- Comair EMB-120 near Monroe, MI
- Accident Overview
- Accident Board Findings
- Accident Board Recommendations
- Relevant Regulations / Policy / Background
- Prevailing Cultural / Organizational Factors
- Key Safety Issue(s)
- Safety Assumptions
- Resulting Safety Initiatives
- Airworthiness Directives (ADs) Issued
- Common Themes
- Related Accidents / Incidents
- Lessons Learned
- Comair EMB-120 near Monroe, MI
Technical Related Lessons:
Certain classes of airplanes that are certified to operate in Appendix C icing conditions will retain sufficient operational safety margins only if icing protection systems are activated immediately upon encountering icing conditions. These airplanes may also require flight deck annunciation of icing conditions. (i.e., ice detector) (Threat Category: Inclement Weather/Icing)
- Due to concerns for "ice bridging" on the de-icing boots, operational procedures initially required delaying activation of the ice protection systems until a specific ice thickness had accumulated. It was later determined as a result of this accident that activation of the ice protection system at the first indication of icing is effective at preventing the degraded margins and handling qualities. Consequently, procedures were modified to require more timely system activation. In addition, an ice detector system, to alert the crew to icing conditions, was subsequently required for the EMB-120.
On transport airplanes, use of ice protection systems should not be predicated on crew monitoring the degree of ice build-up in order to assess need for system actuation. (Threat Category: Inclement Weather/Icing)
- At the time of the Comair accident, it was believed within the aviation community that activation of deicing boots should be delayed until a specified ice thickness had accumulated on the wings. The origin of this procedure was related to the belief that ice bridging could occur if the system were activated prematurely. This made the timing for system activation dependent upon the flightcrew's assessment of ice thickness. After the accident, subsequent testing revealed that the concern for ice bridging was unfounded for this class of boot system. Therefore, procedures were modified to activate the system at the first indications of ice, thereby clarifying the activation criteria, and removing crew judgment as to the thickness of accumulated ice.
Common Theme Related Lessons:
If certified operational characteristics/procedures are shown to be hazardous, regulatory actions should be taken to correct unsafe conditions. (Common Theme: Organizational Lapses)
- This accident was preceded by six in-service incidents related to accumulations of ice, and non-activation of the ice protection system. The manufacturer issued new procedures related to ice protection system activation, and minimum operating speeds in icing conditions. Due to differences in the regulatory and oversight functions within the government of Brazil (the country overseeing the manufacturer of the Embraer EMB-120 airplane), and the government of the United States (the country overseeing the operation of Comair), confusion existed regarding the necessary steps that should be taken in order to change existing operational procedures of the EMB-120 fleet. Consequently, neither regulatory authority (ANAC or FAA) issued airworthiness directives to require incorporation of the revised procedures into air carrier operations until after the accident.
Important safety information provided by the airplane manufacturer should have comprehensive, and timely, distribution to all organizations/individuals responsible for acting upon this information (Common Theme: Organizational Lapses)
- Based on the six in-service incidents, and a series of meetings and operator seminars, the airplane manufacturer issued an AFM revision to update operational procedures and speeds related to icing conditions. Comair elected not to incorporate the AFM revision into their operations, and did not provide a copy of the revision to their Principal Operations Inspector (POI). Due to unclear roles and responsibilities of the various FAA offices involved in oversight, FAA offices who had received the revision did not forward the revision to FAA field offices that could have reinforced its incorporation into air carrier operations. This confusion of responsibilities also prevented the widespread distribution of critical knowledge gained from testing that had been accomplished subsequent to the several incidents involving the EMB-120. Consequently, the majority of operators continued to adhere to previously established procedures that called for delayed activation of deicing systems.
Safety should not be predicated on requiring the flight crew to apply procedures that, in order to be consistently accomplished, are heavily reliant on qualitative judgment. (Common Theme: Flawed Assumptions)
- In this accident, procedures required delaying activation of the deicing boots until a specified thickness of ice had accumulated on the wings. Determination of ice thickness was difficult, especially at night, and was not able to be consistently determined accurately, potentially leading to errors in when to activate the system. Further, as was demonstrated after the accident, beliefs relative to ice bridging were proved unfounded for this class of boot system. The requirement to delay until a specific ice accumulation had formed was not necessary, and procedures were revised. Procedural changes eliminated the human element from the determination of when to activate the deicing system, and resulted in an overall improvement in safety.