What happened
On April 28, 2017, a commercial flight operated by a carrier (flight 6F108) arrived at Keflavik Airport (BIKF) from Alicante, Spain. The aircraft, a Boeing 737-800 with registration YL-PS and 144 persons on board, was performing an RNAV-X approach to runway 19. At the time of arrival, the airport was experiencing heavy snow and deteriorating visibility.
During the approach, the flight crew utilized Autobrake 3 settings based on performance calculations that assumed an uncontaminated runway. However, the aircraft experienced an extended float during the final 20 feet of descent, resulting in a touchdown 310 meters further down the runway than planned. Upon touchdown, the aircraft began to decelerate, but as it progressed down the runway, it encountered areas that had not been cleared of snow. The crew eventually applied maximum manual braking and maximum reverse thrust, but the aircraft could not stop within the available distance and exited the end of the runway. There were no injuries among the 144 occupants, though the left main landing gear sustained damage.
The investigation
The RNSA investigation examined the runway maintenance procedures, the weather conditions, and the flight crew's performance calculations. The investigation established that while snowplows had cleared a 50-meter wide strip of the runway earlier that evening, the runway surface was not fully cleared of snow. The investigators also reviewed the ATIS information provided to the crew, which indicated a "GOOD" braking action based on a measurement taken several hours prior to the incident.
Findings
- The primary cause of the excursion was a deviation from snow removal procedures, which resulted in the runway not being fully cleared of snow.
- The runway conditions had degraded significantly since the last recorded braking action measurement.
- The landing performance calculations performed by the crew were invalid because they were based on an uncontaminated runway, whereas the actual surface was covered in snow.
- The aircraft's touchdown point was further down the runway than anticipated due to an extended float during the landing flare.
- The crew's depth perception was likely degraded by the heavy snowfall and low visibility, contributing to the float.
Safety action
- The ITSB recommended that Isavia implement a formal procedure for communication between snow removal supervisors and Air Traffic Controllers (ATCOs).
- The ITSB recommended that Isavia ANS reconsider the structure of NOTAMs to group relevant information more effectively for pilots.