What happened
On January 5, 2009, an Embraer 145 arriving from Birmingham, UK, was performing a scheduled approach to Stuttgart Airport. The crew elected to conduct a Category II ILS approach to prepare for potentially deteriorating weather. During the approach, the crew set the flaps to 22 degrees, a configuration intended for a CAT II landing after an ice encounter, which resulted in a longer landing distance.
The aircraft touched down in the rear portion of the touchdown zone. While the initial braking felt normal to the crew, they subsequently noted a significant decrease in effectiveness. The crew intentionally avoided using certain taxiways, such as D and B, because they appeared slippery due to snow and ice. As the aircraft continued to roll, the pilot in command applied heavy braking, and the copilot eventually applied the emergency brake. Despite these efforts, the aircraft could not be stopped before exiting the paved surface and entering the Runway End Safety Area (RESA).
The investigation
The BFU investigation examined flight data recorder (FDR) and cockpit voice recorder (CVR) data, as well as runway condition reports. The investigation found that while the ATIS had reported braking action as "good," the actual friction levels had dropped significantly due to ongoing snowfall. Friction measurements taken shortly after the incident confirmed that the braking action had degraded to levels well below "good."
Investigators also reviewed the airport's winter maintenance procedures. While the runway had been cleared earlier that day, the continuous snowfall had created a layer of slush. The investigation noted that the airport's procedures for updating ATIS information relied on physical friction measurements, which prevented the timely communication of the deteriorating runway conditions to arriving pilots.
Findings
- The crew did not apply consistent or maximum braking throughout the entire landing roll.
- The use of a 22-degree flap setting increased the required landing distance.
- The braking action on the runway was significantly reduced and did not match the "good" status reported in the AT/IS.
- The ATIS information provided to the crew was outdated and did not reflect the real-time impact of the ongoing snowfall.
- The application of the emergency brake by the copilot deactivated the anti-skid system.
Safety action
- The BFU recommended that Stuttgart Airport develop procedures for more flexible and timely reporting of expected braking action to air traffic control.
- A recommendation was made to revise airport maintenance instructions to ensure that weather conditions are more heavily considered when deciding when to perform friction measurements.
- The BFU recommended that aircraft operators extend training for crews regarding winter operations to ensure they better recognize and account for reduced braking action during landing planning.