Something Scary

[Tom Davis]

Yesterday afternoon I was flying from Washington, NC (OCW) to Asheville. I was on a IFR flight plan. I noticed on the MFD that there was a plane flying to my north and 3 or 4 miles away from me. The plane showed up, but it did not give its altitude relative to my altitude. I kept looking for it, but never could see it. About the time I flew into a cloud the traffic warning sounded and there was a big yellow blob right on top of me on the map. I could not see a thing. I am pretty sure that it was warning me about that plane.

Just before I got out of the cloud the thing disappeared on my screen. I called ATC and asked if there was anyone near me. The guy told me that there was, but he did not know who it was or what its altitude was.

I was flying straight and level. I have had instances where I did a bunch of convoluted turns and fooled the traffic warning system into thinking I was two planes that were very close. I am pretty sure that was not the case here.

My guess is that it was a plane that was not reporting altitude and the GPS warned me about it irrespective of whether it was way above me or way below me. Nevertheless, flying in that cloud with a traffic warning screaming at me was disconcerting.

Has anything like this happened to any of you? If so, do you know whether my guess in the preceding paragraph is correct?

Thanks,

Tom

[Antoine]

There are two traffic advisory system in our DA40s one is the so called "TIS" which uses info forwarded by ATC and the other one is "TAS" which is a dedicated unit in the aircraft that does its own interrogation of other aircraft's transponders. I am only familiar with the latter.
Transponders come in 4 flavors: ADS-B, Mode S and Mode C all have altitude reporting. IIRC mode A does not.
So if your traffic had a mode A, then neither your TAS nor the controller knew its altitude from transponder interrogation. If ATC had a full blown radar system they should have detected the traffic AND its altitude regardless of transponder capability. It did not seem to be the case in this instance.

[smoss]

Antoine, as it was explained to me by an ATC person before, most "radar" coverage by them is a bit indirect, and indeed uses the transponded altitude combined with a transponder signal receiver. Only "primary" radar coverage gives them targets and altitudes directly--I believe this is the case in the terminal areas, and where you see the big rotating radar dish around big airports. So if flying in the Los Angeles basin, even with no transponder on, they will have the target on their screen. But if flying between L.A. and Las Vegas, in the middle of nowhere, if someone's transponder was not on, or inoperative, no target would be seen by them.

[Lou]

Tom,

I have had the big yellow dot when the target was visually acquired several miles away, and ATC identified the same. The Avidyne TAS manual acknowledges that errors occur. It's disconcerting but it may not be correct.

[Colin]

Radar only gives them the location, not the altitude. Anyone without a transponder shows up without altitude information and they have to assume it is someone you can run into at any altitude.

It wasn't you. You were squawking. It was probably a home built close to the ground.

[Rich]

There's yet another flavor of transponder out there: One basically capable of altitude reporting but that is just mode A for some reason, such as:

- A defect causing it to not include altitude in the response packet.
- Pilot has selected mode A by just turning it to "ON" rather than "ALT".

I often have ATC alert me to traffic like "1 mile, 11 o'clock, altitude unknown (or unreported)". Happens all the time. Depending on the airspace and operation type of the offending aircraft, it may or may not be in some violation.

[carym]

I have had planes fly into IMC many times and they are not talking to ATC. On more than one occasion ATC has warned me of VFR traffic at my 2 O'clock same altitude (unverified) when I am in solid IMC and they don't show on my TIS. This is very scary but it happens all the time (at least in the Midwest) where pilots decide to ignore the FAR's and ignore safety concerns and fly in the clouds without being on an IFR flight plan. While I am unaware of this causing a collision, it still scares me.

[Tom Davis]

i was a little aggravated that ATC did not mention that someone was in the area. They knew someone was near me, and knew that they did not know his altitude.

[Colin]

A fellow DA40 pilot got himself into a little trouble climbing up through what he thought was a wispy layer of coastal haze and turned out to be thousands of feet of solid IMC. Once he was in it he felt like the least dangerous thing was to continue up. He was on autopilot and watching his MFD, but it was before he had an instrument rating. He was squawking 1200 and monitoring approach, since he planned to get flight following as soon as he was at his cruise altitude. He was very surprised to hearing, "VFR pilot over Kxxx airport, you are in IMC without an instrument flight plan. Suggest immediate turn to xxx degrees, you should be VFR in less than two miles."

That was the only time he let that happen and I think his story probably kept it from happening to me.

I was considering flying into Mammoth Mountain airport out here in SoCal and was reading the FBO reviews on AirNav. There was more than one pilot complaining about VFR traffic in IMC and one guy even said, "I won't fly in here anymore unless it is strictly VMC. I've seen too many planes pop out of the clouds on an IMC day, guys flying their own made-up instrument approaches without talking to anyone on the radio or following anything published. Too scary for me."