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Cold temp baroVNAV - EASA language

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Cold temp baroVNAV - EASA language

Old 16th Jul 2019, 08:12
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Cold temp baroVNAV - EASA language

Oh not again, the winter is coming...

Are there any opinions about the DEFINITION / MEANING of the word compensation in this one EASA Air-OPS paragraph?

Reference: AMC2 SPO.OP.116 Performance-based navigation — aeroplanes and helicopters
MONITORING AND VERIFICATION
(d) Altimetry settings for RNP APCH operations using Baro VNAV
(2) Temperature compensation
(A) the flight crew should not commence the approach when the aerodrome temperature is outside the promulgated aerodrome temperature limits for the procedure unless the area navigation system is equipped with approved temperature compensation for the final approach;
(B) when the temperature is within promulgated limits, the flight crew should not make compensation to the altitude at the FAF and DA/H;
(C) since only the final approach segment is protected by the promulgated aerodrome temperature limits, the flight crew should consider the effect of temperature on terrain and obstacle clearance in other phases of flight.



In the (B) above, what are the arguments that the word compensation stands for either
- a feature of the airborne equipment (i.e. activating a temperature compensation algorithm of the FMC)
- a pilot's cognitive task (i.e. applying a temperature correction additive to a published value)




In the search for an answer myself, below is what I found in the regulation. I am reasonably certain the list is exhaustive, all appearances of words correction / compensation / temperature in the context of Baro VNAV.

Originally Posted by AMC1 CAT.OP.MPA.145(a) Establishment of minimum flight altitudes -CONSIDERATIONS FOR ESTABLISHING MINIMUM FLIGHT ALTITUDES
(b) The operator should also consider: [...] (1) corrections for temperature and pressure variations from standard values;
Originally Posted by AMC1 SPA.PBN.105(b) PBN operational approval FLIGHT CREW TRAINING AND QUALIFICATIONS
(b) Ground training [...] (2) General concepts of RNP AR APCH operation [...] (ii) [..] should include [...] in particular [...]
(K) the temperature compensation: Flight crew members operating avionics systems with compensation for altimetry errors introduced by deviations from ISA may disregard the temperature limits on RNP AR APCH procedures if flight crew training on use of the temperaturecompensation function is provided by the operator and the compensation function is utilised by the crew. However, the training should also recognise if the temperature compensation by the system is applicable to the VNAV guidance and is not a substitute for the flight crew compensating for the temperature effects on minimum altitudes or the DA/H


Originally Posted by AMC2 SPA.PBN.105(d) PBN operational approval - FLIGHT CONSIDERATIONS
(a) Modification of flight plan [...] not be authorised to fly a published RNP AR APCH procedure unless [...]
The only other acceptable modification to the loaded procedure is to change altitude and/or airspeed waypoint constraints on the initial, intermediate, or missed approach segments flight plan fixes (e.g. to apply temperature corrections or comply with an ATC clearance/instruction).

(j) Temperature compensation
For aircraft with temperature compensation capabilities, the flight crew may disregard the temperature limits on RNP procedures if the operator provides pilot training on the use of the temperature compensation function. It should be noted that a temperature compensation by the system is applicable to the VNAV guidance and is not a substitute for the flight crew compensating for temperature effects on minimum altitudes or DA/H. The flight crew should be familiar with the effects of the temperature compensation on intercepting the compensated path as described in EUROCAE ED-75C/RTCA DO-236C Appendix H.

The threads on the topic so far:
Cold temperature corrections on LNAV/VNAV minima, Cold temp corrections on LNAV appr, LNAV/VNAV BAROVNAV APPROACH, Temperature correction on Baro-VNAV approach, RNP approaches. A question about the APV version and low temperature
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Old 16th Jul 2019, 13:31
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sounds complicated!

I’ll let the FO do that approach!
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Old 16th Jul 2019, 14:39
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Any chance his second plan is to become an attorney and could explain?
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Old 16th Jul 2019, 18:07
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Compensation in this case means to increase your altitude above those stated in the charts to 'compensate' for your lower geometric altitude due to errors in the altimetry system as a result of the cold temperatures.

In the above case it seems to indicate FMS systems which automatically compensate for lower temperatures. An example is the FLS system in new Airbus aircraft .
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Old 16th Jul 2019, 20:08
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Assuming the "B" speaks of (not) using the FMS compensation function...

(B) when the temperature is within promulgated limits, the flight crew should not make compensationto the altitude at the FAF and DA/H; does not align with the logic of It should be noted that a temperature compensation by the system is applicable to the VNAV guidance and is not a substitute for the flight crew compensating for temperature effects on minimum altitudes or DA/H.

Because the combined meaning would be "you should not activate the FMS compensation function for FAF and DA/H" and supplemented with "if you did activate the FMS compensation function, be aware it is not good enough and you must manually correct minimum altitudes and DA/H." WTH?

I used to think COMPENSATION stood for FMS magic and the term CORRECTION was used for manual add-ons. But that leads to the above broken logic. On the contrary, their use of compensation in the various combinations suggests it is a generic term that stands for either of or even both.

... the temperature compensation by the system ...
... is not a substitute for the flight crew compensating for temperature effects


Then in turn the "B - ..., the flight crew should not make compensation to the altitude at the FAF and DA/H" simply means no cold corrections at all.

Correct?
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Old 17th Jul 2019, 01:13
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Pilots manually apply an altimeter correction to compensate the effect of cold temperature. (But they are still compensating)

Instruments incorporate a temperature compensation system to compensate the effect of cold temperature.

My interpretation of the EASA documents is that ‘compensation’ can mean both a pilot action and an instrument action.
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Old 17th Jul 2019, 10:07
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I used to think COMPENSATION stood for FMS magic and the term CORRECTION was used for manual add-ons. But that leads to the above broken logic. On the contrary, their use of compensation in the various combinations suggests it is a generic term that stands for either of or even both.

... the temperature compensation by the system ...
... is not a substitute for the flight crew compensating for temperature effects


Then in turn the "B - ..., the flight crew should not make compensation to the altitude at the FAF and DA/H" simply means no cold corrections at all.

Correct?
Although it is slightly confusing to use the compensation word in reference to both the automatic baro VNAV adjustment and the manual altitude adjustments, when I read it in context I think the distinction is inferred.

Bearing in mind the compensation of the baro VNAV system is not intended to adjust your altitudes, only to ensure that the correct geomemtric flight path angle is provided to the vertical guidance: [B] is saying that the published temperature limit is that down to which you do not need to correct the platform altitude or DA. In other words, the published temperature is that above which neither temperature compensation to the baro based flight path angle, nor cold error temperature correction to minimum altitudes, is needed to ensure the required obstacle clearance. That is how I read it.
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Old 18th Jul 2019, 17:31
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Thanks @oggers.

My A/C does not have the compensation feature but does have DA/H entry into the FMS. Having never seen what the boxes with the compensation are actually capable of, I let my mind loose too much.

Here's how I could explain now:

1) from the other instances of "temperature compensation" in the regulation, it is clear that the term does not exclusively reference an FMS feature.

2) in the case of AMC2 SPO.OP.116 (B) if we believed it applied solely to operations with the FMS compensation function, then (above the procedures' cold limit)
- (i) pilots with such feature are instructed not to correct the angle (FAF) nor decision minima (DA/H)
while pilots without such equipment, at the absence of EASA guidance but still pursuant to PANS-OPS, would need to
- (ii) not correct the angle (protected) but at the same time increase the minima by making a manual correction.

Clearly, 2 (i) and (ii) above would result in opposing guidance for the same approach under identical outside conditions. Hence the argument stands that the premise of 2) is false, and so AMC2 SPO.OP.116 (B) should be interpreted as being applicable to any form of temperature compensation, in a broader sense.

Additionally, increasing DA/H by a manual temperature correction and keeping the profile itself unchanged would bring the geometrical point of decision further from the runway, invalidating the RVR limit calculation. Avoiding this, as discussed in one of the threads of late, might be the actual reason behind the instruction of AMC2 SPO.OP.116 (B) not to compensate - to be applied to all approaches above the lowest promulgated temperature.

Hope it checks.
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Old 19th Jul 2019, 11:35
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Originally Posted by FlightDetent View Post
2) in the case of AMC2 SPO.OP.116 (B) if we believed it applied solely to operations with the FMS compensation function, then (above the procedures' cold limit)
- (i) pilots with such feature are instructed not to correct the angle (FAF) nor decision minima (DA/H)
while pilots without such equipment, at the absence of EASA guidance but still pursuant to PANS-OPS, would need to
- (ii) not correct the angle (protected) but at the same time increase the minima by making a manual correction.

Clearly, 2 (i) and (ii) above would result in opposing guidance for the same approach under identical outside conditions. Hence the argument stands that the premise of 2) is false, and so AMC2 SPO.OP.116 (B) should be interpreted as being applicable to any form of temperature compensation, in a broader sense.
....
Yes. When I read the 116.d.2.i from the top it says it applies to "baro VNAV" as opposed to compensated systems in particular. In para B there is no mention of compensated systems, hence I consider B as 'applicable to baro VNAV with or without automatic temperature compensation', as in: 'do not temperature correct FAF or DA in either case'.
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Old 19th Jul 2019, 13:43
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Originally Posted by oggers View Post
...116.d.2.i from the top it says it applies to "baro VNAV" as opposed to compensated systems in particular. In para B there is no mention of compensated systems, hence I consider B as 'applicable to baro VNAV with or without automatic temperature compensation', as in: 'do not temperature correct FAF or DA in either case'.
While in agreement otherwise, I am not sure to follow this lead that well.

(d) Altimetry settings for RNP APCH operations using Baro VNAV
--> (2) Temperature compensation
----> (i) For RNP APCH operations to LNAV/VNAV minima using Baro VNAV
-----------> (B) ... temp ...in ... limits, ... no ... compensation to ... FAF and DA/H;
----->(ii) For RNP APCH operations to LNAV minima,

The (B) is still inside the (2) TEMP COMP, second-level ident
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Old 20th Jul 2019, 00:15
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Look at the approach chart...

Does it state" non-compensated baro-vnav"?

The design accounts for the NA below and NA above without compensation.

Without ANY compensation.
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Old 20th Jul 2019, 05:20
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Smythe, thank you for your opinion.

Kindly note that my quest is for arguments on how to interpret the "B". Such as: The term "compensation " as used in "B" means any form of temperature correction on the flight deck, semi-automated or manual, irrespective of the particular instrument system installed, because .... ".

It is the part after the because I have trouble formulating. Writing on an approach plate is not admissible evidence, I am afraid, for the intended use.

The opposing opinion to be dissolved goes like this: Based on PANS-OPS and CAT.OP.MPA.145(a) when temperatures are below ISA-15, a correction to charted minimum altitudes needs to be done, DA/H included. The "B" of AMC2 is nested within (d)(2) BaroVNAV - Temperature compensation. The term "Temperature Compensation" stands for a technical feature of FMC / instrument suite, thus this "B" does not release the responsibility of making manual temp corrections from operators not equipped with such semi-automated device. An example why "Temperature Compensation" must mean an FMC device is easily found on almost any approach chart in the form of notes such as: 1) Uncompensated BARO VNAV NA below XX°C, for which the meaning is well understood without dispute.

I greatly welcome any ideas. To re-iterate, the help needed is on how to argue that "Compensation" is a just general term, in (2)(d) and its "B" included.
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Old 20th Jul 2019, 08:48
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....to me the sub para B is under Temp Compensation sub para (i)...."operatiions to LNAV/VNAV minima using baro VNAV". So it applies to both compensated and uncompensated systems.
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