safetyOVERSIGHT

breaking the ICE jam Directive targets frozen controls in Citations.

BY MARK LACAGNINA

eacting to recurring incidents — within 12 months or 800 an external inspection of the airplane, involving Cessna 560XL rud- flight hours, whichever comes first. the pilot tried to move the by der jamming, the U.S. Fed- The directive is the latest in a series of hand, but it would not budge. Mainte- eral Aviation Administration actions dating back to April 2005, when nance personnel found ice in the tailcone (FAA)R has issued an airworthiness di- Cessna began drilling drain holes in the stinger, and further examination by an rective (AD) requiring modifications bottom of the tailcone stingers on pro- FAA inspector revealed that although a to reduce the amount of water that duction airplanes and issued a service let- drain hole had been incorporated per the can accumulate in the aft and ter, SL560XL-53-05, recommending that service letter, it was smaller than specified. freeze on the rudder control cables owners of existing 560XLs do the same. The inspector examined other 560XLs and pulleys. One of the first indications that the fix in a maintenance hangar at Toledo and Effective April 25, the AD, 2012- was not successful came about five years found three that also had drain holes 06-01, applies to about 475 Cessna later. On Dec. 1, 2010, a pilot was unable smaller than specified by SL560XL-53-05. 560XLs — the Citation Excel, XLS to move the rudder pedals when he at- Twelve days later, on Dec. 13, 2010, and XLS+ — registered in the United tempted to initiate a crosswind correction a flight crew found that rudder control States. It requires, in part, the installa- while landing at Toledo, Ohio. No dam- was “unusually stiff” after disengaging tion of water drain holes and air seals age or injuries occurred, but differential the and yaw damper on final in the “tailcone stingers” — the aftmost thrust and wheel braking had to be used approach to Birmingham, Alabama. As

portion of the fuselage, beneath the to taxi the airplane to the ramp. During in the Toledo incident, the airplane was © Chris Photography Sorensen

20 | flight safety foundation | AeroSafetyWorld | April 2012 safetyOVERSIGHT

landed without further event, and the crew had the pilots saw water dripping from the airplane; to use the brakes to steer the business jet to the further inspection revealed ice in the bottom of ramp. Investigators for the U.S. National Trans- the tailcone stinger. portation Safety Board (NTSB) found another In its response to NTSB, the FAA also noted similarity: Both airplanes had been parked that it had participated with Cessna in test-flying outside in the rain before the incident flights an ASL-compliant airplane equipped with video and had encountered freezing temperatures en cameras in the tailcone stinger. The tests showed route. Unlike the Toledo incident, however, the in part that air could enter through seams in the Birmingham airplane had a drain hole that met bottom of the stinger and through one of the the dimension specified by the service letter. drain holes with enough velocity to splatter water During the investigation, NTSB also found onto the rudder pulleys and cables. Only after that a similar incident had occurred at Idaho building up in a large quantity would water over- Falls, Idaho, on Dec. 20, 2010. come the air flowing into the drain hole and exit The incidents prompted Cessna to issue an the stinger. The FAA told NTSB that the inves- alert service letter, ASL560XL-53-08, on Jan. 21, tigation was continuing and that several design Modifications include 2011, advising owners to seal the hole prescribed changes were being considered. seals to reduce the by the initial service letter and to drill two new NTSB classified the FAA’s response as “ac- amount of water drain holes — in the forward stinger bulkhead ceptable” and stated that the recommendation and air entering the and in the tailcone frame forward of the stinger. would remain open until further action was tailcone, and holes to NTSB recommended that an AD be issued to taken. That action came on Oct. 4, 2011, when improve drainage. mandate compliance with the alert service letter, Cessna issued a service bulletin, SB560XL-53-16, but the FAA cited evidence that the specified introducing “additional modifications to reduce modifications had not the amount of moisture that can enter the tail- solved the problem. cone stinger and improve drainage.” Foremost, there had The FAA followed up in December with a been another incident, proposal to mandate compliance with Cessna’s this time involving a service bulletin, as well as the earlier alert 560XL that had been service letter where applicable. The agency modified accord- explained that while parked or during ground ing to the ASL. The operations in rain, a 560XL can accumulate a airplane was en route large amount of water that pools in the lowest from Baltimore to the point of the stinger. “This water sprays onto the Bahamas on March rudder bias cables and pulley due to the inflow 10, 2011 — after hav- of air into the stinger,” it said. “Therefore, as ing been on a ramp the airplane climbs to temperatures below 32 in moderate rain for degrees F, the water freezes on the cables, pul- 1.5 hours — and was leys and mounting brackets. The ice acts as an climbing through 29,000 ft when the pilot flying adhesive, which prevents the pulleys from rotat- noticed that the yaw damper was not functioning ing and the cables from sliding on the pulleys.” normally. After disengaging the yaw damper and NTSB has told FAA that although it believes the autopilot, he exercised the flight controls and the airworthiness directive will “accomplish found that the rudder was jammed. The crew de- the desired safety result,” Cessna 560XL owners cided to divert to Myrtle Beach, South Carolina. should modify their airplanes before the allotted “Descending through 13,000 ft, normal rudder 12 months or 800 flight hours. “Accomplishing the operation returned, and the subsequent approach AD in the shortest time frame is appropriate, given and landing [at Myrtle Beach] were uneventful,” that the loss of rudder authority may go undetect- the NTSB report said. After parking the airplane, ed until the moment it is needed.” 

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