Atlantic Airways Flight 670

Introduction
Atlantic Airways Flight 670 was a small passenger flight from Stavanger to Molde with a stopover in Stord. The plane overran the runway after hydroplaning caused it to be harder to stop.

Pilots
Captain Niklas Djurhuus and First Officer Jakob Evald flew the BAE-146, and both pilots survived the accident.

The Crash
Flight 670 is beginning to land, shortly after reaching cruising altitude. This is because the first leg of the flight only takes 15 minutes, and is mostly consumed by taking-off and landing. The crew are in a BAE-146, a small plane designed for small commuter flights like this one. Because of this, it is suited for steep approaches and short runways, which is the landing conditions for today. Stord Airport, the airport they're landing at, is built on an island, meaning overshooting the runway could leave you in the sea.

The aircraft lands as it should, and the spoilers are deployed, but then an alarm goes off in the cockpit. The spoilers aren't deploying. Both pilots immediately slam on the wheel brakes to try and stop the aircraft, but it's not slowing. The plane skids off the runway and falls down onto the cliff at the edge of the island. The plane hits multiple trees, setting an engine on fire, before eventually coming to a stop. The pilots and passengers quickly rush to escape the aircraft. 4 don't make it in time. This accident then started an investigation, dedicated to get to the bottom of this.

Investigation
By the time the investigators get to the crash site, they find that most of the evidence has burned. The CVR and FDR have not however, and investigators send them off to a lab to receive data from the two boxes. They also soon discover the faulty spoilers, and how they did not deploy. But the 146 is still able to stop without spoilers, so something else must have been at play.

When investigators look at the runway, they see something unexpected. Grey skid-marks trail down it, which is strange as skid-marks are usually a darker colour. As well as this, small pieces of debris were found on these skid marks, and were described to smell like rubber but were soft and sticky. It is thought that these pieces came from the tires, but why would the tires disintegrate like this? A strange theory that could explain it all is put into place.

Hydroplaning
A set of landing gear is found in the wreckage, and they confirm earlier theories that the debris found came from the tires, but how? After interviewing the tire manufacturer, they find an answer to that question. Hydroplaning happens when a high-speed vehicle is driving across wet land. The friction on the wheels of the vehicle is so much that it heats up the water, converting it to steam. This steam can then lift the tires up slightly, almost like a cushion of air. This makes it a lot harder to get said vehicle to slow. The heat from the friction can also cause small parts of the tire to disintegrate and turn sticky, just like the debris found on the runway. There is an issue with this theory however, as hydroplaning only happens when the wheels lock, but the BAE-146 has specially designed wheels that do not lock. When wheels lock, it is when they stay in one position and don't move. This looks like the best way of braking at first glance, but can cause the vehicle to skid, just like what happened to Flight 670. So why did it skid despite the wheels not locking? After listening to the Cockpit Voice Recorder (CVR) investigators hear a small sound in the background of the mayhem. A chime, which indicates the emergency brakes, was heard in the middle of the landing. Immediately after this, the sound of tires skidding was heard. This means the emergancy brakes, which were deployed by Captain Djurhuus, caused the tires to lock into place and skid, creating the effect of hydroplaning.

A crash animation can be seen here: https://youtube.com/watch?v=0dRxtClnDAE

May those 4 who didn't make it rest in peace.