How this happen? Hawker nose wheel stuck sideways!

they knew something was wrong since they declared an emergency prior to landing.

broken or damaged link in the steering system

some description of the NG system can be found here
http://www.smartcockpit.com/docs/Hawker_00XPC-Landing_Gear.pdf

One scenario is that the aircraft was towed prior to departure and the ground crew did not remove the steering disconnect pin. When they towed it the pin sheared which would then disable the NG steering. They could still have taxied using differential braking and not considered why the normal steering was not functioning properly.

 

It happened to a JetBlue Airbus around 2010

 

I landed in Richmond earlier this evening. Talked to the ops manager who showed me photos from the incident. He said the Hawker veered right after touchdown, shot across one ditch, went airborne momentarily, and then ran through another ditch. The left wingtip dug in to the ground at one point, and the rear of the plane was nearly sitting on the ground once it stopped. They were able to tow it to a hangar.

 

Several aircraft are engineered such that their nosewheels are steered by a single actuator that pulls the wheel to center position opposite a "sprung" side. Failure of the actuator causes a "hardover" condition where the wheel is stuck in the sprung direction. Crazy design but simple...until it fails. Harrier has a nosewheel set up like that, and I watched one rollover upside down on landing after the wheel failed on rollout. Even crazier...the Northrop T-38 has the rudder set up in a similar fashion which can lead to "rudder hardover" which is a bear...

 

Yep

 

Early 737s had the same hard over rudder problem.