Wondering if fellow Northern IFR pilot's had any good suggestions or experience in obtaining an altimeter setting at an aerodrome with remote resources.
If there isn't a UNICOM available, technically I'm only good down to my ASA without a local altimeter setting. This can cause serious issues at ever getting in where some destinations have high surrounding terrain.
Is it viable (and legal) to have a company agent, sitting at home watching TV, have an altimeter sitting in their living room who can report an "unofficial" altimeter setting via the phone before you depart for your flight? Any other suggestions as to a way to obtain an altimeter setting at odd hours?
Sounds like a good way to get killed. You'd be safer just looking at the GFA.
Really, if the capabilities of the airport and aircraft aren't good enough for the actual weather conditions, why are you looking for creative ways to break the rules more safely? Why not just stay home in a nice warm fart sack and go when the weather gets better?
There is a thread titled "Safety Quote of the Week" running right now that you should have a look at.
Who's to say your friend sitting in his easy chair, watching Jeopardy, is reading it correctly? Better yet, how do you know the altimeter he is using is functioning correctly?
If there is no remote altimeter setting instructions on the approach plate, or better yet, an approach plate at all for an airport/strip you are going to, it's not safe to exceed the parameters of your Instrument Flight Rules. Is this a challenging concept?
Nice to see there's still a good supply of folks on avcanada who seem to have never been north of 60 or tried to operate an airplane for a living but are still willing to slam a new poster for asking advice....
I don't think id feel too good about the living room altimeter setting solution either. Sounds pretty illegal as well, if that's important. On the other hand, no matter who you get an altimeter setting from you should ask yourself if it makes sense before blindly setting and descending.
I would suggest asking some of your fellow northern pilots what they do. You will get a variety of answers depending on the operator. Anything from by the book- area safe and no lower- to using the most conservative setting you can find in any direction regardless of direction and distance- to lots of other even more scary ideas.
Nothing illegal about having an agent of your company put an altimeter box on his kitchen table, the only catch is making sure its calibration stays current and he or she is trained on how to read it. You also want to make sure the agent has a radio and accompanying licence to legally pass along the info. Back in the day the company I worked for had about 6 or 7 altimeter boxes set-up in strategic locations.
Gorgons wrote:Nothing illegal about having an agent of your company put an altimeter box on his kitchen table, the only catch is making sure its calibration stays current and he or she is trained on how to read it. You also want to make sure the agent has a radio and accompanying licence to legally pass along the info. Back in the day the company I worked for had about 6 or 7 altimeter boxes set-up in strategic locations.
cgzro wrote:Out of curiosity how accurate is gps altitude up there? I would imgine the low angles to the satelites makes for some largish errors?
The issue with GPS altitude is that it doesn't use the same Earth model as the MSL model... It uses Height Above Elipsoid, which can be hundreds of feet off when compared to MSL altitudes.
Nothing illegal about having an agent of your company put an altimeter box on his kitchen table
-- it is unless they have been trained and the company has done all the required paperwork --
Back in the day Austin Airways had altimeters (dual in their own box) -- great idea but if it had not been for a radalt I would have had a surprise of the nasty kind -- I always made the point of confirming the pressure altimeter with the radalt going through 2000' -- well the pressure dropped dramatically over night and the agent gave me a setting 1 inch out -- surprise --
I would rather extrapolate from surrounding stations - it will be close -- relying on a GPS -- mmmmmm -- it's like guys giving out winds short final and close to the ground -- you never have any way of telling if there has been any lag in the gps position updates -- i know not likely but to depend on a gps altitude when in a decent close to the ground (unless in a lpv approach mode) -- well -- spin the chamber and pull the trigger --
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Last edited by Liquid Charlie on Mon Oct 20, 2014 7:18 am, edited 1 time in total.
CBcloud9 wrote:Is it viable (and legal) to have a company agent, sitting at home watching TV, have an altimeter sitting in their living room who can report an "unofficial" altimeter setting via the phone before you depart for your flight?
This is viable if you can assure that what you are getting is as accurate and current as an official altimeter setting.
However, it is not legal. Furthermore, if you go to the bother of having an accurate altimeter setting, why not go all the way and get it certified so it is legal.
The pressure altimeter used in aircraft is a relatively accurate instrument, but the altitude information indicated by an altimeter may differ greatly from the actual height of the aircraft above mean sea level or above ground. In instances of aircraft operating close to the ground or above the highest obstacle en route, especially when not flying in visual conditions, knowledge of actual ground separation or of "error" in the altimeter indication is of prime importance if such separation is less than what would be assumed from the indicated altitude.
CAR 602.127(2) specifies that "no pilot-in-command of an IFR aircraft shall commence an instrument approach procedure unless the aircraft altimeter is set to an altimeter setting that is usable at the aerodrome where the approach is to be conducted."
TC provides operational guidance regarding altimeter setting procedures in section 9.17 of the AIM. Minimum altitudes in instrument approach procedures meet obstacle clearance requirements when International Standard Atmosphere (ISA) conditions exist and the aircraft altimeter is set to the current altimeter setting for that aerodrome. Altimeter settings are considered current up to 90 minutes from the time of observation. Care should be exercised when using altimeter settings older than 60 minutes or when pressure has been falling rapidly.
Under conditions of extreme cold, aircraft true altitude will be lower than indicated altitude, reducing obstacle clearance to less than the minimum required. Consequently, corrections to published altitudes should be applied to ensure adequate obstacle clearance. The CAP indicates that "in conditions of extreme cold weather pilots should add the values derived from the altitude correction chart to the published procedure altitudes." Section RAC 9.17.1 of the AIM indicates that "for practical operational use, it is appropriate to apply a temperature correction when the value exceeds 20 per cent of the associated minimum obstacle clearance."
Instrument approach procedures designed for use with altimeter setting sources more than 5 nm from the aerodrome reference point (ARP) include adjustments to procedure altitudes corresponding to the horizontal distance and elevation difference between the ARP and the altimeter source. A remote altimeter setting source is not authorized when the altimeter setting source is more than 75 nm from the ARP.
Good thread and good question. I think the takeaway here is to think about it every time regardless. If I ever have to turn that knob significantly after an hours flight or in the morning you can bet I'll be mentally comparing to surounding stations, checking feild elevation if I the ground, or looking at the gps elevation for reassurance.
Doesn't take long, and like lots of similar habits, if you fly long enough it's not an if but a when it will save your neck.
cgzro wrote:Ok but the difference between MSL and the elipsoid model is a constant for any given location on the earth and could be compensated for?
Yes, it is. See http://earth-info.nga.mil/GandG/wgs84/g ... wgs84.html . Differences between MSL and Height above WGS84 Ellipsoid range from -107m to +86m. Some GPS units will display either GPS or MSL altitudes (I know the GTN650 can display MSL - downright fantastic for obstacle clearance).
Assuming you have WAAS coverage and the GPS unit is using it, your GPS MSL altitude should get you within about +/-8m (typically +/-1-2m) vertically. Note that this MSL altitude is true MSL altitude assuming std atmosphere. So, while your pressure altimeter will under-read in cold weather, the GPS MSL version will not. (Don't use the GPS MSL for in-flight altitudes! Most days aren't standard atmosphere days, and everyone else will be flying with the temperature errors on their pressure altimeter. The GPS MSL can differ by 100's ft as it will not have these errors. I have seen temperature errors near 500ft at 12,500ft. After correcting for pressure altimeter temperature error, the pressure altimeter matched the GPS MSL altitude within a few 10's of feet.)
