It doesn't make sense to me. Using the example of the approach posted on page one in Frankfurt, the LNAV/VNAV minima is 400' above runway elevation for category D aircraft.

As far as I know, when an approach procedure designer makes an approach, the make the minimums as low as possible without violating any of the requirements for the approach design with the most important one being minimum terrain clearance.

If the temperature at Frankfurt is at -15 C, the lowest allowable temperature for uncompensated FMC's, the aircraft will be a full 50 feet lower than the 400' height above the runway compared to a standard day.

The only way it makes sense to me that no temperature correction is allowed for the LNAV/VNAV minimums of 720' indicated altitude(400 above the runway) is if the designer of the approach took this alititude error at -15 C into account and raised the minimums the appropriate amount so that the required terrain clearance is always ensured for any temperature down to -15 C.

Is this what happens at the design stage?

Fcom bulletin?!
 

Any link to this Fcom bulletin?

Well, up to -15 I would fly it using LNAV/VNAV minima correcting the 720 to 760, possible correcting the intermediate altitude of 4000 as well. Below -15, say -20, I would use the LNAV minima of 840 corrected to 910 and would modify the alt at lompo to 4570 in the FMS. It would then calculate a new path from LOMPO at 4570 terminating at 50 over the threshold. I would make a little table in which I would correct the distance to alt table and check on my way down to see If I'm on the correct altitude.

This is how we train to do it, other companies may have different procedures.

Yes it is...

Only aircraft flying the approach using a vertical GPS input are not required to correct for cold weather as they fly the vertical profile based on satellite input not a barometric one.

The procedure design is based on the posted GPA. For example, if the GPA is shown at 3 degrees, the temperatures on the plate NA above and NA below, relate to this. The low temp limit is based on a 2.71 GPA and the upper a 3.1 GPA.

The obstacle clearance surface for the final approach is 500 feet at the FAF and tapers to 200 feet at threshold, the slope being basically 2.5%. This is where LNAV/VNAV gets the 250 HAT, 200 + 50 foot momentary descent.

Typically, the obstacles tend to be in the missed, which raises the DA/MDA. Obstacles in the approach phase, that is a whole different world...that is where NOTAMS come from! In design, its called find a different glideslope (based on above) or find a different path. When I was designing the RNP procedures with FAA approval, they did not allow obstacles in the approach.

I remember the test RNP procedure into Bradley, couldnt get it to work with the approach because of the ridge, as the FAA would not allow obstacles in the approach, but to match their design for the test, you had to. Found out that the FAA exempted themselves from that requirement (but no one else)

Sky...ac on LPV or GBAS are not required to compensate for temperature on final approach segment only. Other segements, temp comp is required.

I think I see the issue that Jammed Stab is talking about..

The above section is applicable when the temperature is below (or above) what is shown on the plate....not all the time..

the FCOM blends the conditions a little too much.

Up to what is shown on the plate, say -15, you do not correct the final approach segment. You still must correct the initial and intermediate segments.

Yes, however MDA needs to be corrected.

Negative, but no problems if you do provided you tell ATC and they are happy with the decision.

regards, FD.

addendum: picture hint
http://i67.tinypic.com/9glz05.png

Certainly, due to the missed approach, and when using the public criteria.

Care must be taken to see if the cold temperature correction has been taken into account for a tailored procedure.

As an example, for certain tailored procedures, the low temp listed on the plate was taken into account for the obstacle surfaces, aircraft, and turn performance.

As noted with PASC RNP, the public RNP is good from -18C to 54C (??? place on fire?) Using -18C, the procedure is good for about 25% of the year.

With the tailored procedures, there is another procedure, using the same waypoints, that is good from -50C to -19C. Same waypoints, different altitudes making certain that obstacle clearance in maintained though the missed, and even OEI at those temperatures.

Sorry, but you do. AND if you do, you have to notify ATC as to your calculations, especially to avoid conflicts and separation with other ac..... The criteria only considers non-comp baro for final approach segment, NOT initial, intermediate, missed.

I have a question, since you are aware that the DA considers a 50 momentary descent, and the MDA is a glass basement, do you adjust your DA given your actual momentary descent? Do you adjust your decision altitude, based on temp correction and your actual momentary descent, given the MDA?

SBAS-ABAS
 

You need to correct the temperature on a RNP APCH based on ABAS, that is down to LNAV/VNAV or LNAV minimums and
you don´t need to correct the temperature on a RNP APCH based on SBAS,that is down o LPV or LP minimuns.

SBAS based RNP APCHes use a geographical altitude instead of barometical altitude. A kind of radioaltimeter.

This is what Transport Canada have to say:

Advisory Circular 700-023

Spreadsheet using formula Doc 8168.
 

I use this spreadsheet on ipad/iphone. Formulas obtained from Doc 8168.

PM for questions or suggestions.

EW

http://lh3.googleusercontent.com/-pd...o/IMG_1325.JPG

New to RNAV approaches and having difficulty understanding it all with so many opinions out there. Can anyone confirm/correct the below flow for me please?

https://s13.postimg.org/c0lt3knk7/Capture.png

Picture not available.

Superpilot....

Note on the approach plate if it states non-compensated baro vnav...

http://i64.tinypic.com/sevadx.jpg

if it does, then that is your answer.

not sure where the (if below zero comes from) but look at the NA below/above

If it does, then that means that the minima has been designed down to the NA below/above temperature WITHOUT compensation.

A certain airline in Hong Kong does not even give all information above AND the info we do get is not even correct. The person in charge of it comes to the office on the little bus wearing a helmet.

Hi Superpilot, I take it what you have there is company guidance?

That much is certainly correct. Zero no doubt because that is the warmest temp in the ICAO correction table for a sea level airport. Although somewhere in the ICAO verbiage it says something suitably vague like 'if it is very much colder than ISA'.

This one would seem to refer to 'uncompensated baro-VNAV'. According to the FAA AC 90-105A:
And according to the FAA AIM:

Aircraft using baro VNAV with temperature compensation or aircraft using an alternate means for vertical guidance (e.g., SBAS) may disregard the temperature restrictions.

I assume that is a company or type specific thing.
I'm not sure what the definition of gate is there. Anyway, as far as altitudes, according to the FAA AIM:

The charted temperature limits are evaluated for the final approach segment only. Regardless of charted temperature limits or temperature compensation by the FMS, the pilot may need to manually compensate for cold temperature on minimum altitudes and the decision altitude.

ie if your airport is on the FAA 'Cold Temperature Restricted Airport' list, and it is cold enough, you will correct the requisite segment altitudes. Meanwhile, according to Eurocontrol guidelines:

The flight crew is responsible for any necessary cold temperature corrections to all published minimum altitudes/heights including the altitudes/heights for the initial and intermediate segment(s); the DA/H; and subsequent missed approach altitudes/heights, except for APV/BARO-VNAV approach procedures. In accordance with ICAO Doc 8168, PANS-OPS, Volume I, Part II, Section 4, Chapter 1, § 1.4.1, the final approach path vertical path angle (VPA) is safeguarded against the effects of low temperature by the design of the procedure.

...which sounds a little like 'don't bother correcting your segment altitudes if doing a baro-VNAV procedure'. Whilst according to Transport Canada:

Regardless of whether the FMS provides temperature compensation of the vertical path or not, all altitudes on the approach, including DA, should still be temperature corrected.

:confused: The various references don't exactly dovetail. And I would not second guess company rules; there may be a good reason. But if the airport temp is cold enough for a correction then to my mind it makes sense to correct all segments like the Canadians say (and the FAA now also have a 'correct all segments option'). You would for an ILS so I don't see why you wouldn't for baro-VNAV. Discuss.

Would it be back on profile at minima or at TDZE? It strikes me that an uncompensated baro-VNAV would still be slightly below profile at minima.

Wow. You guys don't half know how to make things difficult.

APV Baro (Lnav/Vnav)
- within charted temperature limits - no correction required to the platform heights but correction required to minimums.
- outside charted temperature limits - correction required to platform heights, some aircraft have a function certified to do this automatically in which case use it. If you don't have the function then calculate it yourself. Correction to minimums is required.

APV SBAS (LPV)
No correction to platform heights required as GPS height isn't effected by cold weather.
Minimums must still be corrected because they are referenced to barometric altimeter.

Sorry hoppy that's incorrect advice. Outside charted temperature limit you cannot do baro-VNAV to LNAV/VNAV minima unless you actually have the compensated equipment. It is not enough to simply temperature correct the 'platform altitude'. The only option is to use LNAV. That's the whole point, amply referenced in this thread. Even if it is somewhat complicated.

oggers,

Many thanks. Nope, this is my own understanding of things. No consolidated company info exists on this. Just a myriad of texts and documents. Gates is me referring to the platform altitudes at various distances. I was hesitant to call them platform altitudes as this might imply some kind of intermediate level off altitude.

Oggers,
You are of course correct. I should have left the "If you don't have the function then calculate it yourself" bit out and said if you don't have the system you can't do the approach.

It's been a long day.