CAP FM Warning

[scooter]

We just put a new TDFM 36 CAP FM radio in one of our aircraft. On there is a sticker that says:

"WARNING: Do not use the TDFM 36 radio during an instrument approach" This is from memory but close to the actual.

Would not have thought too much about this except for the word "WARNING." Using this radio on during an instrument approach would be last on my list of priorities but there must be something bad that happens if you do this. Has anyone seen anything anywhere about this? If its a WARNING it seems to me it should be info given to flight crews!

[SarDragon]

I don't recall the specifics, but some aspect of the FM radio causes interference in the nav gear. This is put out to the pilots, the planes are placarded, and IIRC, it's part of the MP training.

[scooter]

Made a typeo, its the TDFM 136.

Have never seen this in writing anywhere before and none of the MPs I have talked to ever heard of it. None of our wing aircraft are placekicked except this one with the new radio. Where did you see it in writing? Thanks.

[Eclipse]

https://www.safecom.gov/attachments/14586_A.pdf

"Purpose:  Aircraft cockpit must be clearly placarded "Operation of TDFM-136/136A
not approved during instrument approach".  Typically the transceiver exceeds the
harmonic attenuation specifications outlined in the manual however failures have been
reported during the Post Installation EMI Test due to the interaction of the 2nd
harmonic of the transceiver during transmit and the input frequency and sensitivity of the G/S
receiver during approach.  Only solution is an external low pass filter currently in
design/testing"

"Procedure:
Aircraft cockpit must be clearly placarded "Operation of TDFM-136/136A not
approved during instrument approach". 

[lordmonar]

We just put a new TDFM 36 CAP FM radio in one of our aircraft. On there is a sticker that says:

"WARNING: Do not use the TDFM 36 radio during an instrument approach" This is from memory but close to the actual.

Would not have thought too much about this except for the word "WARNING." Using this radio on during an instrument approach would be last on my list of priorities but there must be something bad that happens if you do this. Has anyone seen anything anywhere about this? If its a WARNING it seems to me it should be info given to flight crews!

It is.  All installed equipment is supposed to be in the aircraft records...and pilots are supposed to read and understand all warnings, cautions and Notes.

[EMT-83]

The TDFM 136 will definitely cause interference on ATC frequencies. Good CRM is needed between the MP and MO to avoid using both radios simultaneously.

A previously-agreed-upon hand signal signifying "shut the heck up" ain't a bad idea either.

[vento]

It is not really interference with ATC frequencies, but rather interference with the glide slope signal when operating at the range of 154.575 through 167.500. It is not a TDFM-136 only issue, it is a common problem with all radios operating in those frequency ranges.

Here's a bulletin from US Forest Service Aviation that goes into greater detail.

[Fubar]

The TDFM 136 will definitely cause interference on ATC frequencies. Good CRM is needed between the MP and MO to avoid using both radios simultaneously.

Huh, I haven't experienced interference between the two radios before. Our interference issues are more people-based, the MP insisting on monitoring the FM radio and forbidding the MO from transmitting so he "doesn't get distracted" during takeoffs/landings or MOs who think they need to turn the FM radio off during AEP/DEP in order to "help the pilot" fly the plane.

[EMT-83]

It's very pronounced on certain Coast Guard channels; transmitting on the FM radio will block out ATC traffic.

I don't recall if it's ever happened on CAP frequencies. We just assume that there might be interference, and avoid using both radios at the same time.

[blackrain]

It's very pronounced on certain Coast Guard channels; transmitting on the FM radio will block out ATC traffic.

I don't recall if it's ever happened on CAP frequencies. We just assume that there might be interference, and avoid using both radios at the same time.

Quick question.  Here in land locked Oklahoma we don't normally deal with the USCG/Marine channels. Are these loaded in the TDFM-136 on an as needed basis for missions in coastal areas?

[SarDragon]

It's very pronounced on certain Coast Guard channels; transmitting on the FM radio will block out ATC traffic.

I don't recall if it's ever happened on CAP frequencies. We just assume that there might be interference, and avoid using both radios at the same time.

Quick question.  Here in land locked Oklahoma we don't normally deal with the USCG/Marine channels. Are these loaded in the TDFM-136 on an as needed basis for missions in coastal areas?

Depends on the wing. IIRC, we have a few of them in our channel plan.

[lordmonar]

It's very pronounced on certain Coast Guard channels; transmitting on the FM radio will block out ATC traffic.

I don't recall if it's ever happened on CAP frequencies. We just assume that there might be interference, and avoid using both radios at the same time.

Quick question.  Here in land locked Oklahoma we don't normally deal with the USCG/Marine channels. Are these loaded in the TDFM-136 on an as needed basis for missions in coastal areas?

You should still have them programed in.

a) Marintine channels are used on rivers as well as the coastal areas.
b) Your AOR may not need them too often....but your aircraft are CAP assets that may be moved to a coastal area at a moments notice....and used by people from that area....the more that all our equipment are configured the same...the easier it is to share those assets.

[scooter]

SarDragon and Eclipse, thanks for the info. Going to make this happen in our aircraft.

[cap235629]

It's very pronounced on certain Coast Guard channels; transmitting on the FM radio will block out ATC traffic.

I don't recall if it's ever happened on CAP frequencies. We just assume that there might be interference, and avoid using both radios at the same time.

Quick question.  Here in land locked Oklahoma we don't normally deal with the USCG/Marine channels. Are these loaded in the TDFM-136 on an as needed basis for missions in coastal areas?

Oklahoma has them and actually has a Coast Guard Cutter in Sallisaw.

[denverpilot]

There's lots of opportunities for mixing interference between the IF frequencies plus transmitted frequencies whenever multiple radios and antennas are in close proximity. Harmonics happen.

2a+b and 2a-b at the relative power levels of either transmitter are common.

Physics wasn't rescinded, last I checked.

Transmissions other than those required for ATC comm during real Instrument approaches has never been smart, ever. Doesn't really matter what the radios are.

[blackrain]

It's very pronounced on certain Coast Guard channels; transmitting on the FM radio will block out ATC traffic.

I don't recall if it's ever happened on CAP frequencies. We just assume that there might be interference, and avoid using both radios at the same time.

Quick question.  Here in land locked Oklahoma we don't normally deal with the USCG/Marine channels. Are these loaded in the TDFM-136 on an as needed basis for missions in coastal areas?

Oklahoma has them and actually has a Coast Guard Cutter in Sallisaw.

Didn't know about the cutter in OK. Makes sense to have radios configured consistently across CAP for the reasons mentioned. I remember listening to scanner traffic when I lived in the Memphis area and the Mississippi river had a lot of radio traffic on USCG/Maritime channels. Including some barge captains with some very "colorful language"