Incident Overview
On July 5, 1962, at 07:51 MEZ, a Scandinavian Airlines System (SAS) Caravelle SE-210/III with registration LN-KLR initiated takeoff from Runway 34 at Zurich-Kloten Airport. The aircraft was operating Swissair flight SR 234 to Düsseldorf and carried six crew members and 46 passengers. During the takeoff roll, the two nose wheels detached from the airframe. The crew aborted the takeoff and deployed the drag parachute, bringing the aircraft to a stop 2,390 meters down the runway. No injuries were reported, and damage to the runway was minor.
Technical Findings
The investigation determined that the left wheel nut had loosened because its securing screw was no longer tightened. The securing screw is designed to spread a cone within the nut's thread to prevent unscrewing. However, the axle assembly had been mounted in reverse (left-for-right). This reversed orientation meant that the rotational direction of the rolling wheels would tend to tighten the nut rather than loosen it, assuming the securing mechanism was intact. In this case, the failure of the securing screw allowed the nut to back out despite the reversed thread logic.
Maintenance and Design Factors
The nose wheels had been replaced on June 29, 1962, at Stockholm-Arlanda. The investigation found that the axle assembly was installed in reverse during this maintenance. While the K-Check and V-Check procedures did not require a torque check of the securing screws, the red paint mark indicating proper tightening was not consistently renewed after wheel changes. The design itself was noted to have two weaknesses: the securing screw is not independently secured against vibration, and the reversed axle installation is structurally possible, which inverts the intended self-tightening effect of the thread direction.