giacomo valley.
However, in the left turn before landing, the plane lost too much speed, "tilted" forward and crashed to the ground, killing all occupants.
[5] Partly due to this crash, in November 1935 icing was a main topic at the congress of the International Air Traffic Association.