What happened
On April 1, 1999, at approximately 18:37 UTC, a DC-9-82 (MD-82), registration OH-LMY, arrived at Ivalo Airport for landing on runway 04. The aircraft was carrying 121 passengers and five crew members. Earlier that day, the area had experienced sleet, snow, and graupel, causing the runway surface to become wet with a thin layer of slush.
Airport maintenance had performed runway sweeping earlier in the evening to dry the surface in anticipation of freezing temperatures. Following the sweeping, a maintenance supervisor inspected the runway by vehicle and assessed the braking action as good, noting the surface was wet but not icy. However, as the aircraft approached, the temperature had dropped below freezing.
The aircraft touched down approximately 500–600 meters beyond its normal touchdown point, near the 1000m marker. Personnel monitoring the landing from a taxiway noted that the engine reverse thrust was initially quiet during the early part of the landing roll, but became significantly louder toward the end. The aircraft eventually came to a stop approximately 100 meters before the end of the runway.
The investigation
The investigation examined weather data, maintenance logs, air traffic control (ATC) recordings, and interviews with the pilot, air traffic controllers, and maintenance personnel. The investigation focused on the temperature fluctuations, the effectiveness of the recent runway sweeping, and the functionality of the airport's surface temperature monitoring equipment.
Findings
- The primary cause of the runway slipperiness was the formation of a thin layer of ice on the runway surface, caused by a drop in temperature acting upon the thin layer of water left after maintenance sweeping.
- The airport's runway surface temperature sensor was non-functional because the sensor had been buried too deeply during previous paving work.
- The only available temperature display was located in the maintenance duty room, making it difficult for all active personnel to monitor real-time changes.
- While the air traffic controller proactively informed the maintenance supervisor that the air temperature was dropping below freezing, the supervisor did not take preventative measures to treat the runway.
- The application of liquid de-icing chemicals (such as potassium or sodium acetate) prior to the landing would likely have prevented the ice formation, but the airport lacked the necessary equipment and experience with liquid chemicals at the time of the event.