Prosling Technology
Ask any longline pilot what the hardest part of the job is, and very few will say “flying the helicopter.” The aircraft is the easy part. The hard part hangs thirty metres below it on the end of a line, swinging with a mind of its own.
The project to change how that skill is trained began with Nicolas Broc at Intersim, who originated the concept of a dedicated, physics-accurate HESLO simulator and set its direction. Intersim delivers this training solution under the Prosling brand, and we’ve spent the last few years building the platform together. This post is about why the training gap exists in the first place — and how the simulator addresses it.
What makes HESLO genuinely hard
Sling work breaks a lot of the assumptions that ordinary flight training is built on.
The pilot is flying an aircraft whose centre of gravity is constantly moving and often can’t be seen directly. Control inputs don’t produce an immediate, intuitive result — they produce a result several seconds later, filtered through the dynamics of a swinging pendulum. A poorly timed correction doesn’t just fail to help; it feeds energy into the load and makes the oscillation worse. Learning to not chase the load — to anticipate rather than react — takes a long time to build and is genuinely dangerous to build in a real aircraft.
Then there’s the task variety. Precision placement of a load onto a target. Longline work where the pilot is looking straight down through a bubble window or relying entirely on a crew member’s calls. Aerial sawing, where a suspended saw assembly is flown along a power-line corridor to trim trees — unforgiving, millimetre-scale vertical reference with a rigid, dynamic load. Bambi bucket drops in firefighting, where the mass of the load changes the instant the water leaves. Every one of these has its own failure modes, and every one puts the aircraft close to the ground, close to obstacles, and close to the edge of its performance envelope.
The consequences of getting it wrong are not abstract. Dynamic rollover, wire strikes, load-induced loss of control, and settling with power under load are recurring themes in sling-load accident reports. These are low-altitude, low-margin events where there is often no time and no height to recover.
The training problem
Traditional HESLO training runs into a wall built from three things.
Cost
Turbine time on an AS350 is expensive, and sling training burns it fast. A lot of the value is in repetition — and repetition is exactly what you can least afford by the hour.
Risk
The most valuable scenarios are the ones closest to the edge: a diverging oscillation, a snagged load, a confined-area pickup with obstacles. Taking a student there repeatedly, for real, is how instructors get grey hair.
Repeatability
You can’t summon the same crosswind, load geometry, and confined LZ on demand. Weather, terrain, and load availability all conspire against structured practice. A student might get a handful of meaningful reps in a season.
The net effect is that pilots often build sling proficiency slowly, unevenly, and partly on the job — accumulating the critical “feel” for load dynamics through exposure rather than through deliberate, structured practice. That’s an expensive and slow way to learn a safety-critical skill.
Where VR changes the equation
A simulator only helps with sling work if it gets the load physics right. This is the part that most generic flight sims quietly skip. The helicopter model can be excellent, but if the load underneath it is a rigid, well-behaved box, the student is practising the wrong thing entirely.
Our HESLO plugin — LoadStabilizer — is built on top of the latest X-Plane 12 from Laminar Research, and engineered from the load outward. The rope is modelled as a real, distributed cable, so it stretches, sags, and swings the way an actual longline does rather than behaving like a rigid link. The hook and load carry their own mass and dynamics. The coupling back into the aircraft is two-way: the load pulls on the helicopter, and the helicopter’s every input propagates down the line. When a student over-controls, they see and feel the oscillation build — exactly as they would in the aircraft — and, crucially, they can recover from it, reset, and try again thirty seconds later with zero risk and zero fuel burned.
That physics core drives the training features that matter:
- Longline & precision placementWith a load that actually behaves like a pendulum, so anticipation — not reaction — is what gets rewarded.
- Bambi bucket firefightingIncluding the drop itself, where the sudden mass change at release is one of the trickiest moments to internalise. We built drop-zone prediction guidance around exactly this task, and delivered a system for Bambi bucket training to AformX for operational use.
- Aerial sawingPractise flying a suspended saw along a corridor with the precision the task demands, holding a steady vertical reference against a rigid, swinging load — the kind of exposure that is prohibitively risky and expensive to build in a real aircraft.
- Multi-crew coordinationTrain the whole crew together, not just the pilot. A load master or ground crew member can share the scenario, so the calls, timing, and hook-up-to-release choreography that real sling operations depend on are rehearsed as a team.
- Instructor replayFreeze a run, rewind it, and show a student precisely where an oscillation started — the input that seeded it — rather than describing it after the fact.
Delivered in VR — the system supports professional-grade mixed-reality headsets, with the Varjo XR-4 our recommended choice — the experience closes a loop that a flat screen can’t. Sling work is a spatial, head-out task: the pilot is judging the load’s position in three dimensions, often looking down and to the side, reading swing rate and phase by eye. Stereoscopic depth and a headset that lets you physically look at the load turn the simulator from a procedures trainer into something that builds the actual sensory skill the job requires.
Fixed-base and motion
The platform runs in two configurations, and both have a place in a training programme.
Fixed-base — volume & fundamentals
A static installation with VR and accurate load physics is a remarkably capable trainer on its own. It covers the perceptual and cognitive core of sling work — scan, anticipation, timing, crew coordination, procedures — at the lowest cost and footprint. With no motion system to feed, it’s easy to deploy and easy to run for long, repetitive sessions: ideal for the early reps and for recurrent procedural practice. For much of what makes a good longline pilot, the eyes and the timing matter more than the seat.
Motion — the last part of the loop
Adding a motion platform — such as the Ryan Aerospace integration — closes what a fixed rig can’t. Sling divergence announces itself in the seat before it’s obvious out the window; the onset of an oscillation is something an experienced pilot feels. Motion cues let a student learn to detect and arrest that build-up through the same physical channel they’ll use in the aircraft. This is where the edge-of-envelope handling and the strongest transfer to the real thing live.
The two aren’t rivals; they’re a progression. A fixed-base station is where volume and fundamentals are cheapest to build, and a motion platform is where the most demanding, highest-stakes handling skills are sharpened. A proof of concept realised in France added movement on four axes and measurably improved immersion — while overcoming VR motion sickness through motion synchronisation.
Why it matters beyond one operator
None of this is only about making training cheaper, though it does that. It’s about making training possible — turning the rarest, most dangerous, most valuable scenarios into things a pilot can rehearse dozens of times before they ever encounter them for real. Pilots have achieved a stable hover on their first real flight after motion simulator sessions.
There’s also a certification dimension. Our development is aligned with the EASA CS-FSTD(H) framework — flight model parameter correction, objective test data capture, and validation documentation — built to support the qualification of complete training devices in cooperation with national aviation authorities. We draw on the input of experienced sling pilots to tune and validate the behaviour so that what the simulator teaches transfers cleanly to the aircraft. A simulator that flies convincingly but wrong is worse than no simulator at all; getting the load dynamics validated against reality is the whole game.
Helicopters will keep lifting loads on longlines — for construction, for power-line work, for logging, and for putting water on fires. The demand for pilots who can do it safely is not going away. VR-based HESLO training is how we build those pilots faster, cheaper, and with far more of the hard reps behind them before the stakes get real.