Ka 4 Rhönlerche II Außenlandung aufgrund eines Instrumentenfehlers nahe Thun

Am 1. Mai 1966 erlebte eine Ka 4 Rhönlerche II eine Außenlandung in der Nähe von Thun, Schweiz. Der Vorfall ereignete sich während eines Ausbildungsfluges, als der Flugschüler nach einer Fehlablesung des Höhenmessers erkannte, dass er nicht zum Flugplatz zurückkehren konnte. Das Segelflugzeug musste auf einem Feld landen, was zu Schäden am Flugzeug, aber zu keinen Verletzungen führte. Die Untersuchung bestätigte, dass eine falsche Einstellung des Höhenmessers zur Entscheidungsfindung des Piloten während des Fluges beitrug.

1. Aerotow training flight: The student pilot launched from Thun on an aerotow in a Rhönlerche II to attempt a 30‑minute qualifying soaring flight after a seven‑month training break.
2. Altimeter mis-set: Before takeoff the student either failed to correctly set or later altered the altimeter, which was later found to be set about 25 mb too high, indicating roughly 200 m more height than actual.
3. Sluggish altimeter: The altimeter mechanism was abnormally sluggish, lagging by up to about 120 m, further degrading the accuracy of the height information available to the pilot.
4. Height reserve misjudged: While losing height after release and failing to find usable lift, the student relied on the erroneous altimeter indications and did not maintain the instructor’s minimum height reserves for a safe return to the airfield.
5. Late diversion decision: Only after noticing visually that he was much lower than the indicated 400 m over the town did the student abandon the plan to return to the airfield and choose an outlanding field near the city edge.
6. Too low over houses: The remaining height proved insufficient to clear the last houses and reach the intended field at the city periphery, forcing the pilot to attempt an immediate landing on a closer field directly beneath the glider.
7. Outlanding - damage: In a steep right turn with tailwind toward the nearby field the right wingtip struck the ground, the glider was yanked around and impacted hard on the skid, damaging the fuselage and one wing but leaving the pilot uninjured.