A new Ground Ceicing Hazard Associated with Freezing Drizzle Ingestion by Jet Engines during taxi

On October 31, 2002, twelve United 737 aircraft experienced significant engine damage after experiencing winter precipitation on the ground at Denver International Airport between 1700 and 2100 Mountain Daylight Time (MDT). The damage occurred when ice that had formed on the fan blades was ingested into the engines. The official National Weather Service METAR report during this period was light snow and mist (-SN BR). However, closer examination of surface, radar, and sounding data from this case suggests that the primary precipitation that was occurring was freezing drizzle. Because freezing drizzle was not reported, standard United Airlines procedures to increase the RPMs of the engines every 15 minutes to shed the ice were not implemented. Thus, the lack of freezing drizzle reporting in this case had significant operational impacts, costing United Airlines over $2 Million in aircraft engine repair costs alone. This and two other cases of jet engine damage due to freezing drizzle ingest during taxi will be presented at the conference.