DCA01MA031

On March 19, 2001, about 1825 eastern standard time, an Empresa Brasileira de Aeronautica, S/A (Embraer) EMB-120, N266CA, operated by Comair Airlines, Inc., as flight 5054, encountered icing conditions while in cruise flight at 17,000 feet mean sea level (msl) and departed controlled flight, descending to an altitude of about 10,000 feet. The pilots recovered control of the airplane and diverted to West Palm Beach, Florida, where they landed without further incident. The 2 flight crewmembers, 1 flight attendant, and 25 passengers were uninjured, and the airplane sustained substantial damage to the elevators and the horizontal stabilizer. Flight 5054 was operating under 14 Code of Federal Regulations Part 121 as a scheduled international passenger flight from Nassau International Airport, Bahamas, to Orlando International Airport, Florida.

The flight departed in visual meteorological conditions (VMC). In postaccident interviews, the captain stated that while in VMC, the airplane flew normally. Flight data recorder (FDR) data indicate that about 7 minutes before the upset occurred, the airplane was at about 17,000 feet msl, with the autopilot engaged and airspeed stabilized near 200 knots indicated airspeed (KIAS). These data indicate that beginning about 1818, the airspeed slowed to 185 KIAS over a 1?minute period as the autopilot began trimming airplane nose-up (ANU) to maintain altitude. The airspeed then decreased to about 137 KIAS over the next 3 minutes. The airplane continued to maintain a constant altitude as the autopilot trimmed the airplane from about 0 to about 7 degrees ANU. The first officer stated that immediately before the upset occurred, he switched the leading-edge deicing system inflation cycles switch from "light" to "heavy" and the propeller deicing system cycles switch from "norm" to "cold" because he saw "more ice accumulation than he had ever seen" on the wing and spinner. FDR data indicate that when torque indications for both engines were about 55 percent and the airspeed was about 141 KIAS, the autopilot was disengaged. The airplane then pitched down and rolled about 80 degrees to the left, then rolled back to near level. During the next 20 seconds, engine torque increased to about 98 percent on both engines, the airplane rolled about 110 degrees to the left, returned to level flight, rolled about 130 degrees to the right, returned to level flight, then rolled 360 degrees to the right before returning to near wings level, with torque on both engines stabilized at about 22 percent. The airplane's behavior during the upset is consistent with an ice-induced stall event. The first officer stated in postaccident interviews that the stick shaker and aural stall warning, which is part of the airplane's stall warning/protection system, activated but did not indicate whether it was before, during, or after the upset. The Safety Board's investigation could not precisely determine whether or when the stick shaker and aural stall warning activated.

Meteorological data at the time of the accident indicate that Comair flight 5054 may have encountered an area of icing conducive to the formation of super-cooled large droplets (SLD). The EMB-120 is not certified for flight in SLD conditions. FDR data indicate that airspeed had decreased to only about 137 KIAS before control of the airplane became difficult and altitude was no longer maintained. However, according to the Embraer EMB-120 Airplane Flight Manual (AFM) performance section, the airplane stalling speed is about 115 knots calibrated airspeed for an airplane at the accident airplane's approximate gross weight at the time of the event (23,800 pounds).

History of flight

On March 19, 2001, about 1825 eastern standard time, an Empresa Brasileira de Aeronautica, S/A (Embraer) EMB-120, N266CA, operated by Comair Airlines, Inc., as flight 5054, encountered icing conditions while in cruise flight at 17,000 feet mean sea level (msl) and departed controlled flight, descending to an altitude of about 10,000 feet. The pilots recovered control of the airplane and diverted to West Palm Beach, Florida, where they landed without further incident. The 2 flight crewmembers, 1 flight attendant, and 25 passengers were uninjured, and the airplane sustained substantial damage to the elevators and the horizontal stabilizer. Flight 5054 was operating under 14 Code of Federal Regulations Part 121 as a scheduled international passenger flight from Nassau International Airport, Bahamas, to Orlando International Airport, Florida.

Comair flight 5054 departed Nassau about 1741 in visual meteorological conditions (VMC). In postaccident interviews, the captain stated that before the upset, the airplane flew normally. Flight data recorder (FDR) data indicate that about 7 minutes before the upset occurred, the airplane was at about 17,000 feet msl, with the autopilot engaged and airspeed stabilized near 200 knots indicated airspeed (KIAS). According to both pilots, shortly after cruise flight was established at 17,000 feet (about 1822), the airplane entered a cloud and that, shortly thereafter, the windshield frosted over with pebble-like rime ice. The captain stated that he then instructed the first officer to activate the anti-icing and deicing systems and that once these systems were activated, ice on the windshield started to melt within a couple of seconds. The captain stated that the ice detection light illuminated and, about 1 minute later, went out. He also stated that he looked outside and saw remnants of light ice between the ribs on the wing deicing boots but that there was no buildup of ice on the post where the windshield wiper arm attaches to the fuselage.

FDR data indicate that beginning about 1818, the airspeed slowed to 185 KIAS over a 1-minute period as the autopilot began trimming airplane nose-up (ANU) to maintain altitude. The altitude and speed remained constant for the next 3 minutes. According to FDR data, beginning about 1822, the airspeed decreased to about 183 KIAS then decreased to 137 KIAS over the next 3 minutes. The airplane continued to maintain a constant altitude as the autopilot trimmed the airplane from about 0 to about 7 degrees ANU. The first officer stated that immediately before the upset occurred, he switched the leading-edge deicing system inflation cycles switch from "light" to "heavy" and the propeller deicing system cycles switch from "norm" to "cold" because he saw "more ice accumulation than he had ever seen" on the wing and spinner.

FDR data indicate that about 1825, when torque indications for both engines were about 55 percent and the airspeed was about 141 KIAS, the autopilot was disengaged. The airplane then pitched down and rolled about 80 degrees to the left, then rolled back to near level. During the next 20 seconds, engine torque increased to about 98 percent on both engines, the airplane rolled about 110 degrees to the left, returned to level flight, rolled about 130 degrees to the right, returned to level flight, then rolled 360 degrees to the right before returning to near wings level, with torque on both engines stabilized at about 22 percent. The maximum nose-down pitch attitude was 60 degrees; the maximum recorded airspeed was about 240 KIAS, and the maximum vertical acceleration during recovery was about +3.6 G.

FDR data indicate that airspeed had decreased to about 137 KIAS before control of the airplane became difficult and altitude was no longer maintained. According to the Embraer EMB-120 Airplane Flight Manual performance section, the airplane stalling speed is about 115 knots calibrated airspeed for an airplane at the accident airplane's approximate gross weight at the time of the event (23,800 pounds.) The airplane's behavior during the upset is consistent with an ice-induced stall event. The first officer stated in postaccident interviews that the stick shaker and aural stall warning, which is part of the airplane's stall warning/protection system, activated but did not indicate whether it was before, during, or after the upset. The Safety Board's investigation could not precisely determine whether or when the stick shaker and aural stall warning activated.

Interviews with the flight crew indicated that during the event, both of the electronic attitude display indicators (EADI) in the cockpit blacked out and that red flags appeared on the screens. The EADIs displays reappeared after the aircraft came out of the clouds and recovered from the event.

Personnel information

Both flight crewmembers were properly certificated in accordance with Federal Aviation Administration (FAA) regulations. The captain, who was also the pilot flying at the time of the accident, had about 16,000 hours total flight time, including about 9,000 hours in the EMB-120. The first officer had about 1,350 hours total flight time with about 250 hours in the EMB-120.

Aircraft information

The EMB-120 anti-icing system includes electrically heated windshields, angle of attack and sideslip sensors, pitot/static and outflow valve static ports, and the total air temperature sensor. The deicing system includes inflatable rubber boots installed over appropriate regions of the wing and tail leading-edge surfaces and over the engine air inlet lips and engine air bypass ducts. The propeller deicing system consists of electrical heaters directly bonded onto the blade leading edge over a length of 20 inches.

When the inflation cycles switch is selected to "heavy," each ejector flow control valve is energized for 6 seconds and automatically cycles every minute. When the inflation cycles switch is selected to "light," each ejector flow control valve is energized for 6 seconds and automatically cycles every 3 minutes.

The EMB-120 propeller blade leading edge incorporates imbedded electrical resistances for ice protection. The system incorporates two dual-cycle electronic timers that provide selectable cycles; the "cold" cycle is 20 seconds on and 60 seconds off, and the "norm" cycle is 10 seconds on and 60 seconds off.

The EMB-120 stall warning/protection system consists of a three-stage process: first, the control column vibrates (also known as the stick shaker function), second, an aural warning sounds, and, finally, the control column is pushed forward (also known as the stick pusher function).

Meteorological information

Comair flight 5054 was in VMC until about 1818 when it entered an overcast cloud layer with cloud tops around 23,000 feet. Radar data showed that, between 1820 and 1822, flight 5054 penetrated the core of a level 3 convective cell with tops to about 33,000 feet. The temperature at flight 5054's flight altitude was about -3 degrees Celsius. The airplane exited the cell core around 1822 but remained in instrument meteorological conditions through the upset sequence.

Flight 5054 encountered severe mixed icing as the airplane exited the north side of the cell. The Miami Weather Surveillance Radar-1988, Doppler indicated that a strong convective cell was present beneath flight 5054 about the time that the airplane was experiencing icing. Meteorological data at the time of the accident indicate that Comair flight 5054 may have encountered an area of icing conducive to the formation of super-cooled large droplets (SLD). The EMB-120 is not certified for flight in SLD conditions.

Wreckage and impact information

Initial examination of the airplane at Palm Beach International Airport showed no evidence of hail damage to the leading edges of either wing or the horizontal stabilizer. The damage to the right horizontal stabilizer