Questions tagged [transponder]

A radar transponder is a radio beacon on an aircraft that replies to a radar interrogation. The transponder encodes information into the reply, allowing air traffic control to know the aircraft's altitude and identity.

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41
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3answers
33k views

Why do pilots have the ability to turn off the transponder in-flight?

These days, when reading news about missing Malaysia Airlines Boeing 777-200, I keep coming across a scenario where pilot might have deliberately turned off the transponder which is used for the ...
9
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2answers
9k views

What is the significance of a squawk code?

I've been looking for a detailed explanation for how the transponder works and the importance of a squawk code.
5
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2answers
891 views

What happens to the transponder, FDR and CVR in case of an explosion?

Will the above mentioned equipment still work and transmit data/location information if an explosion occurs inside the aircraft?
45
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9answers
159k views

What are the advantages of squawking 7700?

I was reading this question about how do pilots send distress signals in emergency scenarios, and that got me thinking... In voretaq7's answer, he states that there are three ways to send distress ...
16
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2answers
4k views

When should a transponder be used?

When should a transponder be turned turn on? On the ground? Always in flight? Only when required: during radar service (flight following), above 10,000ft MSL, inside the Mode C Veil, or on IFR flight?...
5
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1answer
862 views

Why would a Mode-C transponder report a different altitude than an altimeter/GPS?

This is related to a small single-engined plane. On a recent flight, the controller kept telling me that I was 300 ft higher than it appeared on my altimeter and GPS (which were in sync). This was ...
0
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1answer
121 views

What additional airspace will be off-limits to an a/c w/ no elect. system or xponder under 91.225 (ADS-B) compared to under 91.215?

Under FAR 91.225 (requirement for ADS-B-out), what additional airspace over the 48 contiguous states in the U.S. will be off-limits to an aircraft w/ no electrical system or transponder, compared to ...
0
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1answer
181 views

FAR 91.215— may an aircraft with no electrical system and no transponder overfly Wheeler AAF at 9500' MSL?

Here are some of the airspaces where FAR 91.215 requires aircraft to have transponders-- (b) ... (2) All aircraft. In all airspace within 30 nautical miles of an airport listed in appendix D,...
0
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1answer
201 views

FAR 91.215 (b)(3)(ii) — transponders— does the “or below 10,000' MSL” clause have any practical significance?

Here are some of the airspaces where FAR 91.215 requires aircraft to have transponders-- (b) ... (2) All aircraft. In all airspace within 30 nautical miles of an airport listed in appendix D,...
43
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6answers
13k views

Why is the range of transponder digits 0 to 7 rather than 0 to 9?

As a controller on IVAO I sometimes assign codes like 0168 and find out later that the code isn’t valid. For me, the range 0-9 seems more logical. Why do we have to use octal numbers and not decimal?
14
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3answers
17k views

What is Transponder Code 2000 actually used for?

On What is the significance of a squawk code? @DeltaLima gave a fairly concise answer. In it he listed several 'standard' codes used for things like emergencies. Also in the list was Code 2000, for ...
29
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3answers
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How does IDENT work?

In order to help ATC identify an aircraft on their screen, they may ask the aircraft to "ident." The pilot presses a button on their transponder, and the controller can verify that the aircraft they ...
27
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3answers
3k views

What could cause an inadvertent squawking of 7700?

I get alerts whenever a plane squawks 7700, using a popular flight tracker application. It happens quite frequently that the aircraft, reported to squawk ...
35
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9answers
12k views

Can a military pilot make his airplane invisible for the ATCs?

I'm writing a story about the pilot of the Austrian Air Force, who uses his Eurofighter Typhoon aircraft for unintended purposes. I've read stories in the internets that civil pilots allegedly can ...
18
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3answers
3k views

Why do the transponders introduce codes instead of using aircraft registration numbers?

(A non-pilot here, just a Aviation.SE reader, recently into listening to ATC. I am wondering...) Why do the transponders use their own codes? (squawk) It seems to me, it would be safer and less of a ...
15
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2answers
2k views

How are airspace violations detected?

Are airspace violations (e.g. entry to class B without clearance) based on primary radar and/or Mode C transponder, or something else? I read that Mode C altitude is based on pressure altitude, i.e., ...
6
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3answers
2k views

How does the modulation of the transponder work?

The transponder works in PCM (pulse code modulation): how does it work in the transponder? I can find explanation of what PCM is, but not if the signal sent from the transponder antenna is digital or ...
4
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3answers
683 views

What aircraft would have these tail numbers?

Last night I was looking at a flight radar on my phone, and I saw two blips flying close to each other over Camden, NJ. They were heading northeast at around 250 knots, and the only information ...
14
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2answers
8k views

Are transponder codes 7701 - 7777 ever used?

I understand that blocks of transponder codes are assigned to different area controls. I am curious if the block 7701 to 7777 is in use anywhere? Maybe the emergency code 7700 needs some extra ...
9
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3answers
2k views

How does ATC locate a stealth aircraft if its transponder fails?

Stealth aircraft are built to have near-zero radar visibility, so that, in a warzone, it'll be harder for the enemy to see it on their radars to shoot it down. However, air traffic control also use ...
9
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2answers
2k views

Does ATC use mode S addresses to identify planes?

By design, Mode S surveillance radar equipment uses global 24-bit airframe addresses to keep track of the aircraft it is tracking. Are these addresses also used by higher levels of the ATC system, ...
9
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1answer
2k views

What is Mode B on the transponder?

Mode A selected on the transponder provides identification of the aircraft to the secondary radar; Mode C will add an automatic height read-out of an aircraft. Mode S is a selective addressing. But ...
5
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1answer
1k views

Is there a relation between the Mode 3/A Code and the ICAO aircraft address?

I would like to know is there is any way to match mode 3/a code (which is assigned by ATC to aircraft) and ICAO address of the aircraft. I mean how mode 3/a code is assigned to each aircraft by ATC? ...
4
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2answers
3k views

When is a transponder required below class B airspace?

I just wanted to clear up questions I have about flying within the 30 mile veil of Class B. My understanding is that the Class B is the inverted wedding cake, having tiers as the airspace moves ...
2
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1answer
172 views

Why does setting the Legacy 600's transponder to standby mode also deactivate its TCAS?

In 2006, a 737 operating as Gol Transportes Aéreos Flight 1907 crashed following a collision with a Legacy 600 business jet; the Legacy's transponder proved to have been in standby mode1 at the time ...
0
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1answer
57 views

Does the FAA construe FAR 91.225 to prohibit aircraft w/o electrical systems w/o ADS-B-out from flying above 10,000' MSL unless below 2500' AGL?

Does the FAA construe FAR 91.225 as imposing a general prohibition on flight above 10,000' MSL (excluding airspace below 2500' AGL) in aircraft without ADS-B-out, even for aircraft without engine-...