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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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What is the purpose of squawking 7777?

Aircraft use transponders to communicate to ATC their position and status. Some squawk codes are reserved, such as 7700 (emergency), 7600 (communication failure), 7500 (hijacking), 1202 (glider), 1200 ...
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231 views

What do you squawk when multiple conditions apply?

There are three standard transponder codes for exceptional situations: 7500 (hijacking), 7600 (radio failure), and 7700 (general emergency). Which code do you use if multiple situations apply? For ...
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1answer
142 views

Is a mode C transponder required underneath Class C airspace?

FAR 91.215 states that a mode C transponder is required for... all aircraft in all airspace above the ceiling and within the lateral boundaries of a Class B or Class C airspace area designated ...
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Should I switch the transponder to STBY or not while changing codes?

I´m now reading Bob Gardner’s book “Say again, please” and there is this instruction on page 54: Do not turn the transponder function switch to STBY while changing codes. What is the reason for ...
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1answer
242 views

In a part 91 formation flight within a mode C veil, are all the aircraft required to have their transponders on?

Two aircraft are planning on conducting a standard formation flight (aircraft remaining within 1 mile of each other) as follows in the U.S.: Maintaining VFR below 10,000 MSL; Remaining outside/clear ...
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0answers
100 views

How to keep a Garmin GTX330 turned off when powering on avionics?

There seems to be an option in the GTX 330 settings that keeps to unit from powering on when receiveing power from the power system. I flew in two different airplanes and one immediately powered on ...
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1answer
195 views

If a pilot has the wrong altimeter setting, will his transponder mode C altitude be off too? [duplicate]

Just wondering if the transponder mode C reported altitude will be off if the pilot accidentally has the wrong altimeter setting.
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1answer
409 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 ...
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1answer
211 views

When do controllers assign a squawk code to VFR aircraft in Canada?

In all of my previous flying experience the controllers provided a squawk code only when I requested flight following. On a recent flight from Buttonville, Ontario (CYKZ), the controller provided a ...
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2answers
152 views

Is a VFR flight following request implied when talking to tower and advising them of your intended airport?

If I am at a towered airport in class delta airspace and I'm departing VFR and tell the ground where I want to go, is it implied to the controller that I'm requesting VFR flight following? Let's say ...
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2answers
92 views

What requirements do A&Ps (AMT) have to work on avionics?

Is there any additional requirement for A&Ps to work on avionics or is that even a totally different license? I just wonder why only a few A&Ps I met, also do avionics.
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How do I tell ATC that I don't have a transponder?

If my plane doesn't have a transponder and ATC tells me to squawk some transponder code, how should I respond? Is it just as simple as "I don't have a transponder"? This is for the United States and ...
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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 ...
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2answers
388 views

If the static port get blocked, and no alternate static air source is fitted, will the transponder keep provide mode C?

If the static port get blocked for any reasons and the aircraft is not fitted with an alternate static source while in Mode C with SSR, will the ATC still get the height information from my ...
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1answer
922 views

Which antenna on an commercial airline airplane is used for the transponder (SSR)?

On the 767-200 image I see no SSR antenna, but since that TCAS uses the transponder I guess that are sharing the same antenna. Am I right ?]1
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1answer
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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 ...
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1answer
296 views

What Height Atc radar reads from pilot selection [duplicate]

Just want to know whether ATC radar always reads aircraft height with respect to standard altitude setting or will read the change in height if we select QNH instead of standard 1013 hPa (QNE)?
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2answers
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Which source to use when reporting the current altitude to ATC?

While flying from KSNA to KVCB VFR at night, Norcal Approach asked for my current altitude. I was somewhere between 12.0 and 12.5 depending on which reading I was going to use. ATC had me confirm. ...
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1answer
404 views

Can a TCAS be alerted when the intruder aircraft has a transponder in stand-by mode?

Can a TCAS give a TAs (traffic advisories) if the intruder aircraft has a transponder in stand-by mode?
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3answers
879 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 ...
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1answer
237 views

Why don't transponders send gps coordinates and other important info in addition to altitude and transponder code?

I heard that they were waiting for the patent holder's patent to expire, but just wanted to confirm.
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1answer
187 views

Are experimental aircraft exempted from the 2 year transponder and avionics checks?

Experimental aircraft and LAS. The 2 year verification test for avionics , transponder and altitude encoder. Are experimental aircraft exempted from this test or they must comply ?
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1answer
854 views

What's required for the ADS-B to function? A GPS or Mode S Transponder?

Jeppesen defines the ADS-B as a surveillance system broadcasting GPS-derived positions and other information such as velocity over the data link. Yet, the Wiki article on ADS-B relates it to the Mode ...
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6answers
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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?
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1answer
724 views

Is it recommended to have an ADS-B transponder in ALT mode on the ground? [duplicate]

Early on in training I was told that unless the airport specifically noted it on the chart, that the transponder was turned to ALT (altitude) mode just prior to taking the runway for take-off (lights, ...
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2answers
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Are transponders required for hot-air balloons in the US when operating within a Mode C Veil?

I've taken some people flying recently for fun, and they noticed some hot-air balloons and asked me if they had transponders. In San Diego (Southern California) I often see hot air balloons well ...
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1answer
635 views

After purchasing an aircraft, how do I put the transponder in my name?

I just purchased an aircraft and the prior owner said that I need to put the transponder to my name. What is the procedure to do that?
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7answers
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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 ...
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1answer
432 views

How does FlightAware correlate flights to Part 91 flight plan data?

I'm looking at some flights in FlightAware. With the scheduled air carrier flights, their call-sign can be crossreferenced with a flight schedule database to determine the origin and destination. How ...
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3answers
3k views

What is the ICAO 24-bit code used for?

I know that each transponder is linked to a unique 24-bit code assigned by ICAO. But to be seen by the Secondary surveillance radar the pilot set the squawk code (4 digit octal code) on the ...
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1answer
725 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? ...
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3answers
591 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 ...
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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 ...
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1answer
361 views

Do interceptor squawk codes suppress TCAS RAs?

Some parts of the world reserve a discrete squawk code for use by military interceptor operations (in the NBCAP, code 7777 is used for this). Does this squawk code, or some equivalent value, suppress ...
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2answers
864 views

When may I change my transponder code to 1200 when being handled by ATC?

When am I allowed to change my transponder code to 1200? Is it after clearing the boundary of controlled "radio-contact-required with transponder" airspace?
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Does the transponder need to be on in the upper limit of Class B airspace?

Is a transponder needed to be turned on to operate above the upper limit of class B airspace?
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1answer
1k views

How can I ensure that I have a mode C transponder?

How can I make sure my aircraft is equipped with a mode C transponder? ====================== If a transponder has an ALT button does that mean that the aircraft is equipped with MODE C?
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2answers
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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 ...
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3answers
963 views

Why don't transponders have active and stand-by value like radios?

This answer explains how pilots when switching code on transponder should either carefully avoid temporarily squawking one of the emergency codes, or should temporarily put the transponder in stand-by....
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3answers
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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 ...
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2answers
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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 ...
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2answers
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Why are there so many 7700 squawks?

I installed an app some months ago, which gives a push message when an aircraft squawks 7700. The first time it happened, I thought the plane was about to crash, ...
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8answers
129k 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 ...
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3answers
13k 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 ...
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2answers
4k 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.
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1k 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, ...
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2answers
906 views

Why does the 1090 ES use the same frequency for both uplink and downlink?

The 1090 ES is the transponder system used in ADS-B. Why does the 1090 ES use the same frequency (1090MHz) for uplink as well as downlink? 1090 ES is an extension of Mode S. The Mode S used 1030MHz ...
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1answer
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How does ATC radar/ADS-B ground stations not get confused with signals sent from multiple aircraft?

I understand that the radar sends a 1030 MHz interrogation signal to an aircraft and the aircraft's transpoder responds using 1090 MHz. When it comes to Mode S squitter, the transmissions are ...
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2answers
1k 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., ...
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Can I find out why an aircraft squawked an emergency code (7x00)?

I have recently been using a mobile app to track flights, which is really cool. I live in the rural heartland of America, so it's an event for me to see an A380 actually flying. Every once in a ...