Are today's Nav systems TOO accurate?

[Big Pratt]

With today's GPS based Nav Systems we can stay within meters of track.
Does anyone else get the uneasy feeling about this? It seems to me that the "old" way actually provided a safety margin.

I think that this will be a contributing factor in the GOL 737 vs Embraer tragedy.

Here's an interesting video:
http://www.scottipc.com/course/content/view/37/61/

Any opinions? Does anyone go a bit right of track within domestic? especially where no radar coverage?

What thinks you???

BP

[Hedley]

um, this isn't exactly a new problem, and recall that since
then, SA has been turned off, so it's gotten a lot worse:

http://www.tsb.gc.ca/en/reports/air/199 ... 5h0008.asp

1.8 Aids to Navigation
Each aircraft was equipped with a global positioning system (GPS) receiver. Bearskin aircraft have the GPS receiver connected directly to the HSI, and company procedures require the pilots to use GPS as an aid to primary navigation systems. Air Sandy company procedures also require the pilots to use GPS as an aid to navigation. The Canadian air navigation system is rapidly moving towards increased reliance on GPS as an inexpensive and accurate navigation system.

Airways are designed to be 8 nm wide (8.6 for non-directional beacon [NDB]) at their narrowest point. This width takes into account the inaccuracies of the ground transmitter and those of the aircraft receivers. GPS receivers, however, are considered accurate to within ± 300 feet and will show course deviations of 0.1 nm--in effect, the airway has become 600 feet wide. A large portion of the ± 300-foot accuracy error is deliberately introduced by the United States (U.S.) military on a random basis and is designed to deny high precision signals to unfriendly military aircraft.

When two aircraft using GPS are flying the same route and are in the same location, they could receive the same signal. Although they can be as much as 300 feet from their intended position relative to the ground, the distance between the two aircraft could be much less (see LP 95/95). Thus, GPS has greatly reduced the lateral displacement of aircraft flying along identical intended tracks.

Since the introduction of GPS, there have been no changes to procedures to take into account the increased risk of mid-air collisions for aircraft navigating by GPS. Transport Canada has acknowledged the problem and has promulgated a leaflet that discusses the use of GPS offset procedures to ensure separation en route. Although the information suggests using an offset track while navigating by GPS, there are no established procedures that would ensure that all pilots using GPS offset their tracks. If procedures for separating aircraft are not used, the probability of collision between aircraft using GPS is significantly higher than between aircraft using conventional navigation aids.

[I Like Myself]

Interesting Video, I've heard of this happening to someone I know near banff where they passed directly under oposite direction traffic by about 150 feet or so (probably altimiter difference) while following the GPS track on autopilot.
I think it's a problem that people usually forget about, but as more people follow those GPS tracks, espically with autopilot this is becoming way more likely.
What are peoples take on flying slightly right of centre?

[eternalhold]

No, I'd rather guess where my destination is and point the nose roughly in that direction, 40% of the time it works evertime.

If you're at an altitude appropriate for direction of flight it shouldn't be a huge problem, at least no nose to nose, for the rest a good lookout, good postion reports and TCAS.

[Wasn't Me]

Plus or minus 200 feet, plus or minus one dot makes for a safer trip. There is a problem when everyone is dead on.

[V1RotateV2]

When flying in South America, non radar areas, pilots on GPS/FMS used to set an offtrack of 0.5 miles right. This kept you within airways limits, but gave you 1 mile of horizontal distance with other traffic on the same airway.

Playing with altitude is a dangerous game, considering altimeter errors and RVSM.

[Hedley]

passed directly under oposite direction traffic by about 150 feet or so (probably altimiter difference) while following the GPS track on autopilot.

Well, with SA (dithering) turned off, all that's left to save you is altitmeter error ... oops, RVSM probably got rid of most of that, too.

[desksgo]

When flying in South America, non radar areas, pilots on GPS/FMS used to set an offtrack of 0.5 miles right. This kept you within airways limits, but gave you 1 mile of horizontal distance with other traffic on the same airway.

I think we should ALL do this.

[TTJJ]

Modern navigation really is "TOO" accurate.
This issue has been addressed on large aircraft by the implementation of Strategic Lateral Offset Procedures (SLOP..no joke really) whereby aircraft fly 1 OR 2 NM right of track.

In North America you normally only hear about it being employed on the NAT Tracks, (IAP RAC-11.23) however it exists in a somewhat patchwork manner around the world (Airways going down to South America, The Pacific, etc). ICAO is trying to convince individual government to allow its use.

Although the above procedures only apply to aircraft capable of maintaining an offset set into the FMS, I have heard anecdotal information from most everywhere in the world of small aircraft offsetting 1 mile or so when not in radar contact. I have heard of flight schools teaching that during comm failures you should fly offset, assuming that you still have a GPS operating. Probably good advise.
Google gave 369,000 hits

[Aunt Jemima]

Yes

[ei ei owe]

When flying in South America, non radar areas, pilots on GPS/FMS used to set an offtrack of 0.5 miles right. This kept you within airways limits, but gave you 1 mile of horizontal distance with other traffic on the same airway.

I think we should ALL do this.

But.....then..... Oh dear God no!

[tiggermoth]

Here is another detail to consider. I have flown with a number of guys who have a "fancy" GPS at their disposal, and they spend probably 70% of the flight fiddling around with knobs, dials, buttons, etc on the GPS and NEVER have a look outside to see if anyone else is around. Hmmmm, could this also be a contributing factor????

Back to the basics, one of the first things I was taught in ground school for my private licence, Collision Avoidance is the responsibility of the pilot no matter what clearances they have been given.
Check the TC-AIM: RAC Chapter 1.7, 3rd last paragragh.

[Walker]

Well that being said I was ferrying an aerostar the other day that had those “fancy” systems onboard, cruising along on the climb out not in controlled airspace yet, when all of a sudden the computer starts yelling and screaming “Traffic 3oclock same altitude less than a mile closing!!!” and all 4 screens light up with COLLISION WARNING!! And are painting this guy on the screen, we turned even thought we couldn’t see shit, sure enough some little 152 popped out of the clouds and appeared right where we would have been had it not been for the bitching betty Im not sure if we would have seen him in time.
That being said one could question what a 152 was doing in the clouds, but that is another story…

[pelmet]

[quote="cpl_atc"]
But flying offsets on NAT tracks? What would this accomplish? [/quote]

I believe the offset NAT tracks are for wake turbulence reasons.

[V1RotateV2]

But flying offsets on NAT tracks? Or along airways in controlled IFR airspace? What would this accomplish? How does that reduce the collision potential? Because a controller may have cleared a/c head-to-head, same track, at the same altitude? Other than that unlikely scenario, there are 1,000 other track combinations that could lead to a collision between same direction, same altitude aircraft, and flying some arbitrary offset distance won't do anything to address that.

In my limited experience, head-ons are not that common in cruise, but in non-radar environments the chance of a close encounter while changing levels -be it climb or descent- is not that small and many times the only reason it did not happen is because the sky is big.

Remember that in non-radar areas time is the only measure of separation, and sometimes pilot's will not know or won't update an estimate (due to better winds or different TAS) and conflict over a waypoint.

I have heard a couple of times after entering a radar zone "XXX you are radar contact" and 10 seconds later "turn now to heading CCC for separation".

Fiddling with GPS/FMS knobs and switches while flying sure does not help, but looking out the window is not the solution. How many times did you have ATC or TCAS call traffic with an exact bearing and distance and still not seen the target? Even when looking at the correct spot an airplane (unless very big or lighted) is hard to see.

I believe that anything you can do to stack the odds in your favour should be seriously considered.

[Spokes]

This all reminds me of the trial I hear was going to be done in England. They want to start driving on the right hand side of the road like the rest of the world. They are going to try it with the trucks first. If that works out then eventuall all vehicles will do this....

[TTJJ]

Cpl_Atc:
While the NAT Tracks are one way (there are only about 10 each way not thousands), the possibility exists to climb or more likely descend into some other aircraft's airspace. Turbulence, Autopilot failure or hiccup, engine problems... they all may make you descend before you can get a call out or turn. It is HF after all and VERY congested on the frequency or you just might be too busy taming the beast to notice your descent. Offset flying just gives you that much more room, another couple of lanes on the highway so to speak.
It also prevents hitting the guy ahead of you in case of a loss of longitudinal separation or to a lesser extent laterally from a gross navigational error.
Wake turbulence has rightly been mentioned, and not just for passenger comfort. The turbulence may toss you into some else’s altitude.

(Let me just clarify that all aircraft don't fly 2 miles to the right of track. That would defeat the purpose of offset flying. You would be creating a new centerline that way. Plane A might decide to fly 1 mile offset, Plane B might stay on centerline, plane C might be 2 or 1 mile off. The idea is to spread them out a bit laterally.)

Besides the above problems, on a normal two way airway in radar controlled airspace you can get mountain wave that tosses you up and down enough to get RA's.
The risks of a head-on are more obvious, but on the NAT Tracks there are an awful lot of blue diamonds on the nav display (no threat traffic).

It wouldn't take too much to come down on somebody, thus the idea of flying offset.

[the_professor]

dble?

[the_professor]

drg

[Hedley]

I'm not sure anybody cares, but turning is often not the best choice for collision avoidance, for several reasons.

[fanspeed]

Cpl_Atc:
While the NAT Tracks are one way (there are only about 10 each way not thousands), the possibility exists to climb or more likely descend into some other aircraft's airspace.

It also prevents hitting the guy ahead of you in case of a loss of longitudinal separation or to a lesser extent laterally from a gross navigational error.

Right. And you say that Plane A flies one offset, while Plane B flies another. How is that coordinated? Do you ask ATC "Who's in front of/behind me?" and then coordinate different offsets among yourselves?


If that is the case, then I can see the benefit, sort of. But when you're talking domestic airspace where an infinite number of direct tracks are possible (and by extension an infinite number of conflict points exist) then an offset is totally meaningless.

In the NAT airspace, you can see who you are following. Domestic airspace? Think of any number of northern communities/minesites/oilfields where there is a lot of traffic between a hub like Sakatoon, Thompson, or Edmonton. Anyone who has flown in any of these areas understands quite easily the utility of an offset, within the lateral confines of an airway or direct track.

[fanspeed]

Also very common to get a radar alt return off the aircraft below you while flying in the high level airspace......stay alert kiddos.

[fanspeed]

There are no crossing tracks in the NAT system.

[fanspeed]

In the NAT airspace, you can see who you are following. Domestic airspace? Think of any number of northern communities/minesites/oilfields where there is a lot of traffic between a hub like Sakatoon, Thompson, or Edmonton. Anyone who has flown in any of these areas understands quite easily the utility of an offset, within the lateral confines of an airway or direct track.

But unless there is specific coordination between each aircraft, the offset is meaningless; If everyone flies a 1nm offset (or 2nm or 3nm), then, as previously noted, all you are doing is shifting the centreline of the airway or track, and everyone ends up in the same potential conflict.

I watch a radar screen all day long, and from where I'm sitting, pilots should be a lot more concerned about crossing track conflicts than overtake conflicts.

Offsets do nothing to address crossing track conflicts, and without specific coordination between same track aircraft, your random offset value (1mile, 1.2miles, 3miles) will do nothing more than introduce a random variable into the chances you're going to run over someone. Introducing a random variable on top of all the other random variables already at play is statistically meaningless in terms of conflict prevention.

Altimeter error/variance is much more likely to save you than an offset will.

I agree, crossing traffic is a problem, however, not as large a problem as opposite direction climbing/descending in uncontrolled airspace to/from the same spot. I have seen conflicts in controlled high level airspace, with a controller issuing a descent clearance to one aircraft which is in DIRECT conflict with another because of the accuracy of each aircraft's nav system.

[North Shore]

I'm not sure anybody cares, but turning is often not the best choice for collision avoidance, for several reasons.

And those reasons are? I can think of the "what direction should I turn?" dilemma - but doesn't the climb/descend alternate carry the same one?
Maybe safer to not go flying - less risk of accidents/incidents/paperwork etc...