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The line that leapt out at me was, "the right wing initially folded downwards almost 90° before breaking away in an upwards direction" This implies that it failed initially from excessive negative g-loading, as evidenced by the wing skin folding around the step on the R main gear leg. I find it hard to imagine a case in which that could occur without being inverted. In a normal upright attitude, even an aggressive forward deflection of the control stick would seem unlikely to result in that degree of failure. And yet, if the pilot had just taken off, and was trying to catch up to the other two aircraft, he surely wouldn't have been attempting aerobatic maneuvers.
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It is absolutely possible to induce more than enough negative G’s to exceed limitations, while in straight and level flight.
Especially if they already reached cruise flight, which is well above maneuvering speed.
For example, If that rear passenger kicked, or somehow fell on the stick pushing it forward, it is very well possible.
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This is the stuff nightmares are made of.Scratch Built 4-place Bearhawk. Continental IO-360, 88" C203 McCauley prop.Comment
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> The rear seat had detached from the airframe and its seatbelt was found unlatched, with the
> buckle in a position that would have been in the center of the passenger’s lap. The pull tab
> of the buckle exhibited downward deformation, but the latch mechanism was still functional.
It isn't clear that the rear seat belt wasn't buckled prior to impact. The words here suggest that the passenger may have been buckled but the buckle may have been released in the accident. Is the LSA rear belt attached directly to the airframe or to the seat that was "detached" from the airframe (by impact?)?
I don't think we will ever know for certain what happened, but to speculate a little... Friends say that he was conservative in his flying. But, friends often say that people are skilled, conservative, respected and then facts come out that show otherwise. I don't know that this is the case here, but the combination of very poor construction and some exuberance while providing an experience for a new passenger could explain a failure under negative G-loads. It could have been as simple as playing with G-loads with "ballistic trajectories". This could have gone a little negative on the G's and pulled fuselage apart at the right wing root when a well constructed airframe would not have been at risk. The pictures of the workmanship are concerning. Flying an aircraft with that sort of work is inconsistent with the friends' claims of conservatism.
Everything in the above paragraph is speculation based on a small amount of text and some pictures. It shouldn't be taken as more than that as there is much I don't know about this incident.
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Kestrel made a couple of wise comments that I agree with. First, "I don't think we will ever know for certain what happened" Indeed. But I think I've learned something positive from studying this tragic incident, and if you'll allow me to speculate a bit, I'll explain why I think there's something positive here:
I was captivated, at first, by that right wing, separated from the fuselage, with half of its strut dangling from the wing and the other half still attached to the fuselage. Others have expressed concerns related to the strut, and since my LSA will rely on the same struts, I was getting pretty nervous that there might be a real weakness there. But I am now less worried about the struts. I don't think that's where the problem lies. I think (remember that I'm just speculating) that there was some other root cause of this accident. Because the right wing failed first in the downward direction, it seems to me that some other factor/failure caused the aircraft the aircraft to roll inverted, maybe the aforementioned "inadvertent flight control operation," subjecting the wing(s) to negative-g loading, perhaps exacerbated by frantic attempts by the pilot to recover, and in turn loading the right wing to the point of failure. That could happen even if the wings and struts were fully up to standards, and I no longer think that this accident should cast doubt on the integrity of these wings and struts. I, for one, have more confidence in my struts now than I had before studying this report. That's the positive nugget that I take from this. The other positive is that it inspires me to carefully consider all the other factors and failure points that could precipitate an accident, keeping in mind that it's often a chain of seemingly innocent small errors that can add up to a big problem.
The other comment of Kestrel's that I now quote is:
"Everything in the above paragraph is speculation based on a small amount of text and some pictures. It shouldn't be taken as more than that as there is much I don't know about this incident." --Amen, and... Amen.Comment
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At what point does a Bearhawk LSA become something else?
From my read of it the accident aircraft was not built IAW with Bearhawk LSA plans, specifications or designers build requirements, therefore it is an experimental home built aircraft that resembles a Bearhawk LSA.
In my mind there are a number of possible causes of this in flight break up, the unorthodox build might be one of them, but it might not be either.
Determining the failure sequence in an accident can be difficult, and more so when unorthodox processes have been used. Was the bunt what caused the failure or was a failure what caused the bunt? Or was it something else altogether.
Again, if we are to look for a learning I think it would be stick to the program, don’t deviate from the plans, use approved methods, and materials of construction, and if you’re out of your depth reach out for help, don’t just go off piste and hope for the best.
Alternatively, if you do want to go off piste and pioneer new territory, then call it something else because that’s what it is.Last edited by Bissetg; 04-11-2024, 09:09 PM.Comment
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My curiosity is, if the trim tab broke and induced a downward pitching moment that overstressed in negative Gs. That could have been the other factor/failure you speak of. Since the trim tab was found broken. I too have great confidence in the design. This accident aircraft has too many inconsistencies in construction which greatly reduced the structural design limitationsOriginally posted by OhioLSA View PostComment
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How many hours was on this aircraft? I’m just trying to imagine how the pilot could induce changes in negative pitch capable of bending the wing down 90 degrees? Was there low level wind shear? Didn’t see anything in the reports about it. My mind leans towards elevator cable failure, maybe stainless which doesn’t last as long as plow steel and frays easier. The NTSB report didn’t mention any cable failure.. don’t they usually identify worn cables and what caused the wear that lead to a failure? I mention this because I found a fairlead C clip in the belly of my Pacer during the first annual after restoration. Thankfully the fairlead hadn’t moved. I’m a meticulous builder. I was really in disbelief when I found it. I checked each and every one and do it every annual or 100 hour which ever comes first. I’m the kind of guy who freely admits I make mistakes, but I’m also the kind of person who will keep at it. If it isn’t right the first time, I build or form it again. I keep at it until I’m satisfied with the quality of the part. Then the trim tab, granular description, does this mean it failed from the accident or did it fail in flight? Even if it did, no matter how sensitive the trim is, if it goes wonky hanging onto the stick shouldn’t cause rapid changes in pitch. So I’m back to cable failure or wind shear. Then thinking about this guys crapsmanship, I just can’t don’t know how someone would believe those welds were acceptable. Could be a whole bunch of reasons this guy didn’t build a good ship or short cut that lead to this thing killing him.Comment
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From what I recall from accident board duty and two semesters of aero lab with Dr. Winkleman (he of the chalk-dust laden powder-blue blazer... we dry-cleaned it one day and found out it was in fact navy blue... man, was he pissed), granular failure is overload failure where elastic limit is well exceeded... usually the result of something like operation past ultimate load in flight or impact with cumulogranite cloud/other hard surface. Broom straw failure of a cable is similar tensile ultimate load exceedance failure of a cable.Originally posted by Mark Moyle View Post
From the detailed airframe/engine doc:
The tail section remained largely intact (figure 11). The vertical stabilizer remained attached at its base, and the rudder was still attached to its hinges, and moved freely. The rudder control cables were continuous from the control surface horn through to the foot pedals.
The elevators remained attached to the horizontal stabilizer at their hinges and could be moved freely. The elevator push-pull tube remained attached to the right elevator bellcrank and was broken away from the left elevator bellcrank (figure 12). The push-pull tube was continuous to the intermediate bellcrank, which had detached from the lower airframe (figure 13). Forward of the bellcrank, the remaining section of the push-pull tube had separated and was located in the primary debris field. The other end of the tube had broken away from the aft control stick within the control column assembly (figure 14). All separated sections of the push-pull tube exhibited bending damage with granular surface features at the partings consistent with overload failure.
For the left horizontal stabilizer, the upper brace and the lower forward braces remained attached. The lower rear brace separated at the outboard fitting, with granular surface features at the break. For the right horizontal stabilizer, the upper brace separated at outboard fitting, with similar granular surface feature at the separation point. Both lower braces remained attached, but the lower forward brace exhibited a 10 ° bend/buckle midspan. Outboard of the lower brace point, the right horizontal stabilizer and elevator had bent down about 20° (figure 11). This damage appeared to be consistent with ground impact (15).
Pitch trim cable continuity was traced through to the control arm in the cabin. The control arm could be moved, and slight friction was felt, which appeared to be consistent with a friction lock system (figure 16). The trim tab actuator torque tube remained connected to each side, but the right trim tab push-pull tube had broken away at the fitting on the tab, with granular surface features noted at the separation surface.
In other words, while one of the push-pull tubes failed at the fitting on the pitch trim system, everything else was there... the rudder cable system was intact , and the horizontal and vertical stabilizer, rudder/elevator, and pitch trim tab were attached to the aircraft on the way down. Sounds like the pitch trim system was operable, but right p/p tube broke at fitting due to overload... so likely ground impact.
Sounds more like the report's postulated 'ostentatious maneuver' or "Darn it!... I dropped my phone/camera... gonna unbuckle to get it..." and an inadvertent negative/positive pitch doublet as seen in the ADS-B data. I agree - we'll never know exactly what happened, which is not uncommon. Short of equipping all aircraft with a Gen Z observer (in which case all mishaps will be automatically live-streamed to social media platforms), we will have to live with these occasional mysteries. We do know the the fuselage was poorly built based on the airframe report, but I did not see anything to suggest the wings suffered from the same sort of slap-dash workmanship. Also did not see where the wing was de-skinned and inspected in detail, but I have to imagine someone spent some time with a borescope looking for that sort of thing.
Last edited by SpruceForest; 04-12-2024, 05:40 AM.Comment
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For what it's worth, I built with a quick detach stick for the right seat. I've occasionally put it in when I had a person there that is actually competent with an airplane with adverse yaw, but that's rather rare. I don't think I've had that thing installed in over 2 years now. It's more in the way with their legs if there's gusty winds on final.
I also protected all the control cables that are exposed inside the fuselage from anything inadvertently pushing or pinching them.Comment
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zkelley2, I'm considering the same for the back seat of my LSA. When I compare the benefits of dual controls vs. the possible safety hazards, I'm interested in being able to choose when I might want to have rear controls in place, for a select few pilot/passengers, but in most cases limiting access to controls. A bit of thread drift, but I'd like to see the quick detach stick you came up with. Could you post photos? Maybe start a new thread? Wondering about rudder pedals too...Comment
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Is the rear seat of the LSA removable or is it welded /bolted in ? Does it rely on passenger weight to retain it ?Nev Bailey
Christchurch, NZ
BearhawkBlog.com - Safety & Maintenance Notes
YouTube - Build and flying channel
Builders Log - We build planesComment
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It's removable, doesn't need weight to retain it. A few slots an pops in placeComment
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I spoke with a Cub pilot that very nearly crashed once when their passenger unbuckled and turned around to get something from the cargo area. Pushing the stick full forward with their foot to help reach back in the process. Fortunately they still had their headset on and he was able to yell at them and get their foot off the stick in time to pull out. So a passenger twisting around to get a picture, or retrieve something and shoving the stick full forward can't be ruled out.
Also, remember that the struts are primarily designed to carry loads in tension and are a lot weaker in compression, ie negative G's.Phil Schaefer
Patrol #073
Working on SparsComment
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I think passenger related issues are better managed with a thorough passenger briefing prior to flight. I include the flight controls and their operation, especially the rudder/brake pedals since landing with the brakes heavily applied by a passenger using them as foot rests can be unnecessarily exciting.Comment
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I was surprised to read the builder used MIG rather than O/A or TIG. From what I've read, MIG is a faster method which may be a disadvantage in that you need to see the penetration taking place as you weld. In the welding method controversy MIG doesn't seem to be a player even though it may be used in a few instances by experts. As an amateur builder I am never going to be an expert at anything. If I achieve an acceptable level of proficiency, that's about the best I can do. And I will get expert advice along the way to have confidence in airworthiness. It's surprising the builder would go off-script in this way. And then neglect to include important components?
Still, since it was apparently not a failure of wing attach welding which caused the right wing to break off, this suggests it could have happened to any Bearhawk LSA no matter how well built. Yes, poor choice in welding method (and possibly a lack of critical inspection along with stubbornness) indicates other build areas may have also contributed. But it was the steel that held and it was the aluminum which tore out.
I hadn't seen LSA maneuvering speed of 75mph published before. And the accident aircraft I think was cruising at 132mph ground speed, winds were light. The load limits for the LSA are unknown to me but I gather there is a general set of +/- g-forces this category of craft is expected to withstand. No aerobatics. This is an area of aviation I need to study and understand better. And if I ever get back into flight training I need to pay particular attention to situations where the airframe I have built is put to the test.
I did earn a pilots license but my training did not include spins and recovery from unusual attitudes. I know you need plenty of altitude for these maneuvers but do they also potentially over-stress the aircraft? Likewise wind shear and turbulence: at what point will the airplane break?
And I like the idea of protecting the flight controls, cables and push rods from inadvertent interference. Even with two pilots onboard it's definitely important to consider possible scenarios and take measures to prevent problems. I think lap belts are inadequate. Shoulder harness at least and stay buckled in.
My own LSA will be first and foremost a training plane if I can find an instructor brave enough to fly with me.
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