AL 2000-04
9 May 2000
Rudder Jam
Recently, a Cessna Model 152 was involved in a fatal stall/spin accident. A flight instructor and student pilot were performing a spin manoeuvre and were unable to recover. When the aircraft was inspected, investigators found the rudder to be jammed. During a 50-hour check the day before the accident, the right pedal rudder bar return spring and its lever arm were found to be broken. The broken pieces of the rudder control system were removed without replacement. On completion of the 50-hour checks, the airplane was returned to service with no reference to the outstanding defect recorded in the logbook.
After examining the accident aircraft and other 152s (swept-tail 150s have the same rudder control system design), accident investigators determined that, under certain conditions, it is possible to jam the rudder past its normal travel limit. The jam occurs when the stop plate on the rudder horn is forced aft of the stop bolt head. The forward edge of the stop plate can then become lodged under the head of the stop bolt causing the right and left pedal rudder bar return springs which maintain tension on the rudder cables. Accident investigators believe that the missing rudder pedal return spring, in addition to extreme rudder pedal inputs, contributed to the conditions that allowed the rudder to jam. Recovery from a spin may not be possible with the rudder jammed beyond the normal rudder travel stop limits.
To prevent reoccurrence of the rudder jamming in this way, The Cessna Aircraft Company is investigating possible design changes to the rudder stops. With or without these design changes, operators and maintenance personnel should be aware of the importance of maintaining the integrity of the rudder control system, including the pedal return springs. There are a number of important items to keep in mind while inspecting the rudder control system:
- The condition of the rudder structure. There should be no damage or distortion, especially in the area of the rudder horn attachment.
- The condition of the rudder horn. A number of in-service rudder horns have been found bent or distorted, thus not allowing the stop plate to contact the stop bolt head squarely or allowing the stop plate to contact the side of the tailcone structure above or below the stop bolts.
- The condition of the rudder horn stop plate. The stop plate should contact the stop bolt head squarely. The lip at the forward edge of the stop plate should not contact the stop bolt head prior to contact with the contact face of the plate. Ensure the integrity of the stop plate lip.
- The condition of the rudder pedals and rudder pedal torque tubes. Check for free movement of the rudder pedals, and verify there is no interference of the pedals, torque tube cable arms or the return spring arm with the surrounding structure or other control system components (the accident aircraft showed signs of interference of the rudder cable attachment bolt with the adjacent aileron cable pulley).
- Correct rigging of the rudder control system, including:
- Proper adjustment of the rudder travel stop bolts;
- Correct adjustment of rudder cable length (to provide correct rudder pedal position and correct cable tension through return spring tension); and
- Proper nose gear steering tube (bungee) length.
As described above, even small deviations can contribute to tragedy.
Any defects or further occurrences should be reported by sending a Service Difficulty Report to Transport Canada, Continuing Airworthiness, Ottawa.
For further information contact a Transport Canada Centre, or call Mr. Mark Stephenson, Continuing Airworthiness, Ottawa, telephone (613) 952-4363, facsimile (613) 996-9178 or e-mail stephma@tc.gc.c.
For Director, National Aircraft Certification
B. Goyaniuk
Chief, Continuing Airworthiness