GFA question

[charrois]

I guess that my thought is that this "oversight", if that's what it is, is unexpected in an industry that almost seems to pride itself in semantics (on tests, they love to ask things like if an altimeter should be set to 29.92 at 18,000 feet and above, or above 18,000 feet.. or want you to distinguish if the standard lapse rate is 1.98 degrees/thousand feet or 2 degrees/thousand feet). In perhaps this industry more than most others, the details and semantics are considered to matter.

As to whether it has an impact on things.. yes, it does. If my airport elevation is at 3000' and they draw a freezing line labelled at 2500' passing over it, as is the case in the GFA I posted, quite simply, is it expected to be freezing at that airport or not? If 2500' is height above sea level as is claimed, it should be freezing at the airport. But a SFC freezing line north of the airport indicates that it would be warmer than that. I understand that a GFA represents a large area, doesn't double as a topographical map, and indicates larger "trends" as opposed to specific detail, but the area I was referring to, around Lethbridge, isn't particularly hilly - it isn't that the implicit resolution in a GFA is too course to represent what's really going on. As was mentioned earlier, if SFC represents a freezing level at the surface, and all the other lines represent freezing level referenced to sea level, they should not necessarily follow the same basic routes, and it would be very likely that often a SFC line would cross the other contours. Yet this isn't what happens.

Plus, if the SFC line really does represent freezing level at sea level, as is seeming possible, the difference in interpretation could yield several degrees C in error with airport elevations of a few thousand feet. Considering that one of the big purposes of freezing level in the first place is to avoid icing conditions, it is hard to imagine that this could be considered insignificant enough to justify sorting out.

And though it may be true that something like 95% of the prairies are under 2500' ASL, at least in Alberta, more than 90% of the population lives above 2000' ASL. So, near a large proportion of airports in the province, we should see the 2500' ASL and SFC lines always very near to one another, yet they aren't.

The T's just aren't crossed and the I's not dotted as well as most things in this industry are, and that's what makes me want to investigate further.

I'm going to try if I can this sorted out by someone at NavCanada - if I do, I'll report back here on what I've found.

Dan

[5x5]

You certainly can entertain any crusade you want, but make sure you aren't indulging in the same "misstatements" that seem to have you so bothered.

I guess that my thought is that this "oversight", if that's what it is, is unexpected in an industry that almost seems to pride itself in semantics (on tests, they love to ask things like if an altimeter should be set to 29.92 at 18,000 feet and above, or above 18,000 feet.. or want you to distinguish if the standard lapse rate is 1.98 degrees/thousand feet or 2 degrees/thousand feet). In perhaps this industry more than most others, the details and semantics are considered to matter.

I don't think Transport Canada's written exams display the nature of the entire industry by any stretch of the imagination. And as for details and semantics why not look at Engineering and Law as just 2 examples of industries much more into details than flying will ever be.

And though it may be true that something like 95% of the prairies are under 2500' ASL, at least in Alberta, more than 90% of the population lives above 2000'

I'd be interested to know where this statistic comes from. Edmonton is only 2200' and as far as I know it makes up much more than 10% of the provincial population all by itself.

I'll apologize in advance for being a bit of an ass, but I am having a tough time figuring out what's got you so bothered about this.

[charrois]

I don't think Transport Canada's written exams display the nature of the entire industry by any stretch of the imagination. And as for details and semantics why not look at Engineering and Law as just 2 examples of industries much more into details than flying will ever be.

Actually, I am both an Engineer (Electrical) and a pilot, so I do consider myself reasonably qualified to make comparisons between the two. Sometimes details do matter (though not always, I'll agree). In this case, the distinction between whether SFC denotes freezing level to be at ground level or at sea level can be worth investigating. In the case of a 3000' elevation airport, a 6 degree C difference between the two can be expected. That's why I'm interested in clarification. Maybe most people aren't interested in resolving the distinction, and that's fine. I posted my question here to see if this is something anyone had considered before, or to see if there was something obvious I had overlooked.

Naturally, TC's exams don't represent the industry as a whole. But they are representative of "official" sources of aviation information, which is why I would be surprised to hear if similar adherence to details is not typical of Nav Canada's GFAs as well.

And though it may be true that something like 95% of the prairies are under 2500' ASL, at least in Alberta, more than 90% of the population lives above 2000'

I'd be interested to know where this statistic comes from. Edmonton is only 2200' and as far as I know it makes up much more than 10% of the provincial population all by itself.

I agree fully. That's why I claimed most of the population lives about 2000', not 2500'.

[AuxBatOn]

So, how many incidents/accidents were due to this?

[charrois]

To put this in context as to why I care about resolving this:

I'm very fortunate to be married to someone who not only tolerates my love for flying, but shares in it. Having flown with me for 12 years, she's now working on getting her PPL and just wrote her PPAER. One of the questions she had was about icing levels on the GFA, and when she asked me about it, it got me looking more closely at them. And that's when I discovered the anomaly, whether it be an anomaly in my understanding in how they are to be interpreted, or whether it be an actual anomaly in the product itself.

So, how many incidents/accidents were due to this?

To me, whether or not there have been any accidents or incidents related to this is irrelevant. I don't believe any industry (particularly this one) is best served by waiting for something to happen before resolving a known problem, if one in fact is identified to exist (and similarly, I don't believe in knee-jerk reactions to issues when they do occur - something that is sadly becoming more and more common in society lately).

I've always lived by the motto that if I see something I don't understand, I want to learn and understand it. If I find something broken, I want to fix it. I have a very hard time accepting the complacent alternate viewpoint of doing nothing to increase one's understanding of a concept, or fixing a known issue. To me, it's akin to a person writing a document, identifying a spelling mistake in it, and then not bothering to fix it. If that's the sort of a personality someone has, they'd better not come to me looking for a job, even if it has nothing to do with spelling.

This isn't an obsessive viewpoint - though I intend to, I still haven't yet gotten around to writing to Nav Canada for their input. Yet, by nature, piloting is a problem-solving activity, and I would expect most competent pilots to also be competent problem solvers, and certainly not problem-ignorers, even for comparatively inconsequential issues.

I'm sure everyone here has heard the clichés, such as the one said by my flight examiner when I got my PPL ("You just got a license to learn" - and he really did say that, as cliché as it is ). But I take that to heart, as I try to do with everything I do. Once, when working on my PPL, my instructor asked me to hold a certain altitude and I asked him how accurately he expected me to hold it. He told me not to think in terms of things being "good enough", but rather, simply, if I was low then climb; if I was high, then descend. If I knew I was 20 feet too high, then why shouldn't I try and descend to the proper altitude? At the time, I thought his expectations of my ability were a bit excessive, but over time I realized it was some of the best advice I'd received. Of course, in reality I very rarely manage to actually hold my altitude within 20 feet all the time, but I do much better in at least trying to do my best. The same applies to the GFAs. If it turns out there actually is a problem (and not just my own misinterpretation), then even if the problem doesn't greatly affect the "big picture", why shouldn't it be fixed?

In any case, I'm not asking that everyone share my desire to fully understand this issue, or identify and fix a problem if there turns out to be one. I only posted my question to see if this was something somebody had already noticed, or to identify if my understanding of it wasn't accurate.

[pdw]

One of the questions she had was about icing levels on the GFA, and when she asked me about it, it got me looking more closely at them. And that's when I discovered the anomaly, whether it be an anomaly in my understanding in how they are to be interpreted, or whether it be an actual anomaly in the product itself.

The freezing level is the educated approximation (interpolated) where the temperature is going to be Zero C and when. Since an icing question precipitated this discussion, it's important to note that there's a chance for ice catch on your aircraft well above or below that line (or either side-of).

The only way to have real confirmation where exactly an icing level is producing ice catch on aircraft surfaces (where it becomes necessary to climb or descend to get out of it) is the P I R E P, an optional safety gesture heard-from / given-to other pilots. Anywhere near an "airport" is verified with hourly metars how close to the GFA's prediction.

A 2500ft interval showing where freezing starts, already hints that it is fairly general to be able to pinpoint exactly at what altitude it will be at where you'll be flying. Only when aiming for a low enroute altitude is IMO where the difficulty of this question would be realized.

[tcott]

@charrois

Did you ever find an answer to this? I am wondering the exact same thing. Mixing AGL and ASL is not done anywhere else, so I don't know why it's done here.