GOVERNMENT NRTC The Implications of Handling Qualities in Civil Helicopter Accidents Involving Hover and Low Speed Flight Daniel C. Dugan, NASA CDR Kevin J. Delamer, USN September 2005 WHEN HELOS GO BAD QuickTime™ and a Sorenson Video 3 decompressor are needed to see this picture. September 2005 • • • • Introduction Background Analysis Results Stability Augmentation Directional Control Teetering Rotors Instrument Flight • Conclusions • Recommendations September 2005 KEY’S STUDY - 1999 • • • • 4 Army Helicopters Hover in DVE (Night, Dust, …) Equipped with Rate Command SAS “Marginal” HQ September 2005 U.S. Army Helicopter Mishap Causes Hovering Flight HQ SA Non-HQ SA Data from 276 Mishaps in Hovering Flight, 1986-1996 UH-60 / CH-47D HQ SA Non-HQ SA Data from David L. Key, “Analysis of AH-64A / OH-58D Army Helicopter Pilot Error Mishap Data and the Implications for Handling Qualities,” 25th European Rotorcraft Forum, Rome, Italy: September 14-16, 1999. September 2005 ADDITIONAL STUDIES SURVEYED • “U.S. Civil Rotorcraft Accidents - 1963-1997” Harris, Kasper, Iseler • “Analysis of US Civil Rotorcraft Accidents, 1990 - 1996 - Iseler and DeMaio …….” • “Final Report of the Helicopter Accident Analysis Team,” DOD, FAA, and NASA • “Near Term Gains in Rotorcraft Safety Strategies for Investment” - Workshop September 2005 HARRIS, KASPER, ISELER 1963-1997 1114 Total Mishaps • Piston and Turbine Rotorcraft • All Flight Regimes 13.2 % Due to Loss of Control 13.2% 247 Fatalities Loss of Control Other Mishaps 228 Serious Injuries 319 Helicopters Destroyed September 2005 THIS STUDY • 547 Accidents, Hover or Low Speed, 1993-2004 (Gyrocopters not Included) • 126 or 23% attributed to Loss of Control which could be attributed to poor HQ • 127 Fatalities, 97 Serious injuries, and 134 Helicopters destroyed September 2005 HOVER AND LOW AIRSPEED MISHAPS 1993-2004 547 Mishaps Reviewed 126 Due to Loss of Control (HQ) 23 % 15 Manufacturers* Over 30 Models Loss of Control Other Causes * - All kit / homebuilt included as one manufacturer Handling Qualities issues accounted for a greater percentage of Hover mishaps than mishaps overall (23% versus 13%) September 2005 STABILITY AUGMENTATION • • • • HELICOPTER IN HOVER VS. AIRPLANE FAR 27 SFENA MINI-STAB HELISAS September 2005 EXTERNAL LOAD OPERATIONS 6% MISHAPS Personal / Instructional External Load Other External Loads FLIGHT HOURS Other 15% • 85 Mishaps • 38 Fatalities • 26 Serious Injuries • 26 Helos Destroyed 30% Other External Load FATALITIES September 2005 Mission Analysis 48.2% Personal / Instructional External Load Personal Use and Instructional Flights Accounted for Almost Half of the Mishaps While Accounting for Only 15% of Flight Hours* Other * - Utilization Rates from FAA Aerospace Forecasts September 2005 DIRECTIONAL CONTROL • LOSS OF TAIL ROTOR EFFECTIVENESS • AC 90-95 “UNANTICIPATED RIGHT YAW IN HELICOPTERS” • MORE CRITICAL IN HOVER AND LOW SPEED FLIGHT • FACTORS: WIND DIRECTION DIRECTIONAL CONTROL POWER AND CONTROL MARGINS POWER APPLIED (COLLECTIVE PITCH) PILOT SKILLS AND EXPERIENCE September 2005 LTE PERCENTAGES Initial Data Survey - 297 Hover/Low Airspeed Mishaps - 45 LTE Related (15%) Expanded Data Set - 547 Hover/Low Airspeed Mishaps - 82 LTE Related (15%) September 2005 QuickTime™ and a Sorenson Video decompressor are needed to see this picture. September 2005 MISHAPS BY TYPE ROTOR SYSTEM Number of Mishaps 350 300 200 Semi-Rigid (Teetering) Articulated 150 Rigid 250 56 % 100 50 0 Type Rotor System September 2005 TEETERING ROTORS (Author’s Opinion/Experience) PROS Rugged Construction Blade Retention Failures Rare Start/Stop in High & Gusty Winds Not Susceptible to Ground Resonance Cost/Low Complexity CONS Susceptible to Mast Bumping Usually Fatal in Flight Control Lags - can Induce PIO Vibration (Two Blade Systems) September 2005 MAST BUMPING - CAUSES & AVOIDANCE • ABRUPT, EXCESSIVE AND UNCOORDINATED CYCLIC CONTROL INPUTS • SIDESLIP • AFT CENTER OF GRAVITY • LESS THAN 1G FLIGHT • RESULT: LARGE ROTOR FLAPPING ANGLES HUB TO MAST CONTACT POSSIBLE September 2005 HELISAS HeliSAS – R44 Installation • 12 Pounds • Approximately $30,000 • Two Servo-actuators, Cockpit switches and Gyro Package * - Pictures and system description, <http://www.helisas.com> [12 Sep 2005] September 2005 CONCLUSIONS • IT REMAINS PUZZLING WHY HANDLING QUALITIES HAVE NOT BEEN PINPOINTED AS ACCIDENT CAUSES OR FACTORS • A SIGNIFICANT NUMBER OF THE ACCIDENTS STUDIED COULD HAVE BEEN PREVENTED BY IMPROVED HANDLING QUALITIES • THE INFERENCE IS THAT A SIGNIFICANT REDUCTION IN ACCIDENTS, INJURIES, AND PROPERTY DAMAGE COULD BE ACHIEVED BY THE INTEGRATION OF STABILITY AUGMENTATION SYSTEMS INTO THE CONTROL SYSTEMS OF THE LOWER PRICED HELICOPTERS September 2005 RECOMMENDATIONS • THE FEASIBILITY OF INCORPORATING LOW COST, LIGHT WEIGHT STABILITYAUGMENTATION SYSTEMS SHOULD BE EXPLORED BY HELICOPTER MANUFACTURERS • REPRESENTATIVE CLASSES OF LIGHT PISTON AND TURBINE POWERED HELICOPTERS SHOULD BE EVALUATED BY THE GOVERNMENT TO ASSESS AND DOCUMENT HQ DEFICIENCIES September 2005