What happened
On July 11, 2017, a Norwegian Air Shuttle flight, NAX4287, arrived at Helsinki-Vantaa Airport from Stockholm Arlanda. The aircraft, a Boeing 737-800 with registration LN-NHF, landed on runway 04L under conditions involving rain clouds and moderate winds. The landing was light and occurred slightly beyond the optimal touchdown point.
Following touchdown, the captain engaged reverse thrust. Although the spoilers were set to automatic, the lightness of the touchdown prevented them from deploying automatically, requiring the captain to deploy them manually. The crew had originally planned to exit via taxiway WK, but due to high speed, the captain decided to bypass this exit and instead use the taxiway at the end of the runway.
During the deceleration process, the captain deactivated the reverse thrust, spoilers, and autobrake systems. This significantly reduced the aircraft's braking effectiveness. While the crew attempted to use heavy braking to reach taxiway WD, the aircraft's speed remained too high for a safe turn. The aircraft veered approximately 20 degrees off the runway centerline, striking runway lighting installations. The nose and three main landing gear wheels left the paved surface and entered the grass, resulting in no fatalities and no injuries to the 168 passengers or 6 crew members.
The investigation
The investigation examined the aircraft's systems, the flight crew's actions, and the environmental conditions. Investigators analyzed the flight data recorder (FDR), cockpit voice recorder (CVR), and ground radar. The inquiry focused on the sequence of braking actions, the manual deactivation of automated deceleration systems, and the crew's decision-making regarding runway exit selection. The investigation also reviewed the airport's emergency response and the physical condition of the runway and lighting equipment.
Findings
- The primary cause of the excursion was the manual deactivation of the aircraft's automated braking and deceleration systems (autobrake and spoilers) during the high-speed rollout.
- The crew's decision to bypass the initial planned exit (WK) due to high speed led to a longer rollout distance, which the reduced braking configuration could not safely accommodate.
- The light touchdown prevented the automatic deployment of spoilers, necessitating manual intervention that was not effectively managed during the subsequent deceleration phase.
- The aircraft struck runway lighting, causing damage to the lights, the aircraft's tires, and foreign object damage (FOD) to one engine fan blade.