I once flew from Weston-on-the-Green as a guest on a sky diving flight, a couple of years after this accident. We went right up to 12,000 feet which I was told was the natural ceiling for this sort of activity.
It amazed me that everyone on board could think straight at that altitude — it really affected me dropping to two thirds atmospheric pressure so suddenly. As I recall we didn’t spend long at altitude: the aircraft and the sky divers went pretty much straight up then straight down again with surprisingly little difference in time spent in the air between them and us. You’d want to have your wits about you anyway when jumping out of a plane, let alone one where the landing site is next to two busy roads (the newly built M40 near the Oxford/Bicester A34 junction.)
(And yes, if you’d told me in the early 90s that you were going to take a flight in a second hand soviet turboprop I’d say take a parachute because you must have a screw loose. Turns out both were the case.)
The highest I jumped without oxygen was 17.7k ft (couldn't quite get that extra 300 feet), and I was quite hypoxic. The odd thing is, I had no awareness of my impaired cognitive ability and I basically staggered out of the aircraft. I wasn't thinking straight for half of the jump. I now think i'd be much more aware of the effects and impact of hypoxia, because i've experienced it.
I've also done the opposite by scuba diving to 30m and begun to get nitrogen narcosis, which is very similar. To understand it better, I've done a "dry dive" in a controlled environment in a hyperbaric chamber where they can simulate a 40m dive, and measure your cognitive ability throughout. This is excellent awareness training, and I now think i'd identify the early signs of it sooner.
> 10-12,000ft is generally accepted as negligible impact on cognitive function
That is just a guideline.
Each person responds to hypoxia differently and starts becoming hypoxic at different altitudes. One person might start having symptoms at 8,000 while another can function without oxygen at 14,000 for hours. It depends on your health and acclimation. All else equal if you live in Denver your tolerance to altitude will be greater.
This also applies to carbon monoxide exposure. For either condition you may not get headaches at all. Or you may get loss of color vision first. Or maybe your fingers tingle first. It is highly variable from person to person. Many people in those situations report they excluded hypoxia or carbon monoxide as a possibility because their symptoms didn't line up with the published lists, unaware that those lists are merely guidelines.
The one constant is that by the time you realize you are hypoxic or have CO poisoning you will either not care or be unable to fix the problem. This seems to be nearly 100% universal. Even when briefed ahead of time in a test scenario almost everyone will fail to take any action to rectify their situation on their own. Sometimes they can be coached into taking action (like descending or putting on an oxygen mask). For that reason a number of GA pilots use a pulse oximeter when flying above 8-10k to detect the signs early, while they are still aware enough to take action.
Also be aware that perversely CO causes your pulse oximeter reading to increase. Those chemical dots are useless, you need an actual detector and the sensor inside them is good for 10 years. Once bound to hemoglobin CO takes a long time (12-24 hours) to be removed and breathing oxygen only speeds that up by half. This is very unlike hypoxia which disappears in seconds once you start on oxygen. For aviation don't use household detectors - they have relatively high thresholds. On a long cross-country or multi-day flight you can accumulate exposure at levels low enough not to trigger a household alarm but cumulatively become very impaired due to the long half-life of CO in the body.
> If the blades are still angled to produce thrust, then instead of the blades taking a bite out of the air, the oncoming air will start to take a bite out of the blades, so to speak, driving the propeller, and thus the turbine, in reverse.
Minor correction for the author, a unfeathered prop continues to rotate in the correct direction. The flow of torque is reversed, not the actual rotation of the prop.
Indeed under certain circumstances the prop can end up speeding past its design RPM to the point that the prop tips become supersonic creating a whole world of other problems and dangers.
It's one of numerous errors in the article that demonstrate Dempsy has fundamental misunderstandings about the stuff she is writing about, which is hilarious given she is routinely and extensively complemented (by people who know nothing about aviation) for her "excellent analysis".
She never even mentions the ultimate cause of the crash: Antonov's design required dual grounds, but the factory in Poland modified the design to group the grounds together, without realizing or caring about the implications.
It's right in the UK DoT crash report - page 30 - and on the summary of the crash on the BAAA's website, which is in the first 6 google results for the crash. It would probably be higher except her article and copies of it on reddit are taking up the first couple of hits now.
Spoiler for people who don't want to read a VERY long article- the electrical circuits in the plane did not follow the plans. A screw that was providing grounding (to the plane body) for the flap system had wiggled loose- causing the electricity to take a different path, through the a circuit that controlled the angle of the propellors. So pressing the flap button cause the propellor to stop spinning.
The problem isn't that they didn't follow the plans, they did, the problem is they didn't include industry standards for safety critical systems like preventing reverse current with diodes and/or independent grounding.
The design was changed slightly shortly before going into production, from two grounding screws to one. It's a minor difference though as there would be no way to detect thata single grounding screw had failed and then the failure of the second screw would cause the same problem. And if one screw is backing out/aging, there's a good chance the other one is too.
> It's a minor difference though as there would be no way to detect thata single grounding screw had failed and then the failure of the second screw would cause the same problem.
Actually, having two grounding screws would have avoided this problem - the flap switch would never have been connected to the ground via the feathering mechanism (unless both screws got loose and somehow entangled). In that case, either the flap mechanism would have failed, which would have been obvious, or the second terminal of the feathering switch would cease to be grounded, which could lead to sudden feathering with sufficient EMI. While still not great, a dual ground-screw setup would have been much better.
Surely any design should also include plans for periodic inspection, like "pull on each screw and make sure it's not loose or wiggly"? Else you eventually get into situations like doors falling out midflight as happened recently. Diodes can also fail and inspection of their current reliability got to be harder than inspection of screws. If you are working with Soviet levels of quality and service, opting for simpler components might be a better bet.
Sounds like the electrical faults in some older cars. Poor grounding or corroded wires lead to the current flowing in an unexpected different path, causing all kinds of bizarre effects.
Yep, that brings up good memories. I spend some time fixing electrical faults in my first two cars when I was 22 and knew nothing about electrical engineering (I did know math and programming though).
That feeling when I understood why taillights are flashing dimly in unison with the left turning light I won't forget, along with a few other eureka moments.
I just bought a new car with poor grounding. Apparently the factory had painted over the terminal where the automatic transmission grounding cable attached. This caused a variety of intermittent faults until the dealership technician figured out the root cause and sanded off the excess paint.
It didn't cause them to stop spinning. It caused them to feather, which meant torque dropped enormously, and there was suddenly a huge disparity between commanded torque / fuel flow and observed torque so the engine control system figured something catastrophic happened (such as a gearbox failure or prop/feathering system failure), and cut fuel flow to keep the engine from overspeeding...and then that in turn triggered automatic deployment of both spoilers, turning the plane into a space shuttle simulator.
Welcome to Dempsey's style: google a plane crash, read a bunch, slap it all together and take multiple paragraphs to say something that only needs one sentence or adding drama...get a bunch of things wrong, and call it "in depth analysis."
She doesn't do the slightest bit of "analysis", she has no training or education in aeronautics or any other relevant field, and despite having spent years reading and writing about this stuff, she routinely gets things wrong. What's hilarious is that a reporter claimed she "extensively fact-checks". What? You can't/shouldn't fact check your own work. A colleague, editor, or expert in the field does.
She missed one critical fact despite those five pages and numerous diagrams and photos, which was the entire reason for the crash: the Antonov design required separate grounding points for the two systems, but the factory modified the design.
Let me go over the numerous ways Dempsey demonstrates she doesn't understand basic physics and aeronautics despite years of "researching" plane crashes.
Dempsey says: "Furthermore, because a failed engine on the An-28 tends to produce a large and sudden yawing moment, the system also automatically deploys the outboard wing spoiler on the opposite side from the engine failure, in order to ensure that drag on both sides is as close to equal as possible."
First off, engine failure on any non-inline-twin will cause this, it's not specific to the An-28, but I'll chalk that up to just shitty writing skills which an editor would have fixed. Second, it's not about "ensuring drag on both sides is as equal as possible" - the yaw happens because the vector of thrust shifts several feet to one side from the centerline of the aircraft - or as it's properly referred to, asymmetrical thrust.
Third, she said spoilers "induce drag" - they aren't designed to cause drag. They're designed to disrupt airflow over the top of the wing - it detaches from the surface and becomes turbulent. They spoil the flow of air - literally in the fucking name, and she doesn't understand what they do.
Fourth, the reason the spoilers are deployed is not to even out drag. It's to cancel the effects from the yaw, which causes the plane to start slipping/crabbing - its yaw angle doesn't match the plane's path through the air. One wing is thrust into the wind and the other retreats, causing a difference in lift...and there's also a difference in lift because the failed engine is no longer pushing air over the wing behind it, and (until feathered) in fact is blocking, and causing enormous turbulence in, air that should be going over the wing generating lift.
She said "The landing gear swiftly collapsed, causing both wings to fold downward and strike the ground." If the landing gear hadn't collapsed, the wings still would have been ripped off the plane, and further, everyone aboard likely would have been more seriously injured because the plane's fuselage (and thus passengers, not in seats) would have had a much stronger vertical acceleration when it hit the ground. The wings folded downward because the heavy engines had high momentum, the airframe's vertical speed was reduced to zero almost instantly. As the airframe's vertical speed went to zero, it exerted a force on the wings that the plane could never be designed to handle.
She said: "If the blades are still angled to produce thrust, then instead of the blades taking a bite out of the air, the oncoming air will start to take a bite out of the blades, so to speak, driving the propeller, and thus the turbine, in reverse."
Fucking what? Propeller blades are airfoils and when the engine fails, the blades stall because the angle of attack of the blade changes enormously. There will be some windmilling - at a tiny fraction of the engine's power (in piston aircraft, around or less torque than even the starter motor) but it's in the same direction the engine normally turns - they don't fucking spin backward because air is still flowing in the same direction. The bigger problem is that the propeller is presenting what is effectively a flat face to oncoming air, and inducing turbulence in air that should be flowing past it and smoothly over/under the wing, generating lift.
Kyra Dempsey writes about shit she doesn't fully understand, doesn't seem interested in or capable of educating herself in basic physics and aeronautical concepts, and as evidenced by the writeup of this crash - gets basic facts wrong because she doesn't throughly research them enough. How she still gets this stuff wrong after years of doing it is bewildering.
I don't understand reddit's obsession with her, or why people keep linking to her articles here. If she was as good as everyone claimed, why is she basically unemployed?
If you want to read actual informed analysis of plane crashes, read aviation news outlets. AOPA, for example, does a lot of extensive writeups about crashes in general aviation, and it's written (and reviewed by) people who are experienced, knowledgeable pilots (and often, instructors.)
The doesn't say whether the C-145As built in Poland for the US Air Force still had the fault, or the SkyTrucks built until 2019. We might guess that since the fault wasn't in the plans, they would not get it, but that might depend on whether they were built in the same factory as HA-LAJ, with the same practices.
It seems as if were both engines to fail, either one prop would be feathered and the lift spoiler on that side extended, or neither prop would be feathered. Presumably the pilot could feather the props himself. It is not apparent whether this would extend both lift spoilers too, or if those were controlled separately.
The design drawings did not have the fault, but the engineering drawings used for building may have. They were done by different teams in different organisations at different times.
I doubt they have the same fault. It's common practice in NATO air forces to use lock wire or another type of anti-backoff mechanism on screws and bolts subject to vibration.
If the original design lacks this it would likely have been embodied as a fleet wide modification/design change.
It would be also quite normal for design plans to just specify that it should be "screwed here", depending on standard practices to use the standard screw locking.
I wonder whether using a switch that didn't have the third normally-closed terminal might have been another option. It then wouldn't have needed to be grounded at all.
You do want to ground it or EMI can come to bite you. If that long bit of wire is left floating it can act like an antenna. (SPST switches exist but they actively chose not to use one)
I did my first jump course at Weston-on-the-green a couple of years after this incident, and it was interesting hearing people talk about this with no actual detail, except blindly blaming 'Russian' equipment. Sad, because this tainted all An-28's for me for many years. Still, the Dornier 228 that replaced it was a fantastic aircraft which you don't seem to see many other places.
I didn't quite understand how the screw being loose triggered the system, but the screw falling out completely would have been ok. Did I misunderstand that section?
It does not say "screw falling out completely would have been ok." The screw provided a single point of electrical contact for grounding. When it became loose (thus less surface area contact with the chassis and hence increased resistance in that part of the circuit) or fell out completely (zero surface area contact with chassis and hence infinite resistance in that part of the circuit) the current took a completely different path to the ground with catastrophic results.
I think this use of phrase "in fact" in the article is a bit Russian or otherwise Slavic. This usage shouldn't be illegal in English but is less common.
Electricity needs both positive and negative connections made between power source to equipment to work, but some old vehicles only ran the positive(sometimes only the negative) wires, and used the entire vehicle body the negative wire. Idea is that the electrons are gonna find its own way, the body's thick as it gets as a conductor, it's fine if you knew what you're doing, it saves lotta weight.
In this case, one of such connections to the body was secured with a screw, which could loosen from vibration, which `in fact` did. It instantly caused electricity to look for an alternative way, which was through propeller feathering switch and feathering relays, which caused the airplane to needlessly stop flying.
I think using "in fact" there is ok, I didn't have any trouble understanding it. "Actually" might have worked as well? And the part that follows, "with the grounding screw pulled out sufficiently far" probably also includes "the grounding screw missing completely".
Screw is forgotten or snapped: nothing is holding the wires, the resistance of ground connection is too high, switches either don't work or misbehave when you test them before flight. A lot of curse words about servicing the damn thing is heard.
Screw gets more and more loose (alternatively, dirt or rust accumulates): less and less current flows through the contact point, more and more voltage is applied to relays. Generally, it is not enough to switch them, until one day another bump changes the position of wires, and ads some more resistance…
If something fails, it should fail as a whole. It's analogous to aborting the program on unexpected error versus ignoring it and hoping that everything else generally works OK.
When the ground screw came loose the voltage coming out of the flap switch traveled back up the feathering ground, causing the system to think the feathering switch was activated.
When part of an electrical circuit starts to "float" like this - becoming no longer anchored to some global reference voltage (usually chassis ground is considered 0V) - the observed voltages in other parts of the system can take on really byzantine values.
Yes. It never said that the screw falling out would have been ok. The effect would have been the same where the flap ground connection would have found its way home via the feather system. Loose vs completely gone are just two points on a continuum of badness.
Readit News
It amazed me that everyone on board could think straight at that altitude — it really affected me dropping to two thirds atmospheric pressure so suddenly. As I recall we didn’t spend long at altitude: the aircraft and the sky divers went pretty much straight up then straight down again with surprisingly little difference in time spent in the air between them and us. You’d want to have your wits about you anyway when jumping out of a plane, let alone one where the landing site is next to two busy roads (the newly built M40 near the Oxford/Bicester A34 junction.)
(And yes, if you’d told me in the early 90s that you were going to take a flight in a second hand soviet turboprop I’d say take a parachute because you must have a screw loose. Turns out both were the case.)
I've also done the opposite by scuba diving to 30m and begun to get nitrogen narcosis, which is very similar. To understand it better, I've done a "dry dive" in a controlled environment in a hyperbaric chamber where they can simulate a 40m dive, and measure your cognitive ability throughout. This is excellent awareness training, and I now think i'd identify the early signs of it sooner.
That is just a guideline.
Each person responds to hypoxia differently and starts becoming hypoxic at different altitudes. One person might start having symptoms at 8,000 while another can function without oxygen at 14,000 for hours. It depends on your health and acclimation. All else equal if you live in Denver your tolerance to altitude will be greater.
This also applies to carbon monoxide exposure. For either condition you may not get headaches at all. Or you may get loss of color vision first. Or maybe your fingers tingle first. It is highly variable from person to person. Many people in those situations report they excluded hypoxia or carbon monoxide as a possibility because their symptoms didn't line up with the published lists, unaware that those lists are merely guidelines.
The one constant is that by the time you realize you are hypoxic or have CO poisoning you will either not care or be unable to fix the problem. This seems to be nearly 100% universal. Even when briefed ahead of time in a test scenario almost everyone will fail to take any action to rectify their situation on their own. Sometimes they can be coached into taking action (like descending or putting on an oxygen mask). For that reason a number of GA pilots use a pulse oximeter when flying above 8-10k to detect the signs early, while they are still aware enough to take action.
Also be aware that perversely CO causes your pulse oximeter reading to increase. Those chemical dots are useless, you need an actual detector and the sensor inside them is good for 10 years. Once bound to hemoglobin CO takes a long time (12-24 hours) to be removed and breathing oxygen only speeds that up by half. This is very unlike hypoxia which disappears in seconds once you start on oxygen. For aviation don't use household detectors - they have relatively high thresholds. On a long cross-country or multi-day flight you can accumulate exposure at levels low enough not to trigger a household alarm but cumulatively become very impaired due to the long half-life of CO in the body.
Many pilots will huff oxygen lower than 10k especially if they're doing anything but straight and level.
Minor correction for the author, a unfeathered prop continues to rotate in the correct direction. The flow of torque is reversed, not the actual rotation of the prop.
Indeed under certain circumstances the prop can end up speeding past its design RPM to the point that the prop tips become supersonic creating a whole world of other problems and dangers.
She never even mentions the ultimate cause of the crash: Antonov's design required dual grounds, but the factory in Poland modified the design to group the grounds together, without realizing or caring about the implications.
It's right in the UK DoT crash report - page 30 - and on the summary of the crash on the BAAA's website, which is in the first 6 google results for the crash. It would probably be higher except her article and copies of it on reddit are taking up the first couple of hits now.
The design was changed slightly shortly before going into production, from two grounding screws to one. It's a minor difference though as there would be no way to detect thata single grounding screw had failed and then the failure of the second screw would cause the same problem. And if one screw is backing out/aging, there's a good chance the other one is too.
Actually, having two grounding screws would have avoided this problem - the flap switch would never have been connected to the ground via the feathering mechanism (unless both screws got loose and somehow entangled). In that case, either the flap mechanism would have failed, which would have been obvious, or the second terminal of the feathering switch would cease to be grounded, which could lead to sudden feathering with sufficient EMI. While still not great, a dual ground-screw setup would have been much better.
That feeling when I understood why taillights are flashing dimly in unison with the left turning light I won't forget, along with a few other eureka moments.
Deleted Comment
Welcome to Dempsey's style: google a plane crash, read a bunch, slap it all together and take multiple paragraphs to say something that only needs one sentence or adding drama...get a bunch of things wrong, and call it "in depth analysis."
She doesn't do the slightest bit of "analysis", she has no training or education in aeronautics or any other relevant field, and despite having spent years reading and writing about this stuff, she routinely gets things wrong. What's hilarious is that a reporter claimed she "extensively fact-checks". What? You can't/shouldn't fact check your own work. A colleague, editor, or expert in the field does.
She missed one critical fact despite those five pages and numerous diagrams and photos, which was the entire reason for the crash: the Antonov design required separate grounding points for the two systems, but the factory modified the design.
...which she would have known if she'd actually read the fucking crash report, or its summary. Summary: https://www.baaa-acro.com/crash/crash-pzl-mielec-28-weston-g... and report: https://www.baaa-acro.com/sites/default/files/2020-10/HA-LAJ...
Let me go over the numerous ways Dempsey demonstrates she doesn't understand basic physics and aeronautics despite years of "researching" plane crashes.
Dempsey says: "Furthermore, because a failed engine on the An-28 tends to produce a large and sudden yawing moment, the system also automatically deploys the outboard wing spoiler on the opposite side from the engine failure, in order to ensure that drag on both sides is as close to equal as possible."
First off, engine failure on any non-inline-twin will cause this, it's not specific to the An-28, but I'll chalk that up to just shitty writing skills which an editor would have fixed. Second, it's not about "ensuring drag on both sides is as equal as possible" - the yaw happens because the vector of thrust shifts several feet to one side from the centerline of the aircraft - or as it's properly referred to, asymmetrical thrust.
Third, she said spoilers "induce drag" - they aren't designed to cause drag. They're designed to disrupt airflow over the top of the wing - it detaches from the surface and becomes turbulent. They spoil the flow of air - literally in the fucking name, and she doesn't understand what they do.
Fourth, the reason the spoilers are deployed is not to even out drag. It's to cancel the effects from the yaw, which causes the plane to start slipping/crabbing - its yaw angle doesn't match the plane's path through the air. One wing is thrust into the wind and the other retreats, causing a difference in lift...and there's also a difference in lift because the failed engine is no longer pushing air over the wing behind it, and (until feathered) in fact is blocking, and causing enormous turbulence in, air that should be going over the wing generating lift.
She said "The landing gear swiftly collapsed, causing both wings to fold downward and strike the ground." If the landing gear hadn't collapsed, the wings still would have been ripped off the plane, and further, everyone aboard likely would have been more seriously injured because the plane's fuselage (and thus passengers, not in seats) would have had a much stronger vertical acceleration when it hit the ground. The wings folded downward because the heavy engines had high momentum, the airframe's vertical speed was reduced to zero almost instantly. As the airframe's vertical speed went to zero, it exerted a force on the wings that the plane could never be designed to handle.
She said: "If the blades are still angled to produce thrust, then instead of the blades taking a bite out of the air, the oncoming air will start to take a bite out of the blades, so to speak, driving the propeller, and thus the turbine, in reverse."
Fucking what? Propeller blades are airfoils and when the engine fails, the blades stall because the angle of attack of the blade changes enormously. There will be some windmilling - at a tiny fraction of the engine's power (in piston aircraft, around or less torque than even the starter motor) but it's in the same direction the engine normally turns - they don't fucking spin backward because air is still flowing in the same direction. The bigger problem is that the propeller is presenting what is effectively a flat face to oncoming air, and inducing turbulence in air that should be flowing past it and smoothly over/under the wing, generating lift.
Kyra Dempsey writes about shit she doesn't fully understand, doesn't seem interested in or capable of educating herself in basic physics and aeronautical concepts, and as evidenced by the writeup of this crash - gets basic facts wrong because she doesn't throughly research them enough. How she still gets this stuff wrong after years of doing it is bewildering.
I don't understand reddit's obsession with her, or why people keep linking to her articles here. If she was as good as everyone claimed, why is she basically unemployed?
If you want to read actual informed analysis of plane crashes, read aviation news outlets. AOPA, for example, does a lot of extensive writeups about crashes in general aviation, and it's written (and reviewed by) people who are experienced, knowledgeable pilots (and often, instructors.)
It seems as if were both engines to fail, either one prop would be feathered and the lift spoiler on that side extended, or neither prop would be feathered. Presumably the pilot could feather the props himself. It is not apparent whether this would extend both lift spoilers too, or if those were controlled separately.
If the original design lacks this it would likely have been embodied as a fleet wide modification/design change.
Electricity needs both positive and negative connections made between power source to equipment to work, but some old vehicles only ran the positive(sometimes only the negative) wires, and used the entire vehicle body the negative wire. Idea is that the electrons are gonna find its own way, the body's thick as it gets as a conductor, it's fine if you knew what you're doing, it saves lotta weight.
In this case, one of such connections to the body was secured with a screw, which could loosen from vibration, which `in fact` did. It instantly caused electricity to look for an alternative way, which was through propeller feathering switch and feathering relays, which caused the airplane to needlessly stop flying.
Screw gets more and more loose (alternatively, dirt or rust accumulates): less and less current flows through the contact point, more and more voltage is applied to relays. Generally, it is not enough to switch them, until one day another bump changes the position of wires, and ads some more resistance…
If something fails, it should fail as a whole. It's analogous to aborting the program on unexpected error versus ignoring it and hoping that everything else generally works OK.
When part of an electrical circuit starts to "float" like this - becoming no longer anchored to some global reference voltage (usually chassis ground is considered 0V) - the observed voltages in other parts of the system can take on really byzantine values.