GPS Nearest Airport feature

"Bravo8500" wrote in message
ups.com...
They all have nearest, but I've never seen one with steepest descent.
It may not be so trivial to provide steepest descent with no
obstructions on the path.

And if you take wind into account then the aircraft may well glide "more
steeply" towards an airport that's not the initial "first pick" of the GPS.

Perhaps a better option is to have the current glide ratios and glide ration
to target get up on an 'emergency options' configured page of the GPS?

Slightly OT, but what I would really LOVE to see is a GPS selectable field
that gives me a bearing FROM a reference, instead of TO one.

ie being able to see at a glance what radial you are crossing/tracking
without having to do the 180 degree mental conversion.

Hopefully it wouldn't pick an airport above you!

Chris W wrote:

It tells me that there is an airport 5 knots to my left and
10 knots to my right. What it didn't tell me is the runway to the left
was at an elevation of 10,000ft and the runway to the right was at an
elevation of 5,000ft.

You sure? My old LORAN used to provide field elevations, radio frequencies, and
other data for the airports listed in the "nearest" feature. I'd be surprised to
learn aviation GPS units don't do as well.

My LORAN didn't provide the glide ratio data you want, though.

George Patterson
I prefer Heaven for climate but Hell for company.

"Robert M. Gary" wrote:

Hopefully it wouldn't pick an airport above you!

The "nearest airport" feature of GPS and LORAN units will happily list airports
above you. They have no reason to exclude them. They don't know the rubber band
just broke.

What you want is a "gimme all the airports I can glide to" feature; not "nearest
airport".

George Patterson
I prefer Heaven for climate but Hell for company.

"Cockpit Colin" wrote, "... what I would really LOVE to see is a GPS
selectable field that gives me a bearing FROM a reference, instead of TO
one."

The Garmin GPSMAP 296 does that -- at least for the nearest airport, VOR,
NDB, Intersection,City, or Waypoint (your choice). I have mine set to
nearest VOR. Right now, for example, it says "From Jeffco VOR (BJC): 8.9 nm
S 162°m." This makes it a snap to report position.

Jon

"Bravo8500" wrote in message
ups.com...
They all have nearest, but I've never seen one with steepest descent.

Huh? The steepest descent is the nearest airport. Even in mountainous
terrain, it's incredibly rare to find an airport uphill.

It may not be so trivial to provide steepest descent with no
obstructions on the path.

The original poster didn't stipulate "with no obstructions on the path".

I don't think the original question was intended to be nearly as
sophisticated and complicated as you seem to be making it.

Pete

"Chris W" wrote in message
newsu6Vd.84$Ci7.63@lakeread07...
I guess I wasn't very clear in my first post.

Nope.

I know they all have the nearest airport feature and give runway length.
Lets say that I am flying along at 14,000ft and the engine starts doing
bad things. Since I was stupid and wasn't paying attention, I ask my GPS
where the nearest airport is. It tells me that there is an airport 5
knots to my left and 10 knots to my right.

You mean "nautical miles"? "Knots" is a measure of speed, not distance.

What it didn't tell me is the runway to the left was at an elevation of
10,000ft and the runway to the right was at an elevation of 5,000ft.

There aren't many airports around at 10,000'. And in mountainous terrain,
airports are usually (though not always, granted) found in the valley
floors. Terrain between you and a lower-altitude airport is probably more
likely to be a problem than a significant difference in altitude between two
choices.

Lets make the math simple and pretend there are 6000ft in a nautical mile.
To make the airport on the left you would have to maintain a glide ratio
of 7.5 to 1. To make the airport on the right you would need to maintain
a glide ratio of about 6.7 to.

So you actually want the least steep descent, not the steepest descent.

Obviously the runway to the right gives you more room to maneuver. This
is of course assuming there are no obstructions in your path. As another
poster pointed out, if you are flying over the rockies you better always
have a plan on where you are going to go if your loose power, you are just
asking for something bad to happen.

Now, you've written "loose" twice. It's "lose". I only "loose power"
during takeoffs and climbs.

Even from a single simulated flight over Colorado, it's pretty clear to
me, careful planing should go into any such flight in real life.

Indeed. That said, as I mentioned, there's at least one product out there
that displays 3D volumes (cones) to aid you in the exact decision making
you're asking about. Since your position relative to the cone depends not
only on your lateral distance, but your altitude above the airport as well,
it gives you the information you're thinking of. (Actually, while the data
is 3D, I believe it simply shows you a 2D cross-section of the cone on your
top-down map display)

That particular feature is not common though (only on one GPS navigation
unit that I'm aware of). I'm honestly not convinced it's really all that
necessary or useful except in very rare instances.

Pete

"Cockpit Colin" wrote in message
...
Slightly OT, but what I would really LOVE to see is a GPS selectable field
that gives me a bearing FROM a reference, instead of TO one.

My Loran will do that. It would surprise me if GPS units didn't generally
allow that.

Gawd Dang - and I've got a 296 as well!

Thanks for the heads up - I'll have to check it out. To be honest, I very
seldom use the 'nearest' function - I mostly just configue the first page
with timers / gps state - the 2nd with enroute infor - and the 3rd for
approach related stuff. Would still be nice to be able to have something
like a BGF (BearingG From) field though.

Cheers,

CC


"Jon Woellhaf" wrote in message
...
"Cockpit Colin" wrote, "... what I would really LOVE to see is a GPS
selectable field that gives me a bearing FROM a reference, instead of TO
one."

The Garmin GPSMAP 296 does that -- at least for the nearest airport, VOR,
NDB, Intersection,City, or Waypoint (your choice). I have mine set to
nearest VOR. Right now, for example, it says "From Jeffco VOR (BJC): 8.9
nm
S 162°m." This makes it a snap to report position.

Jon