In the Class D or not

[Mauleflyer]

I was flying the other weekend and the trip took me over the Reading Class D in Reading PA. The top of the D is 2800 and I was at 3000 and just clipping the northwest corner. They had a TFR starting at 1:30pm but it was only 11:30am at the time. I was on the tower frequency more out of boredom then anything else. The tower comes up on the frequency and says "aircraft at about 5 miles northwest of the airport are you on the frequency?" I was surprised but answered back with my call sig. The tower says "just checking because you are a little bit in the class D".
I call back and say that I was at 3000 feet and I didn't think the TFR started until 1:30pm (at which time the class D goes to 13,000ft). He says "yeah I got you at 3,000 feet and the TFR doesn't start until 1:30pm, just checking to see if you are on the frequency." Now isn't being in a class D like being pregnant? You are either in it or not. Really.

[Loogie]

You are absolutely correct, you would also be legal at 2,850' but then you might have to defend yourself w FAA if the tower files a violation. It could be a lengthy process and they have the tapes and you don't etc. In general it is best to avoid controlled airspace by at least 500'. It gives you and the controllers a better buffer against a violation. Same for lateral deconfliction, use no less than 5 miles from borders etc.

Encoding systems are not perfect, they do glitch. Surveillance radars are not perfect either, environmentals can cause it to put your return in a wrong location etc.

Just some thoughts from lessons learned.

[TomD]

You can preempt the tower by calling and saying you are overflying their airspace at 3,000.

Not required but keeps every body happy.

TD

[crbnunit]

I get freaked out every time I fly over Delta Junction. The place is surrounded by active MOA, FT. Greely, the missile defense system based there (the silos are clearly visible from the air) and Ladd, AFB. It is busy air space. Even clearly above the class D airspace I'm always expecting to be intercepted by fighters!

[captnkirk]

What's fun is when you have some one new out of DCA an they start to nick p56 . Don't want to wake up Bo from his nap---every one starts talkin to ya. We use to have code words and secret handshakes to get in there.

[andy]

Blind encoders only report altitude in 100 foot increments through the transponder. If your encoder is off by 100 feet, which wouldn't be unusual for older units, then it would look to the tower as if you were in the Class D. ATC allows for up to a 300 foot error versus your assigned altitude. After that they don't want to deal with you. I replaced my old encoder earlier this year for that reason. Some of the older ones use a power transistor as a heating element to keep the temperature inside the encoder somewhat constant. These transistors eventually fail and then the encoder starts to drift. When you have an IFR certification done, they don't test the output of the encoder under different temperatures so it might look fine during the certification.

[Tomkatz]

I would like to add, keep your altimeter setting current. Not just ASOS and AWOS, listen to the controller when he speaks to other traffic. It is often the sum of many factor that make the issue.