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

QuickTime™ and aSorenson Video 3 decompressorare 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

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

QuickTime™ and aSorenson Video decompressorare needed to see this picture.

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