Crash During Approach to Landing, Circuit City Stores, Inc., Cessna Citation 560, N500AT, Pueblo, Colorado, February 16, 2005

but not much,” the captain said. “Little sticky ice today,” the first officer said. The flight crew did not activate the deice boots again during the descent and approach. The report noted that the spring-loaded surface-deice switch in the Citation V has two positions: “MANUAL” and “AUTO.” When the switch is held in the “MANUAL” position, all of the deice boots inflate simultaneously and remain inflated until the switch is released. Selection of “AUTO” initiates an 18-second cycle in which the various deice boots are inflated and deflated in a specific sequence. After the cycle is completed, With deice boots of modern design on the airplane, pilots do not need to worry about the phenomenon of ‘ice bridging.’ When the surface- deice switch in the Citation V is selected to ‘AUTO,’ the boots cycle once; in ‘MANUAL,’ all the boots inflate and remain inflated until the switch is released. Christine Lacagnina © Chris Sorensen Photography | 31 WWW.flightsafety.org | AeroSAfetyWorld | May 2007 cAuSAlfactors the boots remain deflated until the surface-deice switch is selected to “AUTO” again. Ice Bridging Fallacy During postaccident interviews, instructors at CAE SimuFlite, Martinair’s training provider, told investigators that they teach pilots to acti- vate deice boots after 1/4 to 1/2 in (6 to 13 mm) of ice has accumulated on them. The report said that the SimuFlite Cessna Citation V Technical Manual states, “Early activation of the boots may result in ice bridging on the wing, render- ing the boots ineffective.” “Ice bridging is a phenomenon in which ice in the shape of an inflated deice boot forms after the boot is cycled,” the report said. “Ice bridging had been known to occur on older deice boot designs that used larger tubes and lower pressures, result- ing in slower inflation and deflation rates.” However, research has shown that ice bridging is not a risk for modern turbine airplanes equipped with segmented, high-pressure deice boots that inflate and deflate quickly, the report said. In Advisory Circular 25.1419-1A, issued in May 2004, the FAA says that pilots should not wait for a specific amount of ice to accumulate before activating deice boots. “Although the ice may not shed completely with one cycle of the boots, this residual ice will usually be removed during subse- quent boot cycles and does not act as a foundation for a bridge of ice to form,” the FAA said. The report said that concern about ice bridg- ing is no reason for pilots of modern airplanes to delay activation of deice boots. “Activating the deice boots as soon as an airplane enters icing conditions provides the greatest safety measure,” the report said. Airspeed Factor Omitted While conducting the “Approach” checklist at 0859, the first officer said that the landing refer- ence speed, Vref, was 96 kt. An approach-airspeed adjustment required by company standard operat- ing procedures (SOPs) had not been applied. “In accordance with company guidance, if any amount of residual ice — that is, ice that re- mains on the deice surface after the deice boots have been cycled — is present, Vref should be increased by 8 kt, which would have resulted in a Vref of 104 kt instead of the 96 kt reported by the first officer,” the report said. At 0905, the approach controller told the crew to fly a heading of 240 degrees. The controller said that the heading was a vector to the final approach course for the ILS approach to Runway 26R. The first officer, who had prepared for the ILS approach to Runway 08L, told the captain, “He did a change on us here.” He then retuned the navigation receivers and set the instruments for the ILS approach to Runway 26R. “During postaccident interviews, the control- ler stated that he was often asked by corporate the Cessna Model 560 Citation V is a derivative of the Model S550 Citation S/II, with a fuselage stretched 2.0 ft (0.6 m) and higher- performance Pratt & Whitney JT15D-5A engines, each producing 2,900 lb (1,315 kg) thrust. Deliveries began in 1989. The Citation V can accommodate two pilots and eight passengers. Maximum takeoff weight is 15,900 lb (7,212 kg). Maximum landing weight is 15,200 lb (6,895 kg). Maximum rates of climb are 3,650 fpm with both engines operating and 1,180 fpm with one engine operat- ing. Maximum operating speeds are 292 kt below and 0.76 Mach above 29,000 ft. Maximum operating altitude is 45,000 ft. The Citation V was replaced in 1994 by the Citation Ultra, which has increased performance, a higher payload, a digital autopilot and electron- ic flight instrument systems. The current version of the Model 560 is the Citation Encore, introduced in 2000 with more powerful engines, a longer wing with improved stall characteristics and other improvements. Source: Jane’s All the World’s Aircraft Cessna Citation V Cessna Aircraft Co. 32 | flight safety foundation | AeroSAfetyWorld | May 2007 cAuSAlfactors pilots to use the runway opposite that being advertised on ATIS [i.e., reciprocal runway] and that, as a service, he would provide the closest runway as a matter of course as long as the winds allowed it,” the report said. SLD Conditions At 0908, while discussing the location of a regional airplane that was holding at 9,000 ft to reduce its fuel load for landing, the first officer told the approach control- ler that the Citation had entered IMC at 9,400 ft. A few minutes later, the control- ler told the crew to fly a heading of 290 degrees to intercept the localizer at 7,000 ft and cleared them for the approach. A study of meteorological data by the National Center for Atmospheric Research (NCAR) found that the air- plane likely encountered supercooled large droplet (SLD) conditions while descending from 9,400 ft to 6,100 ft, where the upset occurred. An SLD is a water droplet that remains liquid at a temperature below freezing until it strikes or is struck by something solid; it then freezes relatively slowly. “SLD conditions can cause [thin, rough] ice accretions that are more aerodynamically detrimental than those that were considered during the initial certification of many existing airplanes for flight in icing conditions,” the report said. The NCAR study found that, during the 4 1/2 minutes the Citation was in the SLD conditions, 1 to 4 mm (0.04 to 0.16 in) of additional ice likely accumu- lated along the wing leading edges. At 0909, the first officer said, “You got a little different ice on there now. It’s clear.” The captain said, “Yeah, and open up those valves all the way.” The report said that the captain likely was refer- ring to the windshield anti-ice bleed air valves. The windshield bleed-air switch has two positions: “LOW” and “HIGH.” At 0910, the first officer said, “OK, ignition is on with the anti-ice, now it’s on for sure. Glideslope is alive.” He then conducted a partial briefing of the approach: “It’s two hundred decision height and three-quarters of a mile.” Soon after the captain announced that he was extending the landing gear at 0911, the approach controller cleared the crew to land and told them to re- main on his radio frequency. Boots Neglected At 0911, the captain said, “Speed brakes coming back out again.” The first of- ficer said, “OK, there’s your glideslope intercept.” The captain told the first officer to extend full flaps. The first of- ficer replied, “Full selected and indi- cated … and you are plus twenty-five.” The captain replied, “Slowing.” The crew did not activate the deice boots, as required by company SOPs and recommended by the SimuFlite technical manual. “When reconfiguring for approach and landing … with any ice accretion visible on the wing leading edge, regardless of thickness, activate the surface deice system,” the manual says. “Continue to monitor the wing leading edge for any reaccumulation.” At 0912:08, the first officer said, “Slowing, sinking seven. Captured the localizer and the glideslope. I’ve got some ground, but stay on the gauges.” He then briefed the missed approach procedure. At 0912:37, three seconds before the upset occurred, the first officer suggested that the captain activate the deice boots and told him that airspeed was at Vref. The report said that the airplane was descending through 6,100 ft, about 1,500 ft above ground level, at 0912:40 when the upset occurred — “a large roll to the left concurrent with a rapid decrease in pitch.” The cockpit voice recorder recorded a tone consistent with activation of the autopilot-disconnect warning horn and a terrain awareness and warning sys- tem (TAWS) “BANK ANGLE” warning; the bank angle was about 50 degrees. The CVR stopped recording at 0912:55. The Citation struck terrain at an elevation of about 4,600 ft. The airplane was destroyed by the impact and post- accident fire. No Warning The report said that the flight crew received no warning of the impending stall, which occurred well above the expected stall speed in icing conditions. Based on input from the AOA sys- tem, the stick shaker in a Citation V acti- vates when airspeed is about 7 percent above the speed at which the airplane, with uncontaminated wings, will stall. The report said that during flight tests of 560-series Citations in 1996, following three icing-related accidents, the FAA found that stall speeds increased 3–5 kt in icing conditions. In 1999, Cessna modified the stall warning system with an ice mode that causes the stick shaker to activate 5 kt above the clean-wing stall speed. The ice mode is armed when the engine anti-ice system is selected. The accident airplane was equipped with the ice mode. The airplane flight manual (AFM) indicated that, at the airplane’s landing weight and with full flaps, its stall speeds should have been 76 kt with uncontaminated wings and 81 kt with ice on the wings; stick shaker activation would occur at 86 kt. Analysis of TAWS data indicated that airspeed was about 90 kt when the stall occurred. The report said that the flight crew should have been maintaining an airspeed of 114 kt at this point. In addi- tion to the 8-kt adjustment of Vref for icing conditions, company SOPs and the AFM say that an additional 10 kt should | 33 WWW.flightsafety.org | AeroSAfetyWorld | May 2007 cAuSAlfactors be maintained until the airplane is over the runway threshold. Impact and fire damage to compo- nents of the AOA and stall warning sys- tems precluded postaccident tests. The captain of the other Citation, which the report called the “sister ship,” had flown the accident airplane the previous day and had found no problems with the systems. “Furthermore, no discrepan- cies were noted during the last sched- uled maintenance inspection of the stall warning system,” the report said. Sister Ship The sister ship was about 19 nm (35 km) behind the accident airplane on arrival at Pueblo. The flight crew of the sister ship told investigators that their airplane accumulated rime ice during descent. “The first officer estimated that the ice was less than 1/2-in thick and stated that the deice boots effectively shed the ice,” the report said. “He stated that there was no ice on the heated inboard wing leading edge or on the top of the wing. The captain stated that they kept the airspeed up on the approach because of the icing conditions.” The report said that performance calculations indicate that the sister ship’s airspeed was more than 160 kt as it descended through 6,200 ft and that 120 kt was maintained until the airplane was about 200 ft above airport elevation, 4,726 ft. “The sister ship landed on Runway 08L about 0926 without incident,” the report said. “A review of the sister ship’s CVR revealed that the pilots conducted several procedures to minimize any icing problems, including cycling the wing deice boots five times, turning the windshield heat to the ‘HIGH’ position, using only approach flaps until close to the ground, and keeping the engine power and speed as high as possible until clear of the clouds and landing was assured.” Slow Pace In response to previous NTSB recom- mendations, the FAA formed the Ice Pro- tection Harmonization Working Group in 1997 to review the icing-certification standards and operational guidance. Among changes proposed by the group are a requirement that manufac- turers demonstrate during transport airplane icing certification either that the airplane can be operated safely in SLD conditions or that a means is pro- vided for the crew to detect and safely exit the conditions, and a requirement for guidance stating that deice systems should be activated as soon as icing conditions are encountered. In the accident report, NTSB said that the working group is addressing some of the issues that were raised in previous recommendations. However, NTSB said that work is proceeding at “an unacceptably slow pace” and that “the FAA has taken no action to issue a final rule adopting the regulatory chang- es proposed by [the working group].” Calls for Action Based on the findings of the accident investigation, NTSB made the following new recommendations to the FAA: • “Require that operational training in the Cessna 560 airplane empha- size the [AFM] requirements that pilots increase the airspeed and operate the deice boots during ap- proaches when ice is present on the wings. (A-07-12); • “Require that all pilot training programs be modified to contain modules that teach and emphasize monitoring skills and workload management, and include opportu- nities to practice and demonstrate proficiency in these areas. (A-07-13); • “Require manufacturers and operators of pneumatic-deice- boot-equipped airplanes to revise the guidance contained in their manuals and training programs to emphasize that leading edge deice boots should be activated as soon as the airplane enters icing condi- tions. (A-07-14) … ; • “Require that all pneumatic-deice- boot-equipped airplanes certified to fly in known icing conditions have a mode incorporated in the deice boot system that will automatically continue to cycle the deice boots once the system has been activated. (A-07-15); • “When the revised icing certification standards (recommended in Safety Recommendations A-96-54 and A-98-92) and criteria are complete, review the icing certification of pneumatic-deice-boot-equipped air- planes that are currently certificated for operation in icing conditions and perform additional testing and take action as required to ensure that these airplanes fulfill the require- ments of the revised icing certifica- tion standards. (A-07-16) … ; [and,] • “Require modification of the Cessna 560 airplane’s stall warning system to provide a stall warning margin that takes into account the size, type and distribution of ice, including thin, rough ice on or aft of the protected surfaces. (A-07-17).” At press time, FAA responses to these rec- ommendations had not been published. ● This article is based on U.S. National Transportation Safety Board Accident Report NTSB/AAR-07/02, “Crash During Approach to Landing, Circuit City Stores, Inc., Cessna Citation 560, N500AT, Pueblo, Colorado, February 16, 2005.” The 86-page report contains appendixes.