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Dynamic Hoisting – why not using a tag line can increase safety

Dale Wang for ITRS 2024

Rocky Mountain Rescue Group Colorado Hoist Rescue Team

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Dynamic flight profile

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Colorado Hoist Rescue Team

  • Colorado Army National Guard and 4 Mountain Rescue Association (MRA) SAR teams
  • 2 bases in Colorado
  • 32 civilian (MRA team) rescuers
  • UH-60 and UH-72 aircraft and crews

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INTRODUCTION

  • Since the introduction of hoist in the US Army during the Vietnam War, tag lines have been the standard for hoist in many US operations.

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  • The standard in the Alps (PGHM, Air Zermatt, many others) has been dynamic hoisting for years.

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Overview of presentation

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The problem – risks associated with hoist

  • Tag line vs. Dynamic Operations

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  • Dynamic hoist – why it works

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  • Dynamic hoist - implementation

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RISKS ASSOCIATED WITH HOIST OPERATIONS

  • Human error
    • secure attachment
    • operation of flight or hoist controls
  • Mechanical failure of hoist components or rescue equipment
    • Hoist motor runaway or failure
    • Cable failure
    • Rescue equipment failure

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RISKS ASSOCIATED WITH HOIST OPERATIONS (cont.)

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Time spent in hover - high risk flight profile

  • Low power margins
  • fewer options for recovery from loss of power or control

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  • Hoist procedure or technique failure

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Load oscillation / pendulum

damage to the hoist cable as a result of cross-loading after contacting the aircraft structure

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Litter spin / tag-line failure

  • ejection of the Subject as a result of rotational centrifugal acceleration
  • vomiting/airway compromise

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Cable oscillation caused damage from contact with exposed bolts

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Overview

  • The problem – risks associated with hoist

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Tag line vs Dynamic operations

  • Dynamic hoist – why it works

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  • Program implementation

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Tag line hoist

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Tag Line/Static - pros

  • Tag-line / Static Extraction Litter Procedure
    • Usually a lighter load (single person) on the hoist
      • most programs fly dynamic with a litter attendant
    • lower hover altitudes can result in better references for pilot (especially at night)
    • sometimes better option in certain confined terrain

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Tag Line/Static - Cons

  • Tag-line / Static Extraction Litter Procedure

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Longest time in hover - high risk flight profile

Spin possible if tag line weak link breaks

Entanglement risk of tag line

  • Requires trained ground asset to operate tag-line
  • Terrain may preclude the required geometry
  • lower altitude hoists results in stronger downwash for ground resources

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Tag line failure -> spin

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Dynamic hoist – pro

  • Eliminates tag line
  • Shortest time in high risk flight profile
  • Gaining forward airspeed reduces the risks of other emergency procedures:
    • Litter/load spin
    • Oscillation and Pendulum
    • Aircraft engine or control system failure

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Dynamic hoist – con

  • Must recognize inappropriate terrain
    • needs clear fly-away path
  • Crew training requirements:
    • Pilot – flight profile
    • Hoist operator – cable management
    • Rescuer – packaging, and use of anti-rotation brake

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Overview

  • The problem – risks associated with hoist

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  • Tag line vs. Dynamic operations

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Dynamic hoist – why it works

  • Program implementation

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Dynamic hoist- why it works

  • Theory
  • Data
  • Procedures
    • Pilot: flight profile
    • Hoist operator: cable management
    • Rescuer: packaging, anti-rotation steering, equipment

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AERODYNAMICS

Zero Wind and/or Static Hoist

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AERODYNAMICS

Light Wind / Fly-Away Below ETL

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AERODYNAMICS

Above ETL Fly-Away

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Test Data - CHRT

  • Term Definitions
    • N – No spin or rotation
    • R – Load may rotate at a period greater than 2 seconds
    • S – If left in this region, a litter spin or oscillate may develop if not corrected
    • Airspeed / Ground Speed – Combination of aircraft speed and/or wind speed
    • Litter Distance From The Aircraft – Hoist cable length

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UH-72 TEST DATA (Passive, no brake)

N - No rotation

R - 360º rotation greater than 2 seconds

S - 360º rotation greater than 2 seconds

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UH-60 TEST DATA (Passive, no brake)

N - No rotation

R - 360º rotation greater than 2 seconds

S - 360º rotation greater than 2 seconds

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WHAT DID WE LEARN?

  • Maximum rotor velocity (Spin) occurs at 1.5 – 2.0 x the rotor diameter below the aircraft (below ETL)
    • UH-60: 81 to 108 ft - (rotor diameter 54 ft)
    • UH-72: 54 to 72 ft – (rotor diameter 36 ft)
    • Bell 205: 72 to 96 ft (rotor diameter 48 ft)
    • H-125/AS350 (similar to UH-72, rotor diameter 35 ft)
  • downwash velocity is related to aircraft weight, rotor area and air density

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Pilot: DYNAMIC PROFILE

  • Wind or forward airspeed place the downwash behind the load
    • Aircraft acceleration should be a flat profile without dipping the nose to prevent induction of a front to back pendulum
    • Slow, but constant, acceleration is preferable to accelerating to specific airspeed, which will also result in a slow front to back pendulum motion
    • Pendulum or oscillation can occur when the litter is allowed to pass in and out of the downwash during the fly-away at airspeeds below ETL

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Dynamic Hoist – HO’s

  • Hoist Operators
    • Rate of cable-up must be timed with aircraft fly-away to maintain litter separation from the downwash
      • HO’s must fight the common tendency of rapidly cabling the litter load up prior to the aircraft passing through ETL
    • We use the following terminology during the recover phase:
      • “Clear of Obstacles” – does not authorize aircraft movement
      • “Cleared for Forward Flight” – P* is cleared to initiate a smooth and level acceleration to a target airspeed of 30 kts/ ETL

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HO: wait to cable up until ETL

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Dynamic Hoist - Equipment

  • We (CHRT) selected the Stable Flight Heli-bag (SFHB) to allow hoist without tag-lines, and thereby REDUCE our time on station in marginal power conditions

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MORE QUESTIONS

  • So what is the “Air Brake” controlled by the rescuer doing for us?
    • The testing data shown previously has been for a passive

load without the rescuer applying the rotational brake

    • This led us to repeat our testing with a rescuer actively

controlling the load

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UH-72 TEST DATA (PASSIVE)

N - No rotation

R - 360º rotation greater than 2 seconds

S - 360º rotation greater than 2 seconds

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UH-72 TEST DATA (ACTIVE)

ETL

Oscillation Avoidance Area

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Stable flight packaged for deployment

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Anti-rotation devices Ferno “ear”

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Anti-rotation devices TSL ”sail”

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Anti-rotation devices PAX bag

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Anti-rotation devices Kong Italy

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DYNAMIC HOIST – Rescuer technique

  • Rescue Technicians (RTs):
    • Packaging – both rescuer and load
      • centered –side/side most important, in-line with cable
      • compact; no loose fabric; pack location
    • Anti-rotation brake use
      • Avoid overcorrecting during brake application
      • continue to “fly” the bag all the way to the aircraft

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MORE QUESTIONS

  • What about obstacles?

– When operating below tree line, or in the alpine with terrain features in the way, how should a crew utilize dynamic hoist profiles?

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UH-60 DYNAMIC FLIGHT PROFILE WITH OBSTACLES

ETL

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DYNAMIC LITTER HOIST WITH OBSTACLES

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CONCLUSION

  • Dynamic operations minimize time in the most dangerous flight profile
  • Dynamic operations reduce multiple risks associated with tag lines
  • Doesn’t have to be “all or nothing” – e.g. hoist in tall canopy

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Overview

  • The problem – risks associated with hoist

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  • Tag line vs. Dynamic operations

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  • Dynamic hoist – why it works

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Program implementation

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Implementation - Pilots

  • Hover altitude:
    • at least 1.5-2x rotor diameter
  • The fly-away target airspeed is above ETL
    • accelerating without dipping the aircraft nose to avoid inducing a mechanical front to back pendulum
    • Announce passing through ETL during the departure to assist the HO in timing

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UH-60 DYNAMIC FLIGHT PROFILE W/O OBSTACLES

ETL

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Implementation – HO’s

  • Hoist Operators
    • cable-up must be timed with aircraft fly-away
      • HO’s wait to cable the load up until after the aircraft is through ETL
      • “Clear of Obstacles” from rescuer – does not authorize aircraft movement
      • “Cleared for Forward Flight” – P* is cleared to initiate acceleration to a target airspeed of 30 kts/ETL

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Implementation - Rescuers

  • Rescue Technicians:
    • Packaging matters - centered
    • Real time radio comms helps (“clear of obstacles”)
    • Practice using the anti-rotation brake – don’t overcorrect
    • continue to “fly” the bag all the way to the aircraft

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RECOGNITION

Oliver Kreuzer – Air Zermatt, Switzerland

Renaud Guillermet – Securite Civile, France

Clayton Horney and Col. William Gentle (ret) – Co. Army National Guard

Colorado Search and Rescue Association

Pilots, Hoist Operators, all support personnel, and MRA rescuers of CHRT

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QUESTIONS ?

dale.wang@rockymountainrescue.org