747.1 747 CF6-80C2 Icing Events Jeanne Mason Propulsion Operability Boeing Commercial Airplanes May 2004 The Boeing Company 747.2 Inclement Weather Event History • Seventeen CF6-80C2 FADEC engine flameout events have occurred between 1991 and 2004 • All 17 events occurred during descent in inclement weather conditions. • Five dual engine events (three 747-400 and two MD-11) have been reported. • All engines were restarted and operated normally for remainder of flight. • No PMC engine flameouts have been reported during descent in inclement weather • Only one event reported on the 767. The Boeing Company 747.3 Inclement Weather Event Locations 1 10 9 8 7 6 5 4 3 2 11 12 13 14 15 16 17 Event no. Date A/C Locn Alt 1 4/29/1991 747-400 WASH, DC 19000 2 6/9/1993 747-400 HONG KONG 30000 3 11/26/1993 MD11 INDIA U 4 1/5/1995 MD11 LAX 11500 5 2/17/1995 747-400 BRAZIL 15000 6 5/13/1995 MD11 JAPAN 17500 7 3/21/1996 747-400 MALAYSIA 19000 8 5/29/1996 747-400 HONG KONG 18500 9 4/6/1997 747-400 JAPAN 22100 10 6/3/1998 747-400 HONG KONG 20600 11 9/1/2000 MD11 HONG KONG 28000 12 12/19/2000 747-400 MALAYSIA U 13 5/4/2002 MD11 FLORIDA 23000 14 1/10/2003 747-400 URUGUAY 28000 15 4/3/2003 767-300ER JAPAN 13300 16 12/26/2003 747-400 BRISBANE 32200 17 3/1/2004 MD-11 BANGKOK 33000 The Boeing Company 747.4 Characteristic Event Details • Engine behavior and climatic conditions were similar in these events. – Engine flamed out: – Descent in icing conditions, – at or near approach idle. – At level-off, during throttle-up, – TAT was typically flat-lined at 0oC shortly before event. – The airplanes were near thunderstorms/convective weather systems. – The icing conditions appear different from “normal” icing conditions. – Engine icing can occur without detectable airframe icing. The Boeing Company 747.5 Characteristic Event Details - Relight – FADEC auto relight typically causes engines to selfrecover without pilot intervention. – Time for relight and recovery to commanded power ranges from 30 sec – 120 sec. – Auto relight has always relit the engine inside the start envelope, and sometimes above the envelope. – In many cases engine anti-ice and ignition were selected prior to the flameout. The Boeing Company 747.6 Characteristic Event Details – Ice Shed • Flameout phenomenon: – Believed to be caused by ice shed from booster static structure. – Believe that temperature rise on descent, and airflow increase during throttle-up causes ice to shed. – On acceleration from approach idle VBVs are closing, ice goes into core. – Resulting heat absorption from ice/water in the combustor quenches the flame. The Boeing Company 747.7 Recent Event Findings HPC airfoil damage was observed after the last two events. • Both events occurred during icing conditions at high altitude • In both events the engines operated normally for the remainder of the event flight after they were restarted • Mechanism for damage is not understood. • Change to AMM/fault isolation manuals/FRM to ensure HPC borescope inspection occurs after flameout in suspected inclement weather events is under consideration. The Boeing Company 747.8 ECU VBV Logic Revised 1996 • GE Introduced change in ECU VBV control logic to open VBV schedule in 1996 – Opens VBV’s to increase ice extraction from booster discharge / core inlet – Targeted 10K to 20K ft altitude range – Typical icing envelope – Phased out completely below 5K and above 25K • Boeing and GE recommend incorporation of the modified schedule. – No events have occurred on airplanes where it is incorporated inside the altitude envelope where it is active. – The software modification does not cover all known events. The Boeing Company 747.9 Operational Considerations • Engine anti ice, which commands approach idle engine speed has not shown to be effective in preventing flameouts due to core ice ingestion. • Continuous ignition selected ON prior to event has not prevented flameout. • TAT freezing does not appear to be a reliable indicator of conditions which can cause flameout. • Airframe icing is not always evident in these conditions. The Boeing Company 747.10 Boeing Safety Service Related Problem (SRP) This issue is being given the highest priority at Boeing and GE • Working together to determine root cause of the flameouts. • Actions include: – Low altitude capability – ensure capability below 10,000 ft. is adequate. – HPC damage – put procedures in place to ensure no follow-on flight with damage. – Determine interim operational procedures that can reduce the likelihood of flameout. – Insure current operational procedures are adequate in the event of flameout – Ensure the operational community is aware of the flameout phenomenon.
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