Altimeter VS Squawk
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AggieMike88
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The original "I don't know it all" of aviation.
Yes, this is normal. Research the different types of altitude in the PHAK or Instrument flying handbook.
From your description, you have a digital transponder that displayed the pressure altitude.
Your altimeter is showing you the baro-corrected altitude.
From your description, you have a digital transponder that displayed the pressure altitude.
Your altimeter is showing you the baro-corrected altitude.
TK211X
Pre-takeoff checklist
I'm confused, I thought they were supposed to be identical.
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tsts4
Pattern Altitude
What's a squawk box?
AggieMike88
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The original "I don't know it all" of aviation.
No, they are not. Read about the different types of altitude and enlightenment will be obtained.
PHAK chapter 3
Hint: when told by a controller or weather broadcast that the altimeter is 30.48, are you able to input that into your transponder?
PHAK chapter 3
Hint: when told by a controller or weather broadcast that the altimeter is 30.48, are you able to input that into your transponder?
set your altimeter to 29.92 and I believe they should match.
AggieMike88
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The original "I don't know it all" of aviation.
Yes, but that's not the lesson the young padawan needs to learn.
TK211X
Pre-takeoff checklist
Into the transponder? No, not that i'm aware of.
TK211X
Pre-takeoff checklist
Here is the problem, I took off from KVDF at about 1000 with altimeter 30.00. My transponder showed 1200. Here is my flight path:
Direct Chemical plant at 1000 over the water direct skyway bridge then at 800ft outside of the shore until I made a turn into Clearwater beach and climbed to 1200 on a course parallel out of Campbell bridge. Contact APP and he is SWAMPED, told to standby, so I decend to 1000 - 1100ft and follow the magenta shade around surface area of Class B direct brewery and landed at KVDF.
Land and FBO has a phone number for me to call. I turned pale white and call them. The guy seemed calm and just told me that they showed me as inside Bravo near the surface area at 1300 or something like that. I have to call another person tomorrow morning and explain to him something about my flight.
Direct Chemical plant at 1000 over the water direct skyway bridge then at 800ft outside of the shore until I made a turn into Clearwater beach and climbed to 1200 on a course parallel out of Campbell bridge. Contact APP and he is SWAMPED, told to standby, so I decend to 1000 - 1100ft and follow the magenta shade around surface area of Class B direct brewery and landed at KVDF.
Land and FBO has a phone number for me to call. I turned pale white and call them. The guy seemed calm and just told me that they showed me as inside Bravo near the surface area at 1300 or something like that. I have to call another person tomorrow morning and explain to him something about my flight.
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AggieMike88
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The original "I don't know it all" of aviation.
Part of my point. Your Bravo bust story sounds like a good opportunity to meet with your instructor and review the flight, the different types of altitudes, what went wrong, and how to correct it.
tsts4
Pattern Altitude
TK211X
Pre-takeoff checklist
Is it possible for my transponder to show me at a higher altitude than what my baro-corrected altimeter shows? I'm very positive I hadn't busted the Bravo. So, I feel like I shouldn't file a ASRS. The person over the phone just told me along the lines of "Just clarify and explain to them tomorrow that I hadn't entered the Bravo."
What should I do?
What should I do?
James331
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James331
I've had them show higher and lower than indicated, if you're not in Alpha indicated is king.
File the NASA anyways, you got nothing to loose at this point.
Tell ATC you were INDICATING XXXX altitude and we're not in bravo.
File the NASA anyways, you got nothing to loose at this point.
Tell ATC you were INDICATING XXXX altitude and we're not in bravo.
FastEddieB
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Fast Eddie B
If you can't go to the PHAK and read and understand the different kinds of altitude*, my suggestion would be an hour of oral with an instructor.
*The ability to define things is often a prerequisite for understanding them.
*The ability to define things is often a prerequisite for understanding them.
tsts4
Pattern Altitude
Don't panic. They will most lIkey just make sure you understand the rules and that's it. You might want to get your static system and encoder checked out to be sure it's all working properly. As far as the ASRS goes, it can't hurt to file it, but since they called you the proverbial horse has already left the barn IMO.
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Velocity173
Sure, your mode C is valid if it's less than 300 ft of what assigned or in this case, what you were flying. So, at 1,100 ft you could theoretically be showing 1,300 ft on the controllers scope and still be a valid mode C. Just tell them tomorrow you were at 1,100 ft and your transponder is slightly off.
JB1842
En-Route
My wife.
tsts4
Pattern Altitude
Originally Posted by tsts4 
What's a squawk box?
I had one of those those models for 33 years......
I wrote her a check and put her out to pasture for others to mate with...
What's a squawk box?
I had one of those those models for 33 years......
I wrote her a check and put her out to pasture for others to mate with...
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Unit74
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The majority of the time, it will show 1200. Then one magical day and a lot less hair on your head and some unexplained weight loss, you actually get to change it!
But it's still only gonna show pressure altitude to the controller, and they know this. So don't sweat over it.
But it's still only gonna show pressure altitude to the controller, and they know this. So don't sweat over it.
Unit74
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Unit74
Originally Posted by tsts4
What's a squawk box?
I had one of those that models for 33 years......
I wrote her a check and put her out to pasture for others to mate with...
Pretty sure that chicken wasn't laying eggs any more.....should put her down
Pretty sure that chicken wasn't laying eggs any more.....should put her down
EPA says you cannot bury hazardous waste in Wyoming....
......
MAKG1
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MAKG
Yes, transponders can be off by a few hundred feet. That's why you have to tell ATC your altitude with every contact.
If you had been on flight following, the discrepancy would be on tape, and would be evidence in your favor. And something that looks like a bust results in repeated requests to say altitude from controllers. BTDT on a Class C transition close below Class B. I even asked Approach if they would prefer it if I descended 100 feet, and was told not to bother.
If you had been on flight following, the discrepancy would be on tape, and would be evidence in your favor. And something that looks like a bust results in repeated requests to say altitude from controllers. BTDT on a Class C transition close below Class B. I even asked Approach if they would prefer it if I descended 100 feet, and was told not to bother.
TK211X
Pre-takeoff checklist
I was not in contact but I was monitoring the approach frequency and they knew I was listening because I got a "Standby" with my cold call, they never talked to me after so I just made a decent below the bravo and circumvented it to KVDF. The controller was swamped.
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Bob Gardner
The takeaway is that you have no control over the altitude reported to ATC by your encoding altimeter, so don't worry about it. There is no connection, electrical or otherwise, between your barometric altimeter (the one with the Kollsman window) and your encoding altimeter.
You ask if your indicated altitude could ever be higher than your pressure altitude, and the answer is yes. Sea level pressure of less than 26 inches have been measured in the eyes of cyclonic storms (hurricanes, tornadoes, typhoons) and the Kollsman scale on your barometric altimeter does not go below 28 inches, IIRC. My personal preference would be to stay away from areas where the sea level pressure was that low.
Bob Gardner
BillTIZ
Final Approach
Don't tell them the transponder is slightly off, they'll ask if you knew it was bad why were you using it? They may ask for the date it was last checked, 91.411 & 91.413.
Just tell them what you said in the above post. You were never above 1000 when under their 1200ft floor.
Read PHAK as recommended. The transponder altitude encoder transmits altitude based on 29.92. ATC corrects it when presented to the controller based on local altimeter setting. If you took off with 30.00 in the altimeter that is a difference of 80ft. So the xpndr could transmit and altitude about 100 ft difference.
What as the altimeter setting at TPA when the "violations" occurred?
Great thread as I was just thinking about this today. I was flying at 7,000 feet and my GTX transponder display showed a pressure altitude of 7,200 feet. Does ATC see whatever is on my GTX display? I wouldn't actually do this, but theoretically, if I had flown at 6,800 feet, would it show at 7,000 feet on the controller's display?
The Mode C / S transponders broadcast altitude based on 29.92 so everyone is all on the same page......
It has been 30+ years but I seem to remember that being covered in my Private pilot training and being on the FAA exam..
..
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Witmo
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Tim
No and no. While the transponder transmits pressure altitude, the controller 's computer automatically corrects it to the local pressure and displays the same msl altitude you see on your altimeter on his radar assuming you have your altimeter set to the local pressure. If you're flying at 7000 feet, the controller sees 7000 feet (theoretically).
timwinters
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That was a nice refresher. Thanks, Mike.
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Velocity173
Negative. The controller's display takes the pressure altitude readout from your transponder and automatically converts it to your actual msl altitude thru a baro feed. If you look on the lower left of this picture you'll see the altimeter setting on the scope from that feed. In the older systems the controller has to update that manually.
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Van Johnston
Pattern Altitude
Looking at your route you said you flew, could they be saying you busted the inner core of the B that goes down to the surface on your leg to the brewery?
TK211X
Pre-takeoff checklist
I think that's what they are suggesting. I flew at about 1000-1100 on the outskirts of that core while monitoring my Garmin and Fore-flight to make sure I was outside of it.
file the report and make the call.
airusa
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Joe Kulbeth SunDancer
The altimeter is corrected for pressure changes as you adjust it for altimeter settings to obtaine true altitude. The trainspnder only records pressure altitude and transmit pressure altitude to ATC. ATC computers knows also what the altimeter setting is and applies it to the transponder it sees. So unless the altimeter setting is 29.92 then the altimeter and the transponder will never agree. The transponder is adjusted at ATC.