It was a lovely June day and I was finishing several months of hard work taming the whirling beast: a Part 141 Commercial Helicopter transition course. Tomorrow I’d take my end of course stage check with the Chief Instructor and the FAA check ride would follow shortly after. I went out to practice hovering maneuvers solo to increase my confidence and just because it was such a kick to fly this thing by myself, something that was not required by the course syllabus. I worked on pirouettes, pick ups and set downs and a few patterns in the light wind. I felt satisfied that the work was up to the level the chief pilot required so I asked the tower for a hover taxi back to the helicopter pad.
The tower asked me to contact ground control for the air taxi clearance, a bit unusual but OK – only that frequency was not in the radio. Helicopters often require more hands than a student pilot is born with and my instructor had warned me against dialing in new frequencies in a hover. So I set it down to make the switch. Almost immediately I felt the machine start to shake with what I recognized as ground resonance. I lifted it back in the air as I was taught and the vibration stopped.
Ground resonance is a phenomenon uniquely experienced by helicopters with fully articulated rotors. Often this happens in your odd numbered blade machines (the Schweizer 300, the Eurocopter, the Enstrom to name a few), although any blade set of three or greater is susceptible. Because these birds deal with dissymmetry of lift (the fact that the blades moving forward into the relative wind produce more lift than the retreating blades) partially by sliding the blades forward and back, it is possible to get the blades out of the normal 120 degree phase with one another. When that happens a vibration develops and harmonics exacerbate the problem rapidly. If you are within the flying range on the engine and rotor RPM, the solution is simple: lift it back into the air and the blades settle back into proper relation. If you are not within flight parameters, you roll off the throttle and the energy reduction should stop the vibration.
I set the helicopter back down on the taxiway, no vibration, changed frequencies and called ground control. They cleared me to cross the airport and land back at the pad, which I did uneventfully. My set down was alright but not as perfect as I’d like so I lifted back into the air to do it again. Practice makes perfect, right? On the second set down, which was a beauty to perceive, I was thrilled that I’d completed my second solo flight and tomorrow I’d face the end of course evaluation.
I followed our usual shutdown procedures: collective down, friction on. The engine is hot after hover work so a cool down is required for two minutes at 2500 RPM. Start the timer, while your hand is up there, turn off the radio, the transponder and the boost pump. Come back and tighten one of two cyclic frictions followed by the other. Only I never got the second one tightened before the vibration began. I recognized the shake but I’d just frictioned the flying controls so solution two was roll off the throttle, which I did next.
It literally took seconds for the helicopter to destroy itself. My instructor told me later that he’d seen the set down and headed out the office door to come see how things went. By the time he made it to the lobby, a hundred foot journey, people were telling him the helicopter crashed. The blades took off the tail rotor, broke the tail boom, severed the left side door frame, broke glass and left the beast sitting on its right hind skid. Inside, my right leg was pinned by the cyclic, I saw some blood on my right arm and I guess you’d say I was pretty much in shock. Thirty some years experience flying fixed wings kicked in and I pulled the mixture, turned off the alternator and the battery. By that time my instructor was standing in the left door which was now higher than me and he reached over to pull the fuel shut off.
He encouraged me to get out of the helicopter but all I could think about was “Oh God, I just destroyed this thing!” Airport rescue personnel were there before I knew it, trying to decide if my leg was broken under the deranged cyclic position. My instructor finally got through to me to get out of being part of a post-crash fire. They walked me over to the golf cart we used to move the helicopter around the airport and waited for the local ambulance to show up.
One of the great debates in helicopter training is “which model do I choose for training?” I followed my husband’s earlier path with the Schweizer. He’d done a bunch of research and found it a very safe option. According to AOPA’s Flight Training blog by David J. Kenny, there are fewer helicopter training accidents than fixed wing, which makes sense. There are fewer helicopter pilots being trained. The percentage of students getting hurt during solo is significantly less in a helicopter, kind of surprising to me.
If you’ve snooped around helicopter training at all, you know there’s a SFAR for training in the Robinson aircraft. The FAA and the manufacturer developed this to reduce the prevalent training accidents when the aircraft came out. The design of the two-bladed Robinsons requires special attention to avoid mast bumping, low rotor RPM (stall), low G maneuver hazards and rotor RPM decay. The Schweizer is a ruggedly designed machine with roots going back to the Hughes TH-55 Osage (also known as model 269), designed for the Army in the 1950s. The rotor design on the Schweizer is not subject to the aforementioned hazards but it is prone to ground resonance. Researching the NTSB accident reports, I found the average loss is one per year; always a total loss for the helicopter, most often with only minor injuries for the pilot and/or passengers.
“Hello?” “Um hi, it’s me. Do you think you could come pick me up at the hospital? I had an accident. I’m ok but the helicopter is not.”
So began the phone call to my husband, not exactly a call I wanted to make, surely not a call he expected to receive. The look on the doctor’s face when he poked his head around the curtain and found me on the hospital bed was only topped by hearing the X-ray technician trying to explain to his boss how I hurt myself. To the ER doc’s credit, by the time he came back to report the findings he’d been all over Google for corroboration of ground resonance. He saw what I later spent countless hours looking at: the videos showing helicopters shaking themselves apart in surprisingly short moments.
Meanwhile, the first text from friends came in. A pilot friend saw the news released on the internet for a local TV station and sent: “So, what’s new?” The airport kindly did not release my name, but they did say a female student (and they mentioned my extremely young middle age) “crashed” a helicopter. My friend knew I was taking lessons. My instructor texted to ask if he could come see me. Sure, why not? My husband called our youngest son, a newly minted commercial fixed wing pilot, who was home from college for the summer. Hubby was a bit distressed and left him a message that left out a few details, like I really was going to be fine, in time.
My husband, son and flight instructor crowded into the ER exam space, their relief at seeing I was banged up but otherwise the same bubbled up with what would be a summer’s worth of jokes at my expense. Pilots are like that. Thank God! The ER doctor proclaimed I was young, I would recover well and released me to my family.
It took a few days of ice packs and ibuprofen to start moving in some sort of spirit of normal. My chiropractor took a look at me in the first few days and explained the reason I had to hold my head in my hands to lay down was because I’d experienced whip lash. The cuts began to heal, the bruises produced some spectacular colors and like most pilots, I compartmentalized the accident into nice, neat explainable boxes. The FAA reached out, the NTSB required forms to be completed along with a statement of what I’d experienced.
I started reading everything I could on ground resonance. I watched videos. I scoured NTSB reports and what I found is the dampers on the skids are most often blamed. The problem with this diagnosis, in my opinion, is that everything is so torn up after the helicopter literally shakes itself apart, how do they know if something failed before or during the DESTRUCTION? It didn’t help that I’d heard my instructor describe the mechanic’s personal experience with the total loss of a helicopter. His student, another female it was pointed out, soloed and landed but instead of rolling the throttle off, rolled the throttle full on. The helicopter started bouncing around on the ramp and shortly thereafter shook itself to pieces. The mechanic explained the situation to the NTSB but the final report blamed the skid dampers.
Long-time helicopter pilots assured me I did everything right, that these things sometime just happen. I found little comfort in that. If I did something wrong, I can change that and do it right from here on out. If we could find out definitively that something broke and that caused the accident, I could live with that. What are the chances that would happen twice in my brief helicopter career? The odds were in my favor. Only, there was nothing anyone could put their finger on for sure. In talking with the mechanic, who has more than 15,000 hours flying much of which is in the 269 models, he assured me what happened couldn’t happen. “If the collective was down and locked, you can’t get ground resonance.” The NTSB reports disagree but hey, he’s got real world experience. None of this gave me much comfort when the “new” helicopter arrived.
Climbing back in and getting back to the meat of prepping for the flight test is probably the hardest thing I’ve ever done. The new machine had more of a ground rock to it than the old one ever did. I hoped the mechanic would somehow adjust that out at the first 50-hour inspection but he just told the instructor these machines rock. Knowing how quickly, not to mention painfully, things could go wrong didn’t help my tension. My instructor’s wit and wicked sense of humor was a double edge sword, trying to tease me out of my fears kept me laughing but didn’t overcome the underlying tension.
Nevertheless, we flew. I flew. I maneuvered; I flew the pattern, pick ups, set downs, autorotations, settling with power demos, confined spaces, slopes and all the rest of the maneuvers. Still the start up and shut down periods left me with every muscle in knots, not an easy way to fly. Not how I like to fly. We polished the flying, I studied the books and finally scheduled the end of course checkride about a month after I returned to training.
The weather was good with winds within my limits on the end of course checkride day. Knowing what I went through, the chief instructor was a calming presence as we briefed and flew. I used every self-help technique I’d ever read to face the ride with confidence and to keep my fears in check. We ran through all the required maneuvers and while it wasn’t perfection it was good enough to get the graduation certificate. One evaluation done, one more to go.
My FAA checkride began just before 10:00 a.m. It was the most thorough flying examination I’d ever done. I thought the combined ATP and King Air 350 type rating ride was a long day. The questions and discussions were deeply comprehensive but the examiner had a long history with helicopters beginning with military training in the years of Vietnam. Everything tied back to safety, to understanding the risks and mitigating them as best as possible.
The oral done and nearly two hours of flying later we landed back where we began. I finished the after landing and shut down checklists; the examiner started to head back inside but I stopped his egress. “Did I pass?” “Absolutely. I’ll just head in and finish the paperwork.” A grin split my face in two and I exhaled completely for the first time in at least a month. It was after 4:00 p.m.
I’ve spent a lot of time sifting through the lessons I learned through this experience, not the least of which was learning to manage and respect my fear. I’d never felt truly afraid in an airplane although there were many times they held my rapt attention. Mostly, I guess, I fall back on the end of the quote by Calvin Coolidge my father had on a plaque in his office: “Nothing in the world can take the place of persistence. Talent will not; nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated derelicts. Persistence and determination alone are omnipotent.”