Covington, KY, USA
N709CA
Bombardier CL600-2B19
The Bombardier CL600-2B19 regional jet experienced aileron control stiffness during cruise flight. The airplane was pushed back during a period of moderate to heavy rain. After pushback, the airplane was held on the taxiway for about 30 minutes while the rain continued. Takeoff also occurred during a period of heavy rain. After leveling off at flight level 280, while in cruise flight, the "AP TRIM IS LWD" caution annunciator illuminated. The first officer disconnected the autopilot, and found the aileron controls to be "stiff and binding." The captain then took control of the airplane, and also found the aileron controls to be stiff and binding. The captain applied "light to moderate" roll input and felt a snap. Aileron control then operated normally. The captain executed left and right turns with no additional problems or binding noted. The crew re-engaged the autopilot, and the flight continued to an uneventful landing. On the same date, two other CL600 regional jets from the same airline also experienced aileron stiffness after taking off at the same airport and in similar weather conditions. Both airplanes landed uneventfully. One of the airplanes diverted to an alternate airport. The investigation revealed that approximately 40 Bombardier CRJ CL-600-2B19 regional jets experienced in-flight aileron control stiffness after standing/taxiing in, or taking off during rainy conditions, then climbing to freezing temperatures. When the jets descended to above-freezing temperatures, the aileron control stiffness ceased. Testing revealed that aileron circuit binding occurred in the area of the Brake and Position Sensor Unit (BPSU) bay. Typically, within the bay, horizontally-oriented pulleys in the aileron control circuit would seize, and the aileron cable, after being subjected to water soaking, would freeze to the pulley. Water ingress to the bay most likely occurred via an aging self-contouring sealing pad on an access panel directly above the pulleys. The horizontal orientation of the pulleys, which had been used without difficulty in transport category aircraft for over 20 years, and the dished cross section of the pulley face allowed the retention of water when the airplane was parked. In addition, the drying of pulley grease over time, combined with water migration from rain, could temporarily allow the bearing to seize when the airplane reached altitude. A test on a dry-bearing pulley revealed that when water was applied to the pulley face, it remained pooled until the pulley was moved, when it flowed into the bearing. Prior to the incidents, the manufacturer had not issued specific instructions to inspect pulleys in the BPSU bay. Subsequent service letters and airworthiness directives to inspect the pulleys, grease the aileron cables and replace aging and seized pulleys, resulted in over 60 seized and deteriorating pulleys being found fleet wide. There have been no further aileron control stiffness events on aircraft which had undergone the new inspection/maintenance procedures.
On May 8, 2002, about 1100 eastern daylight time, a Bombardier CL600-2B19 regional jet (CRJ), N709CA, hull number 7238, operating as Comair flight 5883, experienced aileron control stiffness during cruise flight, after departing Cincinnati/Northern Kentucky International Airport (CVG), Covington, Kentucky. The captain, first officer, flight attendant and 15 passengers were not injured. The flight was operating on an instrument flight rules flight plan to Eppley Airfield (OMA), Omaha, Nebraska. The scheduled passenger flight was conducted under 14 CFR Part 121. According to the company's irregular operations report, the airplane was pushed back during a period of moderate to heavy rain. After pushback, the airplane was held on the taxiway for about 30 minutes while the rain continued. Takeoff, about 1030, also occurred during a period of heavy rain. After leveling off at flight level 280, while in cruise flight, the "AP TRIM IS LWD" caution annunciator illuminated. The first officer disconnected the autopilot, and found the aileron controls to be "stiff and binding." The captain then took control of the airplane, and also found the aileron controls to be stiff and binding. The captain applied "light to moderate" roll input and felt a snap. Aileron control then operated normally. The captain executed left and right turns with no additional problems or binding noted. The crew re-engaged the autopilot, and the flight continued to an uneventful landing. On the same date, about the same time, a second CRJ, N937CA, hull number 7044, operating as Comair flight 5296, also experienced aileron control stiffness after departing Cincinnati/Northern Kentucky International Airport. The captain, first officer, flight attendant and 38 passengers were not injured. The flight was operating on an instrument flight rules flight plan to Will Rogers World Airport (OKC), Oklahoma City, Oklahoma. The scheduled passenger flight was conducted under 14 CFR Part 121. According to the company's director of corporate safety, the flight had also departed about the same time as flight 5883. As reported in the company's irregular operations report, the airplane was climbing from flight level 290 to flight level 310, when the "autopilot RWD trim" caution annunciator illuminated. The crew completed the appropriate quick reference handbook (QRH) procedures, but 1 to 2 minutes later, the autopilot RWD trim caution annunciator again illuminated. The first officer disconnected the autopilot and felt he had jammed aileron controls. The captain then attempted fly from his side and also found the ailerons jammed. The crew completed the QRH jammed-aileron procedures, and diverted to Lambert-St. Louis International Airport (STL), St. Louis, Missouri. About 1330, a third CRJ, N977CA, operating as Comair flight 5261, hull number 7157, also experienced aileron control stiffness while in cruise flight, after departing Cincinnati/Northern Kentucky International Airport about 1245. The captain, first officer, flight attendant and 17 passengers were not injured. The flight was operating on an instrument flight rules flight plan to Lehigh Valley International Airport (ABE), Allentown, Pennsylvania. The scheduled passenger flight was conducted under 14 CFR Part 121. According to the company's irregular operations report, the LWD caution annunciator illuminated while the airplane was in cruise at flight level 290. The captain, who was the non-flying pilot, went through the pertinent QRH procedures and disconnected the autopilot. The autopilot was re-engaged, and the LWD caution annunciator again illuminated. The autopilot was again disconnected, "and the crew attempted to move the ailerons to no avail." The controls were not split. The captain contacted the company's maintenance control personnel, and was advised that his was the third similar event of the day and to descend to a lower altitude. The crew descended the airplane to 15,000 feet and felt the ailerons slowly loosen. The crew declared an emergency and landed without further incident at Lehigh Valley. Weather, recorded at Cincinnati/Northern Kentucky International Airport at 1038, included heavy rain and mist. The weather, recorded at 1251, did not include rain; however, according to Comair's director of corporate safety, the airplane taxied through standing water prior to takeoff. On June 6, 2000, a CRJ, N952C, hull number 7017, also experienced aileron control stiffness, which was documented as Safety Board occurrence number NYC00SA153. At the time, older CRJs, including hull number 7017, did not have main landing gear wheel bay splash shields installed. As a result of the investigation, Transport Canada and the Federal Aviation Administration (FAA) issued airworthiness directives (ADs) to require CRJ hull numbers 7003 through 7323 have the splash shields installed. The incident airplanes were in compliance with the existing ADs. On May 29, 2002, a meeting, facilitated by the Safety Board, was held at Comair facilities in Cincinnati, Ohio. Attendees included representatives from Bombardier Aerospace (BA), Transport Canada (TC), the Canadian Transportation Safety Board (TSB), the Federal Aviation Administration (FAA), the Airline Pilots Association (ALPA), and CRJ operators. Discussions at the meeting included history, benchmarking, and preliminary recommendations. BA reported that approximately 600 CRJs had been delivered, with 68 per cent in North America. To that date, BA had been notified of 29 control stiffness cases, with 27 occurring while airborne. Four cases in Europe involved anti-icing residue. The earlier ADs to install splash shields in the main wheel bays of older airplanes had been effective "until recently." Shields had been designed to allow a 0.040 inch gap between it and a composite wheel bin ("bathtub") in each wheel well. Incident airplanes were found to have much larger gaps, up to 0.20 inch. Immediately behind the wheel bin, about 3 feet inboard the ice guard, was the aileron quadrant assembly. There were four bearings within the assembly, one of which, BA personnel determined to be more susceptible to freezing when saturated with water. As an interim measure, BA recommended lubricating the bearings, which the operators felt was beyond their maintenance capability since it would require maintenance personnel to disassemble, then reassemble and re-rig the assembly. One of the operators recommended, and had produced a new splash guard model that also added a pliable seal on the side of the wheel bin, which BA agreed to evaluate. BA also recommended interim flight procedures to exercise the bearings via the flight controls (the bearing moved less than 1/2 degree, 75 percent of the time) every 5,000 feet during climbs that involved precipitation, which was agreed to by the operators and ALPA; however, they wanted flight testing to determine how much pilot action was required for passenger comfort and concerns. BA also announced a long-term fix to redesign the quadrant assembly. After the meeting, the operators examined and corrected splash guard-wheel bin gaps, and Comair conducted misting and freezing experiments which resulted in a vertical and horizontal pulley freezing to each other, and determined that water splashed onto the ceiling of the wheel well would likely drip onto the pulleys. On June 12, 2002, the ALPA representative suggested that a CRJ be equipped with wheel well cameras to taxi through and take off from water-contaminated runways to validate water flow. That recommendation was passed to BA by the Safety Board; however, BA was not able to flight test until August 29, 2002, and September 12, 2002. On August 9, 2002, BA issued CRJ Temporary Revision (TR) RJ/109-2, effective for airplanes that had accumulated in excess of 5,000 hours of operation. The TR required that after an airplane departed a wet or contaminated runway, and had climbed to 10,000 feet mean sea level or when the temperature reached 32 degrees Fahrenheit, whichever occurred later, the ailerons had to be operated every 5,000 feet until the top of the climb. It also required in the Airplane Flight Manual, Emergency Procedures Section, that if frozen ailerons were suspected after departing a wet or contaminated runway, sufficient force must be applied on the affected side to free the jam. If unable to free the jam, descend into warmer temperatures. If still unable to free the jam, land at the nearest suitable airport, selecting the longest runway available with the minimum turbulence and crosswind. On August 16, 2002, TC issued Canadian AD CF-2002-35R1, which made TR RJ/109-2 mandatory for continued airworthiness in Canada. On September 16, 2002, the FAA issued AD 2002-19-07, effective October 10, 2002, which also required the utilization of TR RJ/109-2 for continued airworthiness in the United States. On September 17, 2002, a second meeting was held at Comair facilities, with the same parties in attendance. BA reported, that since the previous meeting, there had been five additional control stiffness reports with three of those occurring in North America and two occurring in Europe. All occurred in heavy rain and/or standing water, and all were confirmed in climb or cruise. During four of the five events, the autopilot trim LWD/RWD EICAS was illuminated. BA also reported the results of two flight tests, and provided a main landing gear bay video that revealed some ingestion of water, but very little dripping on the control cables and pulleys. Flight test data was still being evaluated. BA had also conducted destructive bearing analysis of aileron aft control quadrants that had been removed from service. In the examinations, seals were found lifted in local areas, and there was the presence of contaminants in the bearings, some corrosion on inner races, and some bearings were not installed per drawings. Short term initiatives by BA were to provide substantiation data to TC in support of an Alternate Means of Compliance (AMOC), to lubricate quadrants in situ, lubricate cable and pulleys inside the main landing gear bay, and dry and lubricate the autopilot clutch. Maintenance intervals were still under consideration, and would depend on the operator environment. The AMOC was subsequently not approved by TC. On April 9, 2003, a third meeting was held, at BA facilities in Montreal. BA reported that there had been 7 more events reported since the previous meeting, for a total of 39. All of the seven airplanes involved had in excess of 9,800 flight hours, and all the events involved heavy rain and/or standing water. On May 22, 2003, BA issued Service Letter RJ-SL-27-060, "Aileron Binding Update and Maintenance Recommendations." The discussion section of the Service Letter described previous actions taken, as well as new findings and developments discussed in the April 9th meeting: One of the findings included additional main landing gear bay testing results. In addition to the lower quantity of expected water ingestion, the monitoring of main landing gear bay temperatures revealed that even in "very low" outside air temperature conditions, the relative warmth of the bay precluded binding by the formation of ice within the bay, or on components within the bay. Another finding precluded the formation of ice on aileron cable seals between the pressurized cabin and the unpressurized wheel well area as a root cause of the binding. In addition, cold temperature testing on exposed and water-soaked flight control components along the rear spar failed to identify conditions where ice might form on normally-functioning components, and result in a binding condition. A further finding by BA was that the staked ball bearings used in the quadrant assembly were not causes for binding. Reported bearing failure events were, in fact, only "ratcheting noises" detected during aileron movement. Nevertheless, BA indicated a redesign the quadrant would occur as a long term product improvement initiative, but not a result of the aileron binding issue. Another scenario emerged which suggested that the combination of ice formation on control cables, along with a seized pulley in the aileron control circuit, could provide the conditions required for a binding event. On one airplane that a binding event had occurred, a horizontally-oriented pulley in the Brake and Position Sensor Unit (BPSU) bay was seized, so that the aileron cable slide back and forth without rotating the pulley. The cable in the area of the pulley was corroded. Seized and deteriorating pulleys had been discovered on a number of airplanes. Likely water ingress was via an aging self-contouring sealing pad on an access panel directly above the pulley. Other contributors to pulley seizure were the horizontal orientation of the pulley, and the dished cross section of the pulley face, which would allow it to retain water when the airplane was parked. An additional possibility of pulley seizure stemmed from the drying of the pulley grease over time, combined with water migration from rain, could temporarily allow the bearing to seize due to icing when the airplane reached altitude. A test on a dry-bearing pulley revealed that when water was applied to the face of the pulley, it remained pooled until the pulley was moved, when it appeared to flow into the bearing. Service Letter RJ-SL-27-060 also recommended the greasing of pulley cables, and the examination of all wing control pulleys on previous jam-event airplanes, and those airplanes over 10,000 hours of operation. Additional information, not included in the service letter, but as part of the overall investigation, included: - The pulleys utilized were a "custom made variation of the standard MS20220 pulley, manufactured for BA by Ralmark [Company]", and had been used for about 20 years, both horizontally and vertically, on a wide range of transport aircraft. The pulleys were a "standard MIL-P-7034, but with a modified cable groove [to] provide better cable support, and hence improved cable life, than the MS version." - There had been no specific inspection procedures or instructions to inspect pulleys in the CRJ BPSU bay. - Worldwide fleet inspection revealed that over 60 pulleys were seized, or suspect. - All four pulleys in the BPSU bay could be subject to water accumulation due to dripping from access panels. - Comair experienced a higher degree of aileron binding after the CRJ fleet had been parked on the ramp for 3 months. - Capillary effect could result in water flow onto bearing faces. - Water could then flow into bearing voids left by dried grease. - Unlike the main landing gear bays, BPSU bay temperatures were close to ambient temperatures. On July 28, 2003, BA issued Service Letter RJ-SL-27-129, "Aileron Control Cable Pulleys - Supply of initial Provisioning Kits to Support Introduction of Service Bulletin SB-601R-27-129, Inspection of the Aileron Wing Pulleys." On August, 7, 2003, revised September 9, 2003, BA issued Alert Service Bulletin A601R-27-129, "Flight Controls - Aileron Control System - Inspection of the Pulleys of the Aileron Control System in the Wings." On January 29, 2004, BA issued Service Bulletin 601R-27-135, "Flight Controls - Aileron Control System - Replacement of the Outboard Aileron Pulleys. On February 2, 2004, BA issued Aircraft Maintenance Manual Temporary Revision 27-313, for the "removal and installation of the outboard aileron pulleys." Following the implementation of the BA/TC/FAA initiatives, there were "one or two" cases where bad pulleys were missed by technicians. BA then introduced a "discard task" which avoided the judgment of the technician to decide if a pulley was bad or good. There have subsequently been no cold temperature binding of any of the new or low time pulleys. On January 6, 2005, TC issued AD CF-2002-35R2, effective January 30, 2005, which superseded AD CF-2002-35R1. The new AD required, within 60 days, that certain Maintenance Tasks be incorporated in the Maintenance Requirements Manual. Tasks addressed the lubrication of the aileron autopilo
The manufacturer's failure to provide inspection criteria for the BPSU compartment aileron control pulleys, which resulted in eventual pulley corrosion, and subsequent control stiffness when seized pulleys and water-soaked aileron cables froze together at altitude. Factors included leaking BPSU bay access panel seals, precipitation, and freezing temperatures.
Source: NTSB Aviation Accident Database
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