What happened
On the morning of 6 December 2002, a near-miss incident occurred approximately 9 NM southwest of the Zurich Kloten VOR involving two scheduled flights. The first aircraft, a Swiss International Air Lines Bombardier RJ1H, registration HB-IXX, departed runway 28 and was cleared to climb to FL 110 following a left turn. Shortly after, an Alitalia Express Embraer E145, registration I-EXMG, departed the same runway 86 seconds later.
As the first aircraft initiated its turn, the departure controller issued a climb clearance to the second aircraft. However, the RJ1H exhibited a lower rate of climb than anticipated, while the E145 climbed much more aggressively. This discrepancy caused the aircraft to converge, leading to a violation of minimum IFR separation. The situation escalated until the RJ1H flight crew received a TCAS climb instruction and the controller's radar triggered a Short Term Conflict Alert. The aircraft eventually passed each other with a lateral separation of 1.7 NM and an altitude difference of 600 ft.
The investigation
Investigators examined the takeoff intervals and the performance characteristics of both aircraft types. It was noted that the takeoff separation of 86 seconds was significantly shorter than the 120-second interval suggested by the TACO coordination system. The investigation also looked into the climb profiles of the aircraft, noting that the RJ1H was utilizing a specific flap setting for noise abatement that resulted in a lower initial rate of climb, whereas the E145 possessed high power reserves and a much higher rate of climb.
Findings
- The primary cause was the departure controller providing an early turn clearance to the HB-IXX relative to the short takeoff interval provided to the I-EXMG, which resulted in the loss of required separation.
- Inadequate knowledge of aircraft performance by the air traffic controllers regarding the specific climb characteristics of the newly introduced aircraft types contributed to the conflict.
- The takeoff interval was significantly reduced compared to the recommended guidelines to increase efficiency.
- The controller's corrective measures after recognizing the conflict were insufficient to prevent the separation infringement.
Safety action
Following the incident, the Chief of Operations for Zurich issued new instructions for departures involving RJ1H aircraft. For departures on runway 28 in the specified direction, the new procedure requires a departure release only after reaching 5000 ft/QNH and adds an additional one minute to the TACO separation proposal to ensure a safer buffer.