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Transponder: Difference between revisions
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→Modes: explained the missing modes, shaded a light of the mode S elementary and enhanced, explained the Traffic Alert for Ground and the Resolution Advisory and the correct use of IDENT
(introduced the notions of situation code vs aircraft code, discrete non discrete and new reference with source documentation / explained the method of code attribution) |
(→Modes: explained the missing modes, shaded a light of the mode S elementary and enhanced, explained the Traffic Alert for Ground and the Resolution Advisory and the correct use of IDENT) |
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https://www.flightradars.eu/squawkcodes.html#top | https://www.flightradars.eu/squawkcodes.html#top | ||
== Modes == | == Modes A, B, C, S == | ||
detailed illustrated explanation ref. https://skybrary.aero/articles/transponder | |||
or also | |||
https://pilotinstitute.com/transponder-modes-explained/<nowiki/>{{hatnote|For a thorough description, see {{wikipedia|Aviation transponder interrogation modes}}.}} | |||
Needs always evolves and technology merely adapt to the change. The Transponder Modes are the reflex of the evolution of theses needs. | |||
=== Mode A === | |||
from 2nd WW era, when aircraft was flying back and closing to the base, it was hard to say if they was Friends Or Enemy (FOE). To avoid unwanted activation from the DCA's, pilots was activating a convention code switching ON/OFF a set of buttons to define an identity code. | |||
After the WW, this has come back to civil aviation, but the mode was really basic and more identification features was wanted. | |||
=== Mode B === | |||
have been an evolution of the mode A, but due some quirks it has been quick abandoned for mode C | |||
=== Mode C === | |||
added report of the aircraft altitude. | |||
These report altitude was read after calibration, which has led to problems and have been update to non calibrated altitude in mode S. | |||
Why ? | |||
Imagine an Aircraft in final approach, the definition of an incorrect altimetric pressure may lead to "hit" the ground before the RWY or hot the RWY to late and trigger a RWY excursion. | |||
Other situation of bust of altitude (lost of vertical separation) also have happened (although more rarely). | |||
Mode C altitude report is by 100 ft | |||
=== Mode S. === | |||
Why not MODE D, E, F ... ? | |||
Mode S have been a game changer. | |||
In Mode C their was too many aircraft sending information at the same time. The Radio Frequency was congested, many time, life and death information become missing as the result of the chaos of all the transponder "speaking at the same time". | |||
In Mode S, transponder are quite and shushing unless "interrogated" by the surveillance system. | |||
Well, almost shush. The surveillance system need to know to whom direct the interrogation. For this all transponder still continue to emit repeatedly a very very short ID called the squitter. | |||
The surveillance system keep a table of all the squitters for management. | |||
The frequency being not any more congested, interrogated transponders have the possibility to send more extensive informations. | |||
The mode S have itself 2 ways, ELS and EHS as ELementary Surveillance and EnHanced Surveillance | |||
The former send altitude (before calibration) speed, direction, ... and few more Aircraft and Flight parameters. | |||
The later one send also the "selected" altitude in the Autopilot, which allow the ATC to detect early misunderstandings and prevent possible level bust before they happen. | |||
ref.: https://skybrary.aero/articles/mode-s | |||
Mode S altitude report is by 10 ft, again, read before calibration ! | |||
To do this the transponder needs an altitude source. In real-life this can be a separate box called an encoder, or may be derived for FMC / ADIRU sources. It's important to note this altitude is referenced to standard pressure (29.92 inHg / 1013 Hpa), and not corrected for actual barometric pressure in the local environment. | |||
Additional support for military modes is possible if anyone wishes to add it. | Additional support for military modes is possible if anyone wishes to add it. | ||
== Transponder "in the flying deck / cockpit" == | |||
Bare in mind that 1 transponder is always different from another transponder. | |||
* Older aircraft may still have old transponder not Mode S capable; | |||
* Several manufacturers | |||
* Boeing ≠ Airbus | |||
* ... | |||
Some Transponder have a knob with position labelled "ALTITUDE" which does not mean the transponder is activating the mode S. The mode C also have a report of altitude. (see above). | |||
The usual modes encountered in RL for the transponder are : | |||
* Off - ( switched off / no power) | |||
* Test - (maintenance) | |||
* Stand-by - (powered on but not sending out informations except the squitter - see above) | |||
* Ground - (send out SQUAWK CODE only - some airport, by rule - expect code 2000 for ground taxiing aircraft's) | |||
* Altitude - (in mode C, sending out altitude information - in mode S, sending out more information) | |||
== TA and TA/RA - Traffic Alert / Resolution Advisory == | |||
On some transponder, TA/RA functions might be switched on separately. | |||
They <big>need</big> the '''mode S''' in order to work ! | |||
A frequent myth is the mode S and the TA/RA must only be activated on air. | |||
Nothing is more wrong. | |||
Airport where the visibility is traditionally not good and foggy, like Paris Orly LFPO, Milano Linate LIML, Bimingham EGBB, among others, other require the departing aircraft to activate the mode S and the TA from the gate/stand, before push ! | |||
TA on ground have a special mode with a different sensitivity adapted to detect closing taxiing aircraft's. It has many time be a matter of sever accidents with fatalities. | |||
e.g. | |||
Flight SCANDINAVIA 686 (Scandinanvian Airlines McDonnel Douglas MD-87) and a private Cessna Citation, making 118 victims. https://en.wikipedia.org/wiki/Linate_Airport_disaster | |||
Paris Orly is "that much so foggy" that it is where have been invented to first "Turbo Clear" the first and fog systems for airports, 1963. The whole world have bought them and used them before the first ATT (Atterrissages Tout Temps) , "Landing With Any Weather", the precursor of the Instrument Landing Systems. https://www.aeroport-paris-orly.com/systemes-anti-brouillard | |||
The myth roots itself in the fact that the rules changes by airports and situations. One discovering the rule enforced in one airport might tend to believe the whole world do the same... | |||
Usually, the airport administration information pages in the airport charts brief clearly about the rules enforced in "that" very airport. | |||
On ground | |||
Mode S + Traffic Alert might be required to be used | |||
Airborn | |||
Mode S + Traffic Alert + Resolution Advisory is as much as possible expected | |||
"Old" aircraft using frequently the controlled airspace are demanded to upgrade their transponder. | |||
== Mode IDENT == | |||
Transponder have a separate function called IDENT and callable by the press on a button. | |||
This actually is not a "mode" like Mode A, C or S. | |||
It should never be pressed unless required by the ATC providing service. | |||
It "must" not be activated by Squawk code changing ! (Frequent error) | |||
IDENT allow to the ATC to spot in a flash an aircraft amongst many and its purpose it solely to help in case of loss of conspicuity. | |||
Squawk codes changes at quite a good rate. If at every time the squawk code is recycled, the IDENT is activated and the BLIP (aircraft on the ATC screen) start to blink, then when the ATC demand to someone to press IDENT, the help will be void because drawn in many other IDENT... | |||
QED. | |||
== Configuration in FlightGear == | == Configuration in FlightGear == | ||
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// and ".../indicated-mach", but this can be changed by setting "airspeed-path" | // and ".../indicated-mach", but this can be changed by setting "airspeed-path" | ||
// and "mach-path" properties respectively as shown above. | // and "mach-path" properties respectively as shown above. | ||