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Altitude offest in the mountains

 


BobxMarley  (B License)

Jan 15, 2014, 1:58 PM
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Altitude offest in the mountains Can't Post

I just watched a video on youtube that shows a free fly group almost free fall into a mountaintop. From first glance, my first assumption is that they didn't spot correctly. However, someone in the comments suggested they should have offset their altimeters to the highest surrounding peak elevation as a precautionary measure. This sounded a bit weird to me so I figured I'd ask the forums to get clarification. In you're examination, what went wrong with this dive.

Link: https://www.youtube.com/watch?v=AiGdqPfztsc


(This post was edited by BobxMarley on Jan 15, 2014, 2:26 PM)


pchapman  (D 1014)

Jan 15, 2014, 3:01 PM
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Re: [BobxMarley] Altitude offest in the mountains [In reply to] Can't Post

That was a popular video for discussion on dz.com a few years back, the classic one of some confusion between pilot and jumpers about jump run, with the green light turning on early, before crossing a Swiss ridge that defined the edge of a deep valley. ... But I haven't found the thread again. Someone will.

Moral was: Look before you leap, especially if jumprun takes you over tall mountains.

And you wouldn't adjust your altis (unless you were planning to land at or swoop the top of the mountain or something).

I have heard of people making slight adjustments to their AADs, when at an airport with slightly higher terrain around. But you aren't going to set it at +10,000' for mountains...


(This post was edited by pchapman on Jan 15, 2014, 3:02 PM)


BobxMarley  (B License)

Jan 15, 2014, 3:29 PM
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Re: [pchapman] Altitude offest in the mountains [In reply to] Can't Post

Ok. That's what I thought. It didn't make sense to me to offset your alti in that situation. My inital reaction was "should have checked your spot." However, I'm fresh off an A license and never jumped in those conditions, so I wanted to make sure my assumption was correct.

Thanks Pchapman!


piisfish

Jan 16, 2014, 1:12 AM
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Re: [pchapman] Altitude offest in the mountains [In reply to] Can't Post

pchapman wrote:
Moral was: Look before you leap, especially if jumprun takes you over tall mountains.
other morals were :
-know who is doing what in your plane, specially your group and the groups before and after yours
-don't be a green light lemming
-err on the side of caution when going to CarnageBoogie


Pobrause

Jan 16, 2014, 12:41 PM
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Re: [BobxMarley] Altitude offest in the mountains [In reply to] Can't Post

It has been discussed before... a lot...

What went wrong?
Actually they had planned a mountain swoop but changed their plans because of changing wind conditiones.
But nobody told the pilot the plan got changed so he dropped them off for a mountainswoop.

Lessons learned, as you can read in the video description.
Spot!!!

offsetting your altimeter does make sense, when the planned landing area isn't on the same altitude from where you started.


bluebird932

Jan 16, 2014, 2:09 PM
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Re: [BobxMarley] Altitude offest in the mountains [In reply to] Can't Post

Does anyone know why altimeters and AADs dont work together with GPS ?


Southern_Man  (C License)

Jan 16, 2014, 3:39 PM
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Re: [bluebird932] Altitude offest in the mountains [In reply to] Can't Post

bluebird932 wrote:
Does anyone know why altimeters and AADs dont work together with GPS ?

GPS is fairly poor at getting an accurate altitude reading for technical reasons: http://gpsinformation.net/main/altitude.htm

This can be corrected somewhat with higher cost (and often larger) receivers but this is not a practical fit for altimeters and AADs. They will remain less accurate for altitude than for horizontal distance.

I'm sure there are people who can offer you a more technical explanation but GPS is simply not the right tool for the job in this case.


Blis  (A License)

Jan 17, 2014, 1:20 AM
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Re: [Southern_Man] Altitude offest in the mountains [In reply to] Can't Post

Southern_Man wrote:
bluebird932 wrote:
Does anyone know why altimeters and AADs dont work together with GPS ?

GPS is fairly poor at getting an accurate altitude reading for technical reasons: http://gpsinformation.net/main/altitude.htm

This can be corrected somewhat with higher cost (and often larger) receivers but this is not a practical fit for altimeters and AADs. They will remain less accurate for altitude than for horizontal distance.

I'm sure there are people who can offer you a more technical explanation but GPS is simply not the right tool for the job in this case.

Most gps devices use rather slow refresh rate, perhaps once a second or two. Second thing to take note is that normal gps devices are accurate only to -+20m or so, with bad lock it is even worse. For greater accuracy you would need a big ass receiver and also pay for a correction signal to be sent to your device..

So, those are the reasons why they dont go well together..


pchapman  (D 1014)

Jan 17, 2014, 5:03 AM
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Re: [bluebird932] Altitude offest in the mountains [In reply to] Can't Post

bluebird932 wrote:
Does anyone know why altimeters and AADs dont work together with GPS ?

Just too big of a project for the market, given that most people jump over relatively flat terrain. So the need hasn't been there.

It isn't that it wouldn't occasionally be useful. Some DZ's have some minor hill or slope nearby, and there is the issue whether to adjust the AAD upwards for all jumps at the DZ or accept that you might be screwed if you need an AAD on a jumprun over that 300 ft higher ground.

Not quite as tough as using GPS to try to sense an accurate altitude for firing purposes, would be to use it only to determine 2-D position over the ground, checking a terrain database for maximum ground level within grid squares of whatever resolution is available. Then it becomes like some TAWS system for aircraft. Instead of the AAD deciding to fire 800 or whatever feet above the takeoff point, it would be deciding to fire 800 ft above the maximum terrain altitude in the grid square. I have no idea how the resolution of GPS terrain databases is these days, although it is probably pretty decent. Obviously you don't want a crappy database where the AAD fires when one jumps a safe distance off to the side of a hill.

Who would most benefit from some GPS integrated AAD? If you were some special forces dude jumping at night through clouds to some hillside position in Afghanistan, you'd probably already have a nice GPS terrain display and maybe suggested flight path commands to start with. (After all, there are already plenty of systems for sending cargo down under parachutes with their own GPS and algorithms to steer themselves to landing.) In such terrain conditions, having a GPS enabled AAD might be more useful than just setting it at X thousand feet above sea level in barometric height.

But you'd probably want money in military style quantities to develop a reliable GPS enabled AAD, even if the concept is simple.


piisfish

Jan 17, 2014, 5:13 AM
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Re: [bluebird932] Altitude offest in the mountains [In reply to] Can't Post

bluebird932 wrote:
Does anyone know why altimeters and AADs dont work together with GPS ?
ask a couple of pilots who were dropping by GPS in Italy when the US planes were leaving for Irak, they can tell you very well LaughLaughLaughLaugh


Doug_Davis  (B 40488)

Jan 17, 2014, 9:23 PM
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Re: [BobxMarley] Altitude offest in the mountains [In reply to] Can't Post

BobxMarley wrote:
In you're examination, what went wrong with this dive.

Seems like they caught a case of dumbass disease, ie not spotting and no altitude awareness.


riggerrob  (D 14840)

Jan 18, 2014, 3:06 PM
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Re: [bluebird932] Altitude offest in the mountains [In reply to] Can't Post

bluebird932 wrote:
Does anyone know why altimeters and AADs dont work together with GPS ?

................................................................................

Not this year ... but in the near future, they will develop GPS-linked AADs that will save even the stupid.


bluebird932

Jan 19, 2014, 4:17 AM
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Re: [BobxMarley] Altitude offest in the mountains [In reply to] Can't Post

Ok but today some smartphones have barometer and GPS working together.

http://www.popsci.com/...ne-have-barometer-it

So for smartphones it's not dangerous and they have it upside down

"the barometer is more likely than not intended to be a source of supplemental data for the GPS sensor, adding altitude measurements for increased accuracy"

There are even apps for skydivers, I think it's just for fun and we shouldn't take it seriously.

https://play.google.com/...om.platypii.baseline

I guess it also depend what software you have. Sometimes when I'm working in metal container and only one window is open my smartphone shows with mistake that I'm about 200 m somewhere else. I think it's because it has only one shoot from one satelite. For 2-D satnav we don't need many satelites because they also know that earth has spherical shape. Of course for jumps in the mountains that's not enough and we need more satelites and also some better offset from terrain databese. I'm not expert but I thouhgt about software that would turn on it self only if it has good shoot from few satelites together. I think it's not pain if we could see 2 informations one from barometer and one from GPS. But the main question is about sizes, costs and all the rest


(This post was edited by bluebird932 on Jan 19, 2014, 5:14 AM)


ChrisD  (No License)

Jan 19, 2014, 10:16 AM
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Re: [BobxMarley] Altitude offest in the mountains [In reply to] Can't Post

I already know that they were freeflying, but what was wrong with pulling high once they saw they weren't where they were supposed to be? I can count on two hands the number of times while in freefall, after noticing we were way off, pulling high gave us time to fly elsewhere to a safe landing area.

This kind of begs the question about freeflying responsibility and spotting? I mean if your going out the door and you loose all sense of direction and are not watching the ground whatsoever you think you would be a little more careful especially in close proximity to ground hazards or a tight landing area???

I'm having a bit of a hard time understanding what exactly your asking here? Cause on one hand you admit by stating that there are significant hazards to NOT looking where your going and then in the same sentence propose a "Back Up Plan." Seems to me that the "precautionary measure" should have been to know where you are before getting out the door. I would say that not only are you correct in your first assumption but you are spot on about the weird'ness of overcomplicating something as simple as the phrase : "Look Before You Leap." Good for you to seek clarification! And good for you for indirectly pointing out that there is no substitute for altitude awareness.

C


erdnarob  (D 364)

Feb 15, 2014, 1:37 PM
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Re: [BobxMarley] Altitude offest in the mountains [In reply to] Can't Post

The guy seems to have landed with his reserve. If so, has the AAD activated the opening ?


mistercwood  (Student)

Feb 15, 2014, 4:41 PM
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Re: [erdnarob] Altitude offest in the mountains [In reply to] Can't Post

erdnarob wrote:
The guy seems to have landed with his reserve. If so, has the AAD activated the opening ?

Go through the video description - they had both audibles and AAD's, but neither went off because they'd screwed up the spot and were well above intended activation altitude for either. Also it was a main deployment, though the guy recognises in hindsight that this was out of reflex and that going silver would've been smarter.



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