Mr Spaceman From Canada, joined Mar 2001, 2786 posts, RR: 9 Posted (10 years 11 months 5 days 19 hours ago) and read 5189 times:
I have a few questions about ATC procedures when an airline pilot first checks in with an airport's terminal approach control.
When I'm at home with my receiver, listening to airline pilots checking in with Toronto International's approach controllers (unfortunately I can only hear the pilots side of the radio work), almost all the aircraft are being assigned a 4 digit code which I assume is a transponder code. Each aircraft is given a different code.
The pilot's transmisions usually go something like this....
"Toronto arrival, Air Canada four seven niner is with you, level at one zero thousand, we're slowing to two fifty knots, we have tango".
(after the silence during the controllers intructions, the pilot's readback always starts with a 4 digit code)
"eight niner niner three, down to eight thousand, two ten on the speed, Air Canada four seven niner".
Then, the pilot's readbacks always involve lower altitudes, slower speeds, and some heading changes, untill reaching 4000 feet or lower where they're finally cleared to intercept the ILS for their runway and are handed off to the tower (Toronto's TWR frequencies are 118.35 or 118.7).
My questions are .... Are the 4 digit codes (such as 8993), assigned to these aircraft, transponder codes? (I can't think of what else they could be). If so, why is it nessesary for each aircraft to have it's own seperate code?
Obviously there's a difference between flying VFR (where you always squawk 1200 on your transponder, unless otherwise instructed by ATC - at least from my experience) and flying IFR in the system.
Some detailed info about these 4 digit codes and why they're required to be different for each aircraft would be much appreciated.
NormalSpeed From , joined Dec 1969, posts, RR: Reply 1, posted (10 years 11 months 5 days 18 hours ago) and read 5132 times:
My guess is that the 4 digit code is probably sea level pressure, and ATC is giving the pilot an updated altimeter setting expressed in milibars (Canada uses milibars, right? Down in the states we use inches of mercury.) IFR arrivals would have been issued a 4 digit transponder code with their IFR clearance before they took off.
So let's see, "eight niner niner three" would be 899.3 milibars, right? Except that translates into about 26.56" hg, so I'm assuming that you are using a hypothetical pilot/controller dialouge.
Mr Spaceman From Canada, joined Mar 2001, 2786 posts, RR: 9 Reply 2, posted (10 years 11 months 5 days 18 hours ago) and read 5118 times:
Thanks for your reply.
Up here in Canada (the "Great White North"), we also use inches of mercury. If you tune into the ATIS for any airport you will hear the altimeter setting is 29.97 for example.
The only place I ever hear milibars being used is for the barametric pressure during the local new's weather report.
The 8993 code I used in my post is from an actual transmision between an Air Canada pilot and Toronto Intl's approach controller a few days ago. I wrote it down for the purpose of asking this question. It's not hypothetical.
AAR90 From United States of America, joined Jan 2000, 3434 posts, RR: 49 Reply 5, posted (10 years 11 months 5 days 15 hours ago) and read 5094 times:
It has been my experience (I fly a lot of LAX-YYC trips) that:
1. YYC arrival controllers almost always provide the current altimeter setting upon initial check-in.
2. They almost _never_ change an aircraft's transponder code, and....
3. ATC Transponders do not utilize digits 8 or 9 in any way/shape/form.
I suspect you've got a distorted reception of the readback of the altimeter setting; "two niner niner three" (29.93).
*NO CARRIER* -- A Naval Aviator's worst nightmare!
Mr Spaceman From Canada, joined Mar 2001, 2786 posts, RR: 9 Reply 6, posted (10 years 11 months 5 days 14 hours ago) and read 5087 times:
OK, I hear you loud and clear regarding your explanation about how transponders never utilize digits 8 or 9 and that they are almost never changed.
NormalSpeed explained that transponder codes are issued with a pilot's IFR clearance before takeoff, and Timz also says transponder codes don't go that high.
So, that tells me that this 4 digit code has noting to do with the transponder.
It is possible that the 4 digit code I used as an example (8993) was off the top of my head, although I really thought it was one that I wrote down because I've been listening to these pilots checking in and have been writting down exactly what the pilot's were reading back in order to prepare for this question.
Regarding my original posted questions, not only did I ask if these 4 digits being read back were transponder codes, but I also wanted to find out why they were all different. Now that I've learned that airline pilots recieve their transponder codes along with their IFR clearance before they depart...can you please let me now if all their codes are different or not, and if so, what's the reason for that?
Unfortunately I'm not at my home right now, so I don't have my receiver to listen to, or the other codes that I've been writting down.
What I can tell you though, as sure as I'm sitting here alive, is that these pilots are always reading back a 4 digit code to the arrival controller, and they are never the same 4 numbers. So these numbers couldn't possibly be altimeter settings. Also, one pilot could check in and readback a code like 4532, then the next pilot checking in 30 seconds later will readback something like 5614, etc, etc, and they always say these numbers at the begining of their readback after their initial contact with the Terminal's ATC.
Gentlemen, I will most definetly post more solid examples of these pilot's readbacks tommorow, including the airline and their 4 digit codes.
> > > Here's a question that you can probably answer right away, because I do have it written down in my pocket. Last night many pilots were also receiving a 3 digit number upon initial contact with arrival. I heard one pilot check in and then ask (loud and clear) "and what's our number for tonight?" to which she read back "OK, 447, Thanks". This same number was read back by several pilots and one pilot said "OK, we've got 447 on the meter".
What does this 3 digit number mean?
PS, I hope I'm not driving you guys crazy with this stuff. I keep hearing pilots saying it, and simply wan't to understand what it means.
XFSUgimpLB41X From United States of America, joined Aug 2000, 4104 posts, RR: 38 Reply 9, posted (10 years 11 months 5 days 13 hours ago) and read 5068 times:
Mr. Spaceman... any way you can get closer to the transmitter for this sector? Hearing the other end might help clear things up.
The three digit code has to do with the altitmeter with the first digit truncated.... the "meter" is slang for the altimeter. Just _447 is impossible though on an altimeter.... no matter with Hg or mb's....
Which brings me to my next point: are you sure you are hearing the numbers right? The first thing i am always told is the altimeter setting after ATC acknowledging my check in. It willl always start with a 2 or 3 and be a 4 digit code though if in Hg, or a 900 or 1000 number for mb's.
NormalSpeed- i was being sarcastic too though on the last post i hope it didnt sound harsh. Just raggin on ya!
AAR90 From United States of America, joined Jan 2000, 3434 posts, RR: 49 Reply 10, posted (10 years 11 months 5 days 13 hours ago) and read 5074 times:
It's 4096 code transponder there, tiger.
That has nothing to do with how high it will go.
If memory serves, there are 4,096 available combination of numbers on the Mode-3 transponder code. Someone want to do the math?
Regarding my original posted questions, not only did I ask if these 4 digits being read back were transponder codes, but I also wanted to find out why they were all different.
ATC uses an aircraft's Mode-3 transponder code to enhance its radar position (more accurate than raw radar) as well as provide additional flight information (stored in a database of active flight plans) such as call sign, type acft, navigation equipment installed, etc., etc. The ATC computers look up the data based upon the 4-digit Mode-3 code assigned to each aircraft.
Now that I've learned that airline pilots recieve their transponder codes along with their IFR clearance before they depart...can you please let me now if all their codes are different or not, and if so, what's the reason for that?
Yes and no, see above. Normally each IFR flight plan is assigned a unique transponder code prior to departure and that code will stay with that flight plan as long as it remains active (aircraft may/may not be airborne). However, with all the aircraft that can be airborne at any given time, 4096 codes isn't enough so ATC will often issue a new transponder code to an airborne aircraft (normally entering a new sector) thereby freeing up the old code for someone else's use in the old (just departed) sector.
*NO CARRIER* -- A Naval Aviator's worst nightmare!
AAR90 From United States of America, joined Jan 2000, 3434 posts, RR: 49 Reply 15, posted (10 years 11 months 4 days 20 hours ago) and read 4978 times:
Mode C transponders use octal notation,
Actually, Mode C is the altitude reporting feature and has no pilot controlled functions except on/off (and maybe "standby").
Xponders will go to 7777. Although don't dial that in. Thats what the military uses on its target drones.
Perhaps, but in the hundreds of range clearance flights I've flown, US military has never used 7777. We've always assigned a specific code [in all modes] for each specific target: drone, missile or plane.
Very good AAR90.... The calculation is 8x8x8x8=4096...the number of combinations.
That's not "good." I'm just a dumb pilot and couldn't figure out the math myself. The trivia knowledge comes from 10+ years of flying around 6 tons of avionics --including the interrogator that queries the transponders and a million+ watt radar system. Then again, it was good to know the "moles" could see everything ATC could not.
*NO CARRIER* -- A Naval Aviator's worst nightmare!
Mr Spaceman From Canada, joined Mar 2001, 2786 posts, RR: 9 Reply 16, posted (10 years 11 months 4 days 19 hours ago) and read 4964 times:
Thanks for all that information about mode-3 transponder combinations, etc.
> XFSUgimpLB41X, I just got this ICOM R-2 receiver (it's smaller than a pack of smokes) for a birthday gift from my girlfriend on Nov 16. Since then, I've only had time to visit Toronto International Airport 2 times with the last visit being a month ago (it's only a 25 minute drive on the highway, but I've been very busy). While I was at Toronto Intl, I could hear everone perfectly...the ATC controllers for arrival, departure, the tower and ground were loud and clear.
Although I wasn't concentrating on the 4 and 3 digit numbers I hear pilot's saying during their readbacks to approach when I was last at YYZ (I was busy reading my new toy's manual), I know that I never heard the word "squawk" used once by anyone.
To answer your question, I will be going out to YYZ tonight or in the morning so I can really listen to the controller's instructions. Also, yes sir, I am hearing the numbers right. I have perfect hearing and the reception on this receiver is excellent!
> AAR90, thanks for that great info about why and when a pilot's transponder code might be changed by ATC during flight.
> > > OK, here we go again. Let's see if the following info can shine any light on this 4 digit question (I'm thinking of changing my user name to "4 DIGITS" ).
Last night and this morning I sat back with my girlfriend (who's also an A.Net member) and listened to the pilot's readbacks after checking in with Toronto's arrival controllers.
Starting at 9:20 pm (Jan 10, 21:20 hrs, Toronto time) I heard the following 4 digit numbers read back by 5 different pilots checking in over a 4 minute period.
In order of pilot's readback.
Several pilots checking in didn't readback any codes other than their flight #.
Between 9:30 and 9:40 pm, 5 different aircraft's pilots read back the same 4 digit code...2970.
These airliners were mostly Air Canada, however some others were American Airlines, Jazz, US Air, as well as a medivac flight. I couldn't pick up the names of many of the airlines checking in because of the pilot's lingo being too quick!
Here's some in detail.....(Jan 10, 22:05 hrs local time) "Good evening Toronto, Northwest one four eight eight's with you at one one thousand, speed showing two fifty knots, with whiskey".
His readback...."two niner six niner, down to seven thousand, Northwest one four eight eight".
This morning (Jan 11, 10:35 hrs local time) I heard this pilot's transmision..." Good morning Toronto, Air Canada seven three three's with you at one one thousand, coming at you at two fifty knots with xray.
His readback...."OK, twenty four right, one zero niner four, air canada seven three three".
A readback code at 11:20 this morning for Air Canada 579 was 2984. Another for Air Canada 555 at 11:28 am was 2985.
That's all folks. I wish I could record these pilots and post an audio, that would surely help. I'm very aware that some of these codes could be an altimeter setting...such as 2985, but, what about 1094, 1832 or 7362?
Incase you guys have had enough of this question about these mysterious 4 digit readbacks, here a quick question that I think I know the answer to, but want to make sure.
Sometimes I've heard pilots say during their readbacks "OK, we've got 5 on the glideslope" I've also heard 4 and 3 "on the glideslope".
Are these pilots simply being told how many aircraft are currently flying down the ILS?
Arv79 From Canada, joined Aug 1999, 31 posts, RR: 0 Reply 18, posted (10 years 11 months 2 days 20 hours ago) and read 4862 times:
When I used to listen to Toronto arrival on squawkident.com, the controller always gave the latest altimeter along with the landing runway. As far as I can recall, I've never heard any 4 digit number that didn't sound like an altimeter reading.
Regarding the "we've got 5 on the glideslope"; I've heard instructions like "leave 5/4/3 on the glideslope" which , if I'm not mistaken, means leave 5000, 4000, 3000 respectively once established on the glideslope.
Mr Spaceman From Canada, joined Mar 2001, 2786 posts, RR: 9 Reply 19, posted (10 years 11 months 2 days 18 hours ago) and read 4861 times:
Well, it's seems like this question will remain a mystery for me, at least for now.
Regarding these 4 digits I keep hearing the pilots reading back to the controllers, some could be the altimeter setting (ex: 2978), however, most couldn't be. Also, for some reason these constantly changing 4 numbers are not always part of the pilot's readbacks. I'll hear them being used for several hours, then suddenly the pilots stop repeating them to ATC for many hours. So, I don't know exactly what the purpose for these numbers is, but, I do know that I'm not going to worry about it anymore.
One last comment ..... as I'm sure you know, every pilots who checks in with Toronto's arrival controllers finishes his initial contact communication with reference to the ATIS identification. Ex: "......we're at two ten knots with foxtrot", so they already have the current altimeter setting. On many occasions I've heard pilot's check in and mention that he had the ATIS info "DELTA" for example, when the ATIS had already been updated to "ECHO", and the controllers always make sure that the pilots have listened to the current ATIS info.
AAR90 From United States of America, joined Jan 2000, 3434 posts, RR: 49 Reply 20, posted (10 years 11 months 2 days 15 hours ago) and read 4843 times:
Can you give me a quick review of exactly what information you're questioning. I'm scheduled to fly AA1856 LAX-YYZ arriving ~1700hrs. on 14th. I'll try and pay attention to anything specific you're asking about.
*NO CARRIER* -- A Naval Aviator's worst nightmare!
Mr Spaceman From Canada, joined Mar 2001, 2786 posts, RR: 9 Reply 21, posted (10 years 11 months 2 days 14 hours ago) and read 4843 times:
Basically, while listening to pilots checking in with Toronto's arrival controllers I've noticed that when reading back their first instructions from ATC, they often include a 4 digit number at the begining of their readback.
1) Pilot checks in with arrival.
2) Pilot receives ATC instructions (unfortunately I can't hear ATC from my home).
3) Pilot reads back ATC's instructions and starts by saying 4 numbers such as 7362, 1832, 1835, 1094, etc.
Question...What's these 4 number's purpose? (if they're not a transponder code or altimeter setting).
PS, I'll be tracking your flight on the internet and listening for your initial contact with Toronto's arrival, etc. I think that will be a blast!
Arv79 From Canada, joined Aug 1999, 31 posts, RR: 0 Reply 22, posted (10 years 11 months 1 day 23 hours ago) and read 4810 times:
I too have heard pilots checking in with an outdated ATIS information. But I've also heard pilots checking in with a more recent ATIS information which the controller doesn't have. For example, once when I was hearing the conversation, majority of the pilots had a more recent version of the ATIS and the controller was unaware that it had changed and his console obviously didn't reflect the change. Lets hope no such problems occur with the radar scope!!! (just kidding).
> Arv79, to me, one of the best things about listening to pilots on a receiver is that you get to hear their different styles of radio jargon/lingo, and when some confusion, laughter or the unexpected happens (like landing gear that won't extend), it becomes very interesting.
Mr Spaceman From Canada, joined Mar 2001, 2786 posts, RR: 9 Reply 24, posted (10 years 11 months 18 hours ago) and read 4719 times:
>AAR90, I heard you check in with Toronto's arrival yesterday evening around 17:15 hrs (local Toronto time). Unfortunately, your first transmission was very fuzzy and all I heard was "fuz fuz American fuz fuz fuz" etc, but I knew it was you because I was tracking your flight on my PC, and you were the only American Airlines flight scheduled for that time.
I don't know if you were given a 4 diggit code or not because your initial contact was unclear, however, none of the other airliners for an hour before you and 15 minutes after were reading back a 4 number code...except one, who read back "three zero one seven" (that sounds like an altimeter setting to me).
As you got closer to me (I'm 14 nm due east of YYZ), your transmissions became much clearer and I heard you read back lower altitudes and then your clearance to intercept the ILS for runway 23. I was hoping you would fly right over my home (a few other airliners were), but I guess you turned inbound around 12 nm DME. I had my binnoculars ready too...Dang!
I heard you read back "one seventy knots to Xray, American fifteen eight six", while you were on the glide slope. Then your last transmission at 17:25 was "Americam fifteen eighty six, Thank You".
How was your landing? Did you have a crosswind? (I'm to far away to receive the ATIS which was Sierra). Also, were you doing the radio work, or was it your first officer?
Question: At YYZ, is the NDB "Xray" located on the ILS for rwy 23 at 3.7 DME the Outer Marker?