What happened
On June 24, 2002, a Cessna 172P and a Boeing 717 collided while taxiing at Stuttgart Airport. The Cessna, operated by a general aviation pilot, was taxiing from the general aviation apron toward runway 25. After receiving taxi instructions from Stuttgart Ground, the pilot crossed a service road and entered taxiway N. Simultaneously, the Boeing 717 was taxiing at a normal speed along taxiway N toward the same runway.
As the Cessna entered the intersection of taxiway N, it collided with the wing of the Boeing 717, which was traveling at 36 knots. The impact caused significant damage to both aircraft: the Boeing's left wing sustained structural damage, including a torn leading-edge section, while the Cessna's propeller blades were deformed and a portion of its right wing was torn away. There were no injuries resulting from the accident.
The investigation
The BFU investigation focused on the coordination between the different air traffic control units at Stuttgart. The airport's ground operations were split between two entities: FSG (responsible for apron control) and DFS (responsible for tower and ground control). The investigation examined the electronic flight plan transfer system (DEPCOS) and the communication handovers between the Ground, Apron, and Tower frequencies.
Investigators reconstructed the sequence of events and found that while the Boeing was under the jurisdiction of Apron control, the Cessna was communicating with Ground control. A critical gap was identified in how information regarding aircraft moving between these different jurisdictions was shared. Furthermore, physical inspections of the taxiway revealed that while a stop line existed for the service road, there was no specific stop mark for entering taxiway N from the GA apron.
Findings
- Inadequate coordination procedures between the FSG and DFS units created an information gap, as the Ground controller was not aware of the conflicting traffic movement being managed by the Tower/Apron controllers.
- Lack of situational awareness by both pilots, who failed to observe the other aircraft despite having clear lines of sight at the time of the collision.
- Non-compliance with established procedures for exiting the general aviation apron.
- A lack of a stop mark at the junction of the GA apron and taxiway N contributed to the uncontrolled entry of the Cessna into the path of the Boeing.
- The investigation noted that the reliance on automated systems and the complexity of the handover process may have inadvertently reduced the vigilance of the controllers.