Flying without mode-C

smbaker

Filing Flight Plan
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smbaker
I was recently informed by tower that my altitude wasn't being reported accurately. Unfortunately, my local field doesn't have any avionics shops handy to diagnose the issue, and it's going to be a while before I can fly it somewhere to have it looked at.

In the meantime, can someone answer for me a question -- is it legal to fly class-D airspace without mode-C enabled? There's no class B or class C anywhere near me. My understanding from the regulations is 'yes', but I'm looking for a second opinion just in case I misread something.

Furthermore, does one advise ground/tower of this prior to departure? or do you just take off with the transponder switched to 'on' instead of 'alt' and they don't care?
 
From the AOPA website :

The following areas require the operation of a Mode C transponder:

  • Operations within Class A, Class B, and Class C airspace.
  • Operations within 30 nautical miles of the primary airport within Class B airspace from the surface to 10,000 feet msl (see airports listed below).
  • Operations above the ceiling and within the lateral boundaries of Class B and C airspace.
  • Operations above 10,000 feet msl in the contiguous 48 states, excluding the airspace at and below 2,500 feet agl.
  • The AIM states in Section 4-1-19(a)(3) that for airborne operations in Class G airspace, the transponder should be operating unless otherwise requested by ATC.
 
You can also have it "fail in flight" repeatedly. We had one that would test fine on the ground but liked to report FL300 in flight. The eventual solution was a new harness. Boston Approach was very understanding though I don't know if they figured out that it was the same tail number over and over.

To be clear we were actively working the issue and not hoping not to get caught. Also always on FF before entering the class-C so they knew about it before hand

Sent from my Nexus 10 using Tapatalk
 
Many Class D airports still have radar and approach control even though they are not Class C. A few examples are KHUF, KWRI, and around TRSA airports like KAZO. Perfectly legal for you not to have it. It just makes it a little easier for controllers and improves their situational awareness.

It is perfectly ok to take-off with it in "on" instead of "alt". I wouldn't bring it up unless they asked. Then I'd just say, "yeah it's INOP"
 
I was recently informed by tower that my altitude wasn't being reported accurately. Unfortunately, my local field doesn't have any avionics shops handy to diagnose the issue, and it's going to be a while before I can fly it somewhere to have it looked at.

In the meantime, can someone answer for me a question -- is it legal to fly class-D airspace without mode-C enabled? There's no class B or class C anywhere near me. My understanding from the regulations is 'yes', but I'm looking for a second opinion just in case I misread something.

Furthermore, does one advise ground/tower of this prior to departure? or do you just take off with the transponder switched to 'on' instead of 'alt' and they don't care?

Class D airspace does not require Mode C or even a transponder. You'd need them only if you were in the Mode C veil around Class B airspace. Just select "ON" instead of "ALT". You don't need to advise the tower before departure.

How far off was the altitude being reported?
 
I was recently informed by tower that my altitude wasn't being reported accurately. Unfortunately, my local field doesn't have any avionics shops handy to diagnose the issue, and it's going to be a while before I can fly it somewhere to have it looked at.
The class C and B controllers are authorized to waive the requirement, just tell 'em you're coming in to get it fixed. Don't forget to tell ground control you want taxi to the local avionics shop :D
 
I was recently informed by tower that my altitude wasn't being reported accurately. Unfortunately, my local field doesn't have any avionics shops handy to diagnose the issue, and it's going to be a while before I can fly it somewhere to have it looked at.

In the meantime, can someone answer for me a question -- is it legal to fly class-D airspace without mode-C enabled? There's no class B or class C anywhere near me. My understanding from the regulations is 'yes', but I'm looking for a second opinion just in case I misread something.

Furthermore, does one advise ground/tower of this prior to departure? or do you just take off with the transponder switched to 'on' instead of 'alt' and they don't care?

It's not the xpndr mode c that's your issue, it's your altitude encoder. you cannot fly in any controlled airspace without at least a mode c xpndr, but you can fly in Class D without an altitude encoder. Only Class B requires the altitude encoder.
 
Within C, but over ok?

No. Read the second post in this thread for the answer. Logical reason -- ATC doesn't want to assume a primary target loitering around the airport is in their airspace when it's really 5000' above the ceiling.
 
you cannot fly in any controlled airspace without at least a mode c xpndr, but you can fly in Class D without an altitude encoder.

Negative. You do not need a transponder simply because you're in Class D. What would be the point of a "mode C" transponder with no altitude encoder anyway?

Of course, at a class D with a radar feed they will probably ask if your transponder is on because they expect to see it and will assume you just forgot to turn it on. But a simple "I don't have one" or "it's INOP, gotta get the darn thing fixed soon" should suffice.
 
I was recently informed by tower that my altitude wasn't being reported accurately. Unfortunately, my local field doesn't have any avionics shops handy to diagnose the issue, and it's going to be a while before I can fly it somewhere to have it looked at.

In the meantime, can someone answer for me a question -- is it legal to fly class-D airspace without mode-C enabled? There's no class B or class C anywhere near me. My understanding from the regulations is 'yes', but I'm looking for a second opinion just in case I misread something.

Furthermore, does one advise ground/tower of this prior to departure? or do you just take off with the transponder switched to 'on' instead of 'alt' and they don't care?


First post......

Welcome to POA....:cheers:
 
Could you point me to the regulation that requires a mode C transponder to fly in controlled airspace :confused:

According to the AIM, Section 4-1-19: In all cases, while in controlled airspace, each pilot operating an aircraft equipped with an operable ATC transponder maintained in accordance with 14 CFR section 91.413 shall operate the transponder on the appropriate code or as assigned by ATC.
Other Airspace Requirements

The following areas require the operation of a Mode C transponder:

  • Operations within Class A, Class B, and Class C airspace.
  • Operations within 30 nautical miles of the primary airport within Class B airspace from the surface to 10,000 feet msl (see airports listed below).
  • Operations above the ceiling and within the lateral boundaries of Class B and C airspace.
  • Operations above 10,000 feet msl in the contiguous 48 states, excluding the airspace at and below 2,500 feet agl.
  • The AIM states in Section 4-1-19(a)(3) that for airborne operations in Class G airspace, the transponder should be operating unless otherwise requested by ATC.
Above 10,000 Feet

All aircraft are required to be equipped with a Mode C transponder when flying at or above 10,000 feet msl, over the 48 contiguous states or the District of Columbia, excluding that airspace below 2,500 feet agl.
Into and Out of the United States

According to 14 CFR 99.13, no person may operate an aircraft into or out of the United States, or into, within, or across an ADIZ designated in subpart B unless operating a transponder with Mode C. Certain exemptions might apply to aircraft that were not originally certified with an engine-driven electrical system; see 99.13(d).
 
you cannot fly in any controlled airspace without at least a mode c xpndr, but you can fly in Class D without an altitude encoder. Only Class B requires the altitude encoder.
Not true. If the Class D airport isn't a satellite from Class B and isn't inside the Mode C veil, you do not need a transponder. Also, Class C requires altitude encoding.
 
According to the AIM, Section 4-1-19: In all cases, while in controlled airspace, each pilot operating an aircraft equipped with an operable ATC transponder maintained in accordance with 14 CFR section 91.413 shall operate the transponder on the appropriate code or as assigned by ATC.
Other Airspace Requirements

The following areas require the operation of a Mode C transponder:

  • Operations within Class A, Class B, and Class C airspace.
  • Operations within 30 nautical miles of the primary airport within Class B airspace from the surface to 10,000 feet msl (see airports listed below).
  • Operations above the ceiling and within the lateral boundaries of Class B and C airspace.
  • Operations above 10,000 feet msl in the contiguous 48 states, excluding the airspace at and below 2,500 feet agl.
  • The AIM states in Section 4-1-19(a)(3) that for airborne operations in Class G airspace, the transponder should be operating unless otherwise requested by ATC.
Above 10,000 Feet

All aircraft are required to be equipped with a Mode C transponder when flying at or above 10,000 feet msl, over the 48 contiguous states or the District of Columbia, excluding that airspace below 2,500 feet agl.
Into and Out of the United States

According to 14 CFR 99.13, no person may operate an aircraft into or out of the United States, or into, within, or across an ADIZ designated in subpart B unless operating a transponder with Mode C. Certain exemptions might apply to aircraft that were not originally certified with an engine-driven electrical system; see 99.13(d).

Where does it say you need one in "controlled airspace?"

It does say you should have it on *if you have one* and it's operable, but there is no requirement to have one unless you're in B or C, in a C veil, over 10,000, etc.
 
According to the AIM, Section 4-1-19: In all cases, while in controlled airspace, each pilot operating an aircraft equipped with an operable ATC transponder maintained in accordance with 14 CFR section 91.413 shall operate the transponder on the appropriate code or as assigned by ATC.

So you don't need the transponder if you're in Class E, and your transponder is broken or your plane isn't equipped.

It's misleading to give a blanket statement that you need a transponder in controlled airspace. There are plenty of old spamcans without transponders, or even electrical systems, that operate in Class E (under 10,000 and outside Mode C veil) perfectly legally.
 
The class C and B controllers are authorized to waive the requirement, just tell 'em you're coming in to get it fixed. Don't forget to tell ground control you want taxi to the local avionics shop :D

I discovered my transponder check was expired.

The shop to do the check was in Knoxville, which is Class C.

Simple phone request for a waiver, granted.
 
It's not the xpndr mode c that's your issue, it's your altitude encoder.

How do you differentiate between the Mode C and the encoder?

you cannot fly in any controlled airspace without at least a mode c xpndr, but you can fly in Class D without an altitude encoder. Only Class B requires the altitude encoder.

I suggest you examine FAR 91.215.
 
You can fly without mode C with permission. Just contact tower by phone and tell them you have no Mode C. They will tell you what they'll allow. Same with any other airspace. Just ask. They'll require you to report altitude and they may assign you altitudes but it isn't a big deal unless they are extra busy.
 
How far off was the altitude being reported?

They reported it as being off by about 1000 feet, which if I'm reading the encoder grey code correctly, could be as simple as one bad encoder line between the encoder and transponder.

So we really don't know whether the problem is the encoder, the harness, or the transponder.
 
It's not the xpndr mode c that's your issue, it's your altitude encoder. you cannot fly in any controlled airspace without at least a mode c xpndr, but you can fly in Class D without an altitude encoder. Only Class B requires the altitude encoder.

Oh boy. Here we go again with another authoritatively presented, blatantly inaccurate statement ...
 
This post came up in my google search "flying without Mode C." I was notified by PDK tower that my Mode C was INOP a couple of days ago. I'm scheduled to have it repaired on Monday. In the meantime, I'd like to take a flight tomorrow from PDK to LZU. PDK lies within the Mode C veil of ATL. LZU does not. As I read this post, it seems I'd be OK as long as I notify ATC. Who, specifically, should I notify? Obviously PDK tower. ATL approach? LZU tower? Thanks.
 
This post came up in my google search "flying without Mode C." I was notified by PDK tower that my Mode C was INOP a couple of days ago. I'm scheduled to have it repaired on Monday. In the meantime, I'd like to take a flight tomorrow from PDK to LZU. PDK lies within the Mode C veil of ATL. LZU does not. As I read this post, it seems I'd be OK as long as I notify ATC. Who, specifically, should I notify? Obviously PDK tower. ATL approach? LZU tower? Thanks.
If the mode C is still inop then a call to Atlanta approach about an hour before the flight satisfies the regulatory requirement for notification. I suspect it is routine for ATC to approve the flight. They may have restrictions or a request. When I had a failed transponder all DEN approach requested was a landline call after the flight was completed.
 
I fly into class "D" all the time in the Cub.
Then I tell them that if they want me to switch to ground it might take awhile. Usually the tower will tell me "With me to destination via ....".
 
Flown in and out of a Class C airport and the Mode C veil for Class B with no transponder at all. Just call first. No big deal.
 
. As I read this post, it seems I'd be OK as long as I notify ATC. Who, specifically, should I notify? Obviously PDK tower. ATL approach? LZU tower? Thanks.

PDK tower should be able to coordinate it for you. Just call CD at PDK and tell them what your request is.

PDK CLEARANCE DELIVERY: 125.2 120.9
 
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