6 ms·

Designed to Crash: the story of Antonov An-28 HA-LAJ and its demise

108 points by sklargh 2y ago

ogurechny 2y ago
It is important to read between the lines. It took 6 years for extension of previous model to turn into production design. Then it was dropped on comrades from a fellow Socialist country in a typical fashion of “intensifying economic development” (i.e. investing in specific industries in exchange for loyalty). Then it took 6 years again for actual planes to come out of factory, and become certified. And it wasn't a Concorde. The project was really low on the list either on the demanding side, or on the supplying side, or on both sides (remember that in “planned” — single big corp — economy, you might be assigned a useless work if it has been decided once, and got into the papers).
Daviey 2y ago
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.
klaussilveira 2y ago
"Designed to Crash" reminded me of this: https://devblogs.microsoft.com/oldnewthing/20180228-00/?p=98125 https://devblogs.microsoft.com/oldnewthing/20180228-00/?p=98...
angiosperm 2y ago
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.
- foobar1962 2y ago
  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.
- nvy 2y ago
  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.
  - p_l 2y ago
    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.
    - nvy 2y ago
      Indeed, though with lock wire there's usually another anchor point you wire it to, so that the nut can't back off.
      - topspin 2y ago
        > there's usually another anchor point The original design supposedly had two screws, but was manufactured with one. When you have two fasteners (typically nuts, as opposed to screws...) they can be mutually secured with lock wire. That is very common. It is decidedly not common to lock wire electrical terminal fasteners in aircraft, or anywhere else for that matter. Typically lock washers and self-locking nuts are used. I'm not a certified aircraft electrical system designer, so I can't say definitively, but there are some pretty obvious reasons: First, these are typically small fasteners: lock wiring is hard enough on large fasteners. Lock wiring tiny little nuts with small gauge wire approaches the unreasonable. Second, lock wire is not insulated, so you would end up with a rats nest of exposed conductors leading to your terminals. Clearly unworkable. I suppose someone, somewhere has done something that involved insulated lock wire, but I've never seen it, wouldn't know where to buy it, and can't imagine how you'd employ it without abrading the insulation. The problem here is the shared ground terminal. Stacking wires on ground terminals is common, stupid and a plague on electrical systems. The clamping force on a wire's ring terminal (and, thus, it's contact resistance, mechanical friction, ability to inhibit corrosion, etc.) is distributed among all of the ring terminals stacked on a stud, screw, whatever. Stack just one new terminal with another and you've cut the clamping force on both in half. Half. You are now the "engineer" and when someone dies as a result of your field engineered electrical system it's your fault.
MadnessASAP 2y ago
> 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.
- foobar1962 2y ago
  I picked this up too: a minor error in an excellent article.
  - KennyBlanken 2y ago
    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.
knodi123 2y ago
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.
- KennyBlanken 2y ago
  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. ...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-green 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.pdf 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.)
jaredhallen 2y ago
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.
- nippoo 2y ago
  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)
robertclaus 2y ago
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?
- ogurechny 2y ago
  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.
- xenadu02 2y ago
  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.
- lanthade 2y ago
  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.
- rramadass 2y ago
  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.
gorgoiler 2y ago
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.)
- Daviey 2y ago
  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.
- plantain 2y ago
  10-12,000ft is generally accepted as negligible impact on cognitive function. Only above that are pilots usually on oxygen.
  - EdwardDiego 2y ago
    That's approximately 3000 - 4000m. You're definitely going to feel a difference going from ASL to 4000m in minutes.
rramadass 2y ago
Enjoyable article. I love debugging/troubleshooting articles like this (loved the TV series "Air Crash Investigation") and always marvel at how much layers-upon-layers of complexity exists in such systems and yet everything works perfectly well most of the time. It is a testament to the scientific prowess, logical layering, technological realization and overall ingenuity of the people involved in designing and implementing the system. Putting on my conspiracy tinfoil hat, i don't think it was bad design/error/accidental that the production introduced this single point of grounding failure even though the original designs had explicitly called out for at least two grounding points. Why? Because it is the easiest method to get rid of "somebody/somebodies" and pass it off as an accident i.e. charter this plane for them, have your assassin loosen the screw before takeoff and let the vibrations in mid-flight do the rest.
- MadnessASAP 2y ago
  That theory fails on 2 points. One is as this crash points out, it's hardly a reliable way of killing someone. The other is that it would be easier to just cut the wire, and it's just as easy to cut 2 wires instead of 1.
  - rramadass 2y ago
    Nah; Cutting the wires will not even get this plane off the ground. As for the first objection, this crash was exceptional in that the pilots seemed to have been quite skilled to have managed the landing the way they did. This is a very low probability event and luck seemed to have been on their side which will not always be the case. There is always some indeterminacy involved in faking an accident and that cannot be helped. But you can certainly stack the odds in your favour. This line of thinking is motivated by what has been going on with Boeing crashes, Boeing whistleblowers dying left and right and of course the most recent chopper crash involving the death of the Iranian President and the consequent swirling theories.
    - MadnessASAP 2y ago
      The plane could absolutely get off the ground, especially if the flaps were set before engine start or on the previous landing. Further to my point, the ground point was in an inaccessible location. Hence why it was able to come loose without being noticed, making it even more unlikely to be tampered with. In addition, it's not like the Soviet Union needed to engineer convenient accidents to kill undesirable people, they were more then happy to do it openly. Finally as an aside, as an actual aircraft mechanic I have some suggestions about where you can put your thoughts on my line of thinking.

108 points by sklargh 2y ago

It is important to read between the lines. It took 6 years for extension of previous model to turn into production design. Then it was dropped on comrades from a fellow Socialist country in a typical fashion of “intensifying economic development” (i.e. investing in specific industries in exchange for loyalty). Then it took 6 years again for actual planes to come out of factory, and become certified. And it wasn't a Concorde. The project was really low on the list either on the demanding side, or on the supplying side, or on both sides (remember that in “planned” — single big corp — economy, you might be assigned a useless work if it has been decided once, and got into the papers).

Daviey 2y ago

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.

klaussilveira 2y ago

"Designed to Crash" reminded me of this: https://devblogs.microsoft.com/oldnewthing/20180228-00/?p=98125 https://devblogs.microsoft.com/oldnewthing/20180228-00/?p=98...

angiosperm 2y ago

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.

foobar1962 2y ago
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.
nvy 2y ago
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.
- p_l 2y ago
  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.
  - nvy 2y ago
    Indeed, though with lock wire there's usually another anchor point you wire it to, so that the nut can't back off.
    - topspin 2y ago
      > there's usually another anchor point The original design supposedly had two screws, but was manufactured with one. When you have two fasteners (typically nuts, as opposed to screws...) they can be mutually secured with lock wire. That is very common. It is decidedly not common to lock wire electrical terminal fasteners in aircraft, or anywhere else for that matter. Typically lock washers and self-locking nuts are used. I'm not a certified aircraft electrical system designer, so I can't say definitively, but there are some pretty obvious reasons: First, these are typically small fasteners: lock wiring is hard enough on large fasteners. Lock wiring tiny little nuts with small gauge wire approaches the unreasonable. Second, lock wire is not insulated, so you would end up with a rats nest of exposed conductors leading to your terminals. Clearly unworkable. I suppose someone, somewhere has done something that involved insulated lock wire, but I've never seen it, wouldn't know where to buy it, and can't imagine how you'd employ it without abrading the insulation. The problem here is the shared ground terminal. Stacking wires on ground terminals is common, stupid and a plague on electrical systems. The clamping force on a wire's ring terminal (and, thus, it's contact resistance, mechanical friction, ability to inhibit corrosion, etc.) is distributed among all of the ring terminals stacked on a stud, screw, whatever. Stack just one new terminal with another and you've cut the clamping force on both in half. Half. You are now the "engineer" and when someone dies as a result of your field engineered electrical system it's your fault.

MadnessASAP 2y ago

> 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.

foobar1962 2y ago
I picked this up too: a minor error in an excellent article.
- KennyBlanken 2y ago
  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.

knodi123 2y ago

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.

KennyBlanken 2y ago
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. ...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-green 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.pdf 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.)

jaredhallen 2y ago

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.

nippoo 2y ago
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)

robertclaus 2y ago

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?

ogurechny 2y ago
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.
xenadu02 2y ago
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.
lanthade 2y ago
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.
rramadass 2y ago
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.

gorgoiler 2y ago

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.)

Daviey 2y ago
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.
plantain 2y ago
10-12,000ft is generally accepted as negligible impact on cognitive function. Only above that are pilots usually on oxygen.
- EdwardDiego 2y ago
  That's approximately 3000 - 4000m. You're definitely going to feel a difference going from ASL to 4000m in minutes.

rramadass 2y ago

Enjoyable article. I love debugging/troubleshooting articles like this (loved the TV series "Air Crash Investigation") and always marvel at how much layers-upon-layers of complexity exists in such systems and yet everything works perfectly well most of the time. It is a testament to the scientific prowess, logical layering, technological realization and overall ingenuity of the people involved in designing and implementing the system. Putting on my conspiracy tinfoil hat, i don't think it was bad design/error/accidental that the production introduced this single point of grounding failure even though the original designs had explicitly called out for at least two grounding points. Why? Because it is the easiest method to get rid of "somebody/somebodies" and pass it off as an accident i.e. charter this plane for them, have your assassin loosen the screw before takeoff and let the vibrations in mid-flight do the rest.

MadnessASAP 2y ago
That theory fails on 2 points. One is as this crash points out, it's hardly a reliable way of killing someone. The other is that it would be easier to just cut the wire, and it's just as easy to cut 2 wires instead of 1.
- rramadass 2y ago
  Nah; Cutting the wires will not even get this plane off the ground. As for the first objection, this crash was exceptional in that the pilots seemed to have been quite skilled to have managed the landing the way they did. This is a very low probability event and luck seemed to have been on their side which will not always be the case. There is always some indeterminacy involved in faking an accident and that cannot be helped. But you can certainly stack the odds in your favour. This line of thinking is motivated by what has been going on with Boeing crashes, Boeing whistleblowers dying left and right and of course the most recent chopper crash involving the death of the Iranian President and the consequent swirling theories.
  - MadnessASAP 2y ago
    The plane could absolutely get off the ground, especially if the flaps were set before engine start or on the previous landing. Further to my point, the ground point was in an inaccessible location. Hence why it was able to come loose without being noticed, making it even more unlikely to be tampered with. In addition, it's not like the Soviet Union needed to engineer convenient accidents to kill undesirable people, they were more then happy to do it openly. Finally as an aside, as an actual aircraft mechanic I have some suggestions about where you can put your thoughts on my line of thinking.