Letters: January 2001

Traffic Avoidance Feedback
What a coincidence. On the very day I decided to spring for a collision avoidance unit, I came home to find the latest article on the subject in the November issue of Aviation Consumer.

However, the unit I had just ordered was not mentioned: The TPAS-RX-100 from Sure Check Avionics. It would be interesting to see what you think of this unit considering it has a digital distance readout and is approximately half the cost of the Monroy ATD-200.

Daniel L. Roper
Fort Walton Beach, Florida

Youre right. At the time we conducted the tests, TPAS wasnt available. Were told by the company that one will be shipped to us for editorial evaluation as soon as it is available.

Nice piece about traffic avoidance. You mentioned the Skywatch missing targets due to shadowing but theres more to it. On our Skywatch, we kept seeing targets just dropping off the screen, not all of them irrelevant. When we had a twin that Philadelphia approach had called 12 oclock, 2 miles, opposite direction and 1000 feet lower, the Skywatch showed zip. I saw him pass below.

I was concerned we had a bad unit or installation (it was the shops first install). They and BFGoodrich listened to our complaints,everything seemed to be okay in the shop, but we had lots of targets dropping out or just not showing up.

Finally BFGoodrich sent two engineers to do a detailed check and found that the unit was working perfectly. What they enlightened us about-and what the demos at Oshkosh dont make clear-is that not all the traffic in the displayed range is shown. Although the manual states it displays the eight most threatening targets, traffic must meet the complex TCAS algorithm to show up. They couldnt easily explain how this works but 1000-feet below isnt bad even if converging and I will say that as far as I can tell, it has been infallible in calling real threats. Ive had more than I ever thought I had before we got the device.

But if one sees known, close traffic thats displayed, this can be normal unless theyre going to penetrate your protective bubble soon.

Drew Doorey
Wilmington, Delaware

Air/Oil Separator
As a longtime subscriber, I am contacting you to get your opinion of the following ideas.

I have only had aircraft with wet vacuum pumps but I have read of short-life problems with dry pumps.

I presently have a 1964 Cessna 210D with a wet pump and the associated air/oil separator. However, it just occurred to me that there might be no need for this separator and the associated plumbing.

Why not just connect the air out port of the pump directly to the air/oil inlet fitting at the back of the IO-520-A? Why blow part of the air overboard and part through the engine? After all, I imagine a lot of the air simply goes out the bottom of the separator, along with the oil.

In fact, it might actually be advantageous to blow all of the pump air through the crankcase and out the breather at the front of the engine and thereby improve scavenging of the water vapor and other undesireable crankcase fumes. To test this, all one would have to do would be to cap the separator outlet and thereby force all the air, instead of half the air, through the crankcase.

Is this just another case of doing it this way because we have always done it this way?

Art Thompson
Via e-mail

We suspect if you cap the separator outlet, the air will find its way back into the crankcase, where it will pressurize the case and spew oil out the crankcase breather.

What the separator does is to dump the air overboard and return the oil back to the crankcase with very little, if any, air pressure.

CO Detector Detection
I have been using a Dead Spot CO detector in my M20K for a number of years. It always changes color to a dirty brown shortly after I place a new one in the airplane. I have never known what exactly this means. Is there a low-grade level of CO contamination in the cabin or not?

You had an article in the October 2000 issue of Aviation Consumer that covers CO detectors, but I still could not evaluate the color change.

Do you know of any pictures that clearly show what changes occur with the Dead Spot under various levels of CO presence? Or any other suggestions?

George Schemm
Via e-mail

What youre experiencing is the fundamental shortcoming of biomimetic detectors; they depend entirely on color change to signal the presense of CO.

We have two recommendations. One is to buy two or more detectors at one time and keep one in the original plastic wrapper as a baseline color key. This might help you judge the color change.

But the better solution is to simply buy one of the AIM detectors reviewed in the October article. If you suspect low-level CO contamination, these are the cheapest and most effective way to confirm it.

Wanted: Reports on New Stuff
Contrary to some, I think the majority of your readers appreciate receiving all of the latest information on what just might be the most exciting new technology since the Wright brothers.

One more homebuilt with a big bore Continental is not news. But 4500 to 5500-pound twin jets with cutting edge propulsion and diesel and turboprop engine replacements for existing aircraft is news. Please keep us updated on the latest info on a regular basis.

Steve Field
via e-mail