What aircraft was involved and where did it happen?

The accident on 2001-07-30 involved a BOEING B737-500, registration OK-CGH, at TMA Zürich, CH.

What was the probable cause of the accident?

The pilot of the Cessna C414 entered restricted airspace because he lost precise navigational positioning following a GPS display failure and failed to maintain situational awareness through visual navigation.

Near Collision in Zurich TMA Following GPS Failure

A Cessna C414 flying under VFR rules penetrated restricted airspace and came within 0.9 NM of a Czech Airlines Boeing 737 after the pilot lost navigational position.

What happened

On the evening of 30 July 2001, a Czech Airlines Boeing 735, registration OK-CGH, was performing a scheduled approach to Zurich from Prague. While being vectored by approach control for an ILS approach to runway 14, the aircraft encountered a potential conflict with a Cessna C414, registration D-IMUB, which was operating under visual flight rules (VFR) from Arnsberg to Zurich.

As the Boeing 735 was descending through 5000 feet, air traffic controllers noticed the Cessna C414 approaching the boundary of the Zurich TMA Sector 5 from the north. Although controllers instructed the VFR pilot to descend below 4500 feet or orbit to avoid the restricted airspace, the Cessna C414 entered the sector at approximately 5500 feet. This resulted in a close encounter where the two aircraft reached a horizontal separation of only 0.9 NM with an altitude difference of 500 feet.

The investigation

The investigation established that the pilot of the Cessna C414 experienced a failure of the GPS-coupled Moving Map Display approximately 10 NM north of the TMA boundary. This failure caused the pilot to lose precise knowledge of his position, leading him to believe he was much further west than he actually was.

Investigators also examined the actions of the air traffic controllers. While the approach controller correctly instructed the Boeing 735 to level off at FL 60 to mitigate the risk, the investigation noted that the crew of the Boeing 735 had misheard the altitude instruction due to having already switched their altimeters to the local QNH, resulting in an incorrect readback.

Findings

The primary cause of the airspace penetration was that the pilot of D-IMUB failed to navigate using terrestrial reference points after his GPS display failed.

The pilot of the Cessna C414 had limited flight experience, with only approximately 300 total hours and 35 hours on this specific aircraft type.

The pilot did not utilize conventional visual navigation techniques to compensate for the loss of electronic aids, which is vital in restricted airspace like the Zurich TMA.

The air traffic controller's instruction to the Boeing 735 was correct in preventing a collision, but the crew's transition to local pressure settings contributed to a communication error during the readback.