Cold Temp Restricted Airports

Let'sgoflying!

Let'sgoflying!

Touchdown! Greaser!
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Dave Taylor
I'd guess everyone else gets the same email notams as me; today was one involving CTRA's.
I was sick that day, can someone give me the abbreviated class notes?
(It is buried in a 700 page 25MB pdf)

I saw some significant altitude aberrations on their chart, at only -10C, and I fly out of 5000'msl airports in the winter, sometimes imc.
Come to think of it, I have never heard any of the language in the document used, between a/c and atc during cold weather flying.

As usual I am especially interested in the practicality of these things rather than the esoteric or legal. Thanks.
 
When the weather is colder, your altimeter will read higher than you actuall are. You are supposed to correct your step downs so you don't get too close to terrain. Pretty straight forward.

The colder air has less pressure but that is not taken into consideration in the altimeter setting you are given.

Use the chart for altitude errors and everything will be okay.
 
The relevant info starts on page 387 of the current NOTAP.

The practical object is to keep you from hitting stuff due to cold weather altimeter errors. It's not airport elevation that matters, but rather the height of the approach altitudes above the airport elevation that determines the error.

You haven't heard it on the radio because it isn't generally taught.
 
Let'sgoflying! said:
So, it's not done because it's so new, or it is generally ignored?
I wonder what cfit accidents are available for review on this?
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It is on the approach plate, it isn't the controller's job to tell you. Just like they don't tell you to do a procedure turn when one is necessary for your entry path.

I hope it is done by pilots flying in those conditions.
 
It's the pilot's responsibility to comply with cold temperature compensation on the approach plate. The pilot should also inform ATC if they're using CTC procedures during the IAP, unless it'll be used only on final. That's so ATC can adjust for separation.

Yes, it is a fairly new procedures. Maybe came out a couple years ago.
 
Velocity173 said:
It's the pilot's responsibility to comply with cold temperature compensation on the approach plate. The pilot should also inform ATC if they're using CTC procedures during the IAP, unless it'll be used only on final. That's so ATC can adjust for separation.

Yes, it is a fairly new procedures. Maybe came out a couple years ago.
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The FAA was last to implement these procedures. Northern countries have done it for years. In 1992 the Air Force got disgusted with the FAA dragging its feet, so they implemented a service-wide procedure. They came very, very close to losing a transport at Tule AFB, Greenland, that got their attention.
 
aterpster said:
The FAA was last to implement these procedures. Northern countries have done it for years. In 1992 the Air Force got disgusted with the FAA dragging its feet, so they implemented a service-wide procedure. They came very, very close to losing a transport at Tule AFB, Greenland, that got their attention.
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Yeah, we were always taught to compensate in the Army as well. Always carried an FIH with the compensation chart while flying.
 
MauleSkinner said:
Cold weather compensation has been in the AIM for at least 10-15 years.
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Correct, but the NOTAM for specific airports, the procedures involved, and the current / future implementation of the "snow flake," on IAP is less than 2 yrs old. The procedures for ATC in handling a pilot's CTC are new changes to the controller's manual as well.
 
Agreed...but if it was in the AIM, it should've been taught/implemented.

Obviously it wasn't required by NOTAM or in the PTS, so as far as instructors and pilots are concerned, it didn't exist. :rolleyes:
 
MauleSkinner said:
Agreed...but if it was in the AIM, it should've been taught/implemented.

Obviously it wasn't required by NOTAM or in the PTS, so as far as instructors and pilots are concerned, it didn't exist. :rolleyes:
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When going through instrument training I wondered what the snowflakes were for on the plates. I had to hunt down the answer for myself.
 
Let'sgoflying! said:
So, it's not done because it's so new, or it is generally ignored?
I wonder what cfit accidents are available for review on this?
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I found this. It seems to me I recall a Alaska Airlines accident that was about cold weather temperature correction.

Another helicopter accident report from the Canadian Aviation Safety Board points out the hazards of failing to correct for temperature. Fortunately, there were no fatalities in this incident:

"The helicopter was dispatched [to an offshore oil rig inside the Arctic Circle] at night, in IFR conditions... The crew descended on the inbound leg to 150 feet, with reference to the pilot's altimeter. The helicopter struck the sea ice and was destroyed by post-impact fire. The crew had not applied a temperature correction to the minimum descent altitude [approximately 40 feet to as much as 100 feet-Ed.], and this omission-combined with the known 50-foot error in the pilot's altimeter-accounted for the mistaken belief the helicopter was higher." (A81W0134)
 
Joshuajayg said:
The colder air has less pressure but that is not taken into consideration in the altimeter setting you are given.
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Can you expand on this? Cold air is more dense, but you're saying it has less pressure? I haven't really read much on this, but I thought is was because of the difference in pressure gradient as altitude increases and that the altimeter setting was corrected for the temp at airport elevation. It doesn't completely make sense to me but I haven't completely thought it through.
 
It says, "pilots without temperature compensating aircraft"
What equipment makes an a/c temperature compensating?

How can the cold weather affect only some runways at an airport and not others?
(Midway)

Why is there no correction (or less correction) as you get closer to the ground in many cases?
 
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Let'sgoflying! said:
It says, "aircraft without temperature compensating aircraft"
What equipment makes an a/c temperature compensating?
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Usually FMSs, maybe some GPS units.
How can the cold weather affect only some runways at an airport and not others?
(Midway)
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It's not the runway, it's the individual obstacles under the approach path.
Why is there no correction (or less correction) as you get closer to the ground in many cases?
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because the altimeter setting is determined by an altimeter on the surface. Any errors are reduced the closer you get to the altitude at which the measurement was taken.
 
Cooter said:
Can you expand on this? Cold air is more dense, but you're saying it has less pressure? I haven't really read much on this, but I thought is was because of the difference in pressure gradient as altitude increases and that the altimeter setting was corrected for the temp at airport elevation. It doesn't completely make sense to me but I haven't completely thought it through.
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It's not that it has "less pressure". As you say, if it were that simple then the altimeter setting would take care of it. You have to think of the entire column above any location. In any column, the pressure decreases with altitude. As the air gets colder, the column contracts and along with it all the pressure levels, so that the altitude at which a given pressure is found goes down. Your altimeter makes assumptions about the temperature to convert pressure into altitude. If the temperature is colder than it assumes, it will read higher than the true altitude. (I'm not certain, but I think it assumes standard temperature.)

It's important to realize that with the altimeter setting broadcast over the AWOS, the altimeter will read correctly in the vicinity of the airport and near airport elevation. The error due to temperature increases with altitude because of the contraction (or expansion, in the case of unusually warm temperatures) of the air column.

That's an oversimplified explanation, but it gives the gist of the mechanism.
 
Let'sgoflying! said:
It says, "pilots without temperature compensating aircraft"
What equipment makes an a/c temperature compensating?
Click to expand...

Some high-end, state-of-the-art, jet airplanes have temperature compensating barometric systems.

How can the cold weather affect only some runways at an airport and not others?
(Midway)
Click to expand...

It can't. What "Midway" are you talking about.

Why is there no correction (or less correction) as you get closer to the ground in many cases?
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The altimeter setting source is corrected for the temperature at the airport's surface. Having your altimeter set at the same setting as the source cause temperature errors to be zero when you land.
 
aterpster said:
Some high-end, state-of-the-art, jet airplanes have temperature compensating barometric systems.



It can't. What "Midway" are you talking about.


The altimeter setting source is corrected for the temperature at the airport's surface. Having your altimeter set at the same setting as the source cause temperature errors to be zero when you land.
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There was an older copy of the Cold Weather Procedures linked through NBAA.org. I think it might have been the original one. It said temperature correction applies to all procedures at an airport unless specified otherwise. RW's 22L/22R at KMDW were specified. I can't figure out how to get it here. Scroll up this page to my link to the other thread on this and then scroll up to @azure's post that had the link
 
Don't believe me, huh? Think I'm lying again, eh?
Here. This is what the FAA is sending out lately, if it is not the exact link in the email, it appears to have the same text. It says at the top, "Notices to Airmen".
A few paragraphs down;
Exception: KMDW, Chicago Midway Intl, Runways 22L and 22 R. Cold temperature altitude corrections will ONLY be applied to approaches for runways 22L and 22R.
 

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Let'sgoflying! said:
Don't believe me, huh? Think I'm lying again, eh?
Here. This is what the FAA is sending out lately, if it is not the exact link in the email, it appears to have the same text. It says at the top, "Notices to Airmen".
A few paragraphs down;
Exception: KMDW, Chicago Midway Intl, Runways 22L and 22 R. Cold temperature altitude corrections will ONLY be applied to approaches for runways 22L and 22R.
Click to expand...
You're not lying, you're just operating with bad information instead of the good information the FAA wants you to reference.

Yes, it says "Notices to Airmen". That doesn't mean it's current, and in fact it's simply a sample to explain the process. Neither the current NTAP nor the previous one have KMDW listed as cold weather corrected airports. The current charts also don't show them as cold weather restricted.
 
The current Cold Temperature Restricted Airports is dated January 7, 2016. It is page 4-GEN-10 of the "Notices To Airmen, Domestic/International" dated September 16, 2016. That document says "Notices to Airmen included in this publication are NOT given during pilot briefings unless specifically requested by the pilot. An electronic version of this publication is on the internet at http://www.faa.gov/air_traffic/publications/notices
 
luvflyin said:
The current Cold Temperature Restricted Airports is dated January 7, 2016. It is page 4-GEN-10 of the "Notices To Airmen, Domestic/International" dated September 16, 2016. That document says "Notices to Airmen included in this publication are NOT given during pilot briefings unless specifically requested by the pilot. An electronic version of this publication is on the internet at http://www.faa.gov/air_traffic/publications/notices
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Yep. Current one is dated effective Sep 15.
 
Let'sgoflying! said:
How can the cold weather affect only some runways at an airport and not others?
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If no one has the answer, I will continue researching it, and let you know if I find anything.
(looks like we've drifted from the original question)
 
Let'sgoflying! said:
If no one has the answer, I will continue researching it, and let you know if I find anything.
(looks like we've drifted from the original question)
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Nonetheless it is relevant. I was somewhat involved with that project, although certainly not at the nuts-and-bolts level. I cannot think of any reason that the entire aircraft would not be affected. Speculation on my part: once the FAA decided to really bite the bullet on this one, their initial plan was to include only those IAPs that had an obstacle issue with very cold temperatures. But, that seems overly complex both for their assessments and for pilots.
 
Let'sgoflying! said:
If no one has the answer, I will continue researching it, and let you know if I find anything.
(looks like we've drifted from the original question)
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the current NOTAM doesn't have any airports with runways listed, but since the issue is obstacles under the approach paths, and approach paths are generally runway specific, they could list runways if they chose to go to that effort.

As Wally said, though, it's probably more work and expense than the return on investment.
 
This is my take on it. How it could affect some runways and approaches and not others is that the biggest altitude errors occur higher up. Higher up is farther out on the descent profile. Some of the restrictions apply to the final segement, some to the intermediate segements, some to the missed approach. Some are all segements and some are two of them. The ones that do not apply to the final segement obviously don't have obstruction problems in close/down low big enough to need correction.. The ones that apply only to to the intermediate segement are ones that have rising terrain out a ways from the airport. It looks like at one time, knowing that the altitude error problems would not be a big enough factor to all runways and approaches to a particular airport, they made provisions to be able to have exceptions to those runways that didn't actually need it. Like at KMDW a few years ago. Since then they don't seem to make a provision for those exceptions anymore. The logic could have been the time and expense to do the obstruction studies. But you would think that seeing as how those approaches were already TERP'd out and the obstruction data was available it wouldn't be that big a deal. There aren't all that many of them. Who knows what the rationale was. Somewhere there is probably a record of the discussions that took place about it. I can't find it.
 
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