San Luis County Regional Airport
Aircraft Accident/Incident Report

Santa Maria, California 93455
Monday, January 2, 2006 14:39 PST

NTSB Narrative Summary Released at Completion of Accident

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.

NTSB Probable Cause Narrative

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.

Event Information

Type of Event Incident
Event Date 1/2/2006
Event Day of the Week Monday
Time of Event 1439
Event Time Zone Pacific Standard Time
Event City Santa Maria
Event State CALIFORNIA
Event Country --
Zipcode of the event site 93455
Event Date Year 2006
Event Date Month 1
MidAir Collision Indicator No
On Ground Collision occurred ? No
Event Location Latitude 350309N
Event Location Longitude 1200718W
Event Location Airport San Luis County Regional
Event Location Nearest Airport ID SBP
Indicates whether the acc/inc occurred off or on an airport Off Airport/Airstrip
Distance from airport in statute miles 22
Degrees magnetic from airport --
Airport Elevation 212
Weather Briefing Completeness --
Investigator's weather source Weather Observation Facility
Time of the weather observation 1451 Pacific Standard Time
Direction of event from weather observation facility (degrees) 220
Weather Observation Facility ID SMX
Elevation of weather observation facility 261
Distance of event from weather observation facility (units?) 20
Time Zone of the weather observation PST
Lighting Conditions Day
Lowest Ceiling Height 2700
Lowest Non-Ceiling Height 2100
Sky/Lowest/Cloud Conditions Scattered
Sky Condition for Lowest Ceiling Broken
Visibility Runway Visual Range (Feet) --
Visibility Runway Visual Value (Statute Miles) --
Visibility (Statute Miles) 9
Air Temperature at event time (in degrees celsius) 13
Dew Point at event time (in degress fahrenheit) 8
Wind Direction (degrees magnetic) 230
Variable Wind Indicator Wind direction could be determined
Wind Speed (knots) 16
Wind Velocity Indicator --
Wind Gust Indicator Gusting
Wind Gust (knots) 27
Altimeter Setting at event time (in. Hg) 29.8
Density Altitude (feet) --
Intensity of Precipitation --
METAR weather report --
Event Highest Injury None
On Ground, Fatal Injuries --
On Ground, Minor Injuries --
On Ground, Serious Injuries --
Injury Total Fatal --
Injury Total Minor --
Injury Total None 28
Injury Total Serious --
Injury Total All --
Investigating Agency NTSB
NTSB Docket Number (internal use) 22145
NTSB Notification Source FAA
NTSB Notification Date Jan 2 2006 12:00AM
NTSB Notification Time --
Fiche Number and/or location -used to find docket information DMS
Date of most recent change to record Mar 4 2009 4:36PM
User who most recently changed record coos
Basic weather conditions Instrument Meteorological Cond
FAA District Office WP-LAX-FSDO

Aircraft Involved

Aircraft #1

Aircraft Registration Number N390AE
NTSB Number LAX06IA076
Missing Aircraft Indicator --
Federal Aviation Reg. Part Part 121: Air Carrier
Type of Flight Plan filed IFR
Flight plan Was Activated? Yes
Damage None
Aircraft Fire None
Aircraft Explosion None
Aircraft Manufacturer's Full Name Saab-Scania AB (Saab)
Aircraft Model SF340B+
Aircraft Series Identifier --
Aircraft Serial Number 340B-390
Certified Max Gross Weight 29000
Aircraft Category Airplane
Aircraft Registration Class --
Aircraft is a homebuilt? No
Flight Crew Seats --
Cabin Crew Seats --
Passenger Seats --
Total number of seats on the aircraft 37
Number of Engines 2
Fixed gear or retractable gear Retractable
Aircraft, Type of Last Inspection Continuous Airworthiness
Date of Last Inspection --
Airframe hours since last inspection --
Airframe Hours 17291
ELT Installed Yes
ELT Activated No
ELT Aided Location of Event Site No
ELT Type --
Aircraft Owner Name WELLS FARGO BANK NORTHWEST NA TRUSTEE
Aircraft Owner Street Address 299 S MAIN ST # U1228-120
Aircraft Owner City SALT LAKE CITY
Aircraft Owner State UT
Aircraft Owner Country USA
Aircraft Owner Zipcode 84111
Operator is an individual? No
Operator Name American Eagle Airlines, Inc.
Operator Same as Owner? No
Operator Is Doing Business As --
Operator Address Same as Owner? No
Operator Street Address 4333 Amon Carter Blvd
Operator City Fort Worth
Operator State TX
Operator Country USA
Operator Zip code 75261
Operator Code AEAA
Owner has at least one certificate Yes - certificate holder
Other Operator of large aircraft? No
Certified for Part 133 or 137 Operation --
Operator Certificate Number --
Indicates whether an air carrier operation was scheduled or not Scheduled
Indicates Domestic or International Flight Domestic
Operator carrying Pax/Cargo/Mail Passenger Only
Type of Flying (Per_Bus / Primary) --
Second Pilot on Board Yes
Departure Point Same as Event No
Departure Airport Code SBP
Departure City San Luis Obispo
Departure State CA
Departure Country USA
Departure Time 1414
Departure Time Zone PST
Destination Same as Local Flt --
Destination Airport Code LAX
Destination City Los Angeles
Destination State CA
Destination Country USA
Specific Phase of Flight Climb - to cruise
Report sent to ICAO? --
Evacuation occurred --
Date of most recent change to record Mar 4 2009 4:36PM
User who most recently changed record coos
Since inspection or accident Time of Accident
Event Location Runway Number and Location N/A
Runway Length --
Runway Width --
Sight Seeing flight No
Air Medical Flight No
Medical Flight --