PB99-910401 ‘I NTSB/AAR-99/01 DCA94MA076 NATIONAL TRANSPORTATION SAFETY BOARD WASHINGTON, D.C. 20594 AIRCRAFT ACCIDENT REPORT UNCONTROLLED DESCENT AND COLLISION WITH TERRAIN USAIR FLIGHT 427 BOEING 737-300, N513AU NEAR ALIQUIPPA, PENNSYLVANIA SEPTEMBER 8, 1994 6472A Abstract: This report explains the accident involving USAir flight 427, a Boeing 737-300, which entered an uncontrolled descent and impacted terrain near Aliquippa, Pennsylvania, on September 8, 1994. Safety issues in the report focused on Boeing 737 rudder malfunctions, including rudder reversals; the adequacy of the 737 rudder system design; unusual attitude training for air carrier pilots; and flight data recorder parameters. Safety recommendations concerning these issues were addressed to the Federal Aviation Administration. The National Transportation Safety Board is an independent Federal Agency dedicated to promoting aviation, raiload, 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, 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 at http://www.ntsb.gov/. Other information about available publications may also be obtained from the Web site or by contacting: National Transportation Safety Board Public Inquiries Section, RE-51 490 L’Enfant Plaza, East, S.W. Washington, D.C. 20594 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 PB99-910401 from: National Technical Information Service 5285 Port Royal Road Springfield, Virginia 22161 (800) 553-6847 or (703) 605-6000 THESE CORRECTIONS ARE INCLUDED IN THIS VERSION OF THE PUBLISHED REPORT: AIRCRAFT ACCIDENT REPORT NTSB/AAR-99/01 (PB99-910401) UNCONTROLLED DESCENT AND COLLISION WITH TERRAIN USAIR FLIGHT 427, BOEING 737-300, N513AU NEAR ALIQUIPPA, PENNSYLVANIA SEPTEMBER 8, 1994 • Pages 29-31 have been updated to correct figure placement. (4 Nov 99) Figures 9 and 10 were originally reversed. • Page 45 has been updated to correct a quotation mark. (4 Nov 99) "wow about 0943:08" was incorrectly quoted. • Page 102 has been updated to correct figure references for the United flight 585 simulations on roll and yaw rate. (16 Feb 00) Aircraft Accident Report Uncontrolled Descent and Collision With Terrain USAir Flight 427 Boeing 737-300, N513AU Near Aliquippa, Pennsylvania September 8, 1994 R A N S P T O L R A T UR I B P L US U A N NUM E O T I I O T A N N S A D F E R NTSB/AAR-99/01 T Y B O A PB99-910401 National Transportation Safety Board Notation 6472A 490 L’Enfant Plaza, S.W. Adopted March 24, 1999 Washington, D.C. 20594 Contents iii Aircraft Accident Report Contents Executive Summary................................................................................................ ix Abbreviations .......................................................................................................... xi Glossary of Terms...................................................................................................xv 1. Factual Information..................................................................................................1 1.1 History of Flight ..................................................................................................1 1.2 Injuries to Persons ...............................................................................................7 1.3 Damage to Aircraft..............................................................................................7 1.4 Other Damage......................................................................................................7 1.5 Personnel Information .........................................................................................7 1.5.1 The Captain.....................................................................................................8 1.5.2 The First Officer ...........................................................................................10 1.5.3 Flight Attendant Information........................................................................11 1.6 Airplane Information.........................................................................................11 1.6.1 Accident Airplane Maintenance Information ...............................................12 1.6.1.1 Inspections.............................................................................................12 1.6.1.2 Events on Earlier Flights .......................................................................14 1.6.2 Boeing 737 Hydraulic System Information..................................................15 1.6.2.1 Hydraulic System Maintenance.............................................................18 1.6.3 Boeing 737 Flight Control Systems..............................................................19 1.6.3.1 Auto-Flight System ...............................................................................19 1.6.3.2 Rudder Control System .........................................................................23 1.6.3.2.1 Main Rudder PCU and Servo Valve ..............................................29 1.7 Meteorological Information...............................................................................33 1.8 Aids to Navigation.............................................................................................34 1.9 Communications................................................................................................34 1.10 Airport Information ...........................................................................................35 1.11 Flight Recorders ................................................................................................35 1.11.1 Cockpit Voice Recorder ...............................................................................35 1.11.2 Flight Data Recorder.....................................................................................35 1.12 Wreckage and Impact Information....................................................................36 1.12.1 On-Site Examination ....................................................................................36 1.12.2 Reconstruction Examination.........................................................................39 1.12.2.1 Flight Control System Components ......................................................40 1.12.2.2 Examination/Reconstruction of Cargo Compartments..........................41 Contents iv Aircraft Accident Report 1.12.2.3 Examination/Reconstruction of the Auxiliary Fuel Tank .....................41 1.12.3 Examination of Wreckage for Indications of Possible Bird Strike...............42 1.13 Medical and Pathological Information ..............................................................43 1.14 Fire.....................................................................................................................43 1.15 Survival Aspects................................................................................................44 1.16 Tests and Research ............................................................................................44 1.16.1 Background Information—Other Significant Yaw/Roll Events...................44 1.16.1.1 United Airlines Flight 585 Accident .....................................................44 1.16.1.2 Eastwind Airlines Flight 517 Incident...................................................51 1.16.2 Wake Vortex Tests and Studies Resulting From the USAir Flight 427 Accident...........................................................................54 1.16.3 Flight and Simulator Tests of Effects of Various Flight Control and System Failures......................................................................................59 1.16.3.1 Eastwind Flight 517 Flight Tests...........................................................61 1.16.4 Flight Control Characteristics Flight Tests (Blowdown and Crossover Airspeed) .....................................................................................63 1.16.5 Examination and Testing of Flight Control Systems/Components ..............65 1.16.5.1 Rudder Pedal Assemblies......................................................................65 1.16.5.2 Tests to Determine the Effects of Rudder Cable External Forces, Breaks, and Blocked Input Linkage ......................................................66 1.16.5.3 Examination and Testing of Standby Rudder........................................68 1.16.5.3.1 Metallurgical Examination of Standby Rudder Components ........68 1.16.5.3.2 Standby System Actuator Binding/Jam Tests ................................69 1.16.5.4 Detailed Examinations and Tests of Main Rudder PCUs .....................71 1.16.5.4.1 Detailed Examinations of Main Rudder PCU Servo Valves..........71 1.16.5.4.1.1 Examination of Exemplar Servo Valves for White Layer.........73 1.16.5.4.2 PCU Dynamic Testing ...................................................................73 1.16.5.4.3 Tests of Hydraulic Fluid.................................................................74 1.16.5.4.4 Tests to Determine the Effects of