Originally Posted by CoastieTX,Jan 26 2006, 11:41 AM

In the simplest terms, the vertical stabilizer gives the plane directional stability. Another way to say this is that it stabilizes the plane about its yaw axis. If you were to look at an airplane from above and push a pin straight down through its center of gravity, the pin would become an axis (the yaw axis) about which the plane could be rotated to the left or the right, which would make the plane's nose rotate to the left or the right.

In flight, you want the plane's nose (and fuselage) aligned with the plane's direction of travel, and this is what the vertical stabilizer does. To explain how the vertical stabilizer accomplished this job, consider the following: Suppose some disturbance causes the plane's fuselage to become misaligned with the plane's line of travel. Instead of the vertical stabilizer being orientated parallel with the air flowing past it (as would be if the fuselage was pointed in the plane's line of travel), it now is orientated in such a way that it presents a portion of its side surface area, or face, to the airstream flowing past it. This gives the airstream flowing past it a surface area on which to push, and when this happens, the vertical stabilizer is pushed back into its original position where it is aligned with the airstream (and plane's line of travel). The vertical stabilizer becomes more effective by either: 1. increasing its surface area, or 2. moving it a greater distance from the plane's yaw axis, which gives the vertical stabilizer more leverage (a longer moment arm).

Attached to the rear (trailing edge) of the vertical stabilizer is the rudder, which is hinged and moveable. Of course, sometimes we want to move the plane's nose to the left or right to change direction of travel, and this is accomplished by the rudder.

When you ask what happens when you lose vertical stabilizer control, I'm assuming you want to know what happens when you lose control of the rudder. If you lost vertical stabilizer control, that would probably mean the vertical stabilizer (and with it, the rudder) became detached from the plane's fuselage. Without these componets, a traditional airplane would lose control about its yaw axis, tumble out of control and either (depending on airspeed) break apart or return to mother earth in one piece most ungracefully.

If you lost rudder control, depending on the situation, enough control could still exist to fly and land the plane. In the event of a jammed rudder in the neutral position, the plane could still be turned using only the ailerons on the wings, but the executed turn would be sloppy, or "uncoordinated." If the rudder jammed in the left or right position, causing the plane to constantly turn, using asymetrical thrust (independently operating the left and right engines on the wings), asymetrical drag (independently operating the left and right flaps/slats/spoilers on the wings), and ailerons might overcome the plane's turning tendencies. If the rudder was jammed in the fully deflected position, these options might not be sufficient to cancel out the turning effect of the jammed rudder but a landing could still be attempted.

All things considered, there's worse things to lose control of than a rudder, because you still have options at hand to control the situation. Losing something like the horizontal stabilizer (used for ascending and descending), however, is an entirely different matter, as that Alaskan Airlines MD-80 crash into the ocean off the California Coast a while back illustrates. That wasn't even a "controlled" crash into the water; rather, a near supersonic, somewhat inverted dive straight in...

Originally Posted by VoIPA,Jan 26 2006, 01:33 PM

OK, so it might sever a cable or two, but that's why every critical system is redundant, sometimes in triplicate or more.

Also note that there were NO injuries in any of the incidents listed above.

Originally Posted by Saki GT,Jan 25 2006, 05:28 PM

As ar as airlines go, I tend to stay away from Northwest and Continental - their fleets are on average over 20 years old, so the planes have a lot of hours and structural stress on them. Overall though, any domestic carrier's planes will be safer than other carriers since the FAA has regulations regarding how long a plane can fly in the US. These older planes end up flying in other countries for many many more years.