Delta Connection incidents highlight CRJ design flaws

 - April 17, 2008, 6:51 AM

The world’s most commercially successful line of regional jets added a pair of new blemishes to its technical record late this spring, when both wholly owned Delta Connection subsidiaries confronted some unsettling moments during scheduled CRJ operations. Cincinnati-based Comair and Atlanta-based Atlantic Southeast Airlines–which together as Delta Connection represent Bombardier’s largest CRJ customer–each made local news following incidents in which their 50-seat jets revealed problems with their respective aileron controls and landing gear.  

In Comair’s case, three separate incidents involving aileron control stiffness, all on May 1, occurred as the aircraft ascended to cruise altitude after takeoff from Cincinnati Northern Kentucky Airport. In the first incident, after experiencing “stiff and binding” aileron controls, the captain applied “light to moderate” roll input and felt a snap, after which the controls worked normally and the crew completed its intended flight to Omaha, Neb. At about the same time, the crew of another Comair CRJ en route to Oklahoma City diverted to St. Louis for an emergency landing after they felt what they described as “jammed” ailerons accompanied by an “autopilot RWD trim” caution. The third airplane completed its flight to Allentown, Pa., without further incident.     

The reports led to an NTSB investigation and a subsequent plan to modify splash shields installed in the main-landing-gear wheel bays on CRJ100s and 200s. The three airplanes, all of which departed in heavy rain, complied with an October 2000 FAA advisory directive to install the splash shields. That AD followed a 1999 Bombardier Service Bulletin, prompted by an incident earlier that year in which a Brit Air of France CRJ experienced similar aileron stiffness in flight after taxiing through snow and slush.

However, the NTSB investigation prompted by the May 1 incidents found that the aluminum shields do not completely prevent water from entering the aileron quadrant when the airplane rolls through standing water. Once the airplane reaches a high enough altitude, the water freezes, affecting the operation of an aileron control bearing. Bombardier director of CRJ100 and CRJ200 programs Gilles Lambert told AIN that contrary to the statements attributed to the pilots in the NTSB report, none of the incidents involved “jammed” controls, but simply stiffness that required no more than 15 lb of force to overcome. The FAA imposes a limit of 60 lb of “break-out” force in its FARs.   

Bombardier engineers have devised a solution to the problem that involves the use of a rubber seal to fit around the splash guards, thereby making the vulnerable areas virtually waterproof. The company must also write new advisory material for the CRJ’s flight manuals. At press time the company continued its work with the FAA and NTSB to agree on the wording. Finally, engineers have begun devising a new inspection and lubrication procedure for the suspect bearing. Lambert said the seal retrofits and new inspection/lubrication procedure need to be performed only during scheduled C-checks, and that the problem didn’t warrant a general fleet-wide retrofit program.

Meanwhile, Bombardier awaited word from the NTSB on an incident whose cost implications could prove more severe. Just a month after the aileron problems at Comair, the left main landing gear of a CRJ flown by Atlantic Southeast Airlines collapsed during landing at Atlanta Hartsfield International Airport. As in the Comair cases, none of the 50 passengers or three crewmembers suffered injuries, but the airplane sustained “substantial” damage. According to a preliminary NTSB report, examination of the airplane found the left main landing gear trunnion fractured just below its attach point to the wing spar. Safety Board officials removed the gear from the airplane and sent it to Washington for further testing and X-ray examination.

The June 2 incident in Atlanta closely resembled a November 1999 event in which a Lauda Air CRJ also experienced landing gear failure in Romania. Although investigators have yet to determine the cause of that incident, a Bombardier Service Bulletin and subsequent FAA AD call for an eddy current inspection to detect cracking of the gear’s main fittings after every 500 flight cycles. They also call for increased service and inspection of the gear’s shock struts.

The incidents involving the Delta Connection CRJs followed an FAA emergency AD in March that addressed a fuel system defect in the 70-seat CRJ700. The problem centered on uncommanded fuel transfer between the airplane’s wing tanks and center tank. Such a condition could cause the center tank to overfill and leak from the vent system, resulting in fuel starvation. Bombardier corrected the problem, determined to be caused by a loose fuel transfer coupling, on all 31 CRJ700s in service by the end of March.