Sunday, June 17, 2007


With good flying weather, being a professional flight instructor during the summer in California can be frustrating. Pilots want to fly, the various GA aircraft I use tend to fly more because of the good weather, and that means things break or need fixing more often. There's a truism that planes that don't fly much don't last very long. But many pilots and aircraft owners don't seem to realize (or want to realize) that planes that fly a lot, require a lot of maintenance. I long ago made peace with the fact that things wear out, that worn out things on airplanes cost lots of money, and fixing planes often takes three time longer than one might think.

This past week has seen so many flight preempted by maintenance issues that it was hard for me to not believe that I had developed a sort of Reverse Midas Touch - everything I came into contact with seemed to turn into baloney. A multi-engine flight in one aircraft had to be rescheduled due to unexpected maintenance. I was able to reschedule the flight in another twin, but then than plane went into maintenance, too, and no other twin was available. A flight in a Cirrus SR22 was scrubbed right before takeoff because ... the right door could not be fully latched. A technically advanced aircraft with technically backward doors! Two flights in a complex aircraft had to be scrubbed when the landing gear system developed problems.

The most remarkable flight was the one that happened, but maybe shouldn't have happened. It involved a brand new Cessna with a WAAS-enabled G1000. Before the flight, we knew there was a database problem: The primary flight display had been updated with the latest aviation data, but the multi-function display would not accept the update and we couldn't figure out why. This caused an advisory message to be displayed, saying that cross-fill between the PFD and MFD was disabled since there was a database mismatch between the two units.

Disabled cross-fill meant that entering a GPS flight plan on the primary flight display would not be reflected on the multi-function display and vice a versa. What's more, changing the communication or navigation frequencies, the altitude bug, or the heading bug on one unit would not be reflected on the other. What was not apparent to me prior to the flight was just how screwed up things could get with cross-fill disabled.

The lesson was to fly several practice approaches at other airports in VFR conditions and then return to Oakland. It was clear we'd need to fly an IFR approach back into Oakland since the airport had an overcast ceiling at 800 feet on departure. Our plan was to fly an ILS approach back home, which wouldn't require an up-to-date GPS database and wouldn't require the GPS. The assumption was that the localizer and glideslope features are independent of, and would not be affected by, the GPS database mismatch. This proved to be a faulty assumption.

While flying a practice ILS in VFR conditions at an outlying airport, I noticed that the PFD thought the localizer frequency we had selected was a VOR - On the PDF, the HSI should have said "LOC" but it displayed "VOR" and the glideslope was not displayed when we intercepted the localizer. We did a full-stop landing and tried different configurations. At one point, I tried putting the system into reversionary mode and discovered that while the PFD continued to say the localizer was a VOR and did not display a glideslope, the multi-function display did appear to display the localizer and glideslope correctly. When we shut the engine down, refueled, then fired up again in reversionary mode at which point both the PFD and MFD displayed the localizer and glideslope. At that point I thought about taking the system out of reversionary mode so we'd have a moving map display on the MFD, but the G1000 was in some non-deterministic state. I know enough about software that I didn't want to explore this any further until we were on the ground at Oakland.

When a plane is broken because something wears out or an inspection is due, I can understand and forgive the inconvenience as well as the hit to my income. When a plane goes into maintenance because someone does something unfortunate or ill-advised, especially if the act takes place with an instructor on board, well that's just a shame. My student flew a very nice ILS approach into Oakland and we landed without incident. No animals were harmed and the plane was not damaged, which somewhat assuaged my anger at my own, faulty decision making. I had let my desire to fly, earn some income, and offset the lost revenue from earlier, scrubbed flights cloud my judgement. Hopefully my luck with planes and maintenance will be better this coming week, but one thing is for sure: I have a profound mistrust of integrated GPS systems that don't appear to be functioning properly.


Ron said...

John, have you considered filing a Service Difficulty Report? They're usually used by mechanics to document mx issues, but it seems to me that in attempting to update the database, you were involved in servicing/maintaining the aircraft. Besides, this information might prove useful to others (including Garmin).

Head in the Clouds said...

We've had similar issues pop up with our C-172 G1000 saying that the MFD and PFD weren't talking to each other. It didn't seem to cause as much trouble as you experienced. We weren't flying it IFR, though, as we're only working on our VFR now... so maybe I just didn't notice! Usually, updating the database again seems to work-- but we're not sure why it was necessary. I do know that we've had to have the MFD replaced twice in the last year (covered by warranty, thankfully!). Lately, it seems to be working ok (touch wood since my checkride is coming up soon!).