LAX06IA076

An in-flight loss of control due to ice accreted in supercooled liquid droplets (SLD) conditions, and the flight crew's failure to maintain the specified minimum airspeed in icing conditions. Contributing to the accident was the flight crew's decision to climb the airplane in known and forecast icing conditions using an autopilot mode contrary to that specified in the operator's Airplane Operations Manual for climbs during periods of ice accretion or when ice was present on the airframe.

After departure and during the cruise climb phase, the flight encountered airframe ice and departed from controlled flight. The flight crew encountered light rime icing on the inbound leg while descending from 9,000 to 5,000 feet. Before the incident takeoff, they reviewed the dispatch package weather and noted two AIRMET (airmen's meteorological information) reports for icing in clouds. The captain decided to perform the departure and turn control of the airplane over to the first officer after completing the climb checklist at the acceleration altitude. In accordance with the operator's minimum equipment list (MEL), the airplane was dispatched with the continuous mode of the boot deice system inoperable, which would require the crew to manually operate the deice boots. Company procedures require activation of the deice system at the first sign of ice accretion, and operation of the deice boots continually thereafter while in icing conditions. The departure was into level 2 weather conditions (defined as 10 degree Celsius or colder with visible moisture). The airline's Airplane Operating manual (AOM) for the airplane calls for computation of a minimum speed (Vcln+15) in icing conditions, which for this flight was 141 KIAS. The limitations section stipulates that Indicated Air Speed (IAS) is the only authorized flight director/autopilot mode while climbing when ice accretion is occurring or with residual ice on the airframe. In IAS mode, the flight control computer gives pitch commands to maintain the selected indicated airspeed as opposed to the Vertical Speed (VS) mode where the autopilot sacrifices airspeed to maintain climb rate. Even though the crew had encountered icing on the inbound leg and the dispatch weather reports predicted an icing encounter during the climb on the outbound leg, the captain engaged the autopilot in the medium (M) climb mode and shortly after taking the controls at 2,500 feet, the first officer changed the autopilot to VS mode. As the airplane climbed through 11,700 feet, the captain noted light rime ice accumulating on the windshield wiper blades and about a 1/2-inch-wide area of ice on the left wing. During this time, the crew failed to detect a decaying indicated airspeed due to the ice that was accumulating. As he began to activate the manual deice boot system, he felt a heavy vibration in the airframe and the windscreen immediately turned white with ice. The airplane's nose and left wing dropped and the autopilot disconnected. As he was grabbing the yoke, the clacker sounded (indicating an imminent stall), the stick shaker activated, and the ground proximity warning system emitted a "bank angle" aural warning. Digital Flight Data Recorder (DFDR) data showed that the indicated airspeed went from 144 to 130 KIAS over the 26 seconds before the upset, and that the rate of airspeed decay accelerated in the final 10 seconds before the autopilot disconnected. The airplane departed controlled flight at an indicated airspeed of 130 knots, and before the stall warning activated. The data establishes that the airplane went through a series of roll and pitch excursions, reaching maximum values of 86 degrees left wing down, 140 degrees right wing down, 23 degrees nose up, and 40 degrees nose down before the flight crew recovered control. The data also revealed that about 26 seconds before the stall while the airplane was at a speed of 144 KIAS, the airplane began to experience a likely ice-induced slight rolling anomaly that was counter to the direction of the aileron input. Aileron input from the autopilot arrested this slight rolling motion. The DFDR data also disclosed that 14 seconds after the initial stall, both ailerons simultaneously traveled to the full up position for approximately 14 seconds. The Safety Board believes that the initial stall that occurred prior to stall warning, the upset, and the aileron upward deflections were caused by ice accreted on the wing in supercooled liquid droplets (SLD) conditions. Furthermore, the period of simultaneous upward deflection of the ailerons were caused by airflow separations over the ailerons, and not by opposite control wheel inputs by the captain and first officer (FO). This conclusion was based on the similar nature of past experience in accidents and incidents involving modification of aileron forces by SLD ice accretions, the higher airspeed and dynamic nature of the initiating events, the captain's and FO's statements, and the captain removing one hand from the control wheel to reduce the power. Also contributing to this conclusion was extrapolation of aileron and control wheel force measurements obtained in high speed taxi testing with a simulated ice shape in front of one aileron, and the development of airflow separation over the ailerons into a complete full wing stall. Recommendations The Safety Board issued several recommendations as a result of the investigation. Urgent recommendation A-06-48 asked the FAA to require all operators of Saab SF340 series airplanes to instruct pilots to maintain a minimum operating airspeed of 1.45xVs during icing encounters and before entering known or forecast icing conditions and to exit icing conditions as soon as performance degradations prevent the airplane from maintaining 1.45xVs. Recommendation A-06-49 and A-06-50 asked the FAA to require the installation of modified stall protection logic in Saab SF340 series airplanes certified for flight into known icing conditions and to require the installation of an icing detection system on Saab SF340 series airplanes. Recommendation A-06-51 asked the FAA to require all operators of turbo propeller-driven airplanes to instruct pilots, to disengage the autopilot and fly the airplane manually when operating in icing conditions. The Safety Board also reiterated the following prior recommendations to the FAA. Recommendation A-03-53 and A-03-54 asked the FAA to convene a panel of airplane design, operations, and aviation human factors specialists to determine whether a requirement for the installation of low-airspeed alert systems in airplanes engaged in commercial operations under 14 Code of Federal Regulations Parts 121 and 135 would be feasible, and if the panel determined that such feasibility exists, establish requirements for low-airspeed alert systems.

HISTORY OF FLIGHT On January 2, 2006, at 1439 Pacific standard time, a Saab-Scania AB SF340B+, N390AE, operated by American Eagle Airlines, Inc., as flight 3008, encountered icing conditions during the en route climb over Santa Maria, California. The airplane was at 11,700 feet mean sea level (msl) when it departed controlled flight, and descended to an altitude of about 6,500 feet msl. The pilots recovered control of the airplane, and continued to their scheduled destination of Los Angeles International Airport (LAX), Los Angeles California, where they landed at 1540 without further incident. The 2 flight crew members, 1 flight attendant, and 25 passengers were uninjured, and the airplane did not sustain substantial damage. Instrument meteorological conditions prevailed for the 14 Code of Federal Regulations (CFR) Part 121 scheduled domestic passenger flight that was operating on an instrument flight rules (IFR) flight plan. The flight originated from San Luis County Regional Airport (SBP), San Luis Obispo, California, at 1414. A review of the American Eagle Airlines, Inc., flight log disclosed that the accident flight was scheduled to be the flight crew's fifth trip of the day, and their second trip in the accident airplane. The 1 hour 26 minute accident flight was scheduled to depart from Santa Barbara at 1408, and terminate in Los Angeles at 1513. The flight crew members stated in post incident interviews that before the incident flight, they had encountered light rime icing and moderate turbulence on the inbound leg to San Luis Obispo as they were descending from 9,000 to 5,000 feet. The pilots stated that, while preparing for the return flight to Los Angeles, they reviewed the weather conditions for the intended route of flight. The operator's dispatch package noted two AIRMET (airmen's meteorological information) reports for icing in clouds and two PIREPs (pilot weather reports) for turbulence. The pilots discussed the conditions that they had encountered on the way in, as well as the conditions for the intended route of flight outbound. Because of the gusty wind conditions and the short runway at San Luis Obispo, the captain decided to perform the departure. He was going to turn control of the airplane over to the first officer after completing the climb checklist at the acceleration altitude. In accordance with American Eagle's minimum equipment list (MEL), the incident airplane was dispatched with the continuous mode of the boot deice system inoperable for the inbound flight and the return incident flight. The flight crew reported that they performed the manual test of the deicer boots as called for in the MEL, and observed the operation of the inboard and outboard wing boot segments. However, they could not see the stabilizer segments, and did not have qualified ground personnel available to observe the test as required by the MEL. The pilots reported that they did confirm illumination of the green boot inflation lights on the overhead panel when they pressed the manual buttons. In accordance with company procedures that require flight crews to activate the deice system at the first sign of ice accretion and operate the deice boots continually, the crew stated that they were prepared to operate the deice boots in manual mode as needed during the flight. They departed in level 2 weather conditions (defined as 10 degree Celsius or colder with visible moisture) and with the engine anti-ice on. The pilots stated that the weather radar was on, and they did not observe any activity on it. The captain had the autopilot engaged in the medium (M) climb mode. Shortly after taking the controls about 2,500 feet, the first officer changed the autopilot to vertical speed (VS) mode, which gave pitch attitude commands to maintain the vertical speed existing at the time of mode engagement. As the airplane climbed through 11,000 feet, the captain noted light rime ice accumulating on the windshield wiper blades and about a 1/2-inch-wide area of ice on the left wing. The captain reported that, as he began to reach up to activate the manual deice boot system, he felt a heavy vibration in the airframe. He said that the windscreen immediately turned white. Immediately thereafter, the airplane's nose dropped, the left wing dropped, and the autopilot disconnected. He grabbed the yoke to take control of the airplane. He said that the clacker sounded (indicating an imminent stall), the stick shaker activated, and the ground proximity warning system emitted a "bank angle" aural warning. The flight crew reported that the airplane vibrated again, but less violently than the first episode. The captain leveled the wings, and began pulling up on the control yoke. At this point, he instructed the first officer to manually operate the deice boots. The captain stated that he pushed the condition levers to the maximum position, and brought the power levers to idle. The airplane stabilized in roll, and he could hear chunks of ice shedding off and hitting the fuselage. He kept the airplane in a nose-down attitude, maintaining a 500 feet per minute rate of descent until the airplane was below the freezing level. PERSONNEL INFORMATION Captain The operator reported that the 34-year-old captain held an airline transport pilot (ATP) certificate with a rating for airplane multi-engine land. He held a commercial pilot certificate with ratings for airplane single-engine land and instrument airplane. He had a type rating in the SF340. The captain held a first-class medical certificate issued on September 21, 2005. It had no limitations or waivers. The captain had a total flight time of 6,764.08 hours, with 3,981.87 hours accumulated in Saab 340 airplanes, of which 2,519.46 hours was as the pilot-in-command (PIC). He had a total of 970 hours of instrument experience and between 1,700 and 1,900 hours of night flight. During the preceding 90 days, 30 days, and 24 hours, he reported that he had flown in both the capacity of PIC and second-in-command (SIC) approximately 172, 47, and 7 hours, respectively. He added that he had acquired numerous hours of aerobatic flight time in a Cessna 150 Aerobat airplane. First Officer (FO) The operator reported that the 32-year-old FO held a commercial pilot certificate with airplane instrument and multi-engine land ratings. He additionally held an SF340 Type Rating, with the limitations of SF340 SIC privileges only and circling approaches to be completed only in visual meteorological conditions (VMC). The FO was also a certified flight instructor (CFI) for instrument and multi-engine land airplane. The FO's second-class medical certificate was issued on May 25, 2005, with the limitation that he must wear corrective lenses. The FO had a total flight time of 1,367.48 hours, with 132.48 hours accumulated in Saab 340 airplanes. He had a total of 94 hours of instrument experience and 185 hours of night flight. During the preceding 90 days, 30 days, and 24 hours, he reported that he had flown approximately 120, 71, and 5 hours, respectively. AIRCRAFT INFORMATION The airplane was a Saab SF340B+, serial number 340B-390. The airplane had a total airframe time of 17,291 hours at the examination following the incident. Systems National Transportation Safety Board investigators reviewed the airplane's maintenance records and logbooks. The day prior to the incident, a flight crew reported that during an en route deice boot check, the timer light illuminated. The deicer timer failure light was later deferred in accordance with the operator's MEL. The deferral procedures required a placard to be placed adjacent to the deicer timer switch and the auto cycling switch to remain in the "off" position. Investigators did observe an MEL placard (sticker) next to the deice system controls in the cockpit. Initial examinations revealed that the airplane's deice systems were operational; the deic