Adamoh
Pre-Flight
What happens if you fly with your Mode C off or in standby in a Mode C area?
What happens if you fly with your Mode C off or in standby in a Mode C area?
The radar service for the mode C area doesn't like it(typically approach/departure). Your lat and long location are determined by your mode A from the TXP but the altitude is determined from the azimuth reflection of the radar(s) in use. Some are better than others. You will be reported as 'traffic xxxx, altitude 2600 feet unverified', meaning they are not getting an altitude output from your TXP. If they know who you are, you may get asked to cycle the mode C, you may be asked to verify altitude, you may be asked to leave the mode C area, or you may be told to call this number.
Interesting. I thought unverified was a mode c return they hadn't been able to verify since nobody is talking with the target rather than an azimuth estimation.
The radar service for the mode C area doesn't like it(typically approach/departure). Your lat and long location are determined by your mode A from the TXP but the altitude is determined from the azimuth reflection of the radar(s) in use. Some are better than others. You will be reported as 'traffic xxxx, altitude 2600 feet unverified', meaning they are not getting an altitude output from your TXP. If they know who you are, you may get asked to cycle the mode C, you may be asked to verify altitude, you may be asked to leave the mode C area, or you may be told to call this number.
What happens if you fly with your Mode C off or in standby in a Mode C area?
Pretty much.If your transponder selector is not in the ALT position the encoder will not send altitude information. If you're talking to ATC the controller will tell you he's not receiving altitude. You will then move your selector to ALT, and all will be right with the world.
In air defense radar systems but not in ATC.
Thank you, I stand corrected. Do you get primary return with any altitude info at all?
I'm curious about this.
If I were to ever take off with the txp not set to ALT, it would probably be in STBY (purely hypothetical of course )
Tower politely reminds me to check it. So, in STBY they saw nothing, and in ALT they may see only mode A? That could mean that if it was set ON they would see the A but no C and neither of would know.
Is this all part of the reasoning for the recent guidance to always leave the transponder set to ALT?
The radar service for the mode C area doesn't like it(typically approach/departure). Your lat and long location are determined by your mode A from the TXP but the altitude is determined from the azimuth reflection of the radar(s) in use. Some are better than others. You will be reported as 'traffic xxxx, altitude 2600 feet unverified', meaning they are not getting an altitude output from your TXP. If they know who you are, you may get asked to cycle the mode C, you may be asked to verify altitude, you may be asked to leave the mode C area, or you may be told to call this number.
You're a bit confused (or I am). If your transponder has an "Alt" setting, by its selection, you are squawking both Modes A and C. There's no way you can only squawk altitude without also squawking mode A (the four digit code). You can squawk just mode A, ususally the "On" setting for the transponder. In Stby, you just power the unit but don't respond or transmit. The reason ATC always wants you squawking both Modes A and C is because they can fix your position in three dimensions vs. two. If they determine that your altitude readout is incorrect, they'll ask you to turn off mode C so that it doesn't confuse them or their computer.
I don't think either of us are confused. Part of the thread was about equipment differences at the tower vs departure which I didn't know about.
So in theory you could take off set to "On" and tower wouldn't notice since they see the mode A and Departure wouldn't see your altitude. That was the interesting part for me.
I don't think either of us are confused. Part of the thread was about equipment differences at the tower vs departure which I didn't know about.
So in theory you could take off set to "On" and tower wouldn't notice since they see the mode A and Departure wouldn't see your altitude. That was the interesting part for me.
And even the dark radar room is pretty much a historical thing. Many of the displays used these days will work just fine in normal room illumination (a room full of windows like the tower is a different story). But, controllers have this history of sitting in dark rooms. What I could never figure out is the guys in the FSS sitting in windowless dark rooms looking at their computer monitors. Crikes, it's not ATC and a window might help these guys ability to relay weather.
I think there are still plenty of radar rooms where turning the lights on turns the radar display into a big yellow-orange disk.
The radar service for the mode C area doesn't like it(typically approach/departure). Your lat and long location are determined by your mode A from the TXP but the altitude is determined from the azimuth reflection of the radar(s) in use. Some are better than others. You will be reported as 'traffic xxxx, altitude 2600 feet unverified', meaning they are not getting an altitude output from your TXP. If they know who you are, you may get asked to cycle the mode C, you may be asked to verify altitude, you may be asked to leave the mode C area, or you may be told to call this number.
You're not saying they'll try to do the "possible pilot deviation..." because of a transponder readout, which for all they know could be a unknown issue for the PIC.
So I live in Alaska and have not had to use my mode C for years. I think Anchorage is the only airport in Alaska that requires mode C.
Juneau is my home base class D. Every so often I hear tower tell some one traffic 3 miles to the South, or something like that. Is the tower picking up mode C to report traffic? I think you need to be above 10,000 feet to be picked up by the nearest radar.
Second question is when operating at a Mode C airport do you turn your transponder to standby on the ground, taxi for departure, then turn to alt after departure?
See my link above. I almost got murdered over it.
You leave it ON all the time unless told by ATC to switch to STBY. AIM 4-1-20(a)(3).
I learned to fly out of the small boat harbor at JNU.
Bob Gardner
Yikes!
That was in the SFRA though, I wouldn't think you'd have received the same treatment had it been in airspace outside of the SFRA
That's just the AIM though, not a regulation.
Mine goes to stand by automatically for ground ops and ALT after I takeoff, not worth reprogramming it over a AIM recommendation IMHO.
Then don't bring it into the SFRA. You're required to keep it reporting Mode-C from landing until you reach parking.
What happens if you fly with your Mode C off or in standby in a Mode C area?
See my link above. I almost got murdered over it.
Really? I almost got blasted to bits when I was TALKING to the controller, he knew who I was AND I was DEPARTING the SFRA!!!!Yeah, but wasn't that in the DC SFRA and/or ADZ? That's a little different.
Then don't bring it into the SFRA. You're required to keep it reporting Mode-C from landing until you reach parking.
Then don't bring it into the SFRA. You're required to keep it reporting Mode-C from landing until you reach parking.
Can you reference that? I don't recall it from my SFRA course nor could I find anything online. Obviously you keep the discrete code until shut down and never use 1200, but I'm 95% sure our GTX-330 goes to "ground" automatically on landing. Ground is different than standby in that it still responds with some mode s data, but I believe it does not send out the mode c altitude number.
Given the enormous number of transponders that automatically switch between ground and altitude modes, I'd think this rule would have to be more prominently emphasized for SFRA operations or we'd hear about busts far more often.
I avoid airspace like that like the pleauge, same deal with LAX, NYC, etc.
Landed in KLAS once, taxiing out with a plane that had the same type of transponder, ground asked me to cycle the transponder, oops, hit the button, that was that.
Airport now uses radar to track aircraft while taxiing. Keep transponder on at all times.