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On April 7, 2007, about 1430 eastern daylight time, a Cirrus Design Corporation SR20, N691CD, experienced a flight control jam during its takeoff roll at Leesburg Executive Airport (JYO), Leesburg, Virginia. The certificated flight instructor (CFI) and student pilot were uninjured. Visual meteorological conditions prevailed, and no flight plan was filed for the local instructional flight conducted under 14 Code of Federal Regulations Part 91.
According to the CFI, the student was making a right turn on to runway 35. The aileron and rudder controls "locked up" when the student pilot applied full right brake and right rudder input to turn the airplane, while simultaneously applying full left aileron to compensate for a crosswind. The student alerted the CFI of the locked controls, and transferred control of the airplane to the CFI, who then aborted the takeoff. The CFI then taxied the airplane from the runway to the aircraft parking area. The flight controls remained in a locked condition. In a written statement to the National Transportation Safety Board, the CFI advised that when the control lock occurred, "two successive clicks were heard."
The CFI held a commercial pilot certificate with multiple ratings, including airplane single-engine land. According to records provided by the CFI, he had a total flight experience of 980 hours, with 300 hours in the incident airplane make and model. His most recent Federal Aviation Administration (FAA) second-class medical certificate was issued on February 6, 2007.
The student pilot had a total flight experience of 49.2 hours, with 1.9 hours in the accident airplane make and model. His most recent FAA third-class medical certificate was issued on August 23, 2006.
According to FAA and airplane maintenance records, the airplane was manufactured in 2006. The airplane's most recent 100-hour inspection was completed on February 21, 2007. At the time of the incident, the airplane had accumulated 34 hours since the inspection and 509 total hours of operation.
Review of the incident airplane's maintenance records did not reveal any previous control problems, or any re-rigging of its flight control system since delivery.
A weather observation taken about 10 minutes after the incident included wind from 300 degrees at 16 knots, gusting to 21 knots, visibility 10 miles, and scattered clouds at 5,500 feet.
JYO was a non-towered airport. It had a single runway, designated as 17/35. The runway was asphalt, in good condition, and was 5,500 feet long by 100 feet wide.
TESTS AND RESEARCH
Initial examination of the airplane by an FAA inspector revealed that upon application of full cross control of the rudder and aileron, the Adel clamp and associated hardware on the rudder-aileron interconnect (RAI) arm became stuck on the forward cable clamp which holds the forward portion of the bungee cord to the right aileron cable.
During manipulation of the cockpit flight controls to replicate the incident scenario, the locking of the flight controls was duplicated several times. Adjustment of the rudder travel and RAI arm eliminated the problem.
Review of the Airplane Maintenance Manual
According to the manufacturer, the rudder-aileron interconnect system rigging procedures required the interconnect arm to be positioned perpendicular to the control cables before the bungee cord clamps were positioned and tightened. This would allow the rudder-aileron interconnect arm to move symmetrically forward and aft of its neutral position.
Review of the maintenance manual revealed that a full slack and cross control check of the RAI system was required to verify cable clearances; however, information pertaining to the positioning of the RAI arm was not included in the manual.
Examination of the RAI
Examination of the incident airplane's RAI system by the National Transportation Safety Board revealed that when the controls were neutralized, the RAI arm was slightly forward of its normal centerline (neutral) position, and was not perpendicular to the control cables. Rub marks were visible on the bungee jacketing in close proximity to the forward aileron bungee clamp.
Multiple attempts to lock the controls were made using different misrigging configurations, however, the only configuration that would result in locking of the flight controls was when the RAI arm was rigged forward of its specified neutral position.
Further examination revealed that when full left aileron and full right rudder inputs were applied, the RAI arm would travel far enough forward to contact the RAI bungee and forward bungee clamp, pass over them, and lock the control system.
A Second Incident
On August 6, 2007, a CFI in Van Nuys, California, advised the Safety Board’s Investigator-in-Charge that another Cirrus, N64CD, had experienced a flight control anomaly. Specifically, she stated that with the airplane on the ground and with the engine off, by moving the flight controls into the cross-controlled condition of left aileron and right rudder, she could feel aileron control hesitation, and could hear rubbing.
On August 16, 2007, Safety Board investigators, along with representatives of the FAA and the manufacturer, examined N64CD. At the time of the examination, the airplane had accumulated 366.2 total hours in service.
Examination of the airplane revealed that during application of full right rudder and full left aileron, the rudder RAI arm center clamp would contact the elevator cable, and the lower surface of the RAI arm would contact the forward portion of the bungee cord.
A check of the rigging of the airplane revealed that with the controls neutralized, the RAI arm was approximately perpendicular to the control cables, all cable tensions were within specifications, the aileron travel limits were within specifications and with the flight controls neutralized, the forward right hand aileron cable clamp was observed to be canted about 25 degrees in an upward direction towards the right wing.
The rudder neutral position was within specifications. The rudder deflection at full travel however, was found to be out of tolerance. Closer examination revealed that the rudder push/pull rod torque stripe had been removed/ broken and replaced in the past, and it was discovered that the rod end had to be turned three full turns, to bring the rudder travel back into specification.
Rub marks were also visible on the bungee jacketing in close proximity to the forward aileron bungee clamp. The forward aileron cable clamp was abutted against the radius swage of the cable terminal with the rear aileron cable clamp, 0.2 inches from the cable terminal swage. Further examination of the forward aileron cable clamp revealed that it was bent, and it exhibited polishing on the forward internal clamp radius (gripping surface) in the area abutted to the aileron terminal.
Once all of the rigging discrepancies were corrected, the interference with the bungee cord and RAI arm was no longer observed.
Bungee Cord Slippage
During the course of the investigation the manufacturer noted that a number of operators and technicians had reported occurrences of bungee cords which had slipped through the bungee cord clamps, and which could have resulted in an increase in the required roll control input forces, or affected operation of the aileron trim system. As a result, the manufacturer initiated testing to determine whether a RAI Bungee slip using normal control input forces was possible.
Over a dozen bungee cords were cyclic tested to 100% or 120% of the maximum load placed on the RAI bungee cord during a full cross control condition. All cords were tested to at least 300 cycles and one cord was tested to over 182,000 cycles before the cord began to fail internally. During the testing, only two cords were observed to slip. The maximum observed slippage was 0.02 inches. The test results were provided to the Safety Board and to the FAA's Chicago Aircraft Certification Office (ACO).
Representatives of the manufacturer and the ACO also observed a Cirrus Authorized Service Center rig an RAI. During the procedure, when standard torque was applied to the hardware securing the Adel clamp to the RAI arm, it was noted that the Adel clamp had pivoted on the end of the RAI arm, and the bungee cord had slipped approximately 1/8 inch.
Manufacturers Corrective Actions
On May 9, 2007, the manufacturer issued Mandatory Service Bulletin SB 2X-27-14, which combined a maintenance manual revision with a design change. The purpose was to enable maintenance technicians to properly rig the RAI system, in order to minimize the probability of a flight control system jam. During the course of the investigation, it was revised three more times as safety information was garnered from additional airplane examinations and bungee testing.
The maintenance manual revision provided detailed rigging instructions including the addition of torque values for the bungee clamps. The design change included replacement of the attaching hardware for the RAI arm, the addition of an "improved bungee clamp," and reoriented right hand rudder cable clamps. These changes were intended to ensure that any possible interference, caused either by bungee slippage or an out-of-tolerance RAI system, would not result in the interconnect arm catching on a cable terminal clamp, increase the required input forces, or affect the operation of the aileron trim system. The manufacturer also revised the production drawing tolerances to better reflect production rigging practices.
The manufacturer revised its production rigging specification to better describe proper rigging. In addition, the design changes included in the service bulletin were incorporated on applicable production airplanes.
The manufacturer's Product Assurance Department added a full cross control check of the flight controls to the inspection process conducted prior to the issuance of a Special Flight Permit.
In addition to the full cross control check of the flight controls which was already performed at the time of RAI installation, the manufacturer's Product Assurance Department added another full cross control check of the flight controls to the inspection process conducted prior to the issuance of a Special Flight Permit, and the Production Flight Test Department also added a full cross control check of the flight controls as part of their test procedures.
Additionally, the manufacturer introduced the SR22 G3 model line, which incorporated a redesigned wing with increased dihedral. This eliminated the need for a rudder-aileron interconnect.
FAA Corrective Actions
On January 29, 2008, the FAA issued airworthiness directive (AD) 2008-03-16, applicable to Cirrus Models SR20 and SR22 airplanes. This AD was intended to prevent the possibility of jamming of the rudder-aileron interconnect system, which could result in loss of control of the rudder and aileron. The AD required inspection of the rudder, aileron, and rudder-aileron interconnect rigging, correction any out-of-rig condition, replacement of the attaching hardware for the rudder-aileron interconnect arm, and reporting any out-of-rig condition that was found.