ATIS temperature measurement.

[Otterman]

ATIS temperature.
I am involved in a little project to increase our payload performance out of some of the more “third” world places that we fly out of.

We leave at a number of places just after the start of nightfall. And we have our doubt about the validity of the ATIS or Tower temperature that is supplied. We think it is a bit high (even a two degrees difference makes a difference of about 1500 kilos, this is a Boeing 777-200). I have looked into how these temperatures come about. The tower temperature at two stations I visited is measured by a big thermometer located (you guessed it, in the tower). The ATIS temperature is measured in one case at least two kilometers away, on top of the building housing the meteorological service. The other is also on top of a building but about one kilometer away.

JAR-OPS Subpart G (performance) 1.490 (c) 2. For take-off performance you should use the ambient temperature at the aerodrome.

My question is:
What are the requirement for measuring an ATIS temperature? At my home base the setup is insane, with over ten temperature probes which are averaged out. At most stations in the less developed world, it is measured at only one place, somewhere on the aerodrome environment. Is there anyone that can supply an answer for me?

Thanks, O.

[john_tullamarine]

you should use the ambient temperature at the aerodrome.

Some would opine that the relevant temperature is that existing over the departure runway .. it might be just as well to let sleeping dogs lie ?

[Otterman]

What you are talking about here is a air volume issue, and is part of certification.

It is not part of the question. As I stated JAR-OPS 1 Subpart G (Performance Class A) states all the items you need to tick off for a valid take-off performance calculation. There is clearly talks about ambient temperature, but does not mention how this ambient temperature needs to be measured.

We have been keeping track of ATIS temperature versus SAT (a very accurate temperature measurement. It comes from the aspirated TAT probe and is therefore corrected for reflective heat from the ground). Here we are seeing difference ranging from 0 to 2 degrees. Most of the time on the upside (SAT being higher than ATIS temperature). We are trying to find the reason behind this. I know at the stations I have visited in the less developed world, the temperature sensors are at a height of 10 meter or greater. At my home base all ten temperature sensors are at a height of 1.5 meters. I am using pprune to see if someone knows what the rules are for measuring ambient temperature at an aerodrome. Anyone that can help me out with this, thanks!
Greetings O.

[Boxshifter]

Did you have a look at ICAO Annex III (http://dcaa.slv.dk:8000/icaodocs/Annex%20III%20-%20Meteorological%20Service%20for%20International%20Air%20Na vigation/)? May be you can find something in there.

I think it is also a liability issue. Whenever I read through an accident investigation I see that the published met data is used. I would considder consulting with the law department of yourcompany.

[John Hill]

Otterman, I work in a company that produces ATIS systems though we dont usually do the instrumentation. Our systems just broadcast whatever the official 'observed' temperature is.

However it is my understanding that the 'official' way of mounting the temperature sensor is in a solar shield (such as the little white louvred Stephenson's Screen) which was about 4 ft above a grass surface. The modern sensors are often in round versions of the old wooden screen.

I do not know, and cant say I have ever noticed, temperature sensors mounted 10 metres or more above ground but if that is happening I would have believed it to be 'wrong'. Possibly a consequence of using isntrumentation packages some of which combine the sensors so they mount everything on the one pole position decided by the height of the anemometer which if I recall correctly is supposed to be mounted 10 metres above ground.

I am hardly suprised that the ATIS temperature measured in a solar screen over a grass surface is somewhat cooler than might be measured over a hard paved surface.


When I trained as a met observer there were well defined rules about positioning of such things but nowadays I see met instruments sticking out of the buildings and in the most unlikely places. Temperatures measured in the tower or on top of a building is just plain poor practice, IMHO.

[GlueBall]

"a 2c difference makes a 1,500 kg difference on a B772"

Are you from the school of pilots who dabble in deciding at what point does 23c become 24c? Are you getting stressed over 1,500kg in a B772? I'm sure that you could easily have a 800kg fuel gage error; . . . and the other 700kg you could "legally" write off for APU burn . . . no?

Just curious, if for absolute technical, super accuracy you had to offload 1,500kg baggage, would the money be coming out of your pocket...?

John Hill: ideally, it's not adventageous to place the thermometer near the runway, as it would be affected by the heat from jet exhausts.

[SIUYA]

Otterman.........

You asked:
What are the requirement for measuring an ATIS temperature? At my home base the setup is insane, with over ten temperature probes which are averaged out. At most stations in the less developed world, it is measured at only one place, somewhere on the aerodrome environment.

The answer's here:

ICAO DOC 8896 MANUAL OF AERONAUTICAL METEOROLOGICAL PRACTICE

2.3.12 Air temperature/dew point temperature

2.3.12.1 Observations of air temperature and dew point temperature should be representative of the whole runway complex.


Also, if you refer to ICAO ANNEX III as suggested by Boxshifter, you'll see in Appendix 3, Section 4. OBSERVING AND REPORTING OF METEOROLOGICAL ELEMENTS that:

4.6 Air temperature and dew-point temperature
4.6.1 Display
Recommendation.— When automated equipment is used for the measurement of air temperature and dew-point temperature, air temperature and dew-point temperature displays should be located in the meteorological station with corresponding displays in the appropriate air traffic services units. The displays in the meteorological station and in the air traffic services units should relate to the same sensors.

4.6.2 Reporting
4.6.2.1 In local routine and special reports and in METAR and SPECI, the air temperature and the dew-point temperature shall be reported in steps of whole degrees Celsius. Any observed value which does not fit the reporting scale in use shall be rounded to the nearest whole degree Celsius, with observed values involving 0.5 [degree] rounded up to the next higher whole degree Celsius.

As JT suggests, perhaps it might be just as well to let sleeping dogs lie? :ok:

[Otterman]

Sorry if I am not being clear Glueball. This 1,500 kilograms is payload, read revenue. Not sure if you are active in this business, there are a lot of people on pprune who’s “profile” is more closely matched to their dreams than their reality. Fudging the books is not the way we do business at my airline, hope it is not at yours.

This whole study that is being done is to come to a updated clear definition, for our operation, on what are the valid conditions for our performance calculations. We are not certain the temperature measurement at some stations is of sufficient quality. Partly because of the departure being just after dusk (the ones I visited certainly don’t meet the ICAO ANNEX III that is being quoted). My enquiry here is to use the vast differences in expertise that is present on pprune. Of course there are many who feel they have something useful to contribute but are sadly mistaken.

Our meteorological department has created a program (running for three years now) to determine the projected weather condition at any given station based on actual weather conditions, forecasts, historical and statistical data. This does not only encompass the temperature, but also the wind and QNH. This allows our load control department to make a fairly accurate projection of the available load about six hours before the flight leaves. As crew, we come on board, and make a quick calculation to determine the maximum performance limited weight (using our electronic flight bag). This will allow the fine tweaking of the load. Either by being able to upload more last minute cargo, or is some cases to off-load some cargo. This is part of our load optimization program.

The airline business is such a solid model, that indeed this revenue translates into a competitive advantage. Something I hope is on the mind of pilots. The time of flying being a purely technical exercise of getting an aircraft from A to B is part of the past. A lot more is required of a modern airline pilot.

As a frame of reference. The airline industry as a whole broke even from the time the first revenue paying passenger/cargo/mail got onto an aircraft up until the end of 2007. This means not a single dollar, euro, or yen was made in this terrific business. The losses since the end of 2007 have exacerbated the situation even more.

The margins are so tight that the survivors in this business indeed make the difference on the outer edge of the business model, hence all the efforts being expanded on such a “measly” number. Doing the same as everyone else is a sure road to extinction.

I thank all constructive contributors to this thread. I certainly will use some of the material that was written.

[GlueBall]

Otterman . . ."Fudging the books is not the way we do business at my airline, hope it is not at yours."

But you also said: "we have our doubt about the validity of the ATIS or Tower temperature that is supplied."

. . . So, not being satisfied in accepting the "official" ATIS temperature would be something other than trying to "fudge" on your takeoff performance . . . ?

[ChristiaanJ]

GlueBall,
What's your point in deliberately missing Otterman's point?

CJ

[ahramin]

Precisely. The point is to get the actual temperature. That has nothing to do with fudging. Talk about obtuse.

would the money be coming out of your pocket...?This question makes no sense. What is the point of hiring pilots if they don't care about whether the company makes money or not? Presumably you care about whether you get paid or not.

Back to the topic at hand though. I think you will find that a thermometer housed in a stephenson's screen 4 feet above grass is going to be measurably cooler than the air above the runway. It is quite possible that the thermometer giving you the high readings is closer to the actual temperature at the runway than a more modern system.

[GlueBall]

Otterman's point is: The ATIS temperature at airport XYZ taken from a centrally located meterological measuring unit is reported as 22c. But captain Otterman's airplane is at the far side of the airport where he argues that the "real" temperature realistically could be as much as 2c lower, because of this and that . . . and that if only the "official" ATIS airport temperature were correctly reported in the immediate vicinity of his airplane and on his departure runway, then it would be 20c and he could have taken another 1500kgs of cargo.

[Otterman]

Glueball, I could explain it once again, but you seem to be incapable of absorbing what you are reading, so it would be a waste of my time. Your contribution has been worse than sub-par, they show a lack of understanding of the central question, and the intent. The question is clear, and a good number of the answers have been as well.

I hope the 1,927 posts you have managed to put together in your time at PPRUNE have contained more useful information than in this thread. You might want to start by backing away from the keyboard if you have nothing useful to add.