What happened
On 21 February 2006, a Belair Airlines Boeing 767-300, registration HB-ISE, arrived at Zurich Airport from Cancun, Mexico. While holding in the GIPOL pattern, the crew faced a complex operational environment due to recent ground technical issues. Although the aircraft was capable of CAT III approaches, the airport's operational capability had been compromised.
During the holding period, a failure in the display of wind and Runway Visual Range (RVR) data occurred on air traffic control screens. This technical malfunction necessitated the downgrading of runway 16 to CAT I operations. Facing limited fuel reserves and a desire to avoid diverting to the alternate airport in Basel, the crew decided to proceed with an approach. Despite the weather conditions not being suitable for a CAT I approach, the crew requested and executed a landing on runway 16.
The investigation
The investigation focused on why the crew proceeded with an approach that did not meet the required visibility minimums. Investigators examined the airport's electrical infrastructure, discovering that a previous short circuit on 18 February had caused issues with the emergency power supply. Specifically, a failure to correctly connect data transfer devices to uninterruptible power supply (UPS) sockets meant that when power was interrupted, the RVR and wind data displays failed for approximately 40 minutes.
Furthermore, the investigation looked into the communication of runway status. It was established that while runway 16 had been downgraded, the crew was unaware that runway 14 had also been restricted to CAT I due to the same technical issues. This lack of information meant the crew's decision-making regarding the 'commitment to proceed' was based on an inaccurate assumption of available runway capabilities.
Findings
- Technical failures on the ground, caused by improper power supply connections to meteorological data transfer devices, led to the loss of RVR and wind data visibility on controller screens.
- The flight crew performed an approach and landing under low visibility procedures despite the weather not meeting the requirements for the downgraded CAT I status of runway 16.
- The crew was not informed via ATIS or radio that runway 14 had also been downgraded to CAT I.
- The crew's decision to continue the approach was driven by the need to manage remaining fuel levels and avoid an immediate diversion.