Some basic aviation questions.......

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Weg
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Some basic aviation questions.......

Post by Weg » 22 Aug 2019, 14:01

What is a transponder for?
Why does atc tell me to change it?
What is a sqawk?
Why do airports say for example: Altimeter 1992?
What is the climb and descent vertical speed for a 767-300?

Well guys, for now this is it. I have always flown on fs but never really studied these things and I would like to start taking the fs lessons. But what are these things I see everytime but I never know what it means?

jan_olieslagers
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Re: Some basic aviation questions.......

Post by jan_olieslagers » 22 Aug 2019, 17:20

You could check out the www, for one example en.wikipedia.org has very fine explanations. Still, for your welcome, a basic beginning of a reply:

Way back in the beginning of aviation, there was no radar, nor was there any need.

Somewhere around WW2, up came the first kind of radar: rotating antenna sends out short "blips", if a reply comes then there is "something" at a distance that can be estimated by the time to return. This is called primary radar today, is still in use. It doesn't require any equipment "on the other side".

Very soon after, secondary radar was added, which is quite a bit more complicated. The more so that it exists in several gradations, called "mode a", "mode c", "mode s", and the military have a few more modes of their own.

Secondary radar still uses a big rotating antenna on the ground, it still sends out blips but they are called "interrogation codes" now, and there are several kinds. The main differrence is that there now is a clever box on the plane that receives the interrogation code, and can respond to it by sending out a packet of data. This box is called the transponder (observe the "responder" bit in this naming); and the data that it sends out can be received and processed and displayed on the ground side, for the benefit of the radio operator who can now get a much clearer image of what/who is flying where.

Mode A transponders only reply to mode A interrogation codes, and on receiving one they send out a code of four digits, each 0-7 because that fits neatly into three digital bits (on/off). The code can be set on the transponder, and is called the squawk. Each radio service, either controlling or information, has a series of squawks available - the number is rather limited - and will assign one as found appropriate. So that when passing from - say - Liege tower to Langen Control, one will get a new squawk assigned. A few squawks have specific meanings.

Mode C transponders will respond to both mode A and mode C interrogations. They will still report their squawk in mode A, to mode C they will respond with altitude information - very relevant to ATC staff. Both the squawk and the altitude reported will be shown on the groundside radar display.

Hoping this helps! Feel free to ask further, but there is much information freely available.

Then again, never will "an airport say 'altimeter 1992' " ;) Someone at the radio might say so - aerodromes are rather taciturn, generally - but even then it is a typical US'an expression, and like many of those it doesn't fit ICAO recommendations. More properly, one hears "QNH one zero one five" or such. One way or other, it is an indication of local barometric pressure. The basic altimeter in aeroplanes is still a kind of "barometer with an inverted scale"; one needs to know where the zero is, as it changes with the weather.
Last edited by jan_olieslagers on 22 Aug 2019, 17:24, edited 1 time in total.

jan_olieslagers
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Joined: 24 Jun 2006, 08:34
Location: Vl.Brabant
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Re: Some basic aviation questions.......

Post by jan_olieslagers » 22 Aug 2019, 17:21

Above all: take REAL flying lessons - pc simulated flying is really a waste of time, ask me how I know :( !

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