Wednesday, September 1, 2010
Hoist Operations Considerations
Over the years, lessons learned have yielded excellent procedures for safe and effective hoist rescues. In my experience, though, many good techniques fail to be shared across user domains. Many of these techniques are codified in written checklists and manuals—you may consider incorporating them into yours and offer concepts missed here in a letter to the editor or e-mail me at firstname.lastname@example.org.
As in all aviation activities, checklists are paramount to remind crews of critical procedures and preparation steps. Hoist checklists are no exception. Prior to conducting hoist ops, the crew should review critical information about the load, pickup point, site description, go-around criteria, type device (penetrator, strop, hook, basket, stokes litter), protective equipment, hover height, power required/available and emergency procedures (loss of power, equipment malfunctions, cable oscillations, damaged cable, comm failure), and be prepared to adjust their plan accordingly based upon variables at the pickup site.
Using the checklist as a guide, let’s consider some important factors. The load provides insight into the weight increase, combined with the temperature and PA at the site, will yield power required/available and margin. Hoist hover height (AGL) is dependent upon many factors and risks, including power available, obstacles, wind, escape paths and military threats. Remember to adequately discuss lee-side downdrafts and turbulence that will require more than normal power. What is often excluded in the AGL discussion for multi-engine helos is height loss in the event of an engine failure.
Several manufacturers produce OEI height loss charts that provide insight to how much descent will occur during the transition to VTOSS airspeed at various weight, temp/PA/wind combinations. Your chosen altitude over the site should be at least this height plus a little extra for “mom and the kids.”
If this OEI height loss performance data isn’t available for your aircraft, you should query the manufacturer for the data or obtain it through flight test from your chain of command. I know for many hoist-equipped units, guidance exists that limits training altitudes for hoist operations. That guidance should be tempered by risks borne out; for example, military operators in combat will minimize AGL height to reduce exposure risk to combat threats, but may be required to hover too low in training to provide “hoist rider safety” which ironically ignores crew safety.
Emergencies during hoists can be task saturating for crews and the subsequent actions must be memorized and rehearsed. I’ve heard many times “if we lose an engine we’ll transition forward down and left to avoid landing on the survivor,” but rarely do crews discuss the developing yaw rate and need to minimize sideward drift prior to impact. Cable shear authority is often a sticky topic. The bottom line is that someone on the crew is designated with cable shear authority and they must be prepared to execute it immediately upon reaching the pre-briefed criteria, (i.e. OEI, uncontrolled descent or battle damage). Intercom failures present another troublesome condition. Crew hand signals should be established, memorized and practiced.
Hoists and cables are the nexus and a single point of failure for hoist ops. Most units treat the hoist cable with the tender loving care it deserves, including complete length inspections prior to any live hoist work. Damaged cables have cost many lives and the damage mechanisms are many. Bird-caged and hour-glassed cables, and cables that contact the aircraft under load are usually damaged and must be inspected and replaced. Shock-loaded cables are also dangerous. Choosing a proper and stable hover altitude, and smooth hoist control, reduces cable shock loading occurrences. Higher heights extend the cable farther providing more available elasticity, which lessens shock loading damage during operations over high waves, for example. Hoists—whether electric or hydraulic—all have load and cycle limits and critical inspection procedures. Do not exceed the limits and religiously comply with the inspections; it’s that simple.
Lastly, don’t forget the impact of hoist ops on ground parties. Static discharge can be debilitating and must be respected. Use a grounding device extended below the cable device to discharge static prior to a rider’s feet contact or survivor touching the device. When hoisting litters or baskets and you have a ground party, always use tag lines with a weak link to stabilize and align the ascending load and prevent oscillation.
Hoist safety is everyone’s responsibility and is easy to improve. Try it.