Investigation Summary
The accident occurred while the aircraft was being vectored for spacing behind an Airbus A320. During the descent and approach, the aircraft encountered icing conditions. Although the crew activated the anti-ice systems for the windshield and propellers, they did not activate the wing deicing boots. This decision was influenced by a long-standing but outdated industry concern regarding ice bridging, where ice supposedly forms a hollow shell over an inflated boot, rendering it ineffective. Comair's manuals at the time still reflected this concern, contradicting the manufacturer's instructions to activate the boots at the first sign of ice. As the aircraft slowed to 150 knots while level at 4,000 feet with flaps retracted, the accumulated ice significantly increased the stall speed. The autopilot attempted to compensate for the increasing drag and asymmetric lift by applying right-wing-down control wheel inputs to counter an uncommanded left roll and by increasing engine torque. When the autopilot reached its authority limit and disconnected, the aircraft immediately snapped into a 145 degree left roll. The crew was unable to regain control before the aircraft struck the ground.
Final Conclusions
The National Transportation Safety Board (NTSB) determined the probable cause was the FAA's failure to establish adequate minimum airspeeds for icing conditions, which led to a loss of control after the airplane accumulated a thin, rough accretion of ice. Contributing factors included Comair's failure to establish unambiguous minimum airspeed values for flight in icing conditions and the crew's decision to operate at the lower end of the flight envelope with flaps retracted. The NTSB also cited the FAA's failure to ensure that Embraer's revised icing procedures were incorporated into Comair's flight manuals.
Video Analysis
In-Flight Icing Encounter and Uncontrolled Collision with Terrain COMAIR Flight 3272 — Official NTSB presentation and animation detailing the icing encounter, the aerodynamic effects of ice accretion on the EMB-120, and the subsequent loss of control.
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Airframe & Maintenance
Crew Experience
Captain
Pilot Monitoring (PM)
First Officer
Pilot Flying (PF)
Systems & Failure Modes
Deicing Boots
Pneumatic surfaces on the leading edges of the wings that inflate to crack and shed ice. The crew did not activate them due to outdated company guidance regarding ice bridging.
Autopilot
The system attempted to maintain altitude and heading by masking the deteriorating aerodynamic state of the aircraft until it reached its control limits and disconnected.
Fast/Slow Indicator
An angle-of-attack based system on the EADI that provides the crew with a visual reference for speed relative to stall margin.
Interesting Facts
- 01The aircraft was an Embraer EMB-120RT Brasilia, a type that had a history of icing-related incidents prior to this crash.
- 02The flaps were in the retracted (zero) position at the time of the stall.
- 03The NTSB found that a layer of ice as thin as 1/32 to 1/16 of an inch could cause a significant loss of lift on the EMB-120 wing.
- 04Comair's flight manual contained instructions regarding deicing boots that were contrary to the manufacturer's updated recommendations.
Safety Actions & Advisories
Icing Airspeed Standards
The NTSB recommended that the FAA establish and require minimum airspeeds for flight in icing conditions for all category aircraft.
Deicing Boot Operation
The investigation led to a shift in industry training, emphasizing that deicing boots should be activated at the first sign of ice accretion rather than waiting for a specific thickness.