Do the high altitude controller's have real time access to the actual altitude of an airplane?

gotWXdagain

Highly Visible Member
I want to post something about you being an a@#$$ but will not do it, ok maybe I did. :) I have never been in RVSM altitudes without an LOA! Just trying to stop other pilots from being up there with us and being off altitude.
Have you ever thought about not freely volunteering information that isn’t asked for? You seem like the guy who gets pulled over for speeding and talks his way into first degree murder.
 

Cessnaflyer

Wooooooooooooooooooooooooooooooo
I'm not sure if this is exactly correct.

@Capt. Chaos can you clarify this? Because I didn't think IAS was pumped into the UAT.
I was playing with Foreflight while waiting on the ramp today. When I clicked on the traffic it had there speed on there. Not sure if it was computed or actual IAS.
 

Roger Roger

Paid to sleep, fly for fun
I’d have to look in one of my manuals, but I think there is provision for heading and airspeed (not just track and groundspeed) to be transmitted over ADSB though I don’t think any of the systems I messed with were set up to do it.
 

greg1016

Trustworthy Source
@Cessnaflyer If you have ADS-B in you will get radar data from non-ADS-B aircraft via TIS, you just won't see a call sign.

And I'll reiterate to the OP. The En Route radar system DOES NOT show the en route controller your exact altitude in cruise unless you are off by more than 150ft. For example, if you are assigned FL390 the scope will show 390 whether you are at FL 38860 or 39140. If you are below 38860 the scope will show 388-390 (it could be 390-388, been a while since I've been at a center) indicating you are below your assigned altitude. If you were given a decent it will show your altitude in 100 ft increments as soon as you leave your assigned altitude with a down arrow instead of a ( - ) or up arrow if you were given a climb. likewise if you are above your assigned altitude it will show a ( + ) instead of a ( - ).

Additionally, something that I think was overlooked: Your ADS-B out is still part of your transponder and it still broadcasts your altitude based on a standard altimeter (just like Mode-C). ATC radar compensates for the local altimeter automatically. It DOES not broadcast your GPS altitude.
 

Capt. Chaos

Well-Known Member
I'm not sure if this is exactly correct.

@Capt. Chaos can you clarify this? Because I didn't think IAS was pumped into the UAT.
According to AC20-165 it is a optional data output, but needs to meet other AC requirements for source. Now if that info is displayed on the controllers screen is uncertain. The data packet includes both Baro Alt and Geo Alt but if the Baro Alt goes out or is turned off Center here loses the Alt readout even though Geo Alt is still being transmitted.
 

Attachments

Corporate Pilot

Well-Known Member
I still have no idea what the point of the OP was supposed to be.
I thought this spelled it out but I guess not.

“There are pilots out there that think with the new RVSM rules, ADS-B, they can just go up there and ATC will tell them if they are off altitude. These are airplanes that are not approved under the old rules. I am wondering if ATC has the ability to see if the airplane is actually off altitude or only have mode C data. Several of us have said that the new rules only do away with the LOA requirements. Some say that they can just go up there and ATC will tell them if their altimeter system is off from the ADS-B data. Just telling them the new rules only do away with the LOA does not work. They just quote the new rules, which is poorly written about how meet the requirements.”

If ATC does not have real time access to the airplanes actual RVSM altitude no one will know if that airplane is actually on altitude until later. Since these airplanes have never been RVSM certified who knows how large their altimeter system error is up there.

With the RVSM AGHME altitude monitoring system it could be quite a while until someone knew their ASE was too large. As I understand the new ADS-B RVSM monitoring the operator will find out will find out a lot sooner. My question is how soon, does ATC have this data real time?
 
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ppragman

Direct BATTY
I thought this spelled it out but I guess not.

“There are pilots out there that think with the new RVSM rules, ADS-B, they can just go up there and ATC will tell them if they are off altitude. These are airplanes that are not approved under the old rules. I am wondering if ATC has the ability to see if the airplane is actually off altitude or only have mode C data. Several of us have said that the new rules only do away with the LOA requirements. Some say that they can just go up there and ATC will tell them if their altimeter system is off from the ADS-B data. Just telling them the new rules only do away with the LOA does not work. They just quote the new rules, which is poorly written about how meet the requirements.”

If ATC does not have real time access to the airplanes actual RVSM altitude no one will know if that airplane is actually on altitude until later. Since these airplanes have never been RVSM certified who knows how large their altimeter system error is up there.

With the RVSM AGHME altitude monitoring system it could be quite a while until someone knew their ASE was too large. As I understand the new ADS-B RVSM monitoring the operator will find out will find out a lot sooner. My question is how soon, does ATC have this data real time?
I mean, that shouldn't be too much of a problems.


91.217 Data correspondence between automatically reported pressure altitude data and the pilot's altitude reference.
(a) No person may operate any automatic pressure altitude reporting equipment associated with a radar beacon transponder—

(1) When deactivation of that equipment is directed by ATC;

(2) Unless, as installed, that equipment was tested and calibrated to transmit altitude data corresponding within 125 feet (on a 95 percent probability basis) of the indicated or calibrated datum of the altimeter normally used to maintain flight altitude, with that altimeter referenced to 29.92 inches of mercury for altitudes from sea level to the maximum operating altitude of the aircraft; or

(3) Unless the altimeters and digitizers in that equipment meet the standards of TSO-C10b and TSO-C88, respectively.

(b) No person may operate any automatic pressure altitude reporting equipment associated with a radar beacon transponder or with ADS-B Out equipment unless the pressure altitude reported for ADS-B Out and Mode C/S is derived from the same source for aircraft equipped with both a transponder and ADS-B Out.


I'd say this is actually about the same level of accuracy. The RVSM altimeter check requires 120' of accuracy at least and that at 3 standard deviations 245' of accuracy.

The data out requirements above list 125' of accuracy at all altitudes and flight levels the aircraft can operate at with 95% probability.

Assuming altimetry error is normally distributed (and I'd be surprised if it wasn't) 95% probability essentially means it's accurate to 125' to 2-standard deviations. So sigma is 62.5. at 3-standard deviations, which sets the maximum permissible error for RVSM compliant airplanes the maximum error should be around 188'.

This is actually pretty close to what we have now. It's a little sloppier at each altitude, but a little tighter at worst. Old airplanes need to have ASE show no more than 245' at 3 standard deviations and newer airplanes need to show ASE to 200'.

For the final question about AGHME, they're seeing your geometric altitude with every ping of the ADS-B, they're also seeing your baro alt, looking at everyone flying in a particular region and figuring out who looks weird would be pretty straight forward. I'd imagine they'll just look for statistical mismatches between you and all the other airplanes. This isn't appreciably different than what AGHME actually does.
 

Roger Roger

Paid to sleep, fly for fun
I thought this spelled it out but I guess not.

“There are pilots out there that think with the new RVSM rules, ADS-B, they can just go up there and ATC will tell them if they are off altitude. These are airplanes that are not approved under the old rules. I am wondering if ATC has the ability to see if the airplane is actually off altitude or only have mode C data. Several of us have said that the new rules only do away with the LOA requirements. Some say that they can just go up there and ATC will tell them if their altimeter system is off from the ADS-B data. Just telling them the new rules only do away with the LOA does not work. They just quote the new rules, which is poorly written about how meet the requirements.”

If ATC does not have real time access to the airplanes actual RVSM altitude no one will know if that airplane is actually on altitude until later. Since these airplanes have never been RVSM certified who knows how large their altimeter system error is up there.

With the RVSM AGHME altitude monitoring system it could be quite a while until someone knew their ASE was too large. As I understand the new ADS-B RVSM monitoring the operator will find out will find out a lot sooner. My question is how soon, does ATC have this data real time?
I’m admittedly not deeply familiar with RVSM minutiae-my employer says the plane is good for it and they ostensibly train us on it-but I’m curious how the pilot would be warned by their equipment that they had an altimetry error if their altimeter was, you know, in error? Typically the ADSB, transponder, and altimeter all get data from the same place, so an error in one is going to reflect to ATC and one of the 3 or so altimeters in the cockpit. Are you implying that the GPS altitude is cross checked against baro to alert of a possible issue?
 

ppragman

Direct BATTY
I’m admittedly not deeply familiar with RVSM minutiae-my employer says the plane is good for it and they ostensibly train us on it-but I’m curious how the pilot would be warned by their equipment that they had an altimetry error if their altimeter was, you know, in error? Typically the ADSB, transponder, and altimeter all get data from the same place, so an error in one is going to reflect to ATC and one of the 3 or so altimeters in the cockpit. Are you implying that the GPS altitude is cross checked against baro to alert of a possible issue?
The pilot wouldn't know but you could figure it out if you had enough data to compare to. That's effectively what AGHME is doing.

That said ATC can't see that information, and pilots using AGHME are specifically told:

  • There are no special monitoring routings; do not ask ATCfor any special treatment to accommodate AGHMEmeasurement, as it is not an ATC responsibility
 

Prino

Well-Known Member
Controllers have no need to see IAS. It’s completely pointless for us. Ground speed is what matters.
Knowing IAS only helps enforce when you know somebody lying about what speed they’re actually doing. Here our feeder sectors have a monitor close to the scope that tells the IAS. Can confirm we hardly use it except to see how badly is lying about their assigned speed vs actual
 

NovemberEcho

Dergs favorite member
Knowing IAS only helps enforce when you know somebody lying about what speed they’re actually doing. Here our feeder sectors have a monitor close to the scope that tells the IAS. Can confirm we hardly use it except to see how badly is lying about their assigned speed vs actual
I figure that out by everyone is showing 270, except Southwest who is showing 290
 
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