Altimeter Setting

[Lance F]

I like to listen to ASOS and AWOS transmissions from airports in the area I'm flying to keep track of how things are going on the ground. If I hear an altimeter setting different from the last one I got when switching to a new TRACON or Center frequency, should I switch to it? I'll try looking this up in my new 2005 AIM when I get home, but if somebody has the reference handy for this now I'd like to hear it.

 

[Jeff Oslick]

You should be on the altimeter setting the approach/center controller gave you. Since that is what everyone else in his airspace is using, that is what matters most until you're getting ready to land. Now, if you notice a big discrepancy, I'd bring it to the controller's attention.

Jeff

 

[AirBaker]

I'd agree with Jeff. You might ask yourself if it is an ATIS or AWOS type broadcast? There could be a chance that the controller has newer baro information. Of course I suppose that could work the other way as well.

 

[Ed Guthrie]

I like to listen to ASOS and AWOS transmissions from airports in the area I'm flying to keep track of how things are going on the ground. If I hear an altimeter setting different from the last one I got when switching to a new TRACON or Center frequency, should I switch to it? I'll try looking this up in my new 2005 AIM when I get home, but if somebody has the reference handy for this now I'd like to hear it.

Good luck. "Altimeter setting" appears 40 times in AIM, but none of them are what you want. The phrase appears 5 times in FAR 91. The one you want to read is 91.1039. While this section does not directly apply to us it does somewhat explain the philosophy to use. Essentially, if available set local facility weather reporting altimeter setting when making the approach, or the number provided by the facility listed on the approch procedure. Enroute, as others have noted, you should be using the ATC provided number since it is the number the computer is using to keep everybody spatial resolved.

 

[Jeff Oslick]

I'll also add that when I'm flying over "open" country and not in contact with a controller, I will also tune in an available AWOS/ASOS every 15-20 minutes or so in order to keep track of the trend.


Jeff

 

[Henning]

I like to listen to ASOS and AWOS transmissions from airports in the area I'm flying to keep track of how things are going on the ground. If I hear an altimeter setting different from the last one I got when switching to a new TRACON or Center frequency, should I switch to it? I'll try looking this up in my new 2005 AIM when I get home, but if somebody has the reference handy for this now I'd like to hear it.

ATC altimeter enroute for traffic avoidance and field altimeter on approach for terrain avoidance.

 

[poadeleted20]

ATC altimeter enroute for traffic avoidance and field altimeter on approach for terrain avoidance.

Agreed.

 

[ejensen]

When I'm flying to a common destination with several planes, not formation, I like to have a common altimeter setting.

Eric

 

[Let'sgoflying!]

ATC altimeter enroute for traffic avoidance and field altimeter on approach for terrain avoidance.

What if the atis is an hour old; isn't approach altimeter more likely to keep you out of the trees? Not that much bp difference can happen in an hour. I guess they issue the atis more frequently when pressure changes more than a certain amount?

 

[Skip Miller]

What if the atis is an hour old; isn't approach altimeter more likely to keep you out of the trees?

At typical enroute altitudes you shouldn't be worried about the trees. What you should be worrying about is traffic. That's why it is good to have all aircraft in the same area on the same altimeter setting.

Not that much bp difference can happen in an hour. I guess they issue the atis more frequently when pressure changes more than a certain amount?

They do, and while doing your preflight, watch for PRESRR or PRESSFR in the METAR remarks. Pressure rising rapidly and falling rapidly.

-Skip

 

[Henning]

What if the atis is an hour old; isn't approach altimeter more likely to keep you out of the trees? Not that much bp difference can happen in an hour. I guess they issue the atis more frequently when pressure changes more than a certain amount?

When you don't have current and verifiable altimeter from a field, you adjust your minimums on approach. If ATIS/ASOS/AWAS and whatever other automatic reporting weather stations there are, isn't valid, what makes you think that ATC has is anymore valid info for that field? ATC enroute altimeter for your sector may be a couple hundred miles away as well. Personally I'd take an hour old ATIS and maybe I can get info from a nearby tower, that's typically good enough for published mins.