My old way to test a transponder versus using a portable tester

For years, I'd just check the transponder reply on the aircraft's own test function and call it good. About 6 months ago, a plane I signed off had a squawk for intermittent altitude reporting, and I felt like an idiot. Now I always hook up my portable tester, run the full interrogation cycle, and verify the Mode S data block. It adds maybe 15 minutes, but it catches stuff the built-in test misses. Anyone else made that switch after getting burned?

4 comments

4 Comments

parker_hall52mo ago

Yeah, that "intermittent altitude reporting" thing is a killer. My buddy got bit by that last year on a 172, the built-in test showed green but his portable found a bad pressure sensor.

wade_anderson2mo ago

That exact scenario is why I don't trust a single green light anymore. It reminds me of my old car's check engine light that would only come on after driving for an hour. Modern systems are so complex that a simple pass/fail test can miss the real problem. We're putting too much faith in a single indicator that says everything is fine. It creates this false sense of security right up until the moment something quietly fails.

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hayes.wade2mo ago

But doesn't the built-in test still catch most major faults? Adding 15 minutes for every check seems like a lot of extra time.

-1

shane_morgan24d ago

And hey, 15 minutes is only a problem if you value your time more than finding out your altimeter has been lying to you since Top Gun came out. (Not that I'm bitter about an afternoon I lost to a faulty encoder or anything.) But honestly, if I'm going to trust a single green light, I might as well trust that one restaurant with a B rating that gives me the same enthusiasm about my meal. The built-in test is like a doctor saying "you look fine" without checking your blood pressure - technically not wrong until you're on the floor. That intermittent altitude thing is exactly the kind of ghost that haunts the system until it decides to ruin your IFR flight plan on a random Tuesday.