Aircraft Accidents and the De-Bogging

I read this morning about a Southwest 737 that found itself nose gear deep in the grass; the aircraft was taxiing to the terminal in Nashville and somehow ended up off the taxiway. Perhaps before I put this in my blog, a statement will be made to shed some light on the accident, but I want to write about the actual concept of being ‘bogged’.
One would think that an aircraft the size of a 737 – probably around 180,000 pounds empty – would be able to go Ba-Ha-ing over the grass at the edge of the taxiway with no consequences, but that’s not the case. If the grass is dry, an aircraft could, perhaps, get away with accidentally cutting a turn short or long, leaving a main tire-shaped divot in the grass or dirt. However, if the dirt is wet, the gear sinks into the mud like quicksand and becomes bogged down. According to the landing gear (two, four or six tire truck) the aircraft can become hard stuck and cannot power out.
A jetliner weighing 180,000 pounds is sure to be more than 200,000 pounds with fuel, luggage, and passengers. In a tricycle gear aircraft, all the weight is centered on the small strut points and the place that the tires (in this case, two) touch the ground. Out of the 200,000 pounds, each main gear supports approximately 80,000 pounds each, if not more. That weight sinks quickly into the mud. The bog then acts as a chock or some tire blocking device, preventing the wheels from turning and crest the well it’s made.
Another issue is the stress placed on the gear. A main or nose gear is not designed for heavy side or shear loads; instead it is designed for compression loads as the plane’s weight settles into the landing. Any rocking or sliding into a bog can rip the gear from its mounts because of heavy weighted inertia, especially with the size of the tires placing more of a pressure target.
De-bogging an aircraft is not easy and requires special equipment to raise the aircraft and move it in a direction, out. It requires special training that prevents unnecessary damage to the gear. That’s why an event like this is not easily corrected.

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