 Now, ISA is not the only atmosphere. So, let us see, let us see some other atmospheres. First of all, let us look at the atmosphere that is applicable in the US. So, you have a 288.16 or 15 at sea level and there lapse rate is 6.5 which is what we know and then there is 0 lapse rate between 11 to 36,000 feet or you know 20 to 20,000 meters. But in ISA, this is constant to 25. In US, it is up to 20. So, you can see there are minor differences. The sea level temperature in the US atmosphere could be the same but there are subtle variations let us look at the chart again. So, this is the variation of pressure density and temperature for the US atmosphere or the US standard atmosphere. Now, tell me at which place in USA is this weather recorded because if we say atmosphere there must be a place. So, what is the location and what is the season, which month of the year and which day of the month on which this particular atmosphere is recorded in USA? Can you guess? Is there a need for something like this? No, because like ISA, you need not have that anywhere. Similarly, you need not have this at one place. This is a standard followed in the US. It does not mean it is there at Denver or at some place. So, why is it done? So, that aircraft which are operating in the US designed by the US people when they talk to each other and if they say we do not follow ISA, we follow IUSA, whatever this is what they refer to. Normally, they do not. Normally people only talk of ISA but there can be. What about India? So, we also have done some studies about atmosphere prevalent in our country. So, we have defined something called as an IRA. So, when we buy an aircraft from somewhere, we say tell us the performance under IRA. Then only it is useful to us. You may fly at mark 1.7 in ISA. I do not care. I do not have ISA. I have IRA. So, tell me in IRA. So, what is IRA? IRA is atmosphere which is considered to be a standard in India which is valid in the Indian equatorial zone up to only 80 kilometers. Above that it goes into space and they have their own way of calculating which I do not really know. This data was recorded way back in 85 and after that there has been no plans to do any upgrade or change. It is a standard where it remains like that. So, what is basically IRA? IRA is a series of tables. It contains the values of temperature in Kelvin, pressure in millibars and density in kg per meter cube and this is just an information for you that in IRA conditions between let us say the temperature you can see. You can see this is a variation over the years recorded in India. So, it is not constant. You can see it goes in cycles. So, that is why what we have done is we have drawn a mean line. So, it varies from 53 to 71 ok. We draw a mean line and similarly we draw a mean line here and we just keep it like that. This is only for information and these are the values recorded on a particular day also a particular year. So, this is the average of so many years recorded in the country. So, you notice that the temperatures are not remaining constant throughout the year. There are seasonal variations also. So, such charts are used mostly mostly by airlines to plan out. You will notice if you look at the if you look at the timetable of an airline you will not find the same time for a flight on all days of the year. There are there is a summer timetable, there is a winter timetable and there is a changes. Yeah ok. So, this is the question that I would like you to answer. I do not know. You have to search on the links. See for everything I quote here I am going to give a link. So, you should go to the link check out yourself and put on the moodle that the question in the class was which to the answer is this. It is nice. It is that is what I would like to do ok. So, we are in Mumbai. So, let us look at Mumbai data. You will be here for some time now. It is better you know when to carry H3 and when not to carry H3. So, November 2016 this is the actual recorded data at Mumbai. The highest was 36 degrees. The lowest was 21 degrees and then you have humidity and pressure also ok and the average was 29 degrees centigrade. So, that is the average temperature in Mumbai in November for the temperature. Now, Mumbai location is 14 meters above mean sea level. So, therefore from 288.16 it will reduce at the rate the temperature will change slightly at 14 meters very slightly ok. So, calculation may under ISA condition Mumbai should have a temperature of 15.16 degree pressure of 1 atmosphere and density of 1.225 roughly under ISA condition assuming almost sea level ok. But the temperature actually is 29 degree centigrade under ISA it would have been 15 degree centigrade. Therefore, we say that Mumbai is ISA plus 14 ok. So, Mumbai is ISA plus 14 or ISA plus 15. So, when it is ISA plus 15 one very interesting assumption is made. We assume that the temperature profile at Mumbai from sea level to say 55 kilometers etcetera it is a parallel line to the ISA line by 14 degree by 14. So, the temperature line only. So, the temperature variation at Mumbai will be 288.16 plus 14 minus 6.5 degree per kilometer up to 11 kilometers it will remain that till 25 it will become plus 3 degrees till 47 it will remain that till 53 above that I do not care got it ok. I really do not care because we are not going into space craft design in this course. What you need to know is now how do you calculate density of air at 2 kilometers in Mumbai. So, you calculate pressure at sea level will be same as 101 because pressure is not changing we assume that the pressure remain 1 atmosphere ok. You can see it is 1016 bar. So, it is roughly the value of sea level. If you are very particular you can say no the average pressure is 1012 ok. So, P1 by P2 equal to no T2 T1 by T2 to the power g by LR correct. So, this T will be T plus 14 and at 2 kilometers it will be T plus 14 minus 6.5 degrees by whatever into 2 because it is 2 kilometers. So, by that you can get the value. So, assume that the pressure at sea level remains same as the sea level under ISA even in ISA plus 14, but temperature changes. So, the only thing that changes is temperature hence density changes. This is how we do the calculations. So, in the tutorial that we do we will do some practice. So, that you can get a feel for this. This is very important this you need to know right yes yes no no no if an aircraft is coming as a passenger aircraft we do not say fly in IRA or something. I am just saying when we buy an aircraft and we want to know its performance we say give us the performance in IRA give us the performance table in IRA. So, when you want when you want to talk about the reference value you say under ISA so much. So, this guy under ISA so much this guy under ISA so much I can compare. But normally when we procure something we say we do not want to worry about ISA. It may be very good in ISA give us the values in IRA. So, if I compare the values in IRA I will get the answers of the parameter that I will normally see in the country ok. Yes what is the adequacy equation? So, do you know the pressure at a higher altitude? At a higher altitude at sea level he has p equal to rho rd that is how you get the value of rho. But at a high altitude pressure is changing, temperature is changing, density is changing what do you do? That is why we need to go for the episodic equation you get dp by p and p is equal to rho rd. Good, good question. Any other question? Yes, how do you answer this question? Kashmir is a Karnakumari Bharat Ek hai that we say but it is not the same as far as temperature is concerned. So, let me put a counter question the same is true for ISA also. I told you that nowhere in the world we have a temperature like ISA. So, then we take a reference. So, similarly in India also we have taken a reference ok. There is no particular place in India where we say Allahabad the temperature here is ISA no. There is one nominal value assumed to be valid in the country ok and that is called as the reference for my country. It does not mean that it has to be present anywhere but it is a rough information. So, basically IRA is equal to ISA plus 15 generally ok. Sometimes we say ISA plus 20, but the IRA is defined there is a document our library has a document. I think professor Oja also has done calculation. In fact, before professor Oja there was one more professor who came from HAL. He has done the calculations and there is a small write up available in our departmental library IRA tables are available ok. Let us look at some other temperatures Arctic minimum and tropical maximum ok. Recorded minimum temperature all over the world is in Antarctica at some place I do not know. It is minus 75 degree centigrade and the recorded maximum value is in Somalia in South Africa which is plus 65. So, we know that the variation is so large at earth. So, therefore, some two more temperature two more SAs have been defined. One is called as a Arctic minimum atmosphere and the other is called as a tropical maximum atmosphere for very cold countries and very hot countries. And these graphs are defining as you notice that as the latitude increases as you go away from the equator temperature falls we know that ok. Now, we come to the question about these various altitudes and how are they reconciled. So, we call them as Q altitudes or Q codes. There are many of them let us see one by one. The first one is called as a QNH. What is QNH? First of all there is something called as QFE. QFE is the height from the current location below. This you measure by a radio altimeter ok. Because you ask a question about how do you measure? The answer is if I want to measure the height from a particular location I can use a radio altimeter I will send a beam and take it back and find out the delta H. That height is called as a QFE ok. But there is something called as a QNH which is the altitude from the location plus the height of the location above mean sea level. So, the mean sea level in Mumbai is 14 meters and let us say I am at Khandala which has got some height. So, the QFE over Khandala will be measured directly above Khandala and the QNH will be from the mean sea level. Remember the mean sea level also changes from place to place. So, this is the location specific. QNH at Mumbai, QNH at Pune can be different because sea level there may be slight variation ok. Then you have something else also ok. We assume that 101.3.2 is the pressure. So, the pressure is measured at the ground reduced to the mean sea level pressure that is called as the QNH and the altitude is displayed above mean sea level. Now, there are others also. Now you can see there is a airport located in some beautiful hill. So, it has got some elevation from the ground. The dark line is so the runway is location at that place. So, QFE will be above that right. Then you have QNH which is sea level datum. As you can see it is not the same everywhere. But we also have the third one which is corrected not to the sea level but to the mercury value corresponding to a standard sea level which can be different from place to place. So, to be very sure because we use it using instruments right. Ultimately the pilot is using instruments. So, we say if the reference is sea level then it is QNH. If the reference is some theoretical place where the pressure is equal to 29.92 inches of mercury that theoretical value reference is QNE. So, QNH QNE there can be a slight difference it could be positive it could be negative also correct. So, what are you concerned about? You are concerned about QFE above the earth. But QNH so basically when you take off from some airport like Mumbai and when you come to land in say Delhi the pilot has to adjust the altimeter to take care of the elevation at Mumbai at Delhi. So, the pilot will ask the ADCO or there are charts available. The ADCO will say so when you I will just show you some communication between ADC and pilots you will see where they talk about this right. Now, the last thing that we have are some very very interesting videos about the effect of weather. I do not think I will be able to show all of you all of them to you but I will try to show you some of them. So, the thing that affect our flying is turbulence, wind shear, clouds, rains and microburst. So, in the interest of time I think I will show you first turbulence no no no turbulence rain because there is a pilot communication about the QNH. So, this is a weather radar which shows presence of heavy rain to the pilot. The pilot is approaching to land you can just increase the volume please. So, this is a tower control tower the ADCO speaking to the pilot saying wind 0 to 0 degrees that means the wind is coming from 20 degrees north onwards at 15 knots speed. So, you have to be aware that I may have some cross winds or head winds or tail winds QNH 1015. So, he is saying the airport where I am located the ADCO is saying has a QNH of 1015. So, adjust karo because your instrument should also have a QNH of 1015 then we are on the same page. Otherwise you will follow the instruments and you will hit the ground clear to land runway 06. Now runway 06 I will explain to you in another video when I come to landing I will explain to you what is when the runway 06. I stopped here because I wanted you to understand. Now see what the pilot says okay. So, for your information sir airport is just above landing minima. So, there are certain landing minima that means you cannot land unless you have these things. So, we are just above the minima and airbus 320 on the runway reported 800 meters visibility one of the basic problem in airport during bad weather is visibility okay. So, every airport and actually every aircraft has got systems which can help. So, there are some minimum values you are not supposed to operate below the minima from safety point of view. So, the ADCO is cautioning the pilot that please understand we are undergoing a weather condition at which we are just above the landing minima and the visibility told by someone who just went recently is 800 meters that means the pilot can see only up to 800 meters beyond that it is hazy. So, he is cautioning the pilot and one more thing you notice this is the place where you should focus because you will see the runway landing lights there okay that is what the pilot is going to report now. Right, it is a caution weather information. So, the first officer says copy weather conditions that means I confirm that I know that there is a 800 meter visibility reported and we have 100 storms. Now, 6.5 miles with the approach lighting system in sight. So, he says according to my instrumentation I am 6.5 miles away and I can see the approach lights which is correct you can also see okay. Now, see what happens. Very important the ADCO is confirming that you can see the runway lights because if you do not see the lights then you may be below the minimum you have to abort. So, he says affirmative remember all the conversations are recorded in the cockpit voice recorder therefore the pilots have to say yes they do not say yes no they talk of negative affirmative this is the language that they use. Thunder storms not visible now okay. So, the pilot will continue to fly till the aircraft reaches the prescribed minima and at the minima if the let me suppose the minima is 400 meters when you are when you are at that place and you cannot see you have to abort. One second out of that you might be able to see sorry okay. So, this is a situation where there is now a confusion there is a slight issue. So, there is a better front of course it is not visible. So, the moment it is visible the pilot communicates again and says 2 miles one short final that means now I am 2 miles away I am on my final okay. There is also short final long final those are details but the moment the pilot sees again it confirms that yes I am on the final. So, ADCO is saying Roger I understand are you still able to see the lights because the rule is if you are not able to see at the final you are supposed to abort. So, now you will hear a inner marker sound rain has come now that is it touch down after this it is touched down okay.