# NTSB MIA99FA252: Boeing B737-300, N17356, West Palm Beach, FL, September 12, 1999 - Type: NTSB accident investigation - Classification: Accident · No injuries · Field investigation · Final report - Date: September 12, 1999, 07:11 local (11:11 UTC) - Place: West Palm Beach, FL - Coordinates: 26.660362, -80.090438 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=26.6604&lon=-80.0904&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 89 uninjured - Status: Completed, report August 3, 2000 - Report: Approved by Office Director - NTSB case key (mKey): 47372 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=MIA99FA252 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/47372/pdf - Page: https://openairdocs.org/ntsb/MIA99FA252 ## Probable cause The fatigue fracture and separation of the high pressure turbine forward rotating air seal due to a manufacturing defect in a bolt hole that was not detected by the engine manufacturer due to inadequate and ineffective inspection techniques. Contributing to the accident was the engine manufacturers failure to provide adequate hole making requirements at the time the forward rotating air seal was manufactured and the engine manufacturers failure at the time of last inspection to require eddy current inspections for the high pressure turbine forward rotating air seal bolt holes. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power(partial) - mech failure/malf, climb - turbine assembly,air seal - fatigue (cause) - insufficient standards/requirements,manufacturer, manufacturer (cause) - turbine assembly,air seal - separation (cause) ## Analysis During climb after takeoff, the flight had an uncontained failure of the No. 1 engine. The flight returned to the departure airport and landed without further incident. Examination of the airplane showed there was damage to the left wing high lift devices, fuselage, vertical and horizontal stabilizers, rudder, and tail cone. The No. 1 engine left thrust reverser had separated. Debris from the No.1 engine was located over an eight block long by three block wide city block area. Examination of the No. 1 engine revealed that it had a 360 degree separation in plane with the high pressure turbine (HPT) rotor and that the HPT shaft and the HPT forward rotating air seal had exited the engine. The HPT rotating air seal was recovered in the debris field. Metallurgical examination showed the rotating air seal had two radial fractures that passed through the bore and the HPT front shaft-to-HPT disk attachment bolt holes. Fatigue cracking was identified in one attachment bolt hole which initiated from a heat affected layer. The heat affected layer was caused by abusive machining during the manufacturing process due to loss of coolant during the drilling process. Based on striation count, the fatigue crack was at detectable length during two in-service inspections, but was not detected. ## Factual narrative HISTORY OF FLIGHT On September 12, 1999, about 0711 eastern daylight time, a Boeing 737-300, N17356, registered to ICX Corporation, and operated by Continental Airlines, Inc., as flight 1933, a Title 14 CFR Part 121 scheduled domestic passenger flight from West Palm Beach, Florida, to Houston, Texas, had a failure of the No. 1 engine shortly after takeoff from West Palm Beach. Visual meteorological conditions prevailed at the time, and an instrument flight rules flight plan was filed. The airline transport-rated pilot, second pilot, 3 flight attendants, and 84 passengers were not injured. The flight was originating at the time of the accident. The captain stated he was in the right seat and acting as a check airman. The second pilot, who was flying the aircraft from the left seat, was receiving initial operating experience as a captain. Both pilots stated that after takeoff on runway 9 left, as they were climbing through about 1,000 feet, there was the sound of a loud bang, they felt a extremely violent jolt, and felt severe shaking of a short duration. The No. 1 engine gauges went to zero. There was no indication of fire. The second pilot continued to fly the airplane and the captain ensured the No. 2 engine was increased to full power. They entered a left downwind leg for runway 9 left and returned to West Palm Beach International Airport, where they landed without further incident. A witness stated he was working on the roof of the Palm Beach Post building. He was to the north of the airplanes flight path, and was looking at the left side of the airplane. He saw flames shoot from the left engine that lasted about 2 seconds, and then the engine exploded and the flames went out. A black smoke cloud remained at the point of the explosion. He then saw a large piece of the airplane falling from the sky. He did not see any more smoke or flame coming from the left engine and the airplane turned to the north and then to the west and was lost from sight. PERSONNEL INFORMATION The captain (who was acting as a check airman) holds a airline transport pilot certificate with a Boeing 737 type rating. Continental Airlines, Inc. reported that at the time of the accident he had accumulated 10,500 total flight hours with 6,500 flight hours in the Boeing 737. The second pilot (who was receiving initial operating experience as a captain) holds a airline transport pilot certificate with a Boeing 737 type rating. Continental Airlines, Inc. reported that at the time of the accident the second pilot had accumulated 10,000 total flight hours with 550 flight hours in the Boeing 737. AIRCRAFT INFORMATION The airplane is a Boeing 737-3TO, serial number 23942, registered to ICX Corporation. Continental Airlines, Inc. reported the airplane had accumulated 34,602 total flight hours at the time of the accident and 222 flight hours since the last inspection. The No. 1 engine is a CFM International, model CFM56-3-B1, SN 720957, that had accumulated 31,732 total flight hours time since new, 16,496 cycles since new, 5,604 hours time since overhaul, and 2,771 cycles since overhaul at the time of the accident. The last maintenance visit for the engine was at General Electric Engine Services Inc., Strother, Kansas, from July - October 1997. The engine was removed by Continental on July 27, 1997, and was sent to GE Strother because of damage to the high pressure compressor 6th-stage compressor blades. The engine was returned to service on October 27, 1997. Prior to the 1997 shop visit, the engine was overhauled by GE Strother in September 1996. The No. 1 engine forward rotating air seal was forged by Wyman-Gordon, Grafton, Massachusetts, and was shipped on January 24, 1986, to NCI Inc., Asheville, North Carolina, for finish machining. There was no maintenance review board (MRB) activity at Wyman-Gordan. The forward rotating air seal was finished machined as PN 1282M72P03, SN NCE24161, and was Fluorescent Penetrant Inspected (FPI). There was no MRB activity for the rotating air seal at NCI. NCI shipped the forward rotating air seal on July 31, 1986, and Continental installed it in CFM56-3-B1 engine, SN 721641, on January 1, 1987. According to the GE Strother's "Received Offlog Configuration" sheet, dated October 10, 1988, the HPT rotor, which includes the forward rotating air seal, was removed from engine SN 721641 and was not disassembled. A GE Strother's "Onlog-Offlog Comparison Final Report", dated April 10, 1989, indicated that the HPT rotor removed from SN 721641 was installed on CFM56-3-B1 engine SN 721729 where it remained until January 1993. The forward rotating air seal had accumulated 5,426 hours TSN and 2,222 CSN when installed in engine SN 721729. According to GE Strother's "Cycle Limited Parts Disposition Sheet", dated January 29, 1993, Work Order (W/O) 905422, the HPT rotor was removed from engine SN 721729 and the front shaft was replaced. Overhaul sheets, marked W/O 905422, indicated that HPT blades were replaced but that the forward rotating air seal, HPT disk, and HPT rear shaft were not disassembled and inspected. Final build sheets indicate that the HPT rotor was installed on CFM56-3-B1 engine, SN 720957, the accident engine, on April 23, 1993, where it remained until October 1996. The forward rotating air seal had accumulated 17,555 hours TSN and 8,289 CSN when installed in engine SN 720957. In October 1996, GE Strother removed the HPT rotor from engine SN 720957, disassembled it, and shipped the forward rotating air seal to GE Engine Services, Aviation Component Service Center (ACSC), Cincinnati, Ohio, for inspection and repair. ACSC paperwork (W/O 26092C) indicated that a visual and FPI was performed on the forward rotating air seal on October 25, 1996, with no nonconformances noted. The FPI was the first in-service inspection of the forward rotating air seal and the second inspection since it was manufactured. A seal teeth coating replacement repair, CFMI Engine Manual Task 72-52-03 was also performed. GE Engine Services ASCS issued a FAA Form 8130-3 Airworthiness Approval tag for the forward rotating air seal on November 1, 1996, and shipped it to GE Strother were it was reinstalled on engine SN 720957. Engine SN 720957 remained in operation until July 1997. The forward rotating air seal had accumulated 27,460 hours TSN and 14,102 CSN when repaired by ACSC. Continental removed engine SN 720957 and shipped it to GE Strother because of damage to the HPC 6th-stage blades. The HPT rotor was disassembled and the forward rotating air seal was FPI'd on September 16, 1997, with no nonconformances noted. The FPI was the second in-service inspection of the forward rotating air seal and the third inspection since it was manufactured. GE Strother's maintenance records also indicate that a part re-marking repair was performed because the part number had become illegible. The forward rotating air seal was reinstalled on engine SN 720957 where it remained until the accident. The configuration comparison final report for engine SN 720957 indicated that the forward rotating air seal had 29,362 hours TSN and 15,067 CSN when installed. The forward rotating air seal had accumulated 5,604.3 hours TSO, 2,771 CSO, 34,966 hours TSN, and 17,838 CSN at the time of the accident. The forward rotating air seal has a published service life limit of 20,000 cycles, and at the time of the accident, 94 percent of the service life had been utilized. METEOROLOGICAL INFORMATION The West Palm Beach International Airport 0653 surface weather observation was clouds 20,000 feet scattered, visibility 10 statute miles, altimeter setting 29.92 inches Hg., temperature 81 degrees F., dewpoint temperature 73 degrees F., wind from 030 at 3 knots. FLIGHT RECORDERS The cockpit voice recorder (CVR) was a Fairchild model A100, serial number 6670. The CVR was taken to the NTSB, Vehicle Recorder Laboratory, Washington, D.C., after ## Aircraft - Registration: [N17356](https://openairdocs.org/deregistered/N17356-2013-03-21), registration cancelled 2013-03-21, S/N 23942, built 1988 (OpenAirDocs) - Reported make and model: Boeing B737-300 - Registry model: [Boeing 737-3TO](https://openairdocs.org/model/boeing-737-3to) (registry code 138447G) (OpenAirDocs) - Registry engine: [GE CFM56 series](https://openairdocs.org/engine/ge-cfm56-series) (registry code 30016, turbo-fan) (OpenAirDocs) - Category: Airplane - Serial number: 23942 - Airframe hours: 34602 - Engines: Cfm CFM56-3B1 20100 lbs thrust turbo fan - Damage: Substantial damage - Flight: Part 121 - Operator: Continental Airlines, doing business as Continental Airlines - Registered owner: Icx Corporation - Airworthiness certificate: Standard, Transport - Last inspection: Continuous airworthiness, August 18, 1999, 222 hours before - Departed: PBI - Destination: IAH, HOUSTON, TX - Flight plan: IFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 52; flight engineer, airline transport; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 1, valid medical--w/ waivers/lim; seat: left; flight hours: 10,500 total, 6,500 in this make and model, 10,100 as pilot in command, 149 in the last 90 days, 58 in the last 30 days, 3 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 30° at 3 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 81 °F, dew point 73 °F - Altimeter: 29.00 inHg - Observed at: PBI, 1 nm away ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 19990912041969A](https://openairdocs.org/incident/19990912041969A), Sep 12, 1999: Boeing 7373T0, West Palm Beach, FL, Substantial damage. (-23) #1 Engine sustained an un-contained failure due to 7th stage turbine disk air seal (high pressure) that is attached to 7th stage disk. Shaft sheared and… From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.