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A jet blast deflector (JBD) or blast fence is a safety device that redirects the high energy exhaust from a jet engine to prevent property damage and injury.

Regarding the incident on July 13, 2017 at Princess Juliana Airport, I see no jet blast deflector installed. Is there any technical reason that prevents installation of such a safety device?

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    $\begingroup$ The airport at Gibraltar[1] has a road crossing the runway, which gets closed whenever a plane is landing. The road and the beach should be closed to avoid such accidents. [1] en.wikipedia.org/wiki/Gibraltar_International_Airport $\endgroup$ – Dohn Joe Jul 14 '17 at 13:25
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    $\begingroup$ This person's death is tragic, and probably will cause the whole jet-blast area beach/party scene to be shut down. On the other hand, the free-will dude inside me says that these people are out there because they choose to be, and if they want to assume a negligible-but-potentially-fatal risk, so be it. $\endgroup$ – Bob Jarvis Jul 14 '17 at 19:17
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    $\begingroup$ They don't have enough warning signs. They need enough signs to deflect the jet blast! $\endgroup$ – Harper Jul 14 '17 at 22:03
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    $\begingroup$ @BobJarvis Is it really that tragic when someone dies because they did something stupid that there was a warning sign about? $\endgroup$ – immibis Jul 15 '17 at 11:37
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    $\begingroup$ @immibis Or simply pad it.. which would arrest their motion. We know how to do that so baseball outfielders and gymnasts don't get seriously hurt when they run into a wall. It is a bit irritating that some initial headlines (not the one the OP linked) said that the jet blast itself killed the unfortunate woman, and not cracking her head on something hard. $\endgroup$ – Spehro Pefhany Jul 15 '17 at 11:53
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An immobile jet blast deflector could not be built far enough away from the runway end to be safely clear of the landing path. Large airplanes like 747s must touch down pretty close to the near end of the runway, which is right at the edge of the beach, a blast deflector would be a serious hazard if an airplane came in a bit too low. Here's what I'm talking about: enter image description here

A static deflector would be extremely close to the path of the landing gear.

It could theoretically be possible to install a retractable one, however sand does not make a good building surface and therefore it would be real engineering challenge.

It seems much more likely that the authorities, if they do anything, will install more fencing or other barriers to deter people from getting so close rather than install a blast deflector. This would be cheaper and achieve the same effect.

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    $\begingroup$ While I feel extremely bad for the woman and her family for her death, I hope, unlike what would happen most other places, the authorities point to the LARGE signs warning of the danger, including the possibility of death, and get on with getting on. $\endgroup$ – CGCampbell Jul 13 '17 at 20:13
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    $\begingroup$ Strongly agree with the sentiment of @CGCampbell. I first saw a video of this practice a few years ago and my reaction was half "Those people are nuts" and half "I wanna try!". $\endgroup$ – bclarkreston Jul 13 '17 at 22:15
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    $\begingroup$ Agreed, @bclarkreston. If consenting adults want to risk their life doing something that doesn't put other people's physical / mental health in danger, they should in general be allowed to. This seems to me a lot like people putting on wing-suits and jumping off cliffs to fly though narrow valleys. People die doing that, but other people keep doing it. Except maybe this is less obviously dangerous, so people don't understand the risk? Maybe mountain climbing (not Everest, just smaller safe mountains) would be a better analogy. $\endgroup$ – Peter Cordes Jul 14 '17 at 1:41
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    $\begingroup$ @CGCampbell The authorities have been warned after an incident around 2012 that the signs were inadequate safety measures since "nobody followed the signs' advice anyway". The court agreed. So, it's likely they'll have to implement additional measures this time. $\endgroup$ – Mast Jul 14 '17 at 10:39
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    $\begingroup$ Great...another victory for the nanny state. $\endgroup$ – bclarkreston Jul 14 '17 at 13:58
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To answer your question directly, the only technical limitation would be the height of the blast deflector due to landing aircraft, but otherwise there is no technical limitation. Landing aircraft have to land beyond the displaced threshold which is indicated by the arrows. The beginning of the runway is located 500 ft beyond the fence (see google maps photo below), so a 6 to 8 ft tall blast deflector at the fence would pose little risk to landing aircraft, while at the same time deflecting the jet blast from the departing aircraft that are allowed to use the displaced threshold for takeoffs.

enter image description here

They could build a modified jet blast deflector that is no higher than the chain linked fence that separates the airport from the public beach, it would reduce some of the blast that is received at ground level where people are standing. They could make a deflector that is a little shorter than these:

enter image description here enter image description here

However, this is a pretty big tourist attraction, and there are plenty of warning signs. Its no different than people going on vacations to Yosemite, every year someone slips and falls to their death while walking on a slippery trail to see one of the water falls.

enter image description here

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    $\begingroup$ I believe your second sentence is the primary reason: it's not just a tourist attraction, it's a big one for them, and apparently a reason that some tourists specifically go there - the planes get real close to the beach. Sadly, the rationale behind keeping people away from the end of runways is now more evident. $\endgroup$ – tj1000 Jul 14 '17 at 15:09
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    $\begingroup$ Yup. It is no different than a roller coaster. Roller coasters give riders a thrill, and once in a while someone gets killed. On this island the signs clearly state the danger so each person is exposing themselves to a known risk, just like roller coaster riders. I say, leave it, as is. $\endgroup$ – Devil07 Jul 14 '17 at 15:23
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    $\begingroup$ But consider the difference between landing gear hitting a chain link fence, and hitting a solid blast deflector. $\endgroup$ – jamesqf Jul 14 '17 at 18:08
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    $\begingroup$ True, but landing gear hitting the chain link fence is not reported as problem at this airport, and blast deflectors don't have to be built of solid material like concrete, often times you will see deflectors at airports made of thin corrugated sheet metal. Still will cause damage if struck, but can be engineer to give way if hit in direction of landing. Additionally, they could build a retractable one like is used on aircraft carriers and only deploy it for take-offs when jet blast is most intense. $\endgroup$ – Devil07 Jul 14 '17 at 19:29
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    $\begingroup$ @tj1000 - Precisely this. They could, but they don't want to. The occasional tourist death is the price you pay for thousands of pounds a day of tourist money. The fenceline is a major draw for the area. $\endgroup$ – Richard Jul 15 '17 at 11:23
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One also needs to remember it was not the jet blast that killed this unfortunate lady (condolences to family), but rather striking the rather awkward and hard retaining wall behind her.

Similar incident...

Although a small deflection fence would not be a bad idea, and could be built to be no higher than the current chain link fence, the least they could do is remove the hard wall that is the real killer.

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    $\begingroup$ The question asked if "any technical reason prevents" building a blast deflector. This answer doesn't look at technical reasons. Instead, it is discussion about an accident. A bit off-topic. $\endgroup$ – Jim DeLaHunt Jul 14 '17 at 16:59
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    $\begingroup$ @JimDeLaHunt as I said a small one is plausible.. it would need to be no higher than the current fence. $\endgroup$ – Trevor_G Jul 14 '17 at 17:07
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    $\begingroup$ @JimDeLaHunt: Classic X-Y problem. This answer is on topic. $\endgroup$ – dotancohen Jul 16 '17 at 7:38

protected by Community Jul 14 '17 at 22:01

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