What happened
On 15 February 2011, a Boeing 737-900ER, registration PK-LHH, operated by PT. Lion Mentari Airlines, was performing a scheduled passenger service from Medan to Pekanbaru. The flight, LNI 295, carried 226 people, including 218 passengers.
During the approach to runway 36 at Sultan Syarif Kasim II Airport, the flight crew received information from Air Traffic Control (ATC) indicating calm surface winds. However, flight data recorder analysis revealed a significant tail wind component, averaging 15 knots during the approach and reaching 17 knots at touchdown. Despite the pilot's attempt to use maximum auto-braking and thrust reversers, the aircraft failed to decelerate sufficiently. The aircraft eventually came to a stop approximately 12 meters beyond the end of the runway. There were no injuries and no damage to the aircraft.
The investigation
The investigation focused on the discrepancy between the reported wind conditions and the actual flight data, as well as the physical state of the runway. Investigators found that the anemometer used by the tower was positioned near vegetation and buildings, which likely caused inaccurate wind readings.
Furthermore, the investigation examined the runway's friction capabilities. While the aircraft was not hydroplaning, the surface was found to have significant rubber deposits and standing water up to 3 cm deep. Testing revealed that the runway's skid resistance had dropped to levels between 0.55 and 0.59, which is below the minimum safety requirement of 0.60.
Findings
- The primary cause of the excursion was the inability of the aircraft to decelerate as expected due to a reduced braking coefficient caused by a combination of wet runway conditions, rubber deposits, and low skid resistance.
- The landing distance required for the aircraft's weight and temperature, compounded by the 17-knot tail wind, exceeded the available runway length.
- The flight crew relied on inaccurate ATC wind information because the wind data was not actively monitored on the Computer Display Unit (CDU) during the approach.
- The tail wind component exceeded the operator's maximum allowable limit of 10 knots.
Safety action
Following two similar runway excursions involving the same aircraft type within two days, the airport authority agreed to several safety improvements, including:
- Transitioning the rubber deposit removal schedule from a fixed six-month interval to an "on-condition" basis based on inspections.
- Performing runway repairs to eliminate standing water.
- Issuing NOTAMs to alert pilots when runway skid resistance falls below the required 0.60 threshold.