I think there might be a difference of understanding regarding failure modes. I don’t think anyone is proposing that we abandon all electronic devices and go back to vacuum-powered gyros. What is being proposed by Brent (and me, I suppose) is that a vacuum-power spinning gyro is perhaps the most reliable backup system available. How can the “least reliable” system be the “most reliable” backup? Two reasons: First, the spinning gyro is not susceptible to catastrophic electrical failures (like a lightning strike) and will keep running as long as the engine is turning. Second, it is logical to limit one’s thinking to “single failure modes”. In other words the ONLY requirement of the gyro system is that it keep working from the time of the electrical failure to the earliest possible landing. What is the likelihood that the gyro will fail in those 15 minutes? What is the likelihood that the electrical system would quit and then the engine stop turning? All this is dependent on the vacuum system being “required equipment” for IMC operation (if the vacuum system fails on the ground, it is a no-go. If it fails in the air under IMC, it is a “land immediately” condition).

The poorest choice for a primary system then becomes the best choice as a backup. Logical, I think.

Gary Casey

Brent,

I suppose I should have been more specific - I assume that pilots of experimental aircraft will exercise sufficient judgment not be flying into thunderstorms, and thus the likelihood of in-flight lightning strike is nearly nil. Not absolutely nil, naturally, but approaching or below the likelihood of vacuum failure, which is fairly common. Of course, perhaps I should not make such an assumption given that a very famous pilot died just last year flying his Bonanza into thunderstorms.

Absent thunderstorms, we will simply have to agree to disagree. Vacuum pumps and vacuum-operated artificial horizons are notoriously fallible, and a poor vacuum can give insidious symptoms causing catastrophic results. While there have been some experimental EFIS units (notably one you mention, also the original pioneer Blue Mountain) which had early individual failure rates much higher than vacuum equipment, still the likelihood of two or more going down simultaneously is rather rare. In my personal experience my TSO Garmins failed just as often as my experimental equipment - anecdotal evidence, to be sure, but 3 TSO failures in 600 hrs not counting vacuum pump failure and attitude indicator partial failure ("lazy" attitude, "sort of" working).

None of this absolves individuals contemplating use of experimental equipment from the burden of research to draw their own conclusions about reliability.

Your statement that TSO is required for legal flight is simply untrue. If you wish to dispute this, please feel free to point out the section of the FARs that you believe says otherwise (it does not exist, but knock yourself out). I don't expect to convince you of that; it seems that there are some folks who have made up their minds and aren't interested in anyone else's opinion. That's fine, you are entitled to yours. I, like many, have reviewed the pertinent FARs along with (among others) my mechanic who was a chief avionics safety inspector for a major airline. For the type of flying for which Experimental aircraft are authorized there is no such rule stating that each piece of equipment must be certified to pass TSO. The altimeter must, or pass the test for equivalent accuracy (performed during the annual pitot-static check). Doesn't mean it's a bad thing, only unnecessary for legal flight. Just as you admonish people who are not engineers (I too was a software engineer by trade) to form unwarranted opinions about avionics, you too should not consider yourself an expert on FARs simply because you build avionics. Glass houses, etc.

Blocked pitot or static tubes are no longer a killer for correct attitude indication on any of the three leading experimental EFIS units (GRT, Dynon, MGL). May also not be on others, haven't kept up. Of course, you will not get accurate airspeed with either blocked and will not get accurate barometric altitude with static blocked, but that would happen irrespective of the type of avionics you use. However, you will still have accurate horizon, and GPS can provide altitude and ground speed which, combined with a pilot's knowledge of their aircraft power settings, etc. should enable you to fly safely to landing.

At the end of the day, you are putting your own life on the line. If you feel more comfortable with spinning gyros, by all means load up. However, if you feel you have done your research and would rather replace that vacuum pump for a second alternator to prevent power-out and ditch the gyro for a small self-contained backup EFIS, then your odds of total failure will ultimately be about the same - just different causes.


Fly safe!

Bill


On 01/-10/-28163 02:59 PM, Brent Regan wrote:

Bill speculates:
<<Given that two EFIS units with battery backup are more reliable than a single vacuum pump, your argument that people must have "TSO'd" equipment is logically ridiculous - especially if they also have as part of their panel an independent 2-axis autopilot.>>

The primary assumption here is false. It is not "given" that "two EFIS units with battery backup are more reliable than a single vacuum pump". Analysis and data show the opposite is true.