A tail strike can occur during either takeoff or landing. Many air carrier aircraft have tail skids to absorb energy from a tailstrike. On some aircraft, the tail skid is a small bump on the aft underside of the airplane, while on others it is a retractable skid that extends and retracts with the landing gear. Most tail strikes are the result of pilot error, and in general, landing tail strikes cause more damage than takeoff tail strikes. In 1978, Japan Airlines flight 115 experienced a tail strike during landing that caused damage to the aft pressure bulkhead. The aircraft was repaired (although the repair was faulty) and returned to service. Seven years later, the aircraft, operating as Japan Airlines Flight 123, crashed as a result of the failure of the improperly-repaired pressure bulkhead. This Boeing document is an excellent analysis of tailstrikes. A portion of the document is reproduced below: Takeoff Risk Factors Any one of these four takeoff risk factors may precede a tail strike: Mistrimmed stabilizer. Rotation at improper speed. Excessive rotation rate. Improper use of the flight director. MISTRIMMED STABILIZER A mistrimmed stabilizer occurring during takeoff is not common but is an experience shared at least once by almost every flight crew. It usually results from using erroneous data, the wrong weights, or an incorrect center of gravity (CG). Sometimes the information presented to the flight crew is accurate, but it is entered incorrectly either to the flight management system (FMS) or to the stabilizer itself. In any case, the stabilizer is set in the wrong position. The flight crew can become aware of the error and correct the condition by challenging the reasonableness of the load sheet numbers. A flight crew that has made a few takeoffs in a given weight range knows roughly where the CG usually resides and approximately where the trim should be set. Boeing suggests testing the load sheet numbers against past experience to be sure that the numbers are reasonable. A stabilizer mistrimmed nosedown can present several problems, but tail strike usually is not one of them. However, a stabilizer mistrimmed noseup can place the tail at risk. This is because the yoke requires less pull force to initiate airplane rotation during takeoff, and the pilot flying (PF) may be surprised at how rapidly the nose comes up. With the Boeing-recommended rotation rate between 2.0 and 3.0 degrees per second (dps), depending on the model, and a normal liftoff attitude, liftoff usually occurs about four seconds after the nose starts to rise. (These figures are fairly standard for all commercial airplanes; exact values are contained in the operations and/or flight-crew training manuals for each model.) However, with the stabilizer mistrimmed noseup, the airplane can rotate 5 dps or more. With the nose rising very rapidly, the airplane does not have enough time to change its flight path before exceeding the critical attitude. Tail strike can then occur within two or three seconds of the time rotation is initiated. If the stabilizer is substantially mistrimmed noseup, the airplane may even try to fly from the runway without control input from the PF. Before reaching Vr, and possibly as early as approaching V1, the nose begins to ride light on the runway. Two or three light bounces may occur before the nose suddenly goes into the air. A faster-than-normal rotation usually follows and, when the airplane passes through the normal liftoff attitude, it lacks sufficient speed to fly and so stays on the runway. Unless the PF actively intercedes, the nose keeps coming up until the tail strike occurs, either immediately before or after liftoff. ROTATION AT IMPROPER SPEED This situation can result in a tail strike and is usually caused by one of two reasons: rotation is begun early because of some unusual situation, or the airplane is rotated at a Vr that has been computed incorrectly and is too low for the weight and flap setting. An example o