Individually Owned: 150,657
Corporate Owned: 137,281
Detroit International Airport
Aircraft Accident/Incident Report
Detroit, Michigan
Sunday, October 23, 2011 16:00 EDT
NTSB Narrative Summary Released at Completion of Accident
On October 23, 2011, 1600 eastern daylight time, a Boeing 747-451, registration number N661US, powered by four Pratt & Whitney PW4056 turbofan engines, experienced a left inboard engine (No. 2) low pressure turbine failure after takeoff from Detroit Metro Wayne Country International Airport (DTW), Detroit, Michigan. According to the flight crew statements, a large compressor stall and a muffled explosion were felt, followed by the No. 2 engine rollback and No. 2 engine fire warning indication. The flight crew performed an air turnback and made a successful three-engine landing at DTW. No injuries were reported.
Examination of the airplane revealed minor impact damage to the left wing, flaps, ailerons, and horizontal stabilizer. Initial examination of the engine revealed evidence of an undercowl fire, three burn-through holes on the No. 2 engine outboard core cowl, numerous exit hole penetrations in the rear turbine case, and a punctured No. 4 bearing compartment oil pressure supply line. Disassembly of the No. 2 engine revealed no damage upstream of the stage 3 low pressure turbine (LPT); one stage 3 LPT outer transition duct segment and two stage 3 LPT vane clusters were missing from their normally installed position, and extensive damage downstream of the stage 3 LPT vane clusters was found. The stage 3 LPT outer transition duct segments were approved but were an older configuration utilizing the riveted rear seal plate design that was prone to failure and had been superceded by a preferred design that incorporated an integral rear seal.
Comparing the airplane and engine damage to the requirements for engine debris containment and safety analysis at the time the engine was certificated revealed that the engine did not comply with the containment requirements set forth in Parts 33.19 and 33.75.
The undercowl fire was due to a failure of the rear riveted seal plates of the missing stage 3 outer transition duct segment that allowed hot gas path air under the duct segment, causing it to thermally distort and disengage from the rear turbine case. Once disengaged from the rear turbine case, the stage 3 outer transition duct segment released into the gaspath where it fractured all of the stage 3 LPT blades, which propelled blade fragments through the rear turbine case that punctured the No. 4 bearing oil pressure supply tube. The atomizing oil mist from the No. 4 bearing oil pressure supply tube ignited when it contacted the hot engine case, which created the undercowl fire.
NTSB Probable Cause Narrative
The penetration of turbine blade fragments through the rear turbine case, which punctured the No. 4 bearing oil pressure supply tube, allowing misted oil to contact the hot engine case and ignite the undercowl fire.
Contributing to the incident was the installation of approved (but not preferred) stage 3 low pressure turbine outer transition duct segments with the riveted rear seal configuration and the failure of the engine design to comply with the engine debris containment requirements of 14 Code of Federal Regulations 33.13 and 33.75.
Event Information
| Type of Event | Incident |
| Event Date | 10/23/2011 |
| Event Day of the Week | Sunday |
| Time of Event | 1600 |
| Event Time Zone | Eastern Daylight Time |
| Event City | Detroit |
| Event State | MICHIGAN |
| Event Country | -- |
| Zipcode of the event site | -- |
| Event Date Year | 2011 |
| Event Date Month | 10 |
| MidAir Collision Indicator | No |
| On Ground Collision occurred ? | No |
| Event Location Latitude | -- |
| Event Location Longitude | -- |
| Event Location Airport | Detroit International Airport |
| Event Location Nearest Airport ID | DTW |
| Indicates whether the acc/inc occurred off or on an airport | -- |
| Distance from airport in statute miles | -- |
| Degrees magnetic from airport | -- |
| Airport Elevation | -- |
| Weather Briefing Completeness | -- |
| Investigator's weather source | -- |
| Time of the weather observation | |
| Direction of event from weather observation facility (degrees) | -- |
| Weather Observation Facility ID | -- |
| Elevation of weather observation facility | -- |
| Distance of event from weather observation facility (units?) | -- |
| Time Zone of the weather observation | -- |
| Lighting Conditions | -- |
| Lowest Ceiling Height | -- |
| Lowest Non-Ceiling Height | -- |
| Sky/Lowest/Cloud Conditions | -- |
| Sky Condition for Lowest Ceiling | -- |
| Visibility Runway Visual Range (Feet) | -- |
| Visibility Runway Visual Value (Statute Miles) | -- |
| Visibility (Statute Miles) | -- |
| Air Temperature at event time (in degrees celsius) | -- |
| Dew Point at event time (in degress fahrenheit) | -- |
| Wind Direction (degrees magnetic) | -- |
| Variable Wind Indicator | -- |
| Wind Speed (knots) | -- |
| Wind Velocity Indicator | -- |
| Wind Gust Indicator | -- |
| Wind Gust (knots) | -- |
| Altimeter Setting at event time (in. Hg) | -- |
| Density Altitude (feet) | -- |
| Intensity of Precipitation | -- |
| METAR weather report | -- |
| Event Highest Injury | None |
| On Ground, Fatal Injuries | -- |
| On Ground, Minor Injuries | -- |
| On Ground, Serious Injuries | -- |
| Injury Total Fatal | -- |
| Injury Total Minor | -- |
| Injury Total None | 394 |
| Injury Total Serious | -- |
| Injury Total All | -- |
| Investigating Agency | NTSB |
| NTSB Docket Number (internal use) | 30798 |
| NTSB Notification Source | P&W Flight Safety |
| NTSB Notification Date | -- |
| NTSB Notification Time | -- |
| Fiche Number and/or location -used to find docket information | -- |
| Date of most recent change to record | Nov 29 2012 10:19AM |
| User who most recently changed record | defc |
| Basic weather conditions | -- |
| FAA District Office | -- |
Aircraft Involved |
|
|---|---|
Aircraft #1 |
|
| Aircraft Registration Number | N661US |
| NTSB Number | ENG12IA003 |
| Missing Aircraft Indicator | -- |
| Federal Aviation Reg. Part | Part 121: Air Carrier |
| Type of Flight Plan filed | VFR |
| Flight plan Was Activated? | Yes |
| Damage | Minor |
| Aircraft Fire | In-flight |
| Aircraft Explosion | None |
| Aircraft Manufacturer's Full Name | BOEING |
| Aircraft Model | 747-451 |
| Aircraft Series Identifier | -- |
| Aircraft Serial Number | 23719 |
| Certified Max Gross Weight | -- |
| Aircraft Category | Airplane |
| Aircraft Registration Class | -- |
| Aircraft is a homebuilt? | No |
| Flight Crew Seats | -- |
| Cabin Crew Seats | -- |
| Passenger Seats | -- |
| Total number of seats on the aircraft | 450 |
| Number of Engines | 4 |
| Fixed gear or retractable gear | Fixed |
| Aircraft, Type of Last Inspection | -- |
| Date of Last Inspection | -- |
| Airframe hours since last inspection | -- |
| Airframe Hours | -- |
| ELT Installed | Unknown |
| ELT Activated | Unknown |
| ELT Aided Location of Event Site | Unknown |
| ELT Type | -- |
| Aircraft Owner Name | U S BANK TRUST NA TRUSTEE |
| Aircraft Owner Street Address | 225 ASYLUM ST |
| Aircraft Owner City | HARTFORD |
| Aircraft Owner State | CT |
| Aircraft Owner Country | USA |
| Aircraft Owner Zipcode | 06103-1516 |
| Operator is an individual? | No |
| Operator Name | DELTA AIR LINES INC |
| Operator Same as Owner? | No |
| Operator Is Doing Business As | -- |
| Operator Address Same as Owner? | No |
| Operator Street Address | -- |
| Operator City | Atlanta |
| Operator State | GA |
| Operator Country | USA |
| Operator Zip code | -- |
| Operator Code | DALA |
| Owner has at least one certificate | Yes - certificate holder |
| Other Operator of large aircraft? | No |
| Certified for Part 133 or 137 Operation | -- |
| Operator Certificate Number | DALA026A |
| Indicates whether an air carrier operation was scheduled or not | Scheduled |
| Indicates Domestic or International Flight | International |
| Operator carrying Pax/Cargo/Mail | Passenger Only |
| Type of Flying (Per_Bus / Primary) | -- |
| Second Pilot on Board | Yes |
| Departure Point Same as Event | Yes |
| Departure Airport Code | DTW |
| Departure City | Detroit |
| Departure State | MI |
| Departure Country | USA |
| Departure Time | -- |
| Departure Time Zone | EDT |
| Destination Same as Local Flt | -- |
| Destination Airport Code | NRT |
| Destination City | Narita, Tokyo |
| Destination State | -- |
| Destination Country | JA |
| Specific Phase of Flight | -- |
| Report sent to ICAO? | -- |
| Evacuation occurred | -- |
| Date of most recent change to record | Sep 6 2012 9:45AM |
| User who most recently changed record | scaj |
| Since inspection or accident | -- |
| Event Location Runway Number and Location | N/A |
| Runway Length | -- |
| Runway Width | -- |
| Sight Seeing flight | No |
| Air Medical Flight | No |
| Medical Flight | -- |