What happened
On September 26, 1961, a Swissair Caravelle SE-210 (registration HB-ICW) was operating flight SR 701 from London to Zurich. Due to heavy fog reported at Zurich, the captain decided to divert the flight to Basel-Mulhouse.
During the ILS approach to runway 16 at Basel, weather conditions deteriorated rapidly. As the aircraft descended, the pilot transitioned from monitoring instruments to looking outside for the runway. During this period of visual scanning, the aircraft descended below the required minimum altitude. At approximately 05:17 GMT, the aircraft made contact with the ground roughly 125 meters before the runway threshold, specifically striking a road and a ditch. The impact caused the right main landing gear to be torn away. The crew successfully initiated a go-around and continued to Geneva-Cointrin, where the aircraft performed an emergency landing. There were no fatalities and no injuries among the 24 passengers and 3 crew members, though the aircraft sustained significant damage.
The investigation
The investigation, conducted by the Swiss Transportation Safety Investigation Board, utilized flight recorder data, radio communications, and testimonies from the flight crew. Investigators examined the weather reports from Basel, which showed visibility dropping below the 800-meter minimum required for the approach, and reviewed the crew's adherence to Swissair's operational procedures regarding instrument approaches and cockpit monitoring.
Findings
- The primary cause of the ground contact was the captain's decision to divert his attention from the instruments to look outside the cockpit, which allowed the aircraft to descend below the safe minimum altitude.
- The crew failed to adequately monitor changing weather reports; specifically, the captain did not explicitly verify visibility after a report indicated the runway was obscured by fog, and the copilot failed to alert the captain that visibility had dropped below the required minimums.
- The copilot failed in his duty as an assisting pilot by not maintaining continuous monitoring of the flight instruments while scanning for the runway.
- A degree of fatigue from the crew's extended duty period may have contributed to the lack of precision during the approach and the failure to notice the deteriorating weather conditions.