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This is one of the videos of the crash: 727 Test Crash. It seems it was more of a hard landing without gears. Why wouldn't the experimenters have made it more of a really hard crash if they needed to study the effects of a crash on a plane? Would slamming down the plane really hard (maybe even nose down) given a more realistic scenario and more valuable data rather than making it soft?

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    $\begingroup$ "Everyone definitely dies, can we have another $50M for the next test?" $\endgroup$ – Stop Harming Monica Jun 2 '16 at 14:52
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    $\begingroup$ They aren't MythBusters, going for the biggest boom possible. They wanted to study a situation that was borderline survivable, and try to improve the survivability of it. $\endgroup$ – abelenky Jun 2 '16 at 14:52
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    $\begingroup$ They already know the results of a hard crash. They were interested in improving the outcomes for people in "softer" crashes. $\endgroup$ – JS. Jun 2 '16 at 16:24
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    $\begingroup$ Not at all. I love their big booms. Its just not applicable to aviation research. $\endgroup$ – abelenky Jun 3 '16 at 1:47
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    $\begingroup$ Reducing an airplane and its contents to pieces no larger than a pack of cigarettes may rank high on the "KEWL!" scale, but it ranks remarkably low on the "We learned something useful" scale. Put another way, the size of the fireball is inversely proportional to the amount of information gained. $\endgroup$ – Bob Jarvis - Reinstate Monica Jun 3 '16 at 17:31
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If the plane crashes with high vertical speed, the decelerations involved are so insanely huge that there is absolutely no way to make it survivable. That is well explained in Even after years of research, why are planes unable to keep passengers alive in case of a fiery crash?.

However in many cases the aircraft is still, at least partially, controllable, so a crash-landing can be made. And that is the case where survivability can be improved by careful design, so that is the case they were testing.

This is also relevant for accidents on landing where the aircraft simply does not have that much vertical speed. Together these scenarios cover more accident cases than the out of control scenario.

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    $\begingroup$ It makes sense that the biggest benefit in terms of lives saved per dollar spent would be taking a crash that was in a barely unsurvivable state to a barely survivable state. If I made a list of scenarios to gather data on, that would be at the top! $\endgroup$ – corsiKa Jun 2 '16 at 15:17
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    $\begingroup$ The Sioux City crash is a good example of a "softer" crash where increasing survivability would be a good idea. $\endgroup$ – Bob Stout Jun 2 '16 at 16:28
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    $\begingroup$ Well, theoretically, if everyone had an ejection seat... $\endgroup$ – Mehrdad Jun 3 '16 at 3:02
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    $\begingroup$ More people would die by failure/wrong activation of the seat than by actual crashes. And planes would have half the capacity and tickets would be several-fold more expensive. $\endgroup$ – Martin Argerami Jun 3 '16 at 5:46
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    $\begingroup$ @MartinArgerami perhaps that's it - decrease aviation-related deaths by pricing most people out of the market! $\endgroup$ – Robert Grant Jun 3 '16 at 12:00
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Because they wanted to analyse survivability, making the crash non survivable would have defeated the point.

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Would slamming down the plane really hard (maybe even nose down) given a more realistic scenario and more valuable data rather than making it soft?

Gone, everything is gone then. What are you going to try to improve from the outcome of such a test? Forget the real airplanes I have never been able to salvage a model aircraft that crashed nose down for any reason whatsoever.

I have on many times crash landed a model safely that had its landing gear malfunction and that's the practice that gives you valuable lessons for future landings. If you had an airplane without a landing gear and you wanted to study how can you improve chances of its survivability you would want to make a survivable attempt in the first place. You wouldn't want to crash it hard deliberately and then try to pick up pieces of the landing gear to find out what could you have done better.

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The basic principle of the airworthiness regulations is risk analysis. If you can demonstrate that a particular scenario has a sufficiently low risk of ever happening, you don't need to consider the consequences if it does happen. As an order of magnitude, "sufficiently low risk" means you might expect something to happen at most once during the full lifetime of all the aircraft of that type - which may be a period of 50 years or more for a popular aircraft type where thousands of aircraft were manufactured.

Landing a partly controllable aircraft with the gear up is more likely to happen than that "extremely rare" probability, so you need to demonstrate what the consequences are, hence the test. But there are thousands of possible but extremely unlikely scenarios that could (and most likely would) lead to the loss of the aircraft. For those scenarios, you design to reduce the risk of the event happening at all, not to deal with the consequences if it does happen.

A topical example: you don't try to design planes that will survive explosions in mid flight. Rather, you try to design systems to ensure that planes don't carry explosive material in the first place.

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    $\begingroup$ Actually, luggage containers do try to take explosive contents into account. It is also wise to take explosive engine failure into account. $\endgroup$ – amI Jun 2 '16 at 19:48
  • $\begingroup$ But this test had nothing to do with airworthiness regulations. $\endgroup$ – David Richerby Jun 5 '16 at 20:39

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