September 2005
The Implications of Handling Qualities in Civil Helicopter Accidents Involving Hover
and Low Speed Flight
Daniel C. Dugan, NASA
CDR Kevin J. Delamer, USN
GOVERNMENT
IND
US
TRY
AC
AD
EM
IANRTC
September 2005
WHEN HELOS GO BADWHEN HELOS GO BAD
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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
HQ SA
Non-HQ SA
HQ SA
Non-HQ SA
AH-64A / OH-58D
UH-60 / CH-47D
U.S. Army Helicopter Mishap CausesHovering Flight
Data from David L. Key, “Analysis of Army Helicopter Pilot Error Mishap Data and the Implications for HandlingQualities,” 25th European Rotorcraft Forum, Rome, Italy: September 14-16, 1999.
Data from 276 Mishaps inHovering Flight, 1986-1996
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
Loss of Control
Other Mishaps247 Fatalities247 Fatalities
228 Serious Injuries228 Serious Injuries
319 Helicopters Destroyed319 Helicopters Destroyed
1114 Total Mishaps 1114 Total Mishaps •• Piston and Turbine Rotorcraft Piston and Turbine Rotorcraft
• • All Flight RegimesAll Flight Regimes
13.2 % Due to Loss of Control13.2 % Due to Loss of Control
13.2%
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
Loss of Control
Other Causes
Handling Qualities issues accounted for a greater percentage Handling Qualities issues accounted for a greater percentage of Hover mishaps than mishaps overall (23% versus 13%)of Hover mishaps than mishaps overall (23% versus 13%)
547 Mishaps Reviewed547 Mishaps Reviewed
126 Due to Loss of Control (HQ) 126 Due to Loss of Control (HQ)
15 Manufacturers*15 Manufacturers*
Over 30 ModelsOver 30 Models
23 %
* - All kit / homebuilt included as one manufacturer
September 2005
STABILITY AUGMENTATION
• HELICOPTER IN HOVER VS. AIRPLANE• FAR 27• SFENA MINI-STAB• HELISAS
September 2005
EXTERNAL LOAD OPERATIONS
Personal /Instructional
External Load
Other
Other
External Loads
15%
MISHAPS
Other
External Load
6%
FLIGHT HOURS
FATALITIES
30%• 85 Mishaps85 Mishaps• 38 Fatalities38 Fatalities• 26 Serious Injuries26 Serious Injuries• 26 Helos Destroyed26 Helos Destroyed
September 2005
Mission Analysis
Personal /Instructional
External Load
Other
Personal Use and Personal Use and Instructional Flights Instructional Flights Accounted for Almost Accounted for Almost Half of the Mishaps While Half of the Mishaps While Accounting for Only 15% Accounting for Only 15% of Flight Hours*of Flight Hours*
* - Utilization Rates from FAA Aerospace Forecasts
48.2%
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 Initial Data Survey - 297 Hover/Low Airspeed Mishaps- 297 Hover/Low Airspeed Mishaps
- 45 LTE Related (- 45 LTE Related (15%)15%)
Expanded Data SetExpanded Data Set - 547 Hover/Low Airspeed Mishaps- 547 Hover/Low Airspeed Mishaps
- 82 LTE Related (- 82 LTE Related (15%)15%)
September 2005
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September 2005
MISHAPS BY TYPE ROTOR SYSTEM
0
50
100
150
200
250
300
350
Type Rotor System
Semi-Rigid(Teetering)
Articulated
Rigid
Nu
mb
er o
f M
ish
aps
56 %
September 2005
TEETERING ROTORS(Author’s Opinion/Experience)
PROS
Rugged ConstructionBlade Retention Failures RareStart/Stop in High & Gusty
WindsNot Susceptible to Ground
ResonanceCost/Low Complexity
CONS
Susceptible to Mast Bumping - Usually Fatal in Flight
Control Lags - can Induce PIOVibration (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 InstallationHeliSAS – R44 Installation
• • 12 Pounds12 Pounds
• • Approximately $30,000 Approximately $30,000
• • Two Servo-actuators, Cockpit switchesTwo Servo-actuators, Cockpit switches
and Gyro Packageand 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