Traffic Service Unreliable - What the Hell is This?!!

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Re: Traffic Service Unreliable - What the Hell is This?!!

Postby 3Dreaming » Thu Sep 03, 2015 1:02 pm

MrMorden wrote: A agree there is an over-reliance on technology, and a lot of it's not required. But I also think that where the tech serves to help make us safer, it's a good thing. And I think "see and avoid" is a hard thing to make happen in two airliners that have limited visibility and potential closing speeds of 800 knots or more.


Having an unreliable ADSB signal will have little effect on airliners with a closing rate of 800knots. Where they can have that closing speed ATC is already providing separation without it.

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Re: Traffic Service Unreliable - What the Hell is This?!!

Postby SportPilot » Thu Sep 03, 2015 1:05 pm

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Last edited by SportPilot on Sun Mar 20, 2016 8:15 pm, edited 1 time in total.

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Re: Traffic Service Unreliable - What the Hell is This?!!

Postby MrMorden » Thu Sep 03, 2015 3:00 pm

SportPilot wrote:Some posters evidently don't know how the ATC IFR system works. Also, what percentage of airlines even have ADS-B now? IDK?


They all have TCAS. It's a requirement.
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Re: Traffic Service Unreliable - What the Hell is This?!!

Postby MrMorden » Thu Sep 03, 2015 3:03 pm

3Dreaming wrote:
MrMorden wrote:


Having an unreliable ADSB signal will have little effect on airliners with a closing rate of 800knots. Where they can have that closing speed ATC is already providing separation without it.


Have you heard about any of the near-misses caused by ATC lately? There have been a bunch.

If an airliner gets a TCAS alert contrary to ATC instructions, they are required by regulation to follow the TCAS resolution and ignore ATC. Whoever writes the regs sure thinks TCAS is important...
Last edited by MrMorden on Thu Sep 03, 2015 3:05 pm, edited 1 time in total.
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Re: Traffic Service Unreliable - What the Hell is This?!!

Postby MrMorden » Thu Sep 03, 2015 3:04 pm

SportPilot wrote:Some posters evidently don't know how the ATC IFR system works. Also, what percentage of airlines even have ADS-B now? IDK?


I know exactly how it works. TCAS alerts take precedence over ATC instructions. For a reason.
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Re: Traffic Service Unreliable - What the Hell is This?!!

Postby CTLSi » Thu Sep 03, 2015 3:31 pm

MrMorden wrote:I know exactly how it works. TCAS alerts take precedence over ATC instructions. For a reason.

If a conflicting ATC instruction coincides with an RA (res advisory), a pilot may assume that ATC is fully aware of the situation and is providing the better resolution. The PIC is expected to "follow the RA" but in practice this does not always happen.

TCAS may induce midair collisions: "In particular, it is dependent on the accuracy of the threat aircraft’s reported altitude (mode C or S xpndr with alt encoding) and on the expectation that the threat aircraft will not make an abrupt maneuver that defeats the TCAS Resolution Advisory (RA)."

https://en.wikipedia.org/wiki/Traffic_c ... nce_system

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Re: Traffic Service Unreliable - What the Hell is This?!!

Postby Nomore767 » Thu Sep 03, 2015 8:48 pm

MrMorden wrote:
3Dreaming wrote:
MrMorden wrote:


Having an unreliable ADSB signal will have little effect on airliners with a closing rate of 800knots. Where they can have that closing speed ATC is already providing separation without it.


Have you heard about any of the near-misses caused by ATC lately? There have been a bunch.

If an airliner gets a TCAS alert contrary to ATC instructions, they are required by regulation to follow the TCAS resolution and ignore ATC. Whoever writes the regs sure thinks TCAS is important...


When two airliners get close enough for an RA remember that the RA is issued to both airplanes since the systems 'talk' to each other in that , for example, one will command climb "Climb, climb NOW" whilst the other may command descent.
It's crucial that the pilot flying puts the airplane's climb/descent right where the TCAS commands it on the IVSI. Doing that, in both airplanes, ensures full separation and the best conflict resolution.

In the days before TCAS I experienced this scenario. Climbing out of KEWR in a 727. Usually we would be given a climb to FL190 and expect further with the next handoff. On this day, it occurred to me that we hadn't been given this clearance. As PNF I was busier than the PF completing after take-off checklist items and company reports etc but I queried the PF and then reminded ATC that we were level at FL190. He resounded with "Climb IMMEDIATELY, Immediately to fl260" and then gave an opposing airplane a sharp turn and expedited descent. It happens.
Fast forward to TCAS and the system should have/would have commanded both opposing airplanes to climb/descend in order to comply.

Complying with the resolution advisory can command a rapid application of power and aggressive use of the yoke, actions contrary to most of airline style flying with FAs and passengers in the cabins. This is why we always trained in the recurrent training simulators to cover TCAS training. During the LOFT, or even in other maneuvers if we had a sneakier instructor, they'd suddenly have a TCAS scenario pop up and we'd be expected to respond immediately and react by putting the IVSI right where it had to be right away. Its actually not as easy as it sounds but I have to say the system work very, very well.
Last edited by Nomore767 on Fri Sep 04, 2015 7:29 am, edited 1 time in total.

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Re: Traffic Service Unreliable - What the Hell is This?!!

Postby BrianL99 » Fri Sep 04, 2015 4:48 am

Nomore767 wrote:
When two airliners get close enough for an RA remember that the RA is issued to both airplanes since the systems 'talk' to each other in that , for example, one will command climb "Climb, climb NOW" whilst the other may command descent.
It's crucial that the pilot flying puts the airplane's climb/descent right where the TCAS commands it on the IVSI. Doing that, in both airplanes, ensures full separation and the best conflict resolution.

In the days before TCAS I experienced this scenario. Climbing out of KEWR in a 727. Usually we would be given a climb to FL190 and expect further with the next handoff. On this day, it occurred to me that we hadn't been given this clearance. As PNF I was busier than the PF completing after take-off checklist items and company reports etc but I queried the PF and then reminded ATC that we were level at FL190. He resounded with "Climb IMMEDIATELY, Immediately to fl260" and then gave an opposing airplane a sharp turn and expedited descent. It happens.
Fast forward to TCAS and the system should have/would have commanded both opposing airplanes to climb/descend in order to comply.

Complying with the resolution advisory can command a rapid application of power and aggressive use of the yoke, actions contrary to most of airline style flying with FAs and passengers in the cabins. This is why we always trained in the recurrent training simulators to cover TCAS training. During the LOFT, or even in other maneuvers if we had a sneakier instructor, they'd suddenly have a TCAS scenario pop up and we'd be expected to resound immediately and respond by putting the IVSI right where it had to be right away. Its actually not as easy as it sounds but I have to say the system work very, very well.


Thanks for posting from experience and not the blind speculation we sometimes get from the amateurs and wannabes.

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Re: Traffic Service Unreliable - What the Hell is This?!!

Postby MrMorden » Fri Sep 04, 2015 8:02 am

CTLSi wrote:
MrMorden wrote:I know exactly how it works. TCAS alerts take precedence over ATC instructions. For a reason.

If a conflicting ATC instruction coincides with an RA (res advisory), a pilot may assume that ATC is fully aware of the situation and is providing the better resolution. The PIC is expected to "follow the RA" but in practice this does not always happen.

TCAS may induce midair collisions: "In particular, it is dependent on the accuracy of the threat aircraft’s reported altitude (mode C or S xpndr with alt encoding) and on the expectation that the threat aircraft will not make an abrupt maneuver that defeats the TCAS Resolution Advisory (RA)."

https://en.wikipedia.org/wiki/Traffic_c ... nce_system


A pilot is simply not allowed to disregard an RA. You may say it happens, and I'm sure it *has* happened. But the pilot is subject to FAA enforcement action for ignoring an RA, so I doubt any well-trained pilot would intentionally disregard one.

Please cite a circumstance where TCAS has "induced a midair collision". I did find where *ignoring* TCAS and instead following ATC lead to a midair killing 72 people:

http://www.ainonline.com/aviation-news/aviation-international-news/2008-04-23/german-collision-was-first-tcas-era

Is it theoretically possible for TCAS to cause a midair? Sure. So is time travel. No evidence either has happened though.
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Re: Traffic Service Unreliable - What the Hell is This?!!

Postby Nomore767 » Fri Sep 04, 2015 8:10 am

Andy,

Don't forget he is a fairly new pilot and the info he's quoting is coming from…Wikipedia!

The big reason to follow a TCAS RA is that the system is designed such that both transponders and TCAS 'talk to each other' such that they 'agree' that one will do one thing and the other pretty much the opposite. If one plane ignored it and the other responded or didn't respond properly there could be less margin. Crews are trained to inform ATC that they are responding to a TCAS RA and ATC will use that to separate other traffic.
Basically the system offers conflict resolution to increase vertical separation. To date TCAS doesn't offer lateral conflict resolution although some crews will also turn away as well as resomd, problem here is if the RA isn't flown as fully commanded as some energy is used to turn away, though the PIC is still the final authority and would of course be liable for failure to respond fully such that a near mid-air ensued.

TCAS is quicker and real time than ATC's look at a radar screen and then trying to offer traffic separation. One of the reasons they want to go to ADSB in lieu of traditional radar.

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Re: Traffic Service Unreliable - What the Hell is This?!!

Postby MrMorden » Fri Sep 04, 2015 8:19 am

Nomore767 wrote:Andy,

Don't forget he is a fairly new pilot and the info he's quoting is coming from…Wikipedia!

The big reason to follow a TCAS RA is that the system is designed such that both transponders and TCAS 'talk to each other' such that they 'agree' that one will do one thing and the other pretty much the opposite. If one plane ignored it and the other responded or didn't respond properly there could be less margin. Crews are trained to inform ATC that they are responding to a TCAS RA and ATC will use that to separate other traffic.

TCAS is quicker and real time than ATC's look at a radar screen and then trying to offer traffic separation. One of the reasons they want to go to ADSB in lieu of traditional radar.


Agree on all counts. I found this on a site for ATP pilots, it seems very relevant (bold added by me) :

"ALWAYS FOLLOW THE INSTRUCTIONS ISSUED IN A TCAS RESOLUTION ADVISORY (RA)

If your TCAS issues a RA, Air Traffic Control has already failed. At this point, the TCAS system is infinitely more valuable than ATC’s instructions. Most enroute radars have update rates between 6 and 10 seconds – the information your TCAS is providing is much more timely and, by design, training, and regulation, takes precedence over ATC commands."
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Re: Traffic Service Unreliable - What the Hell is This?!!

Postby drseti » Fri Sep 04, 2015 8:42 am

designrs wrote:Anybody know if AOPA is acting on this NOTAM?


According to this morning's AOPA e-news, yes.
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Re: Traffic Service Unreliable - What the Hell is This?!!

Postby drseti » Fri Sep 04, 2015 8:51 am

MrMorden wrote:Is it theoretically possible for TCAS to cause a midair? Sure. So is time travel. No evidence either has happened though.


Time travel is more than just theoretically possible. Please read again what I posted tomorrow.
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Re: Traffic Service Unreliable - What the Hell is This?!!

Postby MrMorden » Fri Sep 04, 2015 9:11 am

drseti wrote:
MrMorden wrote:Is it theoretically possible for TCAS to cause a midair? Sure. So is time travel. No evidence either has happened though.


Time travel is more than just theoretically possible. Please read again what I posted tomorrow.


I read it next week, but won't be able to comment until yesterday.
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Re: Traffic Service Unreliable - What the Hell is This?!!

Postby CTLSi » Fri Sep 04, 2015 10:16 am

The PIC is responsible for SAFETY..not the equipment...
Last edited by CTLSi on Fri Sep 04, 2015 10:31 am, edited 1 time in total.


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