What I learned today

Salty

Salty

Touchdown! Greaser!
Joined
Dec 21, 2016
Messages
13,415
Location
FL
Display Name
Display name:
Salty
Published runway lengths are not threshold to threshold as I assumed. They include every foot of level ground without an obstruction. Here’s one example, published 3700 foot runway. I checked a half dozen others and found the same results. I’ll be using google earth in the future to validate any high altitude, short field departures in the future.

there’s a fence on one side and a ditch on the other, but even the grass is included in the published runway length. Even though there are power lines and trees on one side forcing the longer offset.

1682129D-F9F5-4AAC-A4FE-A3411AD86530.png 3B51027A-07F0-4849-8168-89855AAE3984.png
 
Google is not nearly as accurate as you may think either. Runway lengths should be end of pavement, unless it is one of those weird runways that are partial grass/pavement. That being said, I don't know how accurate small GA airports are surveyed. I know the larger airports that receive federal funding have to be surveyed accurate.
 
midwestpa24 said:
Google is not nearly as accurate as you may think either. Runway lengths should be end of pavement, unless it is one of those weird runways that are partial grass/pavement. That being said, I don't know how accurate small GA airports are surveyed. I know the larger airports that receive federal funding have to be surveyed accurate.
Click to expand...
So far google earth has been pretty darn close. If there are lights on the end of the runway, that’s an obstruction and the numbers are pretty close to threshold to threshold, but smaller airports with lights to the side grass seems to count as long as it’s flat and unobstructed.
 
I don't think I'd trust Google Earth for measurements.

It doesn't even know where I'm standing within 100’.

Consistently puts me in my neighbor's house when I'm out in my yard..
.
 
Salty, on the hottest Florida day there's ever been you can take off easy in 3K feet. Heck, you can take off easy in 2K feet, even with those obstacles. I landed and took off a 2200 foot strip on a 98 degree day, and I'm the. most ham-fisted pilot on the board. I honestly think you're over thinking this.
 
CharlieD3 said:
I don't think I'd trust Google Earth for measurements.

It doesn't even know where I'm standing within 100’.

Consistently puts me in my neighbor's house when I'm out in my yard..
.
Click to expand...
Not using GPS, but the measurement tool is extremely accurate.
 
steingar said:
Salty, on the hottest Florida day there's ever been you can take off easy in 3K feet. Heck, you can take off easy in 2K feet, even with those obstacles. I landed and took off a 2200 foot strip on a 98 degree day, and I'm the. most ham-fisted pilot on the board. I honestly think you're over thinking this.
Click to expand...
I'm not talking about when in Florida. I use my airplane to fly other places. I think it's important to know that threshold to threshold is only 2800 feet when the published number is 3700, and 100 feet of that is grass.
 
The grass distance looks like a rounding error, not deliberately counted. Not sure where you are getting a 900 foot delta.
 
dmspilot said:
The grass distance looks like a rounding error, not deliberately counted. Not sure where you are getting a 900 foot delta.
Click to expand...
Threshold to threshold. Not pavement. Maybe I was the only person in the world that assumed runway length would include only the "runway" and not the offsets, since offsets are there due to obstacle clearance needs. I doubt I was the only one with this misunderstanding.
 
Salty said:
Maybe I was the only person in the world that assumed runway length would include only the "runway"
Click to expand...

It does. The displaced threshold is part of the runway. It is only unusable for touchdown.

Displaced Threshold. A displaced threshold is a threshold located at a point on the runway other than the designated beginning of the runway. Displacement of a threshold reduces the length of runway available for landings. The portion of runway behind a displaced threshold is available for takeoffs in either direction and landings from the opposite direction.
 
Salty said:
I'm not talking about when in Florida. I use my airplane to fly other places. I think it's important to know that threshold to threshold is only 2800 feet when the published number is 3700, and 100 feet of that is grass.
Click to expand...
Salty, that's why you plan conservatively. If the book says you can take off in 1500 feet you make certain you have more to deal with. If the strip is starting to bump up into the edge of what you feel you can do maybe you should give it a miss. I would worry less about a rounding error in the runway and a bit more about the fact that my aircraft is a half century old and is flown by a rank amateur. The numbers in the book were put there by a test pilot in a brand new airplane. When I landed the 2200 foot strip I came on on the side that didn't have an obstacle. Took off that way too, even with a small tailwind. I'm fairly certain I could come in the other way (which is occluded) but I'd want some wind on my nose before I did.
 
Regarding the measurement tool in Google Maps: Runway is 75ft wide, here's what I get for the tool. Pretty accurate IMO.

CZVLFtm.png
 
I get 3,626 from end to end on the pavement which seems a bit short of the published 3700. Perhaps the airport manager is an optimist?
 
Published runway length: 3740
Google earth: 3741

I believe the google earth measurement tool is more accurate than the one on google maps.
 
weilke said:
I believe the google earth measurement tool is more accurate than the one on google maps.
Click to expand...

It is, but even the Google Maps one is good enough for this. The measurement tool and the location your phone shows you are two completely different things. Satellite/aerial imagery orthorectification is very accurate.
 
Last edited:
I used Google Earth Pro and checked Panama City (ECP), Calhoun County (F95), Sebastian (X26) and Pilot Country (X05). The published runway lengths for ECP, F95 and X26 matched Google Earth to within a couple feet. X05 was short by 75'.
 
X05 is privately owned, might have something to do with it. I would venture to say that nearly all publicly owned airports receive federal funding thus would have to be surveyed accurately according to midwestpa.
 
dmspilot said:
X05 is privately owned, might have something to do with it. I would venture to say that nearly all publicly owned airports receive federal funding thus would have to be surveyed accurately according to midwestpa.
Click to expand...

With any federally funded construction or runway rehab project, the contractor got paid for exactly the number of feet the FAA approved the funding for.

With private fields, in some states, once you register the strip with the FAA, someone comes around with a GPS to recorde accurate coordinates for the database/map. But that's just to document 'there is an airport', they dont care whether your hay-field is 1600ft or 1620ft.
 
Rgbeard said:
Curious - this example is 80' above sea level and 3,700 feet. What's your criteria in the East for high altitude and short field?
Click to expand...
As I've said to others already. I use my airplane to fly to other airports. Some aren't at 80 feet and 3700 feet long.

Man, Covid has really made everyone cranky.
 
dmspilot said:
It does. The displaced threshold is part of the runway. It is only unusable for touchdown.

Displaced Threshold. A displaced threshold is a threshold located at a point on the runway other than the designated beginning of the runway. Displacement of a threshold reduces the length of runway available for landings. The portion of runway behind a displaced threshold is available for takeoffs in either direction and landings from the opposite direction.
Click to expand...
Some thresholds are due to obstacle clearance. The one on the south side of X05 is a great example. There are power lines and tall trees at the end of the runway, you can't "count" on the threshold portion of the pavement to get you over those power lines. Previous to this revelation, which I guess is only a revelation to me, I assumed the published runway lengths would not include runway that's unusable for takeoff and landing.

I mean, seriously, why would runway that you can't use, be considered part of the runway length? Maybe everyone else knew this and thinks it makes sense, but I didn't, and I don't.
 
Salty said:
As I've said to others already. I use my airplane to fly to other airports. Some aren't at 80 feet and 3700 feet long.

Man, Covid has really made everyone cranky.
Click to expand...

**** you, you're wrong! :nono:





:lol:
 
overdrive148 said:
Regarding the measurement tool in Google Maps: Runway is 75ft wide, here's what I get for the tool. Pretty accurate IMO.

CZVLFtm.png
Click to expand...
Well.. if there's a 2ft error on 75 ft we can assume there's a 3% margin of error here.. on Salty's 3,700 fr runway that turns into 100 ft
 
Tantalum said:
Well.. if there's a 2ft error on 75 ft we can assume there's a 3% margin of error here.. on Salty's 3,700 fr runway that turns into 100 ft
Click to expand...
I know for a fact, it isn't actually 75 feet wide. They just repaved it, 72 is closer to accurate, and it's not consistent the entire length. I'll run a wheel over it in that spot when I get a chance.....
 
Salty said:
I assumed the published runway lengths would not include runway that's unusable for takeoff and landing.

I mean, seriously, why would runway that you can't use, be considered part of the runway length? Maybe everyone else knew this and thinks it makes sense, but I didn't, and I don't.
Click to expand...

No part of the runway is unusable for takeoff. The displaced threshold is only unusable for landing in one direction.

If published runway length was to omit unusable portions, the length would be different depending whether you're taking off or landing and what direction you're landing it. Way too complicated.
 
Sometimes you’ll see “declared distances” for ASDA, TODA, & TORA that will fine tune the runway pavement number, but I’m not seeing that in this case. Apparently they’re just taking the word of the aircraft owner, and maybe his measuring chain is like my grandpa’s was...broken, held together with a vise grip, and a foot short. ;)
 
dmspilot said:
No part of the runway is unusable for takeoff. The displaced threshold is only unusable for landing in one direction.

If published runway length was to omit unusable portions, the length would be different depending whether you're taking off or landing and what direction you're landing it. Way too complicated.
Click to expand...

Don't try to understand what I'm saying, that way there's no danger you might do it.
 
Salty said:
Don't try to understand what I'm saying, that way there's no danger you might do it.
Click to expand...

I understood what you're saying. You asked a question, "why would runway that you can't use, be considered part of the runway length?". And I answered it. If you didn't want the answer, don't ask.
 
dmspilot said:
I understood what you're saying. You asked a question, "why would runway that you can't use, be considered part of the runway length?". And I answered it. If you didn't want the answer, don't ask.
Click to expand...
Nope. You aren’t trying to understand at all. If you were, you’d ask a question instead of telling me I’m wrong while ignoring my point completely.

You can’t use part of the threshold due to obstacles. You are ignoring that. The threshold exists only because of obstacles on the end of the runway. If you expect to use the part of the runway after the threshold to take off, you’re not going to clear the obstacles.
 
Salty said:
As I've said to others already. I use my airplane to fly to other airports. Some aren't at 80 feet and 3700 feet long.

Man, Covid has really made everyone cranky.
Click to expand...

I just figured, being an "East of Mississippi" person, that anything 3-digits above sea level is pretty lofty.

:D

And since I fly an evil T-Tail Lance, I know about the difference of opinion on short runways, too.

:O
 
Salty said:
If you expect to use the part of the runway after the threshold to take off, you’re not going to clear the obstacles.
Click to expand...

Disagreeing with a point does not mean I don't understand it. The displaced threshold has absolutely nothing to do with taking off or being able to clear obstacles when taking off. Lifting off before a displaced threshold does not mean you will clear obstacles.

I posted the definition of a displaced threshold straight from the AIM but you still think it has something to do with takeoff performance, when it doesn't. Clearly you are the one not understanding the point.
 
dmspilot said:
Disagreeing with a point does not mean I don't understand it. The displaced threshold has absolutely nothing to do with taking off or being able to clear obstacles when taking off. Lifting off before a displaced threshold does not mean you will clear obstacles.

I posted the definition of a displaced threshold straight from the AIM but you still think it has something to do with takeoff performance, when it doesn't. Clearly you are the one not understanding the point.
Click to expand...
Well at least this time you posted something that indicated you read my post. Thanks.
 
Looking at your satellite images more closely, it looks like the North side of the runway at X05 is NOT a displaced threshold, but a taxiway leading up to the runway. Similarly, the first third of the pavement on the South side is a taxiway leading up to a displaced threshold with a yellow demarcation bar. The taxiway portions should not be counted in the runway length and as such you are right to point out the runway length as published is not correct.
 
Last edited:
dmspilot said:
Looking at your satellite images more closely, it looks like the west side of the runway at X05 is NOT a displaced threshold, but a taxiway leading up to the runway. Similarly, the first third of the pavement on the east side is a taxiway leading up to a displaced threshold with a yellow demarcation bar. The taxiway portions should not be counted in the runway length and as such you are right to point out the runway length as published is not correct.
Click to expand...
I stand corrected in my use of terminology.
 
I am confused by "west side" though. It's a north south runway.
 
dmspilot said:
Sorry, left and right. Didn't realize it was rotated.
Click to expand...
Ironically, "left" or north, there are no obstacles nearby. I don't recall if the new paint on the south side is yellow or white. I'll check.
 
You must log in or register to reply here.
Back
Top