NTSB/AAR-02/01 PB2002-910401 Aircraft Accident Report Loss of Control and Impact with Pacific Ocean Alaska Airlines Flight 261 McDonnell Douglas MD-83, N963AS About 2.7 Miles North of Anacapa Island, California January 31, 2000 L TRANSP National A O ON E PLURIBUS UNUM RTA Transportation I T AT IO Safety Board N N D SAFETY BOA R Washington, D.C. Aircraft Accident Report Loss of Control and Impact with Pacific Ocean Alaska Airlines Flight 261 McDonnell Douglas MD-83, N963AS About 2.7 Miles North of Anacapa Island, California January 31, 2000 ATION AL TRE PLUARIBUNS UNUSM PORTATIO NS AFETYBO AR DN NTSB/AAR-02/01 PB2002-910401 National Transportation Safety Board Notation 7263E 490 L(cid:146)Enfant Plaza, S.W. Adopted December 30, 2002 Washington, D.C. 20594 National Transportation Safety Board. 2003. Loss of Control and Impact with Pacific Ocean, Alaska Airlines Flight 261, McDonnell Douglas MD-83, N963AS, About 2.7 Miles North of Anacapa Island, California, January 31, 2000. Aircraft Accident Report NTSB/AAR-02/01. Washington, DC. Abstract: This report explains the accident involving Alaska Airlines flight 261, a McDonnell Douglas MD-83, which crashed into the Pacific Ocean about 2.7 miles north of Anacapa Island, California. Safety issues discussed in this report include lubrication and inspection of the jackscrew assembly, extension of lubrication and end play check intervals, jackscrew assembly overhaul procedures, the design and certification of the MD-80 horizontal stabilizer trim control system, Alaska Airlines(cid:146) maintenance program, and Federal Aviation Administration (FAA) oversight of Alaska Airlines. Safety recommendations are addressed to the FAA. The National Transportation Safety Board is an independent Federal agency dedicated to promoting aviation, railroad, highway, marine, pipeline, and hazardous materials safety. Established in 1967, the agency is mandated by Congress through the Independent Safety Board Act of 1974 to investigate transportation accidents, determine the probable causes of the accidents, issue safety recommendations, study transportation safety issues, and evaluate the safety effectiveness of government agencies involved in transportation. The Safety Board makes public its actions and decisions through accident reports, safety studies, special investigation reports, safety recommendations, and statistical reviews. Recent publications are available in their entirety on the Web at <http://www.ntsb.gov>. Other information about available publications also may be obtained from the Web site or by contacting: National Transportation Safety Board Public Inquiries Section, RE-51 490 L(cid:146)Enfant Plaza, S.W. Washington, D.C. 20594 (800) 877-6799 or (202) 314-6551 Safety Board publications may be purchased, by individual copy or by subscription, from the National Technical Information Service. To purchase this publication, order report number PB2002-910401 from: National Technical Information Service 5285 Port Royal Road Springfield, Virginia 22161 (800) 553-6847 or (703) 605-6000 The Independent Safety Board Act, as codified at 49 U.S.C. Section 1154(b), precludes the admission into evidence or use of Board reports related to an incident or accident in a civil action for damages resulting from a matter mentioned in the report. iii Aircraft Accident Report Contents Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xii 1.Factual Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 History of Flight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Injuries to Persons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.3 Damage to Airplane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.4 Other Damage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.5 Personnel Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.5.1 The Captain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.5.2 The First Officer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.6 Airplane Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.6.1 MD-80 Longitudinal Trim Control System Information. . . . . . . . . . . . . . . . . . . . . 13 1.6.1.1 Primary Trim Control System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 1.6.1.2 Alternate Trim Control System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 1.6.1.3 Autopilot Pitch Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 1.6.2 Design and Certification of MD-80 Series Airplanes . . . . . . . . . . . . . . . . . . . . . . . 19 1.6.2.1 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 1.6.2.2 Longitudinal Trim Control System Certification. . . . . . . . . . . . . . . . . . . . . . . . . 19 1.6.3 Maintenance Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 1.6.3.1 Alaska Airlines(cid:146) MD-80 Maintenance Program . . . . . . . . . . . . . . . . . . . . . . . . . 24 1.6.3.1.1 Maintenance Program Development Guidance. . . . . . . . . . . . . . . . . . . . . . . 24 1.6.3.1.2 Alaska Airlines(cid:146) Continuous Airworthiness Maintenance Program. . . . . . . 26 1.6.3.1.3 Alaska Airlines(cid:146) Reliability Analysis Program. . . . . . . . . . . . . . . . . . . . . . . 26 1.6.3.2 Jackscrew Assembly Lubrication Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 1.6.3.2.1 Jackscrew Assembly Lubrication Intervals. . . . . . . . . . . . . . . . . . . . . . . . . . 31 1.6.3.2.1.1 Manufacturer-Recommended Lubrication Intervals. . . . . . . . . . . . . . 31 1.6.3.2.1.2 Alaska Airlines(cid:146) Lubrication Intervals. . . . . . . . . . . . . . . . . . . . . . . . 32 1.6.3.2.2 Chronology of Grease Type Changes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 1.6.3.2.3 July 19, 2002, Alaska Airlines Maintenance Information Letter . . . . . . . . . 36 1.6.3.3 Procedures for Monitoring Acme Nut Thread Wear. . . . . . . . . . . . . . . . . . . . . . 37 1.6.3.3.1 Defining and Calculating Wear Rate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 1.6.3.3.2 Development of End Play Check Procedures . . . . . . . . . . . . . . . . . . . . . . . . 38 1.6.3.3.2.1 Alaska Airlines(cid:146) End Play Check Procedure . . . . . . . . . . . . . . . . . . . 43 1.6.3.3.3 Horizontal Stabilizer Restraining Fixture . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 1.6.3.3.3.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 1.6.3.3.3.2 Alaska Airlines-Manufactured Restraining Fixtures . . . . . . . . . . . . . 44 1.6.3.3.4 End Play Check Intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 1.6.3.3.4.1 Manufacturer-Recommended End Play Check Intervals. . . . . . . . . . 47 1.6.3.3.4.2 Alaska Airlines(cid:146) End Play Check Intervals . . . . . . . . . . . . . . . . . . . . 47 1.6.3.4 Accident Airplane(cid:146)s Maintenance Information. . . . . . . . . . . . . . . . . . . . . . . . . . 49 1.6.3.4.1 Accident Airplane(cid:146)s Last C Check Requiring an End Play Check. . . . . . . . 50 Contents iv Aircraft Accident Report 1.6.3.4.2 Maintenance Personnel Statements Regarding the Accident Airplane(cid:146)s Last End Play Check. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 1.7 Meteorological Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 1.8 Aids to Navigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 1.9 Communications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 1.10 Airport Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 1.11 Flight Recorders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 1.11.1 Cockpit Voice Recorder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 1.11.1.1 CVR Sound Spectrum Study. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 1.11.2 Flight Data Recorder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 1.12 Wreckage and Impact Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 1.12.1 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 1.12.2 Horizontal Stabilizer Jackscrew Assembly Components. . . . . . . . . . . . . . . . . . . . . 58 1.13 Medical and Pathological Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 1.14 Fire. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 1.15 Survival Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 1.16 Tests and Research. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 1.16.1 Airplane Performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 1.16.1.1 Airplane Performance Simulation Studies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 1.16.2 Metallurgical Examinations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 1.16.2.1 Horizontal Stabilizer Forward Spar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 1.16.2.2 Acme Screw. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 1.16.2.3 Acme Screw Torque Tube. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 1.16.2.4 Lower Mechanical Stop and Corresponding Spline Area on the Acme Screw. . 71 1.16.2.5 Acme Nut. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 1.16.2.6 Acme Nut Thread Remnant Examination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 1.16.3 Shear Load Capability of the Acme Nut Threads . . . . . . . . . . . . . . . . . . . . . . . . . . 77 1.16.4 Studies of Thread Stress and Deformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 1.16.5 Torque Tube Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 1.16.6 Additional Safety Board Jackscrew Assembly Examinations. . . . . . . . . . . . . . . . . 80 1.16.6.1 February 2000 Post-AD 2000-03-51 Jackscrew Assembly Examinations . . . . . 80 1.16.6.2 Examinations of Hawaiian Airlines(cid:146) Jackscrew Assemblies. . . . . . . . . . . . . . . . 81 1.16.6.3 Examinations of Alaska Airlines Reports of Acme Screw (cid:147)Wobble(cid:148). . . . . . . . . 83 1.16.7 Chemical and Microscopic Analyses of Grease Residues from the Accident Jackscrew Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 1.16.8 Additional Grease Testing, Experiments, and Analysis . . . . . . . . . . . . . . . . . . . . . 85 1.16.8.1 Standardized Grease Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 1.16.8.2 Experiments and Analysis on the Surface Chemistry of Acme Nut Material When Exposed to Various Greases or Grease Mixtures . . . . . . . . 85 1.16.8.3 Wear Testing Under Various Grease Conditions. . . . . . . . . . . . . . . . . . . . . . . . . 86 1.17 Organizational and Management Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 1.17.1 Alaska Airlines, Inc.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 1.17.2 Alaska Airlines Flight Crew Training . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 1.17.2.1 Stabilizer Trim Check Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 1.17.2.2 Runaway Stabilizer Checklist Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 1.17.2.3 Stabilizer Inoperative Checklist Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 1.17.2.3.1 Postaccident Boeing Flight Operations Bulletin on Stabilizer Trim Inoperative/Malfunction Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 92 1.17.3 FAA Oversight of Alaska Airlines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 1.17.3.1 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 Contents v Aircraft Accident Report 1.17.3.2 Preaccident FAA National Aviation Safety Inspection Program Inspection. . . . 93 1.17.3.3 FAA Air Transportation Oversight System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 1.17.3.3.1 Seattle CMO Memorandum on Staff Shortages for Surveillance of Alaska Airlines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 1.17.3.4 FAA Postaccident Special Inspection of Alaska Airlines . . . . . . . . . . . . . . . . . . 95 1.17.3.4.1 FAA Proposed Suspension of Alaska Airlines(cid:146) Heavy Maintenance Authority. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 1.17.3.4.2 Alaska Airlines Airworthiness and Operations Action Plan. . . . . . . . . . . . . 99 1.17.3.4.3 FAA Followup Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 1.17.3.4.4 DOT Office of the Inspector General Report on FAA Oversight of Continuing Analysis and Surveillance Programs . . . . . . . . . . . . . . . . . . 102 1.17.4 Other Safety Evaluations of Alaska Airlines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 1.17.4.1 DoD Capability Survey of Alaska Airlines. . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 1.17.4.2 Criminal Investigation of Alaska Airlines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 1.17.4.3 Postaccident Independent Safety Assessment of Alaska Airlines. . . . . . . . . . . 104 1.18 Additional Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 1.18.1 Postaccident Airworthiness Directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 1.18.1.1 Safety Board and FAA Correspondence Regarding the 2,000-Flight-Hour End Play Check Interval Specified in ADs 2000-03-51 and 2000-15-15 . . . . . 106 1.18.2 Safety Board Statistical End Play Data Study. . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 1.18.3 Previous Safety Recommendations Resulting from the Alaska Airlines Flight 261 Investigation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 1.18.4 Alaska Airlines Fleetwide MD-80 Jackscrew Assembly Data and Tracking History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 1.18.5 MD-11 Jackscrew Assembly Acme Nut Wear History. . . . . . . . . . . . . . . . . . . . . 116 1.18.6 Safety Board Observations of Jackscrew Assembly Lubrications. . . . . . . . . . . . . 116 1.18.7 End Play Check Anomalies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 1.18.7.1 Safety Board End Play Check Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 1.18.7.2 Postaccident Alaska Airlines-Reported Near-Zero End Play Measurements . . 118 1.18.8 Jackscrew Assembly Overhaul Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 1.18.8.1 Jackscrew Overhaul Specifications and Authority . . . . . . . . . . . . . . . . . . . . . . 119 1.18.8.2 Review of the Boeing DC-9 Overhaul Maintenance Manual . . . . . . . . . . . . . . 120 1.18.8.3 Safety Board Maintenance Facility Observations . . . . . . . . . . . . . . . . . . . . . . . 121 1.18.8.4 Overhauled Jackscrew Assembly Data From 1996 to 1999 . . . . . . . . . . . . . . . 122 1.18.9 Industrywide Jackscrew Assembly Maintenance Procedures . . . . . . . . . . . . . . . . 122 1.18.10 FAA Commercial Airplane Certification Process Study. . . . . . . . . . . . . . . . . . . . 123 1.18.11 Fail-Safe Jackscrew Assembly Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 2.Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 2.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 2.2 Accident Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 2.2.1 Takeoff and Climbout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 2.2.2 Jamming of the Horizontal Stabilizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 2.2.2.1 Cause of the Jam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 2.2.3 Release of the Jam and the Initial Dive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 2.2.4 The Second and Final Dive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 2.2.5 Flight Crew Decision-Making. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 2.2.5.1 Decision to Continue Flying Rather than Return to PVR . . . . . . . . . . . . . . . . . 135 2.2.5.2 Use of the Autopilot. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 2.2.5.3 Configuration Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 Contents vi Aircraft Accident Report 2.2.5.4 Activation of the Primary Trim Motor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 2.2.5.5 Adequacy of Current Guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 2.3 Evaluation of Potential Reasons for Excessive Acme Nut Thread Wear. . . . . . . . . . . 140 2.3.1 Use of Aeroshell 33 for Lubrication of the Jackscrew Assembly . . . . . . . . . . . . . 141 2.3.2 Acme Screw Thread Surface Finish. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 2.3.3 Foreign Debris . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 2.3.4 Abnormal Loading of the Acme Nut Threads. . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 2.3.5 Summary of Possibilities Ruled Out as Reasons for the Excessive Acme Nut Thread Wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 2.3.6 Insufficient Lubrication of the Jackscrew Assembly. . . . . . . . . . . . . . . . . . . . . . . 144 2.3.6.1 Analysis of How Many Recently Scheduled Lubrications Might Have Been Missed or Inadequately Performed Before the Accident . . . . . . . . . . . . . 146 2.3.6.2 Alaska Airlines(cid:146) Lubrication Interval Extension. . . . . . . . . . . . . . . . . . . . . . . . 146 2.3.6.2.1 Safety Implications of Lubrication Interval Extension. . . . . . . . . . . . . . . . 147 2.3.6.3 Adequacy of Lubrication Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 2.4 Monitoring Acme Nut Thread Wear. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 2.4.1 Alaska Airlines(cid:146) Preaccident End Play Check Intervals . . . . . . . . . . . . . . . . . . . . 151 2.4.1.1 Adequacy of Existing Process for Establishing Maintenance Task Intervals . . 153 2.4.2 Adequacy of Current End Play Check Intervals . . . . . . . . . . . . . . . . . . . . . . . . . . 154 2.4.3 Adequacy of End Play Check Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 2.5 Deficiencies of Jackscrew Assembly Overhaul Procedures and Practices. . . . . . . . . . 159 2.6 Horizontal Stabilizer Trim System Design and Certification Issues . . . . . . . . . . . . . . 162 2.6.1 Acme Nut Thread Loss as a Catastrophic Single-Point Failure Mode . . . . . . . . . 162 2.6.2 Prevention of Acme Nut Thread Loss Through Maintenance and Inspection. . . . 165 2.6.3 Elimination of Catastrophic Effects of Acme Nut Thread Loss Through Design. 166 2.6.4 Consideration of Wear-Related Failures During Design and Certification. . . . . . 167 2.7 Deficiencies in Alaska Airlines(cid:146) Maintenance Program. . . . . . . . . . . . . . . . . . . . . . . . 167 2.7.1 April 2000 FAA Special Inspection Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 2.7.2 Maintenance-Related Deficiencies Identified During This Accident Investigation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 2.7.2.1 General Policy Decisions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 2.7.2.2 Specific Maintenance Actions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 2.7.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 2.8 FAA Oversight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 3.Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 3.1 Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 3.2 Probable Cause. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 4.Recommendations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 4.1 New Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 4.2 Previously Issued Recommendations Resulting From This Accident Investigation . . 184 Board Member Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 5.Appendixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 vii AircraftAccidentReport Figures 1. The accident airplane(cid:146)s flightpath, starting about 1609 (about the time of the initial dive) and ending about 1620 (about the time of the second and final dive).. . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Radar altitude data and selected ATC transmissions from about 1609 to 1620.. . . . . . . . . . . . . . . . . . 6 3. Installation of jackscrew assembly within the horizontal and vertical stabilizers.. . . . . . . . . . . . . . . 13 4. The MD-80 horizontal and vertical stabilizer tail structure.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5. Acme screw and nut.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 6. Detailed schematic of the longitudinal trim actuating mechanism. . . . . . . . . . . . . . . . . . . . . . . . . . . 16 7. Cockpit switches, handles, and indicators for the longitudinal control system.. . . . . . . . . . . . . . . . . 17 8. Depiction of how restraining fixture should be placed on the horizontal stabilizer during an end play check. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 9. View of a typical dial indicator set up for end play checks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 10. Two Alaska Airlines-fabricated restraining fixtures and three Boeing- manufactured fixtures. . . . . 46 11. The September 27, 1997, MIG-4.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 12a. The acme screw immediately after it was brought on board the recovery ship . . . . . . . . . . . . . . . . . 59 12b. The acme screw immediately after it was brought to shore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 12c. The acme screw during initial inspection.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 13. A photograph of the acme screw thread remnants wrapped around the screw, the red rust areas, and the white deposits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 14. A photograph of the sand/grease mixture packed between the acme screw(cid:146)s lower threads. . . . . . . 69 15. A photograph of an overall view of the recovered acme nut assembly. . . . . . . . . . . . . . . . . . . . . . . . 73 16. A photograph of a closer view of the interior of the acme nut. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 17. A diagram of a cross-section through the acme nut(cid:146)s grease passageway and fitting. Red areas denote the locations where red grease was found, and gray areas denote the location where the dry residue was found. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 18. A photograph of the grease passageway and counterbore after the acme nut was sectioned.. . . . . . 75 Figures viii AircraftAccidentReport 19. A summary of the results of the high-load wear tests, including the contamination and low-temperature tests.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 20. A graphical depiction of the stages of acme nut thread wear to the point of fracture. . . . . . . . . . . 131