Cold temp correction problem

[stephen6ix]

I’m practicing some cold corrections from the aim using the examples given below the chart, however the problem occurs when I try to work out the MDA straight in approach, I’ve calculated the PT correction correctly but not the MDA using the same method as the PT. Can anyone help me out and point out what I did wrong? I’ve attached both my working and the chart for reference

[Gannet167]

It looks like you're using an avg temp delta per foot between 2000 and 600. At 578 AGL, 500 and 600 would be a more appropriate range to use.

That's a very time consuming way to get your new minima. I've never seen it done like that in real life. For the purposes of an exam, perhaps it's necessary. But I'd just take 578 as being 3/4 of the way between 500 and 600. Therefore, use 3/4 of the range between 150 and 180, about 175' correction. Or, preferably, round up to 600 and use the temp correction for the more conservative number if the weather isn't close to minimums.

[Gannet167]

Rounding up:
2280 MDA - 2262 = 578 AGL.
600' AGL = 180' temp correction.

2840 + 180 = 3020' temp corrected MDA.

[Gannet167]

To go full nerd:
500' AGL = 150' correction
600' AGL = 180' correction

600 - 500 = 100
180 - 150 = 30

Therefore, 0.30 foot correction per foot AGL

578' * 0.3 = 173.4' correction at MDA

173.4 + 2840' = 3013.4' temp corrected MDA @ - 50c.

About 6' 8" off of the round up technique. Or, 1' 8" off using my original method. If you can fly within 8 feet......

[stephen6ix]

To go full nerd:
500' AGL = 150' correction
600' AGL = 180' correction

600 - 500 = 100
180 - 150 = 30

Therefore, 0.30 foot correction per foot AGL

578' * 0.3 = 173.4' correction at MDA

173.4 + 2840' = 3013.4' temp corrected MDA @ - 50c.

About 6' 8" off of the round up technique. Or, 1' 8" off using my original method. If you can fly within 8 feet......

dammit i see where i went wrong, thanks so much for taking the time out to help, really appreciate it

[leftoftrack]

there's an app for that

[co-joe]

there's an app for that

Which one do you use?

[valleyboy]

I assume this is for exam purposes because operationally you will need to do most of it in your head. Remember that in an approach all altitudes are minimum altitudes and there is nothing about any altitude above that. So if you refer to the charts just add fat numbers for the procedure and quadrant altitudes and round up for the MDA or DH - Examples it's -40 and correction gives you a correction for procedure turn corrected to 2700 feet -- just use 3000 ft and if the MDA says 230 set 250 you know it's all about safety and not churning out numbers to 5 decimal points. You need to do this is seconds operationally with all the distractions going on as well. Oh ya -- no correction on LPV MDA

I'm impressed that you got the information you were looking for and this thread was as all should be and the posters fielded good information. This site needs more of this-- cheers

[rxl]

It’s handy to note that at temps down to -10C the corrections on the TC cold correction chart are all 10% of the height above the altimeter setting source except above 2,000’ where it’s a little bit less. Much easier than -

Figure 9.9—Correction for Cold
Temperatures: Equation
Correction = H ×
((15 – t0)/(273 + t0 – 0.5 × L0 ( × (H + Hss) ))

where:
H = minimum height above the altimeter setting source
(setting source is normally the aerodrome
unless otherwise specified)
t0 = taerodrome + Lo * haerodrome aerodrome (or specified
temperature reporting point) temperature adjusted
to sea level
L0 = 0.0065˚C per metre or 0.00198˚C per foot
Hss = altimeter setting source elevation
taerodrome = aerodrome (or specified temperature reporting
point) temperature
haerodrome = aerodrome (or specified temperature
reporting point) elevation

[leftoftrack]

there's an app for that

Which one do you use?

Aviation cold temp correction. though that's just the first one on the list.

[co-joe]

there's an app for that

Which one do you use?

Aviation cold temp correction. though that's just the first one on the list.

I paid for one on my old phone, but the subscription didn't transfer. I couldn't remember which one it was.

[leftoftrack]

I never pay for anything

[NotDirty!]

Oh ya -- no correction on LPV MDA

Do you have a source for that? I am trying to understand why cold temperatures would affect the barometric altimeter on every other approach type, but not LPV... so if there is an ILS and LPV approach to the same runway, with the same charted mins, you can go lower on the LPV when it’s below freezing?

[valleyboy]

I guess if you want to apply temperature corrects that's you prerogative if it's more in your comfort zone. I do have to chuckle how complicated, with formulas and Apps when it can all be done by quickly viewing your chart and adding a fudge factor. Take it from me sitting many hours flying approaches at -40 and below it's was always entertaining watching people try and work out altitudes to the 20 feet in the dark and after the traffic and airport information. They caught on very quickly. The key is to brief what you are going to do.

Here is a link on a WAAS/LPV approach. You can did deeper if you like.

http://blog.duncanaviation.com/index/bi ... re-Effects

[2R]

One of the best tools is the GPS altitude display . Hard to find on some older gps models but well worth the effort for the added safety .
The GPS altitude is easy to use and display on modern GPS units . If you are flying in cold air or fast moving air it will show huge differences between what is displayed on the barometric altimeter and actual altitude above ground . Fun to use in mountainous areas when the wind in blowing . Barometric shows a climb and the gps shows descent .
Nice to know where the ground is , helps to maintain MDAs in real time and get on the correct descent path for a smooth efficient descent profile
The old whiz wheels have an easy window in them for altitude corrections , but I have not seen anyone carrying The small wheels for years ,some pilot watches have that function . But in a turbulent approach at night completely inaccurate and not as safe as modern methods.

[Rockie]

Oh ya -- no correction on LPV MDA

Do you have a source for that? I am trying to understand why cold temperatures would affect the barometric altimeter on every other approach type, but not LPV... so if there is an ILS and LPV approach to the same runway, with the same charted mins, you can go lower on the LPV when it’s below freezing?

Yes, you temperature correct an LPV DA (not MDA) just like you do on a CAT I ILS and any non-precision approach including LNAV, LNAV/VNAV and RNP AR.

Every approach except CAT II/III uses barometric minimums and are always subject to temperature errors (Note: some rare CAT II's use barometric minimums vs radalt in case of extreme terrain issues leading up to the runway threshold). Perhaps what valleyboy meant was that the FAF does not need to be temperature corrected on an LPV which is true.

[AuxBatOn]

One of the best tools is the GPS altitude display . Hard to find on some older gps models but well worth the effort for the added safety .
The GPS altitude is easy to use and display on modern GPS units . If you are flying in cold air or fast moving air it will show huge differences between what is displayed on the barometric altimeter and actual altitude above ground . Fun to use in mountainous areas when the wind in blowing . Barometric shows a climb and the gps shows descent .
Nice to know where the ground is , helps to maintain MDAs in real time and get on the correct descent path for a smooth efficient descent profile
The old whiz wheels have an easy window in them for altitude corrections , but I have not seen anyone carrying The small wheels for years ,some pilot watches have that function . But in a turbulent approach at night completely inaccurate and not as safe as modern methods.

GPS altitude does not equal barometric altitude. Also, depending on the terrain model and the slope of the actual terrain, altitude above ground derived from GPS can be wildly inaccurate.

[2R]

GPS is just one tool in a good situational awareness discipline . The great thing about GPS is when it is wrong it is not twenty feet wrong , more like four miles wrong . Although if you use all the equipment on each flight you do not have to wait until you are at the short finals to realize something is not working . I like the advice Flight Safety give about anomalies or issues “ resolve them above MDA “

[rxl]

I assume this is for exam purposes because operationally you will need to do most of it in your head. Remember that in an approach all altitudes are minimum altitudes and there is nothing about any altitude above that. So if you refer to the charts just add fat numbers for the procedure and quadrant altitudes and round up for the MDA or DH - Examples it's -40 and correction gives you a correction for procedure turn corrected to 2700 feet -- just use 3000 ft and if the MDA says 230 set 250 you know it's all about safety and not churning out numbers to 5 decimal points. You need to do this is seconds operationally with all the distractions going on as well. Oh ya -- no correction on LPV MDA

I'm impressed that you got the information you were looking for and this thread was as all should be and the posters fielded good information. This site needs more of this-- cheers

An RNAV GNSS approach with published LPV and/or LNAV/VNAV minima have a DA or Decision ALTITUDE not an MDA or minimum descent ALTITUDE They both must be corrected for cold temperature.
A modern augmented and temp compensated RNAV system is capable of accurately defining the required approach path through 3D space, but the point on that path where the decision to continue to land or go-around must be made is still defined by an ALTITUDE above mean sea level provided by a good old fashioned altimeter or air data computer. Altimeters and ADCs are only certified to be correct at standard temperatures. This means you must correct for colder than standard temperatures 0C and below or 10C and below if the DA or MDA is 1000’ HAA or higher.

[AuxBatOn]

GPS is just one tool in a good situational awareness discipline . The great thing about GPS is when it is wrong it is not twenty feet wrong , more like four miles wrong . Although if you use all the equipment on each flight you do not have to wait until you are at the short finals to realize something is not working . I like the advice Flight Safety give about anomalies or issues “ resolve them above MDA “

In some (extreme I’ll admit) cases, height above ground derived from GPS can be off by 1,000 or more feet, even if your GPS position is accurate to 0 feet (horizontally and vertically)