The Airport Emergency Plan is the framework that supports the ARFF operations; that would be ‘The Plan,’ if you will. The major mishap exercise is th

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PB90-9 I 0406 I · NTSB/AAR-90/06

NATIONAL · . TRANSPORTATION

SAFETY .BOARD I _____ – _,_ — —

AIRCRAFf ACCIDENT REPORT

UNITED AIRLINES Fl.IGHT 232 ··~ .. · McDONNELL DOUGLAS DC-I0-10 SIOUX GATEWAY AIRPORT SIOUX CITY, IOWA JULY 19, 1989

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TECHNICAL REPORT DOCUMENTATION PAGE 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.

NTSB/AAR-90/06 PB90-910406

4. Title and Subtitle Aircraft Accident Report·- 5. Report Date United Airlines Flight232, McDonnell Douglas DC-10-10, November 1, 1990 Sioux Gateway Airport, Sioux City, Iowa, July 19, 1989

6. Performing Organization Code

7. Author(s) 8. Performing Organization Report No.

9. Performing Organization Name and Address 10. Work Unit No. 51580

National Transportation Safety Board 11. Contract or Grant No. Office of Aviation Safety

Washington, D.C. 20594 13. Type of Report and

Period Covered Aircraft Accident Report

12. Sponsoring Agency Name and Address July 19, 1989

NATIONAL TRANSPORTATION SAFETY BOARD 14. Sponsoring Agency Code Washington, D.C. 20594

15. Supplementary Notes

16. Abstract This report explains the crash of a United Airlines McDonnell Douglas DC-10-10 in Sioux City, Iowa, on July 19, 1989. The safety issues discussed in the report are engine fan rotor assembly design, certification, manufacturing, and inspection; maintenance and inspection of engine fan rotor assemblies; hydraulic flight control system design, certification, and protection from uncontained engine debris; cabin safety, including infant restraint systems; and aircraft rescue and firefighting facilities. Safety recommendations addressing these issues were made to the Federal Aviation Administration and the U.S. Air Force.

17. Key Words 18. Distribution Statement This document is available to the public through the Nationai Technical Information Service, Springfield, Virginia 22161

19. Security Classification 20. Security Classification 21. No. of Pages 22. Price (of this report) (of this page)

UNCLASSIFIED UNCLASSIFIED 126

NTSB Form 1765.2 (Rev: 5/88}

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1. 1.1 1.2

. 1.3 1.4 1.5 1.6 1.6.1 1.6.2 1.6.3 1.7 1.8 1.9 1.9.1 1.10 1.11 1.11.1 1.11.2 1.12 1.12.1 1.12.2· 1.12.3

1.12. 4 1.13 1.14 1.14 .1 Ll4.2 1.14. 3 1.15 1.15 .1 1.15. 2 1.16 1.16.1 1.16.2 1.16.3 1.16. 4 1.16. 5 1.16. 6

1.17 1.17.1 1.17.2 1.17.3

1.17.4 1.17.5 1.17.6

CONTENTS

EXECUTIVE SUMMARY • e • e e ••• e e e e t •• e a a a I a a a 'a I I I a a a I a I I e a I I I I I I I

FACTUAL INFORMATION Hi story of Flight ……………………………………. . Injuries to Persons ..•……………………………….. Damage to Airplane ………. –. ………………….. · ….. · .. ·. Other Damage ……………………………………….. -. Personnel Information ……………………………….. . Airplane Information …..•…•……•…………………… No. 2 Engine Historical Data ………..•……………….. Stage 1 Fan Disk Historical Data ………… i ••••••••••••••• Airplane Flight Controls and Hydraulits–Oescription ……. . Meteorological Information …………………………… . Aids to Navigation ………………………………….. . Communications …….•…….•………..•……………… United Airlines Company Flight Following ………….•…… Airport Information …………………………………. . Flight Recorders ………………… · ….. · ……………… . Cockpit Voice Recorder ………………………………. . Fl i g ht Data Recorder •……•………………………….. Wreckage and Impact Information ………………………. . -Impact Marks and Ground Damage ……………………….. . Reconstruction of Empennage ..•………………………… Damage to Inlet Duct and Vertical Stabilizer Spars (Banjo Frames) …….. , …………………………….. .

Hydraulic System Damage ………………………………. . Medical and Pathological Information ……….•…………. Fi re ………………………………………………. . Airport Response ……………………………………. . Off-Airport Response ………………………………… . The Kovatch P-18 Water Supply Vehicle …………………. . Survival Aspects ……………………………………. . Cabin Preparation …………………………………… . Infants ……………………… · ……………………. . Tests and Research ………………………………….. . Design of CF6-6 Engine Stage 1 Fan Disk ……………….. . Examination of No. 2 Engine Stage 1 Fan Disk ……..•..•…. Examination of Containment Ring ..•……..•…………….. Other No. 2 Engine Hardware ………………………….. . s;ster Fan Disks …………………………………… . No. 2 Engine Fan Disk Fracture Surface Chemical Residue Examination …….•………………………………….

Additional Information ………………………………. . Fan Disk Manufacturing Processes and Hard Alpha ………… . ALCOA Forging and Records …………………………….. · GEAE Fan Disk S/N MPO 00385 Machining and Finishing · Records …………………………………………… . Inspections During Disk Manufacture •…………………… Responsibility for Continuing Airworthiness ……………. . Certification Requirements ………•……………………

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I 5 6 6 6

11 12 15 15 19 19 19 19 20 21 21 23 24 25 30

32 32 35 35 35 38 38 39 39 40 41 41 41 47 47 48

49 49 49 51

53 57 59 62

1.17.6.l 1.17.6.2 1.17.7 1.17.8 1.17.9 1.17.10

Certification Requirements – Aircraft …..•…………….. Certification Requirements – Engine …………………… . Field Inspection Programs …. ~ …..•…………………… Hydraulic System Enhancement ….•…..•………………… Hi stori cal Review .. • ………………………………… . Airplane Flight Characteristics with Immovable Control Surf aces ………………………………………….. .

1.17.10.1 General Characteristics ……………………………… . 1.17.10.2 Flight Simulator Studies ..•….•…………..• : ……….. . 1.18 Useful Investigative Techniques •…………••…•………. 1.18.1 Special Investigative Techniques – Photograph Image

2. 2.1 2.2 2.3 2.4 2.4.1 2.4.2 2.4.3 2.4.4 2.5 2.5.1 2.6 2.7 2.7.1

2.7.2 2.8 2.9 2.10 2.10.l a.10.2 2.10.3 2.10.4

Analysis ………………………………………….. .

ANALYSIS General ….. ···-···· …….. ~ ………………………….. . Ace i dent Sequence …•……………………..•………… Performance of UAL 232 Fl ightcrew …………………….. . Analysis of Fan Diak Fracture …………………… ~ ….. . Separation of Fan Disk …………•.•…•………………. Initiation·and Propagation of fatigue Crack …………….. . Source of Hard Alpha Defect ………………………….. . Formation of Cavity ………….•…….•………………. Origin of Accident Fan Disk MPO 00385 …………………. . Quality Assurance During Manufacturing Process …………. . Operator Inspection Program and Methods ……………….. . Philosophy of Engine/Airframe Design ………………….. . Hydraulic Systems/Flight Control Design Concept and Cert i fi cation ……………………………………… .

Future Certification Concepts ………………………… . Survival Aspects …………………………………….. . Emergency Management ……………•………………….. ·. Adequacy of Actions Taken Since the Accident …………… . CF6-6 Fan Disk Inspection Programs ……………………. . Hydraul i.c System Enhancement …………………………. . Industry Task Group Efforts ………………………….. . Damage Tolerance for Commercial Transport Engines ………. .

3. CONCLUSIONS

62 63 64 66 67

70 70 72 73

73

73 74 75 77 77 77 78 79 80 83 85 89

89 90 92 93 95 95 97 98 99

3 .1 Findings • . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 3.2 Probable Cause . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

4. RECOMMENDATIONS • .. . • . • • • • • • • • • .. • • • • • • • • .. . .. .. . • . • . • .. . . . . . 102

5. APPENDIXES Appendix A–Investigation and Hearing ………………….. 111 Appendix B–Personnel Information • . . . . . .. .. . . .. .. . .. . . .. . .. . 112 Appendix C–Horizontal Stabilizer Damage Diagram………… 115 Appendix D–Douglas Aircraft Company Letter: Controllability with all Hydraulic Failure .. …. . .. . . . .. .. . . .. .. . .. .. .. .. . . 116

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EXECUTIVE SUMMARY

On July 19, 1989, at 1516, a DC-10-10, Nl819U, operated by United Airlines as flight 232, experienced a catastrophic failure of the No. 2 tail-mounted engine during cruise flight. The separation, fragmentation and forceful discharge of stage 1 fan rotor assembly parts from the No. 2 engine led to the loss of the three hydraulic systems that powered the airplane's flight controls. The flightcrew experienced severe difficulties controlling the airplane, which subsequently crashed during an attempted landing at Sioux Gateway Airport, Iowa. There were 285 passengers and 11 crewrnembers onboard. One flight attendant and 110 passengers were fatally injured.

. The National Transportation Safety Board determines that the probable cause of this accident was the inadequate consideration given to human factors limitations 1n the inspection and quality control procedures used by United Airlines' engine overhaul facility which resulted in the failure to detect a fatigue crack originating from a previously undetected metallurgical defect located in a critical area of the stage 1 fan disk that was manufactured by General Electric Aircraft Engines. The subsequent catastrophic disintegration of the disk resulted in the liberation of debris in a pattern of distribution and with ·energy levels that exceeded the level of protection provided ·by design features of the hydraulic systems that operate the DC-lO's flight controls.

The safety issues raised in this report include:

1. General Electric Aircraft Engines' {GEAE} CF6-6 fan rotor assembly design, certification, manufacturing, and inspection .

2. United Airlines' maintenance and inspection of CF6-6 engine fan.rotor assemblies.

3. DC-10 hydraulic flight control system design, certification and protection from uncontained ~gine debris.

4. · Cabin safety, including infant restraint systems, and airport rescue and firefighting facilities.

Reconunendations concerning these issues were addressed to the Federal Aviation Administration, the Secretary of the Air Force, the Air Transport Association and the Aerospace Industries Association.

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NATIONAL TRANSPORTATION SAFffi BOARD WASHINGTON, D. C. 20594

AIRCRAFT ACCIDENT REPORT

UNITED AIRLINES.FLIGHT 232, McDONNELL DOUGLAS DC-10-10 SIOUX GATEWAY AIRPORT

SIOUX CITY, IOWA JULY 19, 1989

1. FACTUAL INFORMATION

1.1 History of Flight

United Airlines (UAL) flight 232 (UA 232), a McDonnell Oougl as DC-10-10, registration No. Nl819U, was a scheduled passenger flight from Stapleton International Airport, Denver, Colorado, to Philadelphia, Pennsylvania, with an en route stop at Chicago, Illinois. The flight was conducted under Title 14 Code of Federal Regulations (CFR) Part 121. Flight 232 departed Denver at 1409 central daylight time. There were 285 passengers and 11 crewmembers on board.

The takeoff and the en route climb to the planned cruising altitude of 37 ,000 feet were uneventful. The first officer (copilot) was the flying pilot. The autopilot was engaged, and the autothrottles were selected in the speed mode for 270 KIAS. The flight plan called for a cruise speed of

. Mach 0.83.

About 1 hour and 7 minutes after takeoff, at 1516:10, the flightcrew heard a loud bang or an explosion, followed by vibration and a shuddering of the airframe. After checking the engine instruments, the fl ightcrew determined that the No. 2 aft (tail-mounted) engine had failed. (See figure 1). The captain called for the engine shutdown checklist. While performing the engine shutdown checklist, the second officer (flight engineer) observed that the airplane's normal systems hydraulic pressure and quantity gauges indicated zero.

The first officer advised that he could not control the airplane as it entered a right descending turn. The captain took control of the afrplane and confirmed that it did not respond to flight control inputs. The captain reduced thrust on the No. 1 engine, and the airplane began to roll to a wings-level attitude.

The flightcrew deployed the air driven generator (ADG), which powers the No. 1 auxiliary hydraulic pump, and the hydraulic pump was selected non." This action did not restore hydraulic power. ·

At 1520, the flightcrew radioed the Minneapolis Air Route Traffic Control Center (ARTCC) and requested emergency assistance an.d vectors to the nearest airport. Initially, Des Moines International Airport was suggested by ARTCC. At 1522, the air traffic controller informed the flightcrew

2

Wing Mounted Engines

Aft Tail Mounted Engine

Figure l.–DC-10 airplane view illustrated with engine arrangement .

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3

that they were proceeding in the direction of Sioux City; the controller asked the flightcrew if they would prefer to go to Sioux City. The fl ightcrew responded, aaffirmative. 11 They were then given vectors to the Sioux Gateway Airport (SUX) at Sioux City, Iowa. (See figure 2). Details of relevant air traffic control (ATC) communications, cockpit conversations, airplane maneuvers, and airplane and engine system parameters are contained in Sections 1.9 and 1.11 of this report.

Crew interviews indicate that shortly after the. engine. failure, the passengers were informed of the failure of the No. 2 engine, and the senior flight attendant was called to the cockpit. She was told to prepare .the cabin for an emergency landing. She returned to the cabin and separately informed the other flight attendants to prepare for an emergency landing. A flight attendant advised the captain that a UAL DC-10 training check airman,, who was off duty and seated in a first class passenger seat, had volunteered his assistance. The captain immediately invited the airman to the cockpit, and he arrived about 1529.

At the request of the captain, the check airman entered the passenger cabin and performed a visual inspection of the airplane's wings. Upon his return, he reported that the inboard ailerons were slightly up, not damaged, and that the spoilers were locked down. There was no movement of the primary" flight control surfaces. The captain then directed the check airman to take control of the throttles to free the captain and first officer to manipulate the flight controls.

The check airman attempted to use engine power to control pitch and roll. He said that the airplane had a continuous tendency to turn right, making it diffi<;ult to maintain a stable pitch attitude. He also advised that the No. 1 and No. 3 engine thrust levers -could not be used symmetrically, so he used two hands to manipulate the two throttles.

About 1542, the second officer was sent to the passenger cabin to inspect the empennage visually. Upon his return, he reported that he observed damage to the right and left horizontal stabilizers.

Fuel was jettisoned to the level of the automatic system cutoff, leaving 33,500 pounds. About 11 minutes before landing, the landing gear was extended by means of the alternate gear extension procedure.

The flightcrew said that they made visual contact with the airport about 9 miles out. ATC had intended for flight 232 to attempt to land on runway 31, which was 8,999 feet long. However, ATC advised that the airplane was on approach to runway 22, which was closed, and that the length of this runway was 6,600 feet. Given the airplane's position and the difficulty in making left turns, the captain elected to continue the approach to runway 22 rather than to attempt maneuvering to runway 31. The check airman said that he believed the airplane was lined up and on a normal glidepath to the field. The flaps and slats remained retracted .

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0.00 6.00 12.00 18.00 24.00 30.00 36.00 42.00 48.00 54.00 60.00

Scale (NM)

Figure 2.–Ground track from radar plot.

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During the final approach, the captain recalled getting a high sink rate alarm from the ground proximity warning system (GPWS). In the last 20 seconds before touchdown, the airspeed averaged 215 KIAS, and the sink rate was 1,620· feet per minute. Smooth oscillations in pitch and roll continued until just before touchdo~n when the right wing dropped rapidly. The capta1 n stated that about 100 feet above the ground the nose of the airplane began to pitch downward. He also felt the right wing drop down about the same time. Both the captain and the first officer called for reduced power on short final approach.

The check airman said that based on experience with no flap/no slat approaches he knew that power would have to be used to control the airplane's descent .. He used the first officer's airspeed indicator and visual cues to determine the flightpath and the need for power changes. He thought that the airplane was fairly well aligned with the runway during the latter stages ·of

· the approach and that they would reach the runway. Soon thereafter, he observed that the airplane was positioned to the left of the desired landing area and descending at a high rate. He also observed that the right wing began to drop. He continued to manipulate the No. 1 and No. 3 engine throttles until the airplane contacted the ground. He said that no steady application of power was used on the approach and that the power was constantly changing. He believed that he added power just before contacting the ground.

The airplane touched down on the threshold slightly to the left of the centerline on runway 22 at 1600. First ground contact was made by the right wing tip followed by the right main landing gear. The airplane skidded to the right of the runway and rolled to an inverted position. Witnesses observed the airplane ignite and cartwheel, coming to rest after crossing runway 17/35. Firefighting and rescue operations began immediately, but the airplane was destroyed by impact and fire.

The accident occurred during daylight conditions at 42° 25' north latitude and 950 23' west longitude.

1.2 Injuries to Persons

In1uries Crew passengers Others Total

Fatal 1 110 0 111 Serious 6 41* 0 47 Minor 4 121 0 125 None _Q 13 Q _n Total 11 285 0 296

*One passenger died 31 days after the accident as a result of injuries he had received in the accident. In accordance with 49 CFR 830.2, his injuries were classified "serious."

1.3

6

Damage to Airplane

The airplane was destroyed by impact and postcrash fire.

Photographs of the airplane were taken by observers on the ground during its final approach to Sioux Gateway Airport. They showed that the No. 2 engine fan cowling and the fuselage tail cone were missing. The remainder of the No. 2 engine appeared intact. Postcrash examination of the wreckage revealed that the No. 2 engine fan rotor components forward of the fan forward· shaft, as well as part of the shaft, had separated from the engine in flight. (See figures 3 through 5). ·

The airplane's right wing began to break up immediately following touchdown. The remainder of the airplane broke up as it tumbled down the runway. The fuse 1 age center section, with most of the 1 eft wing st il 1 ·attached, came to rest in a corn field after crossing runway 17/35.

The cockpit separated early in the sequence and came to rest at the edge of runway 17/35. . The largely intact tail section continued down runway 22 and came to rest on taxiway "L." The engines separated during the breakup. The No. 1 and No. 3 engines came to rest near taxiway "L" and the intersection of runway 17/35, between 3,000 and 3,500 feet from the point of first impact. (See figure 6).

The No. 2 engine came to rest on taxiway "J" to the 1 eft ·of runway 22, about 1,850 feet from the point of first impact. The majority of the No. 2 engine fan module was not found at the airport.

The value of the airplane was estimated at $21,000,000.

1.4 Other Damage

Airplane parts, which separated and fell to the ground on cultivated land, caused no significant damage. There was some minor damage to airport facilities and adjacent crops as a result of the crash landing.

1.5 Personnel Information

The flightcrew consisted of . a captain, first officer, second officer and eight flight attendants. (See appendix B).

The captain was employed· by UAL on February 23, 1956. He had 29,967 hours of flight time logged with UAL, 7,190 hours of which was in the DC-10. He held an airline transport pilot certificate with type ratings in the DC-10 and B-727. He possessed a current first class airman medical certificate. His most rec.ent proficiency check in the OC-10 was completed on April 26, 1989.

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Figure 3.–Photo (C. Zellmer) taken while flight 232 was approaching Sioux Gateway Airport. Arrows indicate damage to the right horizontal stabilizer. It is also evident that the No. 2 engine fan cowl door and the tail cone are missing.

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Figure 4.–CF6-6 engine.

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Spinner cover

Forward

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Figure 5.–CF6-6 fan rotor assembly. '

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EIBY 1,093 Fl

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Airport Diagram

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Ft. LI_._…_ ….. -''L.-L'….L-'.._.1_.. …………. ~· 0 2,000 4,000 6,000

10

Closed Runway

1,000 Ft. Stopway

Flap Hinge

No. 3 Engine

Touchdown Area

Right Wing Tip

Right Main Landing Gear (2 Places}

Right Wing Tip

Figure 6.–Sioux Gateway Airport and wreckage path of UA flight 232.

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The first officer began airline employment on August 25, 1969. He estimated ·that he had logged 20,000 hours of flight time. He had accrued 665 hours as a first officer in the DC-10. He held an airline transport pilot certificate with type ratings in the DC-10 and L-1011. He possessed a current first class airman medical certificate. His most recent proficiency check in the DC-10 was completed on A~gust 8, 1988.

The second officer was employed by UAL on May 19, 1986. He estimated that he had 15,000 hours of flight time. UAL records indicated that he had accumulated 1, 903 hours as a second officer in the B-727 and 33 hours in the DC-10. He held a flight engineer certificate for turbojet airplanes. He possessed a current second cl ass airman medical certificate. His most recent proficiency check ·in the DC-10 was completed on June 8, 1989.

A review of flightcrew duty time indicated that the crew had complied with all relevant duty time limitations. The accident occurred on the third day of a 4-day scheduled trip sequence. The crew had a 22-hour layover in Denver prior to the departure of flight 232. The cockpit crew had flown together six times in the previous 90 days.

The off-duty check airman was employed by UAL on January 2, 1968. He held an airline transport pilot certificate with type rating in the DC-10 and a first class medical certificate. He had completed captain-transition training in the DC-10 on April 25, 1989, and was assigned as a DC-10 training check airman at UAL's Flight Training Center in Denver, Colorado. He had about 23, 000 hours tot a 1 flight ti me with 2, 987 hours 1 ogged in the DC-1 O. He had 79 hours as captain in the OC-10.

1.6 Airplane Information

UAL operated a total of 55 OC-10 airplanes; 47 airplanes were model OC-10-10, and 8 airplanes were model DC-10-30. The accident airplane, Nl819U, fuselage No. 118, factory S/N 44618, was delivered in 1971 and was owned by UAL since that time. Prior to departure on the accident flight from· Denver on July 19, 1989, the airplane had been operated a total of 43,401 hours and 16,997 cycles.

The maximum certificated takeoff weight for Nl819U was 430,000 pounds. The center of gravity {CG) computed· for departure was 21.9 percent mean aerodynamic chord (MAC). The calculated CG limits for this gross weight were 13.4 percent and 30.8 percent MAC, respectively. The takeoff gross weight was 369,268 pounds.

The accident airplane was powered by General Electric Aircraft Engines {GEAE) CF6-60 high bypass ratio turbofan engines. The CF6-6 engine was certified by the FAA on September 16, 1970.

Table l provides identification and historical information for the engines in Nl819U at the time of the accident.

12

Table 1

Engines Historical Data

Data

Engine Serial Number (ESN) Total Time Total Cycles Time Since Last Maintenance Cycles Since Last Maintenance Time Since Last Shop Visit Cycles Since Last Shop Visit Date of Installation

Number 1

451-170 44,078 16,523

1,047 358

3,635 1,318

5-9-88

Number 2 ·

451-243 42,436 16,899

2,170 760

2, 170 760

10-25-88

Number 3·

451-393 39,338 11, 757

338 116 338 116

6-11-89

Figure 7 contains a c·utaway sectional drawing of the flow path and construction of the CF6-6 engine. The figure also shows the fan and accessory drive sections. Figure 8 displays the CF6-6 rotating assemblies. The portion of the No. 2 engine that departed the airplane is outlined by the dashed lines.

1.6.1 No. 2 Engine Historical Data

Engine S/N 451-243 was first installed on June 23, 1972, in the No. 3 position of a UAL DC-10-10, registration airplane N1814U. Fan module S/N 51406, which contained stage 1 fan disk P/N 9137M52P36, S/N MPO 00385, was installed on engine S/N 451-243 during a shop visit in July 1988, at ,_-_ UAL. At that time, the engine had accumulated 40,266 hours and 16,139 cycles since new.

Engine S/N 451-243 was installed in the No. I position on UAL airplane registration Nl807U on September 15, 1988. It was removed "for convenience" 8 days later after one flight and was installed in ·the No. 2 position on N1819U on October 25, 1988. The engine had accumulated 42,436 hours and 16,899 cycles at the time of the accident.

Examination of service records, crew writeups, action items, trend monitoring data, and flight recorder data indicated no abnormal engine operation prior to the in-flight incident, with the exception of certain autothrottle anomalies. The autothrottle system's inability to hold steady Nl was noted in the reported difficulties, and corrective action entries in U L's Aircraft Maintenance Information System (AMIS) were dated on July 14, 17, and 19, 1989. On July 19, corrective action for the discrepancy was indicated accomplished at Phil adel phi a with the replacement of the autothrottle speed control and was signed off as "system ops check nor~al."

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1.6.2 Stage 1 Fan Disk Historical Data

The stage 1 fan disk, part

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