It’s tempting to think that flying a modern “glass panel” airplane with redundant alternators, batteries, buses, screens, sensors, and instruments means you’ll never have to fly partial panel again, doesn’t it?
These avionics suites are professionally-designed, installed, FAA-certified and can run $50,000 or more even for a lowly single-engine piston aircraft. They benefit from the latest technology and are designed to be fault tolerant. They’ve been torture-tested and engineered to withstand the environmental rigors they will endure.
So, at the very least, the odds of a major in-flight failure should be lower than when flying behind a panel with 30 year-old analog gauges with all their vibration and attitude-sensitive moving parts.
Alas, in my experience this has not proven to be the case. Quite the contrary, in fact. Much like flying a multi-engine aircraft, there are simply a lot more parts and systems to fail on a glass panel. Those systems are electronic and as such tend to be far more sensitive that their predecessors to things like moisture, improper or unstable voltage, and grounding issues.
When they work as designed, for the most part they are a major asset to flight safety. When they don’t, it can really leave you scratching your head about what’s going on. While it’s rare for the whole panel to go dark, when problems do crop up they can be quite vexing to troubleshoot. I had a flight like that recently in a Cirrus SR22.
I had just departed Napa County Airport (KAPC) for John Wayne (KSNA) with a planned route covering about 320 nautical miles. It was a low IFR departure at night with ceilings of about 500′ AGL. I broke out of the clouds at about 2000′ and continued climbing southbound.
The first problem I encountered was a failure of the #1 Garmin GNS-430 data card. This was more or less a non-issue. Data cards are inserted and removed every 30 days to update the database, and every now and then the jostling will cause one will go bad. The 430 was still useful for radio communication, so I simply elected to use it’s screen as a place to display traffic.
I was passing east of San Jose a few minutes after departure when the traffic sensor failed. Again, I’ve seen this before. After checking that no circuit breakers were blown, I rebooted the avionics bus and the traffic sensor came back online.
About 10 minutes later, the PFD suddenly failed. It was receiving power, as evidenced by backlighting around the buttons surrounding the screen bezel, but the screen was badly corrupted. Again, I’ve seen this on various SR22s, but it usually happens on boot-up. So I powered down and rebooted the entire electrical system, batteries, alternators, avionics, the whole works. No change. Again, no breakers were blown and the emergency checklist for PFD failure was not much help.
When I encounter avionics issues in an aircraft, one of the first things I check is the health of the electrical system. As I mentioned earlier, unstable or improper voltage does bad things to electronics. In this case, the bus voltages were a bit odd. Normally in an SR22 the main bus should run at 28 volts and the essential bus at 28.75. What I saw on the MFD engine page was ~28.5 and ~29.3. Roughly a half-volt too high on both buses.
I’d never seen that before. Was it possible that both alternators were producing too much voltage? They are independent devices and a malfunction in one alternator shouldn’t affect the other, so perhaps the problem was in the Master Control Unit or somewhere else.
It was about this time that the yellow “Alt 2” light appeared on the annunciator panel, indicating that alternator #2 was offline. Yet the according to the MFD, the essential bus (which is powered by alternator 2) was still running about three quarters of a volt higher than the main bus — a sign that alternator 2 was still working.
Like I said, a head scratcher.
(For you Cirrus gurus out there, I should note that this is one of the SR22 aircraft with the improved electrical systems built after they replaced the analog engine gauges with the storage box in the upper right corner of the panel.)
Anyway, a bit more sleuthing revealed that TAWS, sferics, and autopilot systems were also offline. A TAWS system test said “TAWS system unavailable. Computer OK. AHRS bus not available.” The sferics system was coming and going.
The autopilot, despite what the PFD failure checklist said about being able to use the autopilot without the PFD, would not work correctly in any mode. It always wanted to turn right. The S-Tec 55X is a rate-based autopilot, and it gets rate-of-turn information from an analog turn coordinator located behind the instrument panel. I recalled something about the S-Tec only being able to connect to GPS 1 for navigation guidance without the PFD, and since that radio had no navigation data available due to the faulty data card, it was stymied. But it should have at least been able to function as a wing-leveler.
So there I was, flying southward on a very dark (though clear and technically VFR) night with no visible horizon in an all-electric aircraft with a bum electrical system. From the flight up to Napa, I knew there was a horizon out there, it was just masked by all the light emanating from the instrument panel. After reducing the panel lights to the minimum possible, I was able to make out a faint horizon. I’m sure my ophthalmologist would have commented on the eye strain this was sure to cause, but you gotta do what you gotta do, right?
The next step was to advise ATC of the issue. By this time I was well south of the San Francisco metropolitan area and over the San Joaquin Valley, which was socked in with low fog all the way to the Los Angeles basin. The best course of action seemed to be a diversion to the west since the fog wasn’t present in that area, so I proceeded in that direction and let Oakland Center know what was happening. Along the coast, there were plenty of VFR airports and the situation became more “visual” once I was in an area with city lights and highways.
The next question: weather to land at an intermediary airport or continue on to Los Angeles. I monitored the electrical system for the next 20 minutes and nothing got any better or worse. The PFD failure didn’t bother me. I just wasn’t keen on flying without communication radios. But the way I saw it, none of this stuff was going to affect the engine. I had good VFR conditions in an area and along a route I was very familiar with. In fact, it was hard to find a field I hadn’t been to. Even if all electrical power was suddenly lost, I had no concern about being able to make a safe landing at a known airport. So I continued the flight, and landed uneventfully at Santa Ana about an hour later.
In reviewing my logbook, about 2/5ths of my 5,500 hours are in glass panel airplanes. Yet they account for 100% of the electrical and partial panel abnormalities I’ve encountered. It’s not that the aircraft are poorly designed, built, or maintained. I believe it’s due to the fact that they are just more complex and, as I mentioned at the top of the page, less tolerant of voltage, humidity, and other conditions which are outside the design specifications. The failures can take on interesting forms.
On the plus side, I was discussing the flight with a fellow SR22 pilot and realized that even under “partial panel” conditions, I was still flying with a suite of avionics which would be the envy of many general aviation pilots.
I don’t look back on the situation as a hazardous one, but rather a puzzling scenario I have not been able to fully explain or duplicate. Nor is it one which I’ve ever seen simulated, something that’s worth considering when you think about the possibility of flying with broken glass.