Transponder - Switch to ALT not just ON
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Transponder question
I just read the article and it said that the transponder uses the aircraft's pressure altitude, and then ATC automatically adjust this using the local altimeter setting so it shows your actual altitude on their screens. I've noticed before when i've been putting around in the 172 (it displays altitude on the transponder) that the transponder altitude has been 200-300 feet different to the altimeter on some flights. i assume that rather than the transponder being faulty, it is just showing the pressure altitude like how ATC initially receive it without correction for actual altitude. Is this correct?
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Spot on.
It always gives your flight level (rather than altitude), so if you're flying at 2000 ft on a QNH of 1031, your transponder should transmit FL015 (1500 ft). That's why it's important for aircraft in the same control area to use the same QNH (aside hopefully stopping you from hitting a hill).
If you were to ask ATC for a transponder check, they would hopefully tell you that you're indicating about 2000 ft.
It always gives your flight level (rather than altitude), so if you're flying at 2000 ft on a QNH of 1031, your transponder should transmit FL015 (1500 ft). That's why it's important for aircraft in the same control area to use the same QNH (aside hopefully stopping you from hitting a hill).
If you were to ask ATC for a transponder check, they would hopefully tell you that you're indicating about 2000 ft.
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Typo gets me....
Hey Cloud Cutter,
Well spotted mate, I have obviosly held the shift key down a fraction too long as I wanted the = not the +. Was probably stating the obvious to most, however it is not always obvious to everyone.
While I understand fairly well my own a/c systems and how a Transponder/Encoder work, I would never claim to know everything. But I am surprised a few people here asking about the newer transponders and their displaying PA, which of course they do based on 1013.2, and it seems that at the elementary level, PPL we are not being taught this. I know i was not taught it, but I figuerd it out myself how the system worked long ago.
I think topics such as this are of great interest and benefit to all, new and old pilots, in some cases it may be a significant thing to a trainee reading these pages and similar threads where knowledge can be passed on from generation to generation.
Off now to edit my post!
J
Well spotted mate, I have obviosly held the shift key down a fraction too long as I wanted the = not the +. Was probably stating the obvious to most, however it is not always obvious to everyone.
While I understand fairly well my own a/c systems and how a Transponder/Encoder work, I would never claim to know everything. But I am surprised a few people here asking about the newer transponders and their displaying PA, which of course they do based on 1013.2, and it seems that at the elementary level, PPL we are not being taught this. I know i was not taught it, but I figuerd it out myself how the system worked long ago.
I think topics such as this are of great interest and benefit to all, new and old pilots, in some cases it may be a significant thing to a trainee reading these pages and similar threads where knowledge can be passed on from generation to generation.
Off now to edit my post!
J
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Here's a good article on Transponder Basics from US AOPA which I've found useful:
http://www.public-action.com/911/transpon/
http://www.public-action.com/911/transpon/
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PAF
This is why we have them calibrated every 2 years I believe. Maybe not everyone does this.
And one of the benefits of the PA display on newer units, is that with a simple mental maths calculation you can always verify if the encoder is working properly.
J
This is why we have them calibrated every 2 years I believe. Maybe not everyone does this.
And one of the benefits of the PA display on newer units, is that with a simple mental maths calculation you can always verify if the encoder is working properly.
J
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Roturb - brilliant article that. I never new the squawk was in octal, or that the xpdr can take time to warm up. In one of the a/c I fly it automatically comes on with the radio master, but the other I usually turn from off to alt while holding short.
Very useful atricle, I'll be recommending it to my CFI.
Very useful atricle, I'll be recommending it to my CFI.
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Education campaign
Hey all...
Maybe the, probably millions, of dollars spent on making those posters to stick on the walls of flying schools and operators could have been worded differently. "Turn your transponder ON" may be too literal by looking at the posts here, should it read "turn ya xpndr ta ALT"???
Just a dumb thought, but hey, might help...
Another point, I like to switch my xpndr to alt whenever I enter or cross a runway (supposed to be for TCAS craft) Any thoughts on that, I also have one of them sparkly new units, bloody thing keeps turning itself to ALT after startup, I sometimes miss this, I will read the book oneday when I get chance... My q'n on this is, does a plane dunging around on the ground with xpndr on ALT affect TCAS operators??? I think that it would!!!
Thanks...
Maybe the, probably millions, of dollars spent on making those posters to stick on the walls of flying schools and operators could have been worded differently. "Turn your transponder ON" may be too literal by looking at the posts here, should it read "turn ya xpndr ta ALT"???
Just a dumb thought, but hey, might help...
Another point, I like to switch my xpndr to alt whenever I enter or cross a runway (supposed to be for TCAS craft) Any thoughts on that, I also have one of them sparkly new units, bloody thing keeps turning itself to ALT after startup, I sometimes miss this, I will read the book oneday when I get chance... My q'n on this is, does a plane dunging around on the ground with xpndr on ALT affect TCAS operators??? I think that it would!!!
Thanks...
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In principle I think it's quite a good idea to switch your transponder on when entering an active runway. This will not have any adverse effects on aircraft with TCAS, but is not normally encoraged by radar controllers as it clutters their screens with info that is not relevant to them. The RA (resolution advisory) feature of a TCAS unit is disabled (TA Only) when operating close to the ground (I think normally below 1000 ft radar altitude), so it won't create any problems there (provided your transponder is working properly).
Most larger aircraft have a feature that automatically turns the transponder off on the ground so it is left on at all times, this means that the TCAS is still able to "see" other aircraft, even though you're aircraft is not transmitting a signal.
Most larger aircraft have a feature that automatically turns the transponder off on the ground so it is left on at all times, this means that the TCAS is still able to "see" other aircraft, even though you're aircraft is not transmitting a signal.
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For GAAP zones, if operating wholey within, it is still transponder standby, and if inbound or outbound then mode C. Early on this may generate the confusion or habbit of skipping that check in the line up checks that then continues indefinately.
Suunto
Suunto
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As far as transponder being on whilst crossing runways, it is not normally an issue - generally the transponder returns within a small area defined around the major airports are normally reception inhibited by the radar data processing computers. Also inhibted below 2-300 FT.
Clutter as such is not an issue (not sure about SMR, but I think this is only in YSSY anyway?)
(Your SSR radar track will not activate until you have left this inhibition area, on the correct code, with ALT selected, at a ground speed above 30KTS. This will then activate your flight plan if it has been coordinated - i.e. code has been issued to you)
suunt022 - do you have a ref for the SBY at GAAPS?
Clutter as such is not an issue (not sure about SMR, but I think this is only in YSSY anyway?)
(Your SSR radar track will not activate until you have left this inhibition area, on the correct code, with ALT selected, at a ground speed above 30KTS. This will then activate your flight plan if it has been coordinated - i.e. code has been issued to you)
suunt022 - do you have a ref for the SBY at GAAPS?
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Thanks to Cloud Clutter and ****su Tonks...
If that is the case with regard to TCAS and Radar, then is there a good reason to not have your Transponder on ALT all the time??? This would reduce errors associated with forgetting... There would have to be the special proceedures at some airports, like Sydney and maybe the GAAPs, but thats what we deal with all the time anyway...
Cheers... 256.
If that is the case with regard to TCAS and Radar, then is there a good reason to not have your Transponder on ALT all the time??? This would reduce errors associated with forgetting... There would have to be the special proceedures at some airports, like Sydney and maybe the GAAPs, but thats what we deal with all the time anyway...
Cheers... 256.
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****su,
Old home copy of AIP, but this stuff doesn't change too often so should be correct. ENR 1.6.8.1.8
When operating in, or in the vicinity of, a GAAP control zone, a transpoonder should be selected to:
a) STANDBY - for flights wholly within a GAAP CTR
b) ON/ALT - prior to take-off departing a GAAP CTR, or
c) ON/ALT - when operating in GAAP lanes of entry.
I suspect it's because GAAP's are busy (well, used to be anyway) with vfr traffic and it removes the clusters of black tracks and labels from the screens.
Old home copy of AIP, but this stuff doesn't change too often so should be correct. ENR 1.6.8.1.8
When operating in, or in the vicinity of, a GAAP control zone, a transpoonder should be selected to:
a) STANDBY - for flights wholly within a GAAP CTR
b) ON/ALT - prior to take-off departing a GAAP CTR, or
c) ON/ALT - when operating in GAAP lanes of entry.
I suspect it's because GAAP's are busy (well, used to be anyway) with vfr traffic and it removes the clusters of black tracks and labels from the screens.
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Thanks R-S,
I assume that would have been introduced before TCAS?
Interestingly it does not seem to be something that is applied / taught / practiced at YBAF. Aircraft in the circuit there usually squawk. In fact, until about 12 months ago, AF TWR would not have known if the aircraft were squawking or not (when they got their own TSAD link).
Approach will see them of course, but only as 'black tracks'. It is the MODE A only ones that cause the aircraft inbound on the 01 ILS to BN the most concern.
I assume that would have been introduced before TCAS?
Interestingly it does not seem to be something that is applied / taught / practiced at YBAF. Aircraft in the circuit there usually squawk. In fact, until about 12 months ago, AF TWR would not have known if the aircraft were squawking or not (when they got their own TSAD link).
Approach will see them of course, but only as 'black tracks'. It is the MODE A only ones that cause the aircraft inbound on the 01 ILS to BN the most concern.
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Some words from the latest AIP
AIP GEN 1.5 6.1 Aircraft Requirements
6.1.1 All aircraft must be fitted with an operable Mode A and Mode C SSR transponder for operations within classes A, B and C airspace and any class of airspace at or above 10,000FT AMSL. Aircraft operating in GAAP control zones are exempted from this requirement.
6.1.2 All aircraft, except aircraft operating to the VFR which are not fitted with an engine driven electrical system capable of continuously powering a transponder, must be fitted with a serviceable Mode A/C or Mode S SSR transponder when operating in Class E airspace.
Note 1: Mode C operation requires the provision of pressure altitude information to the transponder equipment.
Note 2: Procedures for operational use of SSR transponders and transponder codes are detailed at ENR 1.6 Section 8.
AIP Gen 3.3 4.4.12 (pertaining to restricted airspace) Pilots of aircraft fitted with TCAS and transponder equipment must select the equipment on at all times.
AIP ENR 1.1 71. OPERATING REQUIREMENTS FOR TRANSPONDERS
71.1 Pilots of aircraft fitted with a serviceable Mode 3A transponder must activate the transponder at all times during flight, and if the transponder is Mode 3C capable, that mode must also be operated continuously.
AIP ENR 1.6 7.1.2 Unless advised otherwise by ATC or in accordance with para 7.1.8, pilots of Mode 3A or Mode S transponder-equipped aircraft operating in Australian airspace must activate their transponders, and where a Mode 3C capability is also available it must be activated simultaneously with Mode 3A.
7.1.7 A pilot operating at a radar controlled aerodrome must:
a. on departure, leave the transponder selected to STANDBY until entering the departure runway; and
b. on arrival, select the transponder to STANDBY or OFF as soon as practicable after landing.
7.1.8 When operating in, or in the vicinity of, a GAAP control zone, a transponder should be selected to:
a. STANDBY -- for flights wholly within a GAAP CTR,
b. ON/ALT -- prior to take-off departing a GAAP CTR, or
c. ON/ALT -- when operating in GAAP lanes of entry.
7.1.9 Pilots must select the transponder to STANDBY before effecting an SSR code change and returning the transponder to ON/ALT.
Note: This action is required to prevent possible loss of displayed aircraft position/label information and possible misidentification of aircraft in automated Australian ATC systems due to temporary selection (while effecting the change) of a code already in use.
6.1.1 All aircraft must be fitted with an operable Mode A and Mode C SSR transponder for operations within classes A, B and C airspace and any class of airspace at or above 10,000FT AMSL. Aircraft operating in GAAP control zones are exempted from this requirement.
6.1.2 All aircraft, except aircraft operating to the VFR which are not fitted with an engine driven electrical system capable of continuously powering a transponder, must be fitted with a serviceable Mode A/C or Mode S SSR transponder when operating in Class E airspace.
Note 1: Mode C operation requires the provision of pressure altitude information to the transponder equipment.
Note 2: Procedures for operational use of SSR transponders and transponder codes are detailed at ENR 1.6 Section 8.
AIP Gen 3.3 4.4.12 (pertaining to restricted airspace) Pilots of aircraft fitted with TCAS and transponder equipment must select the equipment on at all times.
AIP ENR 1.1 71. OPERATING REQUIREMENTS FOR TRANSPONDERS
71.1 Pilots of aircraft fitted with a serviceable Mode 3A transponder must activate the transponder at all times during flight, and if the transponder is Mode 3C capable, that mode must also be operated continuously.
AIP ENR 1.6 7.1.2 Unless advised otherwise by ATC or in accordance with para 7.1.8, pilots of Mode 3A or Mode S transponder-equipped aircraft operating in Australian airspace must activate their transponders, and where a Mode 3C capability is also available it must be activated simultaneously with Mode 3A.
7.1.7 A pilot operating at a radar controlled aerodrome must:
a. on departure, leave the transponder selected to STANDBY until entering the departure runway; and
b. on arrival, select the transponder to STANDBY or OFF as soon as practicable after landing.
7.1.8 When operating in, or in the vicinity of, a GAAP control zone, a transponder should be selected to:
a. STANDBY -- for flights wholly within a GAAP CTR,
b. ON/ALT -- prior to take-off departing a GAAP CTR, or
c. ON/ALT -- when operating in GAAP lanes of entry.
7.1.9 Pilots must select the transponder to STANDBY before effecting an SSR code change and returning the transponder to ON/ALT.
Note: This action is required to prevent possible loss of displayed aircraft position/label information and possible misidentification of aircraft in automated Australian ATC systems due to temporary selection (while effecting the change) of a code already in use.
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****su,
The AIP ENR 1.6 was the one i had. I assumed it was for radar clutter, possibly dating back to pre TAAATS.
I think most GAAPS have TSAD now but clutter shouldn't be too much of an issue if the screen range is something like 30nm or less. I know at 70nm range it can get cluttered by labels at times.
Suunto
The AIP ENR 1.6 was the one i had. I assumed it was for radar clutter, possibly dating back to pre TAAATS.
I think most GAAPS have TSAD now but clutter shouldn't be too much of an issue if the screen range is something like 30nm or less. I know at 70nm range it can get cluttered by labels at times.
Suunto
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CAR256
Many airports don't use radar filtering (particularly the tower), and aircraft with TCAS aren't able to filter out aircraft on the ground so best not to leave your transponder on (in fact, you will be asked to sqwark standby at most airports if you do).
Many airports don't use radar filtering (particularly the tower), and aircraft with TCAS aren't able to filter out aircraft on the ground so best not to leave your transponder on (in fact, you will be asked to sqwark standby at most airports if you do).
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In principle I think it's quite a good idea to switch your transponder on when entering an active runway. This will not have any adverse effects on aircraft with TCAS, but is not normally encoraged by radar controllers as it clutters their screens with info that is not relevant to them.
With regard to leaving xpndrs on all the time, I was only suggesting a proceedure change, done by the correct path... I only try to have mine on at the appropriate time but I seem to be having an almost constant battle with my Garmin (airbus) whats it doing now! Xpndr...
256...
CAR256 and others
At the gate or taxiing with your XPDR switched to ON or ALT if an A/C with TCAS is taking off nearby they will get a "traffic traffic" alert. Quite a bugger when you are at 300' going up!!
Although I think there was a software mod to fix this problem? can't recall the details though.
At the gate or taxiing with your XPDR switched to ON or ALT if an A/C with TCAS is taking off nearby they will get a "traffic traffic" alert. Quite a bugger when you are at 300' going up!!
Although I think there was a software mod to fix this problem? can't recall the details though.
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CAR256
Not really, radar controllers aren't normally interested in what's going on on the ground.
As ACMS said, while you won't get a TCAS RA from an aircraft on the ground, however you may still get a TA which would certainly be an unwanted distraction during departure or approach. Of course you would probably quite appreciate a TA if an aircraft was about to enter the runway you are landing on, so I still think it's a pretty good idea to turn on your transponder as you enter the active runway, rather than just with the line-up checks. You can see why it's not a good idea to leave it on all the time though.
Not really, radar controllers aren't normally interested in what's going on on the ground.
As ACMS said, while you won't get a TCAS RA from an aircraft on the ground, however you may still get a TA which would certainly be an unwanted distraction during departure or approach. Of course you would probably quite appreciate a TA if an aircraft was about to enter the runway you are landing on, so I still think it's a pretty good idea to turn on your transponder as you enter the active runway, rather than just with the line-up checks. You can see why it's not a good idea to leave it on all the time though.