Piloting an aircraft requires certain skills. It also requires certain amounts of discipline, situational and self-awareness. Piloting a helicopter requires even more of each of them.
The main reason is the significant amount of dynamic energy created by large and heavy parts moving at high velocity, such as the main rotor(s), but mostly because a rotary wing aircraft is flying in an unstable manner, as opposed to the stable flight characteristics of most civil airplanes. Turn over a bowl and try to carry around a marble or golf ball steady on top of it, and you will understand what the difference is between this exercise and the one carrying the ball inside the bowl.
The wings of traditional airplanes are aligned in a slight V shape, which increases roll stability and even allows self-recovery to a certain degree; the center of lift is located behind the center of gravity for pitch stability, and the airflow opposite to the heading for yaw stability (CCV/fly-by-wire controlled aircraft function differently, but their computers take care of intentional instability, not the pilots). The best way to achieve a comfortable cruise in a well-designed, well-trimmed plane is to keep your hands off the controls, at least in calm weather conditions.
Helicopters are different. They tend to increase any stick input by themselves. The lighter the helicopter is, the less inertia is opposing this trend, but it’s the light helicopters which are mostly not equipped with costly, sometimes heavy stabilizing systems.
In a rotary wing aircraft (without an autopilot), you never should take your hand off the stick – even trim systems are just keeping the stick in the dialed position for less counter pressure, but don’t provide any aerodynamic stabilizing aid.
I recall probably the most embarrassing moment of my career as a pilot. I wasn’t on top of my mental strength after a night with little sleep, and I never would have decided to fly single pilot in that condition. But even though not mandatory, we were planning the upcoming flight dual pilot anyway, so I joined in as co-pilot and pilot flying for the outward flight. This flight above Central Kalimantan, Borneo, was leading over vast, dense rainforest as flat as a pancake for the first 40 minutes. Its monotone route was routine already, and with the sun burning through scattered clouds, it was tiring even under normal conditions.
At some point, after maybe half an hour, fatigue took its toll on my concentration and even though I wasn’t completely dozing away, my senses and reaction ability were cut down to the point that I suddenly realized I was climbing towards the clouds in a slow, flat turn after it had started to happen. That was the point when I turned controls over to the pilot, and decided to never ever touch controls again if not 100% fit for it, not even when trying to take every chance to build flight hours. As said before, I’d never have flown single pilot in such condition anyway.
Nevertheless it is estimated that pilots falling asleep have been the cause of several unsolved airplane crashes, especially by controlled flight into terrain (CFIT).
Besides the human factor of this story, it illustrates that a helicopter needs to be restrained at all times, while an airplane can fly straight by itself. This fact adds to the workload of a helicopter pilot in any situation, and especially in emergency situations. When experiencing engine failure in helicopters with heavy rotor systems, as most Bell helicopters have for example, you’ve got plenty of time to lower the collective and enter autorotation (even though not as much as in an airplane, cruising at twice the speed of Vs, to lower your nose). But light rotor systems are less forgiving.
For example, in a Robinson R22 you’ve got no more than 1.2 seconds after an unanticipated engine failure to smash your collective lever down before your rotor RPM drops below minimum self-preservation rotor speed of 85%. And during the whole autorotation process, you need to keep your rotor RPM within the limits while looking for and approaching a suitable landing field. And even though I don’t want to get into the details, other emergency procedures such as tail rotor control failure are no less demanding for the pilot.
Well-trained helicopter pilots have learned to cope with the high level of awareness required for their job, but it narrows the additional mental resources available in situations which can be hazardous not only for helicopter pilots, but for all aviators, such as whiteout, or the phenomenon of flat light.
Most of us have heard of blackout. It describes a condition when a pilot’s vision and/or his consciousness is narrowing or completely vanishing due to a lack of blood circulation in the upper body parts, caused by high positive G forces. The opposite, a so-called red-out, occurs when high negative G forces cause minuscule blood vessels in the eyes to burst and to leak into the eye, obscuring the vision.
It is mostly military jet or aerobatic pilots who have to deal with these problems (i.e. to avoid them), but a further definition of blackout is a loss of visual references, for example during night VFR.
A whiteout can be the same effect in clouds, but the term is mostly used for loose snow, sand or dust being blown up (the latter sometimes referred to as “gray-out”) and blocking visual references for the pilot upon landing or takeoff. Helicopters in particular whirl up all kinds of stuff, and helicopters are vulnerable to serious outcomes, because visual references are specifically important for controlling helicopters at little or no forward speed, with the unstable flight characteristics described above.
That’s why helicopter pilots use certain techniques to minimize the dangers of whiteout, which aim at minimizing the risks of whirling up loose materials, and trying to escape or blow the dust or snow cloud in a direction they don’t have to go at the same time.
Generally much more underestimated is the occurrence of flat light, for two reasons: knowledge about it somehow is not as widespread as topics like whiteout; and even when present, flat light often leaves us with the mistaken impression that we still can see what we need to see.
The danger of flat light occurs in hazy weather conditions or in an environment of low contrast, but also with the sun shining from a flat angle, literally generating flat light.
What is happening to our eyes? Well, it’s not a coincidence that we have two of them – both are necessary for three-dimensional vision. Our brain is permanently doing an incredible job comparing the pictures supplied by both eyes, and creating 3D-vision out of the slight variation in perspective of our eyes just a few inches apart from each other. Not even the most advanced computer can master this amount of necessary calculations in the same time for a resolution as high as our eyes.
Of course the more contrast, and the more detailed the picture our eyes can get, the better and the more reliable the result. Try to guess the distance to an object 50 ft away in clear skies; it won’t be a problem. Try the same in dense fog, and you won’t be so sure anymore. That’s because diminished contrast in limited visual conditions can’t provide the eyes with information detailed enough for proper depth perception. As a result, we have a hard time correctly guessing distances.
Reflecting surfaces like snow coverage can leave your eyes without any depth perception and no clue as to the actual distance to the ground or obstacles close by. In the worst cases, there is not enough left for our eyes to focus at, which leaves us with empty-field myopia.
A few years ago the German arctic research ship Polarstern lost both of its shipboard helicopters in one day and in VFR conditions, because the uninterrupted flat white surface combined with light haze and the sun shining at a low angle dissolved any contrast between earth and sky, and both pilots lost their visual horizon and thus their spatial orientation at low altitude.
Even more lethal is the ability of our brain to “interpolate” such an insufficient picture: if you can see merely the contours of multiple obstacles of similar shape, like trees, houses, dunes or hills, then your brain might combine the information of each eye falsely, and suddenly grouped objects or evenly structured surfaces appear much closer or much further away than they actually are.
This sounds strange, but I remember a certain kind of picture that used to be very popular two decades ago. They were showing just some apparently messy structures at first, but if you would try to look through the picture, which meant adjusting your eyes to an imaginary point somewhere behind the picture, you suddenly could see some hidden object evolve three-dimensionally from the picture.
That’s exactly how this works. You can try it yourself in a simple experiment: just position yourself a meter or two behind a fence of wire mesh, and try to fix your eyes to something ten meters away, looking through the fence. It could happen that suddenly the fence looks much closer than it actually is.
How to deal with it
The best way to stay safe is, as always, to avoid these conditions. When flying helicopters, that’s not always possible. After all, the advantages of helicopters which make them popular are their ability to operate under circumstances entailing such environmental conditions.
Papua has the reputation of being the most challenging area for aviation in the world. Mountains as high as in Switzerland on a tropical island of more than 300,000 square miles ensure unique weather situations. Good weather conditions in the morning tend to deteriorate by noon, whereas they can be completely different from one valley to another. We used to say, “the mountains are boiling,” because sometimes you could literally watch the weather changing and walls of clouds evolving. The reliability of weather information and forecast is very limited there, and sometimes quick decisions must be made. When flying there, I appreciated the many years of on-site experience to learn from – not my own, but of my senior pilots.
If wisps of clouds are ensnaring mountainsides under a closed stratus layer above, I wouldn’t dare to enter the valley in an airplane – better to hope for your way back still being open.
Helicopters can reduce their speed and turn radius significantly in conditions close to the VFR minima, and in a worst case land in small spots, in consideration of hover OGE limits and the dead man’s curve, of course. In fact, in EASA airspace the VFR minima for helicopters are at only two-thirds of those for other aircraft.
On the other hand, taking advantage of those priceless advantages increases the risks of flat light occurrence, spatial disorientation and white/gray-out. In order to stay alive and safe, it is essential for a pilot to know and respect not only the limits of his aircraft, but also his personal ones.
In Papua it happened frequently that we had to sit out sudden weather changes, and even though I never got to have my innings, some of our pilots had to stay overnight in the hamlets from time to time. Better you return home tomorrow than not at all.
- Helicopter flying in the jungle – lessons learned - June 23, 2016
- Helicopter techniques – (not) for dummies - May 2, 2016
- Mistaken identity – mike romeo times two - October 21, 2015
Great article! Really enjoyed the difference outlined in rotorcraft vs. fixed winged. Your description of how our eyes and mind interact to create a 3D image was excellent. How our eyes can often be fooled in certain lighting conditions makes one pause should we be faced with a similar condition. Knowing this is like flying IFR. Knowledge of adverse consequences often keeps us from experiencing the trap that has cost others dearly. Thank you for sharing this valuable information and your insights.