Cold temperature corrections on LNAV/VNAV minima
 

Hey guys,

I cannot really come to an end weather it's necessary or not to apply cold temperature corrections to minimum altitudes when performing RNAV GNSS apch using LNAV VNAV minima on A320/330.

According to the latest 2015 issue of Getting to grips with cold weather operations :

5.2.1 Low* altitude* temperature* corrections Corrections* on* an* indicated* altitude* have* to* be* applied* on* the* published* minimum altitude,* except* when* the* criteria* used* to* determine* minimum* flight* altitudes* are* already published* and* take* into* account* low* temperature* influences. (Reference to LFBO 14L RNAV GNSS Baro-Vnav minimum temperature is made).

On the other hand ICAO and EASA reminds crews to apply temperature corrections in APV approaches (regardless if the Baro-Vnav system incorporates or not a VPA auto compensation system or not):

ICAO PBN MANUAL DOC9613
6.3.4.2.12 Temperature compensation.* For aircraft* with* temperature* compensation* capabilities, approved* operating procedures may allow* pilots to disregard the* temperature* limits on RNP AR* APCH procedures if the operator provides pilot training on* the use of* the temperature compensation function. Temperature compensation* by* the system is applicable* to the baro-VNAV* guidance* and is* not a substitute* for the* pilot compensating* for the cold temperature effects on minimum altitudes or the DA. Pilots should be familiar* with* the* effects of* the temperature* compensation* on intercepting the compensated path described in EUROCAE ED-75B/ RTCA DO-236B Appendix H.

6.3.5.3.2 k) temperature compensation —* pilots* operating* avionics systems* with* compensation* for altimetry* errors introduced* by* deviations from ISA may disregard the temperature* limits on RNP AR APCH procedures, if* pilot training* on* the use of the temperature compensation* function* is provided* by* the operator and the compensation function is* utilized* by* the crew. However, the training* must also recognize the temperature compensation* by* the system is applicable to the* VNAV guidance and is not a substitute for* the pilot compensating for the cold* temperature effects on minimum altitudes or the DA.

6.4.2.11.3 The effect of extreme* temperature (e.g. extreme* cold* temperatures, known local atmospheric or* weather phenomena, high* winds, severe turbulence) on barometric* altitude* errors on the* vertical path is mitigated through the procedure* design* and crew* procedures,* with an allowance for* aircraft that compensate for this effect to conduct procedures regardless of the* published temperature limit.* The effect of* this error on minimum segment altitudes and the DA is addressed in an equivalent manner to all other approach operations.

EASA AMC 20-27A, Appendix 4* par.1.2:
For* APV* BARO-VNAV* operation,* pilots* are* responsible* for* any* necessary* cold temperature* compensations* to* all* published* minimum altitudes/heights.* This* includes: a)*** the* altitudes/heights* for* the* initial* and* intermediate* segment(s); b)*** the* DA/H;* and c)*** subsequent* missed* approach* altitudes/heights. APV* BARO-VNAV* procedures* are* not* permitted* when* the* aerodrome* temperature* is below* the* promulgated* minimum* aerodrome* temperature* for* the* procedure,* unless* the RNAV* system* is* equipped* with* approved* cold* temperature* compensation* for* the* final approach.

What's your or your operator idea?

Txs for sharing.

Not necessarily, there are quite a few procedures that are certified to a certain temperature, at my home base for example down to -15°C. In that case no correction is necessary to those procedures if the OAT is above or the same as the certification temperature.

However, the OPs question was about APVs, which is something i do not know much about as we do not fly them at all. None of our boeings or airbii is equipped for that.

Can you provide a link for the latest issue getting to grips with cold weather 2015?

Thanks

That you are not allowed to modify the procedure except for speed constraints. RNAV Approaches to LNAV/VNAV minima usually specify a minimum temperature in order to apply said minima, if no temperature is reported than we take 0 deg as a reference temperature. In all other conditions (temperature below the minimum specified for the procedure) we revert to LNAV minima and yes we start applying temperature corrections for the different characteristic altitudes (FCOM-PER-OPD).
Hope it makes sense.

sonicbum has the right approach to this situation.

There is a difference to LNAV, LNAV/VNAV and APV altitudes.

LNAV minima, like VOR, LOC, NDB and visuals are to be corrected for Cold Weather.
LNAV/VNAV minima are not, as the procedure is defined up to a minimum temperature for which it is safe to be used. This temperature must be displayed on the chart in order for the approach to be used.

APV minima are a different animal all together.
As the previous minima all apply to Barometric VNAV aircraft, the APV minima ONLY apply to aircraft which benefit from a vertical GPS input (eg not the 737). These minima do not require correcting as they are more accurate then barometric VNAV which relies on the correct QNH input to prevent a Blunder Error.

Ultimately, it is this latter Blunder Error we are trying to avoid, getting too close to terrain, when we are not supposed to be...

Hi Skyjob,

as far as the regulations permit, you can fly APVs with GNSS+Baro VNAV. The APV with GPS+SBAS will give you a lower minima.
Check out this document

6.3.2 Vertical accuracy for APV BARO*VNAV operation.
a) Altimetry System Error (ASE)
Altimetry system performance is demonstrated separately from the APV BARO*VNAV certification through the static pressure system certification process. With such approval (e.g. CS 25.1325), each system must be designed and installed so that the error in indicated pressure altitude, at sea*level, with a standard atmosphere, excluding instrument calibration error, does not result in an error of more than ±9 m (±30 ft) per 185 km/hr (100 knots) speed for the appropriate configuration in the speed range between 1·23 VSR0 with wing*flaps extended and 1·7 VSR1 with wing*flaps retracted. However, the error need not be less than ±9 m (±30 ft).

7.4 Recommended Function for APV BARO*VNAV operation
AMC 20*27
Item
Functional Description

1
Temperature compensation: Capability to automatically adjust the vertical flight path for temperature effects. The equipment should provide the capability for entry of altimeter source temperature to compute temperature compensation for the vertical flight path angle. The system should provide clear and distinct indication to the flight crew of this compensation/adjustment.

As an operator we make the cold weather corrections if required by the approach limits published.

Could you show me an example of that.

Thanks.

I am supposed to compensate for DA on ILS GP. The way I was trained to understand why, gives no option but to do the same for all other approaches too.

Hi,

check this chart page 5 of 7. Just below authorization required the chart reports a minimum temperature of -10 deg C.

Jammedstab

Rnav rnp ar follow a different certification process. I'm talking about rnav gnss with lnav/vnav minima.

Citation2

Sorry my company provided me the document, I don't have a link

On our LIDO charts there is usually a note at the baro vnav minimum which indicates the lowest usable temperature for uncompensated use of said minimum.

For example a random RNAV (GPS) approach from a well known airport nearby.

Following is an example of how its done at an airport that the FAA has designated as a "cold temperature" airport. Burlington, Vermont is one such airport. Below I show the Jeppesen cold temperature correction chart and the Jeppesen chart for the RNAV (GPS) Runway 15 IAP. The assumption I make for this example is the airplane I am flying has IFR-certified Baro VNAV but not WASS (SBAS).

There are two separate temperature issues for flying to LNAV/VNAV minimums.

Note 2 are the temperature limits within which I must be to use the VNAV glide-slope to the LNAV/VNAV DA. Note 3 requires me to apply cold station temperature corrections below -14 degrees Celsius.

on a day when the airport temperature is -15 degrees Celsius I can still fly to LNAV/VNAV minimums but I must apply temperature corrections to the terminal arrival area in which I am arriving. I'll leave that calculation to others. My calculation for the intermediate segment is a 201 foot additive to the 2,000' minimum altitude. I have to advise ATC of the fact I am going to fly the intermediate segment at 2,200.' For the DA I will add 40 feet. I do not have to advise ATC of the DA additive.

Finally, if the temperature were below -19 degrees Celsius I would have to fly to the LNAV MDA with the appropriate additive from the chart to MDA and to the 1,020’ stepdown altitude:

http://i201.photobucket.com/albums/a...pscicomwig.jpg

http://i201.photobucket.com/albums/a...pssqmiazgc.jpg

In the preceding example, if I were WAAS (SBAS) equipped there would be no temperature limitation for flying to LPV minimums, but I would nonetheless have to apply the appropriate corrections to the minimum altitudes for the TAA, intermediate segment, and DA.

I always thought the published altitudes were minimums, and if the pilot were to choose to descend on the intermediate segment to 2500 feet, level off, and intercept the vnav slope from 2500 ft then that was perfectly fine and atc did not need to be told. Exceptions of course it the chart says an "at" altitude.

Was this ever the case aterpster?

hawk37:

You are correct and that still is the case much of the time. But, the FAA includes the requirement in the cold temp procedure, because it has to cover 100% of the cases, especially where there is a mandatory altitude. The temperature correction would take precedence over the mandatory altitude.

If you fly a RNAV approach to non precision or LNAV minima, you correct all minimum altitudes.
If you fly a RNAV approach to VNAV minima or an GPS AR approach, both with minimum temperature stated on the chart, no temp corrections except your minima. If you are outside the minimum temp on the chart, you can't fly the approach.

Kiaman:

So, in the Burlington chart I show above, you aren't going to temperature correct the applicable minimum TAA altitude or the intermediate segment altitude?

I just recently done the in the sim. I was told to temp correct it all regardless of the temp limitation on the chart (outside the temp limitation of course you can't fly the approach.)