tax1k
Topic Author
Posts: 45
Joined: Thu Aug 25, 2016 5:02 am

Question about vertical separation

Fri Mar 20, 2020 1:30 pm

Was just watching flight aware around LAS out of curiosity about current tower situation. It looked like a WN flight to STL and a SKW flight had only about 4,000 feet of vertical separation. I realize that flight aware lines are not precise down to the last inch (obviously) but I’m curious whether that’s a normal occurrence. Especially in somewhat empty skies right now. 4,000 feet doesn’t seem like a lot especially with some margin of error.
 
iRISH251
Posts: 763
Joined: Fri Nov 26, 2004 3:56 am

Re: Question about vertical separation

Fri Mar 20, 2020 1:33 pm

tax1k wrote:
Was just watching flight aware around LAS out of curiosity about current tower situation. It looked like a WN flight to STL and a SKW flight had only about 4,000 feet of vertical separation. I realize that flight aware lines are not precise down to the last inch (obviously) but I’m curious whether that’s a normal occurrence. Especially in somewhat empty skies right now. 4,000 feet doesn’t seem like a lot especially with some margin of error.


In RVSM airspace 1,000 feet is the minimum. https://en.wikipedia.org/wiki/Reduced_v ... ion_minima
 
CriticalPoint
Posts: 935
Joined: Thu Jan 19, 2017 5:01 pm

Re: Question about vertical separation

Fri Mar 20, 2020 1:48 pm

tax1k wrote:
Was just watching flight aware around LAS out of curiosity about current tower situation. It looked like a WN flight to STL and a SKW flight had only about 4,000 feet of vertical separation. I realize that flight aware lines are not precise down to the last inch (obviously) but I’m curious whether that’s a normal occurrence. Especially in somewhat empty skies right now. 4,000 feet doesn’t seem like a lot especially with some margin of error.


Usually it’s 1,000 Feet above FL 290. 4000 feet is MILES apart.
 
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airportugal310
Posts: 3561
Joined: Sun Apr 11, 2004 12:49 pm

Re: Question about vertical separation

Fri Mar 20, 2020 1:52 pm

Could have stuffed a few more in there!
“They bought their tickets, they knew what they were getting into. I say, let 'em crash.”
 
tax1k
Topic Author
Posts: 45
Joined: Thu Aug 25, 2016 5:02 am

Re: Question about vertical separation

Fri Mar 20, 2020 2:03 pm

Thanks. I didn’t realize 1,000 feet was first choice. I thought that was just when the automatic anti collision kicked in.
This may be a stupid question but I thought there is some margin of error for altimeters based on departure airport, weather, etc.
 
tax1k
Topic Author
Posts: 45
Joined: Thu Aug 25, 2016 5:02 am

Re: Question about vertical separation

Fri Mar 20, 2020 2:03 pm

Thanks. I didn’t realize 1,000 feet was first choice. I thought that was just when the automatic anti collision kicked in.
This may be a stupid question but I thought there is some margin of error for altimeters based on departure airport, weather, etc.
 
737tanker
Posts: 369
Joined: Fri Dec 30, 2005 2:47 am

Re: Question about vertical separation

Fri Mar 20, 2020 2:25 pm

Also if one aircraft is operating VFR and the other is IFR you only need 500 ft separation
 
ATCJesus
Posts: 25
Joined: Tue Aug 27, 2019 3:39 am

Re: Question about vertical separation

Fri Mar 20, 2020 2:32 pm

Another fun fact, in the enroute world at least, planes have a +\- 250 buffer before the system will give an alert. Theoretically, you could have a plane at 29750 and 29250 and it’s all good separation wise.
 
QXorVX
Posts: 25
Joined: Sun Aug 07, 2016 5:45 am

Re: Question about vertical separation

Fri Mar 20, 2020 2:47 pm

tax1k wrote:
Thanks. I didn’t realize 1,000 feet was first choice. I thought that was just when the automatic anti collision kicked in.
This may be a stupid question but I thought there is some margin of error for altimeters based on departure airport, weather, etc.


In the United States all aircraft operating at or above 18,000' (FL180) use a standard altimeter setting, 29.92, to avoid these types or errors. Aircraft below 18,000' are given a local setting to use and updated frequently as they fly along their route.
 
rfields5421
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Joined: Thu Jul 19, 2007 12:45 am

Re: Question about vertical separation

Fri Mar 20, 2020 5:28 pm

TCAS systems are very good at deterring if altitudes are in conflict. I don't know their threshold, but with thousands of aircraft per day flying with a standard vertical separation of 1,000 ft, the TCAS isn't going off all the time.

Some areas out of range of radar and VHF comms use a greater separation.

I've never flown anything above the Cessna level, but a 1,000 ft vertical separation is a lot when in the air.
Not all who wander are lost.
 
GalaxyFlyer
Posts: 4959
Joined: Fri Jan 01, 2016 4:44 am

Re: Question about vertical separation

Fri Mar 20, 2020 5:38 pm

Not when when you’re beak-to-beak with a opposite direction B747. I vividly remember about 50W in a C-5, in the first few months of NAT RVSM seeing an oncoming Whale. It looked like it was very close after years of seeing 2,000’ separation. Then came the wake.
 
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Starlionblue
Posts: 19704
Joined: Fri Feb 27, 2004 9:54 pm

Re: Question about vertical separation

Fri Mar 20, 2020 11:32 pm

tax1k wrote:
Thanks. I didn’t realize 1,000 feet was first choice. I thought that was just when the automatic anti collision kicked in.
This may be a stupid question but I thought there is some margin of error for altimeters based on departure airport, weather, etc.


There are protections in place. In order to operate in RVSM airspace (FL290-FL410) you need:
- Two independent and functioning altitude indicating systems.
- An altitude deviation warning system.
- An automatic altitude maintaining system (part of the autopilot).
- Must fly on autopilot.

Below FL290 and above FL410 you need 2000 feet vertical separation, and in the terminal area you'll typically get more because aircraft are climbing and descending.


rfields5421 wrote:
TCAS systems are very good at deterring if altitudes are in conflict. I don't know their threshold, but with thousands of aircraft per day flying with a standard vertical separation of 1,000 ft, the TCAS isn't going off all the time.

Some areas out of range of radar and VHF comms use a greater separation.

I've never flown anything above the Cessna level, but a 1,000 ft vertical separation is a lot when in the air.


TCAS doesn't use distance per se. It uses time to potential collision. The alerts come in three layers:
- Intruder. Awareness only. Traffic changes symbology on ND.
- TA. Traffic Alert. Aural warning and change to amber.
- RA. Resolution Alert. Aural warning, change to red, flight path commands.

Image
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
e38
Posts: 668
Joined: Sun May 04, 2008 10:09 pm

Re: Question about vertical separation

Sat Mar 21, 2020 8:43 pm

Quoting Starlionblue (Reply # 12), “Below FL290 and above FL410 you need 2000 feet vertical separation . . . “

In the United States, below FL290 (non-RVSM airspace), you need 1000 feet vertical separation.

e38

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