Confined Area Operations
This is a high risk area of operations where several different techniques are often taught. In this article, we'll talk first about the proper departure techniques and also another technique which is often taught but improper and unsafe. In the later part we'll talk about approach techniques. Pilots should be well aware of the hazard of Settling with Power during approaches to confined areas.
The figure to the left depicts the safest departure technique when steady but slow airspeed is used and steady and constant power is applied. The helicopter should be flown on a path which will safely clear the obstacle and also that which will allow a stop safely short of the obstacle if the obstacle can not be cleared. The pilot must also keep in mind that there may be a down-flow of air near the obstacle which must be avoided.
The pilot must be aware that if an abort becomes necessary, the helicopter must be slowed to a stop into the wind well short of the obstacle. As the helicopter comes to a stop, a minimal sink will occur (the red line) as any previously gained translational lift is lost. The helicopter will settle to a high hover at which time it must be flown rearward preferably to the point of departure where it must be reconfigured for another attempt. Changing to the accelerate-and-climb technique is not an acceptable option however an attempt at the vertical climb method is an option. The best option is to remove weight (cargo or fuel).
It is never acceptable to do a pedal turn to abort a confined area departure. The only acceptable abort is to fly the helicopter rearward to a point of safe landing, or to the point of departure if possible. It is always wise to reposition the helicopter to the rearward most safe location in any confined area to allow the longest forward movement for the departure which will result in gained translational lift.
Flying rearward into a confined area can be a hair raising experience; so how to you do it? It is that lack of knowledge which leads some pilots to execute a pedal turn into a downwind condition to abort. Bad Idea! Well let me explain the best procedure and that which I have always taught. If you're uneasy, first attempt this procedure in a safe open area, then proceed to your confined practice area. Once safe on the ground, shut down and look the area over thoroughly; in the process, find a noticeable heavy object like a rock, tree branch, or something else similar. Next, pace off the length of your helicopter. Then walk to the rearward most position in your LZ, and pace forward using the same size steps plus fifty percent more paces; place your marker at this location. Take notice of bushes, trees, or anything else which will help in locating your marker as you hover rearward in your abort. Land at your marker; you can't hit anything because you walked the area, and you marked the safe landing point.
This figure depicts a departure profile which may be used to depart a very tight confined area. This is the technique most commonly used by EMS pilots to exit the many tight scene areas which they land in. The danger of this technique is that the helicopter is lifted vertically into the HV curve but in a stabilized and safe climb after a hover power check has been accomplished.
Flying under the wires is not a safe option. The obstacle could be just about anything, trees, buildings, etc. If sufficient power can not be achieved to clear the obstacle, the helicopter can simply be landed back to the point of departure for reconfiguring. In the event that a departure can not be made as in the profile depicted in the first figure above, an attempted departure using this technique is a safe alternative. If a departure can not be accomplished using either one of these methods, then the only remaining option is to reconfigure the aircraft.
The figure to the left depicts a common but poor and unsafe confined area departure technique. This is the accelerate-cyclic-climb technique. This technique is unacceptable for several reasons.
The first time I experienced this, I was flying with another senior flight instructor who wanted to exchange different methods of teaching confined area operations. When he pushed the cylic forward and began his unstable departure procedure I was shocked.
- Most importantly, this technique does not demonstrate stabilized flight. As the helicopter is pulled into the cyclic climb, translational lift gained while accelerating toward the obstacles is lost at a very rapid rate and a sink can develop as this lift is lost especially with a heavy or under-powered aircraft. This could result in either a crash into the obstacle or an over-torque in an attempt to avoid a crash.
- A cyclic push-over is necessary at the top of the climb to regain lost airspeed and translational lift. Although an experienced pilot may do this gently to avoid a mast bump, a less experienced pilot may not.
- As the helicopter is accelerated forward, it may be flown into the down-flow of air over the obstacle caused by the wind passing over the obstacle. This airflow is invisible but must be known by, and mentally visualized by the pilot.
This figure depicts two different approach profiles either of which is acceptable. Neither has a significant advantage over the other however the difference is that following the blue line you will spend a longer time deeper in the HV curve while along the black line although you will not be as deep in the HV curve, if you loose your engine you will be snacking on trees.
In either case, the helicopter must first be slowed to a stabilized airspeed prior to commencing the approach. Along the black line approach, the steeper angle is intercepted at an airspeed at or above ETL where on the blue line approach, an airspeed at or above ETL is utilized during the entire approach.
Most importantly, prior to commencing on the final approach profile, at least one of the three conditions conducive to Settling with Power must be eliminated. Those three conditions are (the 10, 20, 30 rule):
- 10 - Airspeed less than ETL (often taught 10-knots or less)
- 20 - 20% or greater power applied
- 30 - Rate-of-descent greater than 300-fpm
The only condition that can be eliminated is the rate-of-descent which absolutely must be less than 300-fpm before the aircraft is slowed to less than ETL.
Remember that the vibration during the descent is not ETL! It is often taught that way, but that's WRONG! That vibration is transverse flow effect which occurs at an airspeed just below ETL, so you have slowed to much if you are feeling this vibration and your descent rate is not less than 300-feet per minute. END Jump to Top