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Lessons in Windshear


Aircraft Type – R22
Location – Qld, Australia

Maybe I should retitle this story HARD LESSONS in wind shear! As a pilot I was well aware of the dangers of windshear, however being a rotary-wing pilot with a small amount of fixed wing time my experiences had taught me that windshear was much less of an issue in a helicopter than for an aeroplane. The dangers of a stall are not an issue and generally in a helicopter you can pull more power to overcome any speed or height loss. This of course changes with high density altitudes or when operating heavy (high, hot, heavy, humid) and also in mountainous terrain with its associated downdrafts. I did have experience in mountain flying but in the following situation I was operating at sea level and power was not an issue – or so I thought!!

I was instructing in Robinson R22’s at the time, I had about 300 hours on type, and was starting to feel very comfortable in the machine. I also had about 1000 hours in the Hughes 269 (H300) which was a much more forgiving machine. The lesson for the day was advanced auto-rotations (engine failures with glide and subsequent landing). Advanced auto-rotations involve manipulating the speed, rotor RPM and bank angle to land in an area only a little bigger than the helicopter. When performed well they are quite satisfying and give good piece of mind. They are however very complicated with many variables and quite difficult to do. The weather this particular day was humid with a temperature in the high 20’s. There was a forecast for strong winds of 30 knots plus with areas of severe turbulence. It was the first flight planned for the day and we were scheduled to depart at 0800.

On the flight to the training area the student was flying. He was nearing the end of his commercial license and he had a pretty good aptitude. As we were flying to the training area it was apparent the wind at 2000ft was very strong. I decided to get the most from this flight as the rest of the day’s training would probably have to be cancelled due to the strong wind. I also liked to give the better student’s some exposure to poor conditions in order to prepare them for the “real world”. Once we arrived at the training area we completed a series of auto-rotations. The target area was a patch of grass that stood out in the middle of a large paddock. The target was always the same but I would get the student to position the helicopter at different heights, directions and speeds before I would chop the throttle. There was only one rule: make it to the grass area however you could whilst keeping the helicopter within parameters. The auto’s would terminate in a hover after I re-engaged the engine in the flare. Depending on the student, some would need to be shown the auto from every angle whereas some could work it out themselves with only one or two demonstrations. This particular student was pretty good so he did most of the auto’s. Throughout the exercise I noticed the wind was rapidly getting stronger at an increasingly low height but I dismissed my concerns. As we were nearing the end of the lesson I decided to give the student a very challenging auto by positioning the helicopter downwind at 500ft. At this height a 180 turn in the auto is very difficult. The turn need’s to be started the moment the auto is entered and you have to be very aggressive to be able to do a full turn and stabilize before the flare. This is compounded even more with a strong tail-wind. As we positioned and I rolled off the throttle the student was not aggressive enough and I was not happy with the auto so I took over control and initiated an early go around from 200ft. This was the opportunity I had been waiting for as throughout the lesson I had not really touched the control’s and advanced auto’s is as good an opportunity to practise for the instructor as it is for the student. So I positioned for the next one and explained what the student had done wrong – followed by the statement “I’ll SHOW YOU HOW TO DO IT!!!” (said before many a crash!). As I positioned I made sure to chop the throttle later for myself to show that the previous auto could have been successful. As I chopped the throttle I immediately rolled through to at least 45 degress in a left turn. The R22 drops like a rock once you get past 30deg. As I continued the turn the aircraft suddenly plummeted. We were already descending at around 1800ft/min but this now felt like the descent rate had tripled. It felt like one of those amusement park rides that accelerate you toward the ground. I immediately knew something was wrong and stared to abort the auto. In the time it took me to roll disk level and roll the throttle on we had lost 300ft. As the power increased the ground rushed up at us at an unbelievable rate and it didn’t feel like we would recover. To my amazement we levelled off at less than a foot from the ground! We were zooming along at what I estimated was around 50kts with the low rotor RPM horn blaring. I was able to glance quickly inside as I tried to milk the collective for extra height. My glance scared me even more as I realised that we had only 90% rotor RPM (the red line) and we were well bellow the engine operating RPM range. I had full throttle but because of the low engine RPM and lack of power there was no engine acceleration. As this was happening and my eyes shifted focus outside again the long grass was whipping at the skids and even hitting the bubble. I was low and could do nothing about it! We were doing 50 odd kts and running-on was not an option on the uneven surface.

I considered flaring to get my RPM back but we were so low I didn’t dare do so in case that caused us to hit the ground or if we did contact the ground I wanted the aircraft to touch down skids level. To make matters even worse I knew on the other side of the paddock was a large log just under the grass line! I just didn’t know if we would hit it or not. I even had time to contemplate that if there was one log I knew about were there others I didn’t??? The field was fast shrinking – we had covered at least 75m and still we had too much speed and the low RPM horn was blaring like a fog horn in my headset. As I was thinking “I am going to have to commit to the flare or try and run it on”, I looked inside and saw that the rotor RPM had crept up to 95%. With a great feeling of relief the helicopter slowly climbed and after what felt like an eternity we reached 2-3ft! I flared the disk which increased the RRPM to the normal range before setting a climb attitude.

As we climbed out I handed control back to the student and said “I think that’s enough for today’s lesson!” As he flew us back I was trying to process exactly what had happened and why we had dropped the way we did – also why the hell were we flying away and not just a wreck in the field! It was a very quiet cockpit on the flight home. Once we returned to base I debriefed the very quiet and very shocked student and discussed the wind shear. It was with great relief I cancelled the remaining lessons as I didn’t really feel like flying for the rest of the day.

In retrospect and having relived the experience over and over I think we hit a large vertical windshear layer which happened at the worst possible time while we were auto-rotating with a high bank angle. I think we were very lucky. I’m sure we would have both died had we contacted the ground. All it would have taken was another foot of descent. At that speed the skids would have dug in and we would have rolled forward. In the R22 there is no protection in the front of the aircraft and it would have been like being in a car crash whilst sitting on the bonnet. It still gives me shudders thinking about it. I have often thought what would I have done differently and the only thing I would have changed (with the knowledge I had at the time) would have been to not say “I’ll show you how to do it!” That made me more committed than we needed to be. However If we had been on a normal straight in auto we still would have had problem’s. I did learn however that even though windshear and severe turbulence may not affect you for hundreds of flights it is insidious and only needs to give you a bad day once. Although I no longer instruct I am now very wary of these conditions and came out much the wiser – and fortunately with nothing more than a bruised ego!

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