Cold temperature corrections on LNAV/VNAV minima

[longobard]

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.

[Denti]

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.

[Citation2]

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

Thanks

[sonicbum]

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.

What's your or your operator idea?

Txs for sharing.

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.

[Skyjob]

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...

[I-2021]

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 (http://www.icao.int/APAC/Meetings/2013_APRAST3/5%20-%20CFIT%203%20CASA%20AC%20008A%20APV%20Final.pdf)

[Avenger]

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.

[JammedStab]

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.



Could you show me an example of that.

Thanks.

[FlightDetent]

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.

[I-2021]

Could you show me an example of that.

Thanks.

Hi,

check this (https://www.caanepal.org.np/publication/AIP%202011%20Amendment/AIP_AMDT_AIP_SUP_2012/RNP%20AR_AIRAC%20AIP%20SUP%2003%20May%202012_22-05-2012%20Final.pdf) chart page 5 of 7. Just below authorization required the chart reports a minimum temperature of -10 deg C.

[longobard]

Jammedstab

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

[longobard]

Citation2

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

[Denti]

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 (https://drive.google.com/file/d/0B7xVk204frwQbXZSbVQtZ2UwOE0/view?usp=sharing).

[aterpster]

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/aa214/aterpster/KBTV%20Correction%20Table_zpscicomwig.jpg

http://i201.photobucket.com/albums/aa214/aterpster/KBTV%20RNAV%20GPS%20Rwy%2015_zpssqmiazgc.jpg

[aterpster]

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.

[hawk37]

I have to advise ATC of the fact I am going to fly the intermediate segment at 2,200.'

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?

[aterpster]

hawk37:

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?

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.

[Xiamen]

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.

[aterpster]

Kiaman:

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.

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?

[B737900er]

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.)

[I-2021]

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.)

Hi B737,

just curious about which technique you have used to correct the altitudes according to your manufacturer/operator procedures.

Thanks.

[Denti]

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.)

Interesting, that would be a different according to our OM/A here. It states quite clearly:

"No corrections are needed for reported temperatures above -15°C or if the aerodrome temperature is at or above the minimum published temperature for the procedure being flown;"

[B737900er]

My company are new to RNAV/RNP approaches so they may be a bit confused as I am to this topic.

We are told if the temp is below 0 degrees we cold temp correct all procedure altitudes (platform, MSA, MDH, Dist/ALt ).

I understand that below the stated temp limitation on the chart Vnav can no longer be used.

[wiggy]

FWIW our EASA-land OM, paraphrased, for RNAV.../uncompensated VNAV states:

Always fly ATC assigned altitudes without corrections, unless considered unsafe.. etc etc.

If you are at or warmer than the charted minimum temperature for using VNAV then it can be used with no corrections to procedure altitudes.

If it is colder than the limiting temperature, you use the non-VNAV minima if they exist (and vertical mode to be used is V/S or FPA).

If it's any colder than ISA -25 you apply low temp corrections (using an approved table/calculator) to any platform/FAF altitude and MDA/DA. Tell ATC what your Platform/FAF crossing altitude is going to be.

[Avenger]

Cold Temperature Altitude Corrections
Extremely low temperatures create significant altimeter errors and greater potential for reduced terrain clearance. When the temperature is colder than ISA, true altitude will be lower than indicated altitude. Altimeter errors become significantly larger when the surface temperature approaches -30°C or colder, and also become larger with increasing height above the altimeter reference source.
Apply the altitude correction table when needed:
• no corrections are needed for reported temperatures above 0°C or if the airport temperature is at or above the minimum published temperature for the procedure being flown
• do not correct altimeter barometric reference settings
• ATC assigned altitudes or flight levels should not be adjusted for temperature when under radar control
• corrections apply to QNH and QFE operations
• apply corrections to all published minimum departure, en route and approach altitudes, including missed approach altitudes, according to the table below. Advise ATC of the corrections
• MDA/DA settings should be set at the corrected minimum altitudes for the approach
• subtract the elevation of the altimeter barometric reference setting source (normally the departure or destination airport elevation) from the published minimum altitude to be flown to determine “height above altimeter reference source”
• enter the table with Airport Temperature and with “height above altimeter reference source”. Read the correction where these two entries intersect. Add the correction to the published minimum altitude to be flown to determine the corrected indicated altitude to be flown. To correct an altitude above the altitude in the last column, use linear extrapolation (e.g., to correct 6000 feet or 1800 meters, use twice the correction for 3000 feet or 900 meters, respectively.) The corrected altitude must always be greater than the published minimum altitude
• if the corrected indicated altitude to be flown is between 100 foot increments, set the MCP altitude to the closest 100 foot increment above the corrected indicated altitude to be flown.

[Goldenrivett]

This document http://www.developpement-durable.gouv.fr/IMG/pdf/ST-GuideO1-_PBN-RNAV_GNSS__ENGv3.pdf says that no temperature corrections are required if the airport is at or above the minimum published on the chart.

If the temperature is below the published minimum then:
"7.5.4 Case of temperatures below minimum temperatures published on the approach chart

On the RNAV(GNSS) approach charts for which there is an APV BaroVNAV approach (presence of LNAV/VNAV minima), a minimum temperature use is published.
As a general rule, pilots should not use the FMS (Baro)VNAV function when the temperature is below the temperature limit published on the approach chart.
The associated non-precision approach (LNAV) can be performed but management of the vertical plane should use another flight technique (vertical speed (V/S) or flight path angle (FPA).
Pilots should then apply the cold temperature corrections necessary to comply with the different published minimum altitudes, i.e.:
- The altitude heights for the final segment (FAF, SDF, altitude/distance table);
- The MDA/H; and
- The V/S and/or FPA values. "

[JammedStab]

This document http://www.developpement-durable.gouv.fr/IMG/pdf/ST-GuideO1-_PBN-RNAV_GNSS__ENGv3.pdf says that no temperature corrections are required if the airport is at or above the minimum published on the chart.

If the temperature is below the published minimum then:
"7.5.4 Case of temperatures below minimum temperatures published on the approach chart

On the RNAV(GNSS) approach charts for which there is an APV BaroVNAV approach (presence of LNAV/VNAV minima), a minimum temperature use is published.
As a general rule, pilots should not use the FMS (Baro)VNAV function when the temperature is below the temperature limit published on the approach chart.
The associated non-precision approach (LNAV) can be performed but management of the vertical plane should use another flight technique (vertical speed (V/S) or flight path angle (FPA).
Pilots should then apply the cold temperature corrections necessary to comply with the different published minimum altitudes, i.e.:
- The altitude heights for the final segment (FAF, SDF, altitude/distance table);
- The MDA/H; and
- The V/S and/or FPA values. "

That is interesting. But it leaves things potentially open to interpretation. They should specifically mention whether the MDA needs to have a temperature correction as this is very important.

[Goldenrivett]

They should specifically mention whether the MDA needs to have a temperature correction

You should find that clarification in your company OPS Manual.
Ours says:

"Low Altitude Temperature Corrections
..... These corrections must be applied, as appropriate, when conducting an instrument approach:

To DA (except Baro-VNAV procedures that are published with a temperature limit) and MDA. ...."

[JammedStab]

You should find that clarification in your company OPS Manual.
Ours says:

"Low Altitude Temperature Corrections
..... These corrections must be applied, as appropriate, when conducting an instrument approach:

To DA (except Baro-VNAV procedures that are published with a temperature limit) and MDA. ...."

Thanks,

But I want official government publication info. I find that ops manuals tend to have a much higher rate of erronous info based on the individuals misinterpreting official information.

[Goldenrivett]

Hi JammedStab,
But I want official government publication info
Will Jeppesen do?
http://www.jeppesen.com/download/briefbull/den00-arnav.pdf See Page 8
"Cold Temperature Limitations. Considering the pronounced effect of nonstandard temperature on BARO-VNAV operations, a minimum temperature limitation will be published for each procedure for which BARO-VNAV operations are eligible.
This temperature represents the airport temperature below which use of the BAROVNAV will not be authorized to the LNAV/VNAV minimums."

[777AV8R]

The reference document for the construction and operational use of BARO-VNAV and temperature limits is: ICAO Doc 8168. For those of you who are using Jepp FD or Jepp FD Pro, this document is available in the manual list. The manuals located inside should be read. There is a wealth of information contained therein.

Jepp. is NOT regulatory material, it so happens that they produce material based on what regulatory and SARPS promulgate.

I've quoted most of the information here directly from Doc 8168.

In essence, when the procedure designers build an approach for BARO/VNAV, limited temperature effects are accounted for on the descent segment. The temperature limits are there to protect the shallow gradients during a managed or IAN type approach. That said however; the DH/DA/MDAs still must be accounted for with the correct non-standard temperature corrections found in the tables. If the temperature is outside of the published limits then the procedure can still be flown but not managed or IAN and all the altitudes in the descent must be corrected for temperature error.

Some aircraft equipment are certified to calculate their own corrections from the FMS to certain limits. If that is the case, then other corrections can be disregarded as long as the temperatures being flown are within the certification limits of the installed equipment.

This is directly from ICAO Doc: 8168

1.2.2 Atmospheric effects

1.2.2.1 Atmospheric errors associated with non-standard temperatures are considered in the design of the approach obstacle clearance surface. When temperatures are lower than standard, the aircraft’s true altitude will be lower than its barometric indicated altitudes.

1.2.2.2 Most existing VNAV systems do not correct for non-standard temperatures. At temperatures below standard, these errors can be significant and increase in magnitude as altitude above the station increases. The gradient of the approach obstacle clearance surface is reduced as a function of the minimum temperature promulgated for the procedure.
Note.— International Standard Atmosphere (ISA) temperature is 15°C at sea level with a lapse rate of 2°C per 1 000 ft of altitude.

1.2.3 Along-track position uncertainty
All RNAV systems have some amount of along-track error. This along-track uncertainty can mean that the VNAV system will start the descent too early and result in an error in the vertical path. This is compensated for in procedure design by relocating the threshold level origin of the approach obstacle clearance surface.

1.2.4 Flight technical error (FTE)
Flight technical error (FTE) is assumed to be contained within the standard non-precision margin of 75 m (246 ft). This is added below the VPA before the obstacle clearance surface is adjusted for cold temperature and along-track error.

1.2.5 Other system errors
Other errors include static source error, non-homogenous weather phenomena and latency effects. These are insignificant compared with the other errors already addressed and are considered as contained within the existing margin.

1.2.6 Blunder errors
Application of an incorrect or out-of-date altimeter setting, either by air traffic control or the pilot, is possible and must be prevented by appropriate operational techniques.

1.3 EQUIPMENT REQUIREMENTS
1.3.1 APV/baro-VNAV procedures are intended for use by aircraft equipped with flight management systems (FMS) or other RNAV systems capable of computing barometric VNAV paths and displaying the relevant deviations on the instrument display.

1.3.2 Aircraft equipped with APV/baro-VNAV systems that have been approved by the State of the Operator for the appropriate level of lateral navigation (LNAV)/VNAV operations may use these systems to carry out APV/baro- VNAV approaches provided that:

a) the navigation system has a certificated performance equal to or less than 0.6 km (0.3 NM), with 95 per cent probability. This includes:

1) GNSS navigation systems certified for approach operations;

2) multi-sensor systems using inertial reference units in combination with certified DME/DME or GNSS; and 3) RNP systems approved for RNP 0.3 operations or less;

b) the APV/baro-VNA V equipment is serviceable;

c) the aircraft and aircraft systems are appropriately certified for the intended APV/baro-VNAV approach operations;

d) the aircraft is equipped with an integrated LNAV/VNAV system with an accurate source of barometric altitude; and

e) the VNAV altitudes and all relevant procedural and navigational information are retrieved from a navigation database whose integrity is supported by appropriate quality assurance measures.

Note.— Acceptable means of compliance can be found in documents such as the United States Federal Aviation Administration (FAA) Advisory Circular (AC) 20-138, AC 20-130A and AC 120-29.

1.3.3 Where LNAV/baro-VNAV procedures are promulgated, the approach area has been assessed for obstacles penetrating the Annex 14 inner approach, inner transitional and balked landing surfaces. If obstacles penetrate these surfaces, a restriction is placed on the minimum value of OCA/H permitted (see 1.1.5).

1.4 OPERATIONAL CONSTRAINTS

1.4.1 Pilots are responsible for any necessary cold temperature corrections 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.

Note.— The final approach path VPA is safeguarded against the effects of low temperature by the design of the procedure.

1.4.2 Temperatures below the promulgated minimum
Baro-VNAV procedures are not permitted when the aerodrome temperature is below the promulgated minimum aerodrome temperature for the procedure, unless the flight management system (FMS) is equipped with approved cold temperature compensation for the final approach. In this case, the minimum temperature can be disregarded provided it is within the minimum certificated temperature limits for the equipment. Below this temperature, and for aircraft that do not have FMSs equipped with approved cold temperature compensation for the final approach, an LNAV procedure may still be used provided that:

a) a conventional RNAV non-precision procedure and APV/LNAV OCA/H are promulgated for the approach; and

b) the appropriate cold temperature altimeter correction is applied to all minimum promulgated altitudes/heights by the pilot.

1.4.3 A VPA deviation chart may be published on baro-VNAV instrument procedure charts, correlating an aerodrome temperature with an associated true VPA. This chart is intended to advise flight crews that although the non- temperature compensated aircraft’s avionics system may be indicating the promulgated final approach VPA, the actual VPA is different from the information presented to them by the system.

1.4.4 This chart is not intended to have the pilot increase or decrease the VPA flown to achieve the actual promulgated VPA. A sample of the chart is provided in Table II-4-1-1.

1.4.5 Some baro-VNAV systems have the capability to correctly compensate the VPA of an instrument approach procedure following an input of the aerodrome (altimeter source) temperature by the pilot. Pilots operating aircraft with this feature active are expected to ignore the VPA chart and fly the system-corrected VPA guidance

I hope that helps. Doc 8168 contains a wealth of information including correct entry procedures for conducting GNSS approaches, something that many still misunderstand.

So, when sitting there in the middle of the night as you're hauling *ss across the NOPAC/SOPAC/NATS or POLAR, haul out the manual and have a look. That's flying!
Seasons Greetings and a safe flying for New Year 2016 to all.

[JammedStab]

Thanks. The way I interpret the above, is that regardless of the type of Baro-VNAV approach being performed, corrections must be made to all published minimum altitudes/heights.

[777AV8R]

If you are under radar control, there is no need to correct for vectoring altitudes. If you are cleared for a full procedure approach (complete with procedure turn) but you are under radar control, there is no need for corrections for procedure turn altitudes It is good airmanship to be aware of what the correction is, in case of LossComms or automation difficulties.

If using BARO/VNAV andyou are within the temperature limit of the approach, you may descend on the vertical descent path established either 'managed, VNAV/IAN' without having to make any corrections, however; it is a good idea to know what these corrections are (in the case of DME fix or FAF), in-case there is a failure of the automation and you're able to maintain a vertical descent using an alternative method (VS).

What MUST be done is: The DH/MDA/DA must be corrected for temperature for the approach, otherwise you could reach minimums and actually be below the obstruction clearance altitude (due to altimeter error).

If the OAT is colder than the Limit Temperature, the procedure cannot be flown using the automation and an alternative approach would be selected using a constant descent profile...good old VS!

Previously I mentioned referenced Regulatory material...ICAO is NOT regulator, it provides Standards and Recommended Practices (SARPS). From ICAO's documentation and technical publications, performance engineers and procedures engineers develop approach profiles that meet local regulatory requirements.

I hope that helps.

[FlightDetent]

Thank you very much. I think your post is true in every word. Also, the only correct one so far!: O

[underfire]

terpster is correct.

Temperature limits are listed for non-compensated baro, and the cold limit on a 3 degree glideslope is 2.71 degrees.

What is also important are the associated ROC per segment. Initial segments have a 1000' ROC, the intermediate has a 500' ROC, final approach segment tapers from 500' ROC to a 200' ROC. (assuming non-mountanous)

The FAA, in the design criteria, adjusts the FAS ROC per the coldest anticipated temperature at airport, but NOT the intermediate segment, or more important, the missed approach segment(s).
This is important to know when it gets colder, how important the obstacle clearance reduction is, especially with terrain.

Custom criteria may go further in the obstacle clearance criteria with temperature, especially when OEI procedures are considered.

In consideration of the design criteria, the FAA has a special Cold Temp Restricted Airports list, with special instructions.

ICAO criteria in general, looks more like the special cold restictions

Notices to Airmen Cold Temp − Restricted Airports
GENERAL 4−GEN−15

Pilots must make an altitude correction to the published, “at”, “at or above” and “at or below” altitudes on designated segment(s) (see list below), on all published procedures and runways, when the reported airport temperature is at or below the published airport cold temperature restriction.

Pilots without temperature compensating aircraft are responsible to calculate and make a manual cold temperature altitude correction to the designated segment(s) of the approach using the AIM 7-2-3, ICAO Cold Temperature Error Table.

Pilots with temperature compensating aircraft must ensure the system is on and operating for each segment requiring an altitude correction. Pilots must ensure they are flying at corrected altitude. If the system is not operating, the pilot is responsible to calculate and apply a manual cold weather altitude correction using the AIM 7-2-3 ICAO Cold Temperature Error Table. PILOTS SHOULD NOT MAKE AN ALTIMETER CHANGE to accomplish an altitude correction.

Pilots must report cold temperature corrected altitudes to Air Traffic Control (ATC) whenever applying a cold temperature correction on an intermediate segment and/or a published missed approach final altitude. This should be done on initial radio contact with the ATC issuing approach clearance. ATC requires this information in order to ensure appropriate vertical separation between known traffic.

Pilots must not apply cold temperature compensation to ATC assigned altitudes or when flying on radar vectors in lieu of a published missed approach procedure.

Pilots should query ATC when vectors to an intermediate segment are lower than the requested intermediate segment altitude corrected for temperature.

Pilots are encouraged to self-announce corrected altitude when flying into uncontrolled airfields.

[JammedStab]

Thank you very much. I think your post is true in every word. Also, the only correct one so far!: O
Mine is as well, correct the minimum altitudes.

[aterpster]

JammedStab:

Mine is as well, correct the minimum altitudes.

So was mine. :)

But, mine was limited to FAA-land.

To repeat myself, in FAA-land Baro VNAV final approach segment temperature limits are different than procedural altitude corrections for cold temperature. :ugh:

[longobard]

Guys, I opened the thread with both
ICAO SARPS references AND
EASA regulatory, but not exclusive, references (AMC 20-27)

Said that...I made reference to the new Airbus getting to grips with cold wx Ops,which clearly contrast to EASA AMC...

Company OMs can be on one side or the other but if I have to choose, I would preferably stay more on the safe side (EASA) than Airbus interpretation.

[underfire]

With the line breaks, the OP is a bit difficult to read.

It is important to know, depending on the procedure type, and which criteria, which segments are compensated for, and which one are not.

In reading through the sections, I am not sure I see a conflict...The EASA is a bit more comprehensive...

[flyburg]

Copied straight from my FCOM bulletin regarding RNAV GNSS approaches:

Cold Temperature Altitude Corrections
In the design of RNP APCH APV procedures with LNAV/VNAV minima, the
allowable temperature range is specified and the procedure design accounts for
operations and obstacle clearance for any temperature within the specified range
on the approach plate. If the actual temperature is within the specified temperature
range the pilot can fly the RNP APCH APV procedure and no temperature
corrections are needed. If the actual temperature is outside the specified
temperature range, the crew cannot fly the RNP APCH APV procedure.
In this case an RNP APCH NPA procedure with LNAV minima may be used and
the altitude constraints at FMC waypoints on the final approach need to be
modified according BOM 8.3-3, as the procedure design does not take
temperature variations into account.
For both RNP APCH APV (LNAV/VNAV minima) and RNP APCH NPA (LNAV
minima) approaches, the initial, intermediate and missed approach segment flight
plan fixes need to be corrected for cold temperature.
Note: DA/MDA must also be corrected for low temperatures


Makes perfect sense to me!!

Note: in case the temp is below the min temp specified, you can still fly the approach with LNAV and VNAV modes!!! Just not to LNAV/VNAV minima, but to LNAV minima raised for cold wx corrections.
(When temp is below 0 but above temp specified for LNAV/VNAV minima, you still have to raise the LNAV/VNAV minima)

[JammedStab]

Copied straight from my FCOM bulletin regarding RNAV GNSS approaches:

Cold Temperature Altitude Corrections

Makes perfect sense to me!!



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?

[longobard]

Any link to this Fcom bulletin?

[flyburg]

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.

[Skyjob]

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?

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.

[underfire]

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.

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.

[underfire]

For both RNP APCH APV (LNAV/VNAV minima) and RNP APCH NPA (LNAV minima) approaches, the initial, intermediate and missed approach segment flight plan fixes need to be corrected for cold temperature.
Note: DA/MDA must also be corrected for low temperatures

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.

[FlightDetent]

Up to what is shown on the plate, say -15, you do not correct the final approach segment. Yes, however MDA needs to be corrected.

You still must correct the initial and intermediate segments. 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

[underfire]

Yes, however MDA needs to be corrected.

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.

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

[chuchote]

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.

[oggers]

This is what Transport Canada have to say:

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.

Advisory Circular 700-023

[Dadanawa]

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

PM for questions or suggestions.

EW

http://lh3.googleusercontent.com/-pdMaG9Cg1rE/Vo529ykyHiI/AAAAAAAABG0/ZMzEYN0nlfM/s2048-no/IMG_1325.JPG

[Superpilot]

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

[FlightDetent]

Picture not available.

[underfire]

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.

[The Visionary]

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.

[oggers]

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

Is VNAV minima available?

If yes you may fly down to VNAV minima provided that:


The VNAV minima has been corrected for cold temperature (if below zero) thereby increasing


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'.


The actual temperature is not below the published minimum temperature


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

"Uncompensated baro-VNAV systems may not operate to the LNAV/VNAV DA when the actual temperature is below or above the temperature limitations. The temperature limitation will be shown as a note on the procedure. If the aircraft contains a temperature compensation capability, manufacturer instructions should be followed for use of the baro-VNAV function."

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.



The approach must be flown with the autopilot on and fully managed


I assume that is a company or type specific thing.


There is no requirement to increase altitude gates as terrain separation is guaranteed up to the minimum published temperature


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.


A typical autopilot coupled approach will fly below the profile up to minima where it will be back on profile.


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.

[FE Hoppy]

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.

[oggers]

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.


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.

[Superpilot]

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.

[FE Hoppy]

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.

[SR71]

A related question....

Is it a regulatory requirement to use an autopilot to fly a RNAV approach to LNAV/VNAV minima?

[ManaAdaSystem]

No, is the answer.

[Nick 1]

Can someone refresh my knowledge (or not ) , on two set of Minima for the same LNAV approach in this procedure ?


https://cimg5.ibsrv.net/gimg/pprune.org-vbulletin/1138x1835/02488e01_e7bb_44ad_8ebe_340debdf15e7_bce1b84ed952ddd9be791c6 20f601e25f86ae229.jpeg

[TeeS]

Hi Nick
The higher limit is based on an obstacle in the missed approach procedure and because at the standard assumed climb gradient that obstacle will not be cleared by the required minima the minimum descent altitude has to be raised from the minima calculated for the final approach sector on its own. However, if an aircraft can climb at 4.3% the the obstacle can be cleared from the lower minimum descent altitude. An MDA(H) has to be published based on the standard climb gradient.
Cheers
TeeS

[Nick 1]

Ahhhh…..yes . I’m an idiot . Thanks TeeS.

[Matey]

ICAO DOC 8168 (Flight Procedures) refers. The certification missed approach climb gradient is 2.1% for a twin jet. Most procedures are based on a missed approach climb gradient of 2.5% and produce the minima of 940ft from your chart to clear obstacles. If the aircraft can achieve a higher missed approach climb gradient then lower published minima can be achieved (670ft in your example at 4.3% gradient). The achievable gradient depends on temperature, airfield altitude land flap setting and aircraft weight. As an example, the 737 NG 27K engines and short field performance package can achieve about 3.2% at 78 tonnes (typical max T/O Weight) at a sea level airfield and 30 degrees C using flap 30 for landing. At 30 degrees,1000ft airfield elevation and a typical max landing weight of 65 tonnes with flap 30 it can achieve around 5.3% and so could comfortably use your lower minima. This would be a consideration when, for example, considering tankering fuel to a destination with poor weather, as the higher landing weight might not allow the use of the lower minima to increase the chance of a successful approach. From memory, an example would be the Runway 01R ILS minima at Dalaman in Turkey (LTBS) which give minima of around 850 feet for 2.5% missed approach gradient and 210 feet for 5% as you can start the missed approach from closer to obstacles with the better gradient. Lower land flap settings (flap 30 instead of flap 40 on the 737) give better gradients due to the higher approach speed, and further improvements can be achieved with bleeds off for landing.

[alf5071h]

Every question asked should trigger other thoughts (idiots rarely ask questions).

If lesser performance aircraft, higher DH, were required to fly a GA from below DH, i.e. a rejected landing (baulked landing), the ICAO doc appears to assume all engines operative, but also knowledge of procedural routing for engine failure after takeoff.

Is this correct ?

ICAO Doc 10064 - Aeroplane Performance Manual Page 27-28

https://www.sapoe.org/wp-content/uploads/2013/02/10-ICAO-Friction-Task-Force-and-EASA-Rulemaking-Task-Force.pdf#page60

“A distinction needs to be made between a missed approach and a rejected landing. A one-engine-inoperative missed approach from the minimum descent altitude (height) (MDA (H)), decision altitude (height) (DA (H)), or above can frequently be flown following the published missed approach procedure. A rejected landing from a lower altitude may require some other procedure (e.g., following the same one-engine-inoperative procedure as used for take-off). In any case, the pilot should be advised of the appropriate course of action when the published missed approach procedure cannot be safely executed.”

[compressor stall]

IIRC, the 2.5% starts at the Mapt for Terps and for PANSOPS at the MDA longitudinally 15 seconds at your max category speed further along the runway. If you’re below MDA, you’re below profile, and you’ll need more than 2.5 to get back above, if you don’t hit anything first. You should go another way. Like your EO SID.

[Nick 1]

This is a concept that many pilots are not aware of , flying the missed approach below the MDA thinking to be on the safe side , not always true.
Thank you gents .