Cirrus Design last week issued a mandatory service bulletin for all 3,300 SR20 and SR22 piston singles, calling for owners to modify the aircraft's rudder-aileron interconnect mechanism within 25 flight hours or three months to prevent possible jamming. This is the second full-fleet alert in as many months for Cirrus. In April, the company mandated changes to the aircraft's parachute recovery system following a flawed parachute deployment on an SR22 in Australia in February.
The interconnect bulletin follows a 7 April incident where the rudder and aileron controls on an SR20 "locked up" as a student pilot and his flight instructor taxied on to a runway in Leesburg, Virginia, for take-off. US National Transportation Safety Board investigators say the jam occurred when the student applied full right rudder and right brake to turn on to the runway while applying full left control wheel to compensate for a strong crosswind. The instructor aborted the take-off and taxied back to the ramp, with the flight controls "still in a locked position".
Ian Bentley, vice-president of customer service for Cirrus, explains that the SR20 and SR22 have a bungee chord interconnect between the two controls because the Cirrus wing dihedral is not large enough to adequately control the aircraft with rudder alone, a US Federal Aviation Administration certification requirement. The new SR22-G3, introduced at the Sun 'n' Fun show in Florida in April, has an extra degree of dihedral specifically to eliminate the rudder-aileron interconnect, says Bentley.
Cirrus officials determined that the jam was related to improper control system rigging and developed a fix that involves "minor hardware changes" that include low-profile screws. Bentley says Cirrus found that a number of aircraft had been "mis-rigged" in the field, but it was not clear who was at fault. The NTSB, in its preliminary report, said information key to correctly rigging the system was not provided in the aircraft maintenance manual.
Bentley says Cirrus has asked the FAA to follow up the service bulletin with an airworthiness directive that would require all operators to have their interconnect rigging checked. By incorporating the hardware changes called out in the service bulletin however, Bentley says a control jam will not occur even if the rigging is incorrect.
Source: Flight International
