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
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Introduction
Background
Analysis
Results
Stability Augmentation
Directional Control
Teetering Rotors
Instrument Flight
• Conclusions
• Recommendations
September 2005
KEY’S STUDY - 1999
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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
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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