While traditionally, the helicopter is in a static hover during hoisting operations, during dynamic hoisting, the distinctive feature is that the helicopter is in motion and this means a reduction in the exposure of people on the ground to the effects of down wash, as well as spinning.

When conducting dynamic hoist operations, there are two simultaneous, yet distinct flight profiles of the aircraft and the load. “Both use the rudimentary concepts of ‘descent’ and ‘closure’ rate,” says Bob Cockell, Vice-President of Air Rescue Systems. “These two movements combined comprise the components of ‘lineal deceleration’. By employing this composite movement, the aircraft descends to a predetermined point in space while progressively slowing to a hover. The load, via the hoist/cable also descends to a fixed point on the ground, vessel, tower, cliff, ocean etc. When accomplished properly, arrival of the load to target should be timed with the aircraft coming to its holding (hover) position above the target.” 

Developing critical mass

Even though the search and rescue (SAR) world is getting smaller and SAR operators are increasingly exposed to non-traditional practices – be it only because of social media – the use of dynamic hoisting is not yet significantly widespread across the world, according to experts. “It is more common in Europe at this point than in the US. All helicopter providers in Switzerland are practising dynamic hoisting,” noted Oliver Kreuzer, a SAR Paramedic at Air Zermatt.

“The first time we saw this technique being deployed was in Europe for a para-public operator performing a glacier rescue in 2000, and the particular method was called ‘drop and drag’,” said Brad Matheson, President and Director of Training for Priority1 Air Rescue. “We modified the technique for our use to correlate with our risk management and safety standards and we have been teaching a modified short-final version of ‘dynamic hoisting’ to our customers since 2003.” According to Matheson, although dynamic hoisting is performed by certain civil and para-public operators, the most common military standard for hoisting is the traditional hover hoist insertion/extractions, and he still doesn’t see many military agencies performing dynamic hoisting unless involved in combat SAR (CSAR) or personnel recovery missions. “As a cross-section of the industry, now that many commercial and para-public operators are conducting hoist SAR missions that were previously operated by military programmes, less traditional methods of hoisting, hoist training, and civil aviation approved human external cargo and SAR standards have become more prevalent,” he told AirMed&Rescue.

Operational advantages

There are some significant advantages that can be obtained from deploying dynamic hoisting procedures. Apart from reduced rotor wash on the scene or hoist extraction point, a primary benefit is reduced hover time. “It reduces the time the aircraft is below single engine fly away speed. As a result, it also reduces the time the rescue personnel are outside the aircraft below single engine fly away speed,” pointed out Casey Ping of Travis County STAR Flight Dynamic. “Dynamic hoisting also reduces aircraft power requirements. This is especially important for us, because of the high temperatures and high gross weights characterising our operations. The use of dynamic hoisting has virtually eliminated exceedances of the five-minute power limit of the EC145.”

The fact that the aircraft is moving at altitude offers better options for aircrews in the event of aircraft emergencies, and provides a better chance of flyaway if they already are in forward motion rather than in a hover and/or the corresponding ‘dead man’ curve. 

“Another example [of the advantage of dynamic hoisting] is related to open ocean SAR procedures for a person in water, [where] traditional hoisting from a static location over the target will generate greater winds below the aircraft, which will correspondingly form surface winds that can blow the survivor in the water away from the helicopter in the hoisting position, causing the aircrews to end up ‘chasing’ the survivor. This is also a very relevant factor for smaller pleasure vessels and sailboats,” pointed out Matheson.

According to Cockell, in many parts of the world, the benefits of dynamic hoisting are under-utilised for several reasons, including misunderstanding of the technique, and the mistaken belief that there is necessarily greater risk involved. He said: “When correctly performed, dynamic hoist operations reduce risk through decreased exposure, and the team gains increased situational awareness by performing checklist functions, pre-door opening safeties and hoist hook-ups prior to arrival at the target. Through completion of these requisite procedures early on, the team has time to gain composure, reassess the go-no-go statement and chose alternate tactics prior to taking on the exposure associated with the extended hover.”

Challenges

While it provides for significant operational advantages, dynamic hoisting also brings some challenges. “The hill country around Austin and San Antonio frequently floods, resulting in significant impact to people in vehicles and homes. Many of these incidents result in the victims on trees, vehicles or other obstacles. After searching for victims and locating them, the last thing we want to do is lose sight of them, especially at night,” said Ping. “As a result, we will use a modified dynamic hoist technique that may result in a short approach flight before becoming stationary.” 

As with any other technique in SAR, dynamic hoisting also requires the correct application and training. “We strongly advocate training in recognising and reacting to hazards related to entanglement and the actions to take in the event the cable or load becomes entangled during a hoist operation, especially for dynamic hoisting,” said Matheson. “Operators would never be able to simulate this type of emergency procedure and situational awareness type training during live flight flying evolutions, due to the high amount of risks involved and the impossibility of creating organic or staged events for cable entanglement, or power failures, and then cutting the cable during flight for training purposes.”

When correctly performed, dynamic hoist operations reduce risk through decreased exposure

A common practice for aircrews employing dynamic hoisting is to transition to forward flight as soon as possible when the hoist load is clear of terrain and obstacles, and consequently, there is a possibility for the aircraft to inadvertently depart the scene with the tag-line still attached. “Although it seems obvious to release the tag-line, hoist system operators that are used to traditional hoisting are now being conditioned to transition forward as soon as possible, and therefore aircrews should address the possibility of ‘what actions would the rescue specialist take as an emergency procedure if the aircraft jumps the gun and takes off with the tag-line still attached to the rescue device?’ If that tag-line is pulled off the deck and gets airborne it is highly likely it could get entangled in the tail rotor as the aircraft is flying away,” pointed out Matheson.

Rescue scenarios

Examples of scenarios where dynamic hoisting is particularly suitable include clear area hoist extraction points that are free of obstructions such as maritime operations, and high-altitude hoist operations where there is possible risk of power issues due to variable winds and the operators want to reduce the risks associated with hovering the helicopter for long periods of time. 

“Another scenario is high-rise rescues due to fire and smoke. We provided this particular mission training to the Estado de Mexico Unidad de Rescate Aereo, and as odds would have it, they responded to a live high-rise incident in Mexico City shortly after and were able to perform multiple hoist rescues saving people from the top of a burning high-rise,” Matheson told AirMed&Rescue. “This technique is very well suited [to this scenario] as it reduces the possible risk of ingesting smoke into the engines during a hover, and does not create significant sustained winds that would make the fire worse. We have also used this technique with the New Jersey State Police to conduct hoist rescue training from a 165 ft construction tower crane.” 

the benefits of dynamic hoisting are under-utilised for several reasons

According to Ping of Travis County STAR Flight Dynamic, the technique is not just for special occasions: “We use it on all rescues. Even when we modify the technique with a very short approach distance. Our crews have the authority to use both static and dynamic hoist procedures. We have found that training for static hoisting is not necessary; if you can perform a dynamic hoist you can manage a static hoisting event. While we rarely use tag lines, we carry them in case a static hoist with tag line is needed.”

Indeed, dynamic hoisting may be used in almost every execution, even those requiring some component of static operations. “There are basically no limitations to the use of dynamic hoisting. This operation can be executed even in canyons or above tall trees. The helicopter just needs to take the load above the tree top or the obstacles and whenever the axis is clear, the helicopter flies away while the hoist is taking in the load,” said Kreuzer.

Cockell of Air Rescue Systems agrees that a mixture of dynamic and static hoisting can be used to great effect: “Canopy insertion or extraction, for example, requires dynamic hoisting of the load to the canopy insertion point, then maintaining a static hoist position until the load has negotiated the height of the canopy and made it to ground. This ‘combination hoisting’ technique is used in many other hoist missions such as ship transfers, urban operations, power utility function and ‘vertical picks’. The overriding objective is to reduce the exposure and impact of the rotor-flow by minimising the hover in one place longer than required.” 

Safety precautions

Hoist operations almost inevitably entail the risk of entanglement during the approach and departure to the insertion/extraction site. “This risk is significantly compounded when applying dynamic hoisting during night time operations, be it aided or unaided, and consequently, we use a more conservative modified version of dynamic hoisting,” says Matheson. “Best practices for dynamic hoisting include the assessment of where the crews are at most risk and deciding which method will best address that risk. We would also strongly recommend not doing double rescuer insertions, or making any high gravitational force/acceleration turns when performing insertions or extractions. This safety concern is due to the subsequent G-loading and the associated cautions with the overload protection clutch system on various hoist models when the aircraft is operating in conditions outside the relevant external load operational flight envelopes.”

In addition to the traditional hoist failures, dynamic hoisting requires the development of two additional emergency procedures by the operators wanting to adopt dynamic hoisting. “One is in case the load starts to spin (most likely because the helicopter has insufficient forward speed), then it is difficult to arrest the spin if the hoist operator continues to retrieve the load. The procedure [in this case] is to tell the pilot to fly between 35-45 knots while letting the hoist cable out again to ensure it is out of reach of the downwash. The load will then stabilise, and it will be possible to hoist up the load once the helicopter has sufficient forward airspeed,” said Kreuzer. “The other emergency procedure is in case any obstacle is hit between the load and the hoist or between the load and the helicopter (a suspended cable, for example). An immediate release of the load is paramount, and the cable cut away button should be on the hoist pendant instead of inside the aircraft on a panel. Gravitational force may pull the hoist operator outside the cabin, [and] this would make [it] impossible to release the load in time.”

Some of the other factors to consider before exploring dynamic hoisting are the size of the rotorwash produced by the aircraft, the power available to hover and the one engine inoperative (OEI) performance, the type and features of the automatic flight control system on the aircraft, the frequency of night time operations, and the speed and safety features of the hoist system, including the slip or reactive overload clutch. 

dynamic hoisting may be used in almost every execution, even those requiring some component of static operations

“We would not recommend employing this method without understanding all of the variables,” cautioned Matheson. “If an operator is interested in performing dynamic hoisting only because of spins and rotor wash issues, then we would suggest perhaps starting by utilising a tag-line to prevent spins when possible and practising the relevant emergency procedures for spins. For mitigating rotor wash, it may be sufficient to come to a higher altitude in the hoisting position, or move back and left from the scene when possible. If conducting dynamic hoisting were mainly to reduce exposure and risk to the aircraft and crews from possible power failure or OEI, we would strongly recommend evaluating the method further.”

Without doubt, risk managed and safety-orientated training is the overriding consideration in being able to perform dynamic hoisting to the degree required. Cockell told AirMed&Rescue that it is a case of ‘slow and steady wins the race’ when it comes to starting dynamic hoist operations: “Focus on team communications is paramount in developing a true dynamic hoisting capability. This training should reflect the missions it is intended to respond to, and must be built upon robust safety management. Teams that lack experience should develop these techniques and competencies in a crawl, walk, run manner and only proceed to the next level when ample time in training and response has been amassed.”

Dynamic hoisting, then, is not to be underestimated in its complexities, but certainly those responders that do already practise such operations are fulsome in their praise of its benefits.