Digging deep

I’ve been working on legacy Cessnas since well before production ceased in 1986. I’m very familiar with the idiosyncrasies of the service manuals and parts catalogs. Of course, there’s plenty of information not included in the published manuals which may become a problem in certain rare situations. Cessna engineering has always been exceptional at digging through their archives to help in those times. I recently had the necessity to put their capabilities and willingness to the test. In this situation, the subject airplane is one that Cessna didn’t even build.

Cessna Aircraft purchased Columbia Aircraft in late 2007, in part to have an aircraft to compete with the very popular Cirrus SR22. In 2008 when I attended the first Cessna maintenance training class for the plane at Bend, Oregon, the factory was still undergoing major changes in an effort to reduce production costs. The expressed plan was to only produce the turbocharged version called the 400. The economic downturn of 2008 couldn’t have been worse timing for the future of the Bend factory. Production eventually relocated to Independence, Kansas, with composite work in Chihuahua, Mexico. More problems occurred, but full production finally resumed in the form of the TTX. By this time much of the original Columbia tribal knowledge moved on, and Textron has been working hard to learn anew what was lost.

The Columbia 350 (nonturbocharged) was expected to enjoy product support from Cessna in the form of maintenance information and parts. It was less certain what would happen with support for the out of production 300, which was the first steam gauge equipped version Columbia. Cessna only resumed production of the turbocharged version called the 400. Fast forward through the economic and technical problems and we have Cessna producing the turbocharged, Garmin G2000, FIKI equipped version called the TTX.

We’ve learned a lot about the Columbia series as a Cessna authorized repair facility in the last ten years. One very important fact learned is that the Columbia-produced technical manuals are not particularly complete. The wiring diagrams are, at best, engineering drawings for system production. This gives most all the details one needs for troubleshooting problems but is about as cumbersome to use as possible.

Overall, the series is very reliable, and rarely do we have need to dig into the detailed wiring diagrams for troubleshooting help. The early versions of Columbia with 14 volt electrical systems and Avidyne avionics were never produced by Cessna, so all the wiring diagrams available are Columbia documents. Sometimes good wiring diagrams are essential to resolve a problem.

One of the very cool features of the Columbias is audible voice warnings for some specific alerts. One in particular is the “Fuel Valve” warning which notifies when the fuel tank selector is not positioned. It may not seem like a big feat today, but thirteen years ago this was a significant safety feature for a piston single engine airplane. Just to have a warning light illuminate when an issue is detected is one thing. Having an actual voice tell the pilot in audible words about a problem is big iron cool.

The technology needed to turn on a warning light is as simple as a switch that sends power to the light. Columbia decided to go another step forward and also send this same information to an audio generator box. This small box built by PS Engineering sends various verbal warnings to the flight crew via the aircraft audio panel. The box is so reliable that it’s largely forgotten about. I never even considered its existence until just recently.

A customer with an Avidyne equipped 400 arrived at our shop, noting that he no longer was getting the audible warning for the fuel valve. This version of the Columbia has an annunciator panel mounted just to the left of the primary flight display. One of the many warning lights in the panel is the “Fuel Valve” light. A little further to the left is the analog fuel level gauge. When the fuel selector is selected in the left or right position, a couple of switches send power to illuminate a corresponding indicator light on the fuel gauge. If the fuel tank selector valve is not properly engaged in the left or right position, the switch system signals the warning annunciator. If the system senses the engine is running, as the “Fuel Valve” light illuminates, a voice comes over the audio system repeatedly calling out “Fuel Valve…Fuel Valve…Fuel Valve…”. This continues until the pilot either corrects the problem or pushes the acknowledge button. Acknowledging only clears the audible warning, and the warning light stays on until the problem is corrected.

Digging through the technical information available in the service manual, service bulletins and service letters on this system’s design and installation, we did not find any wiring diagrams that showed detailed pin outs. Without that, we were not able to test and confirm the validity of inputs or outputs. It was time for a call to Textron tech support.

Apparently, this audio box is a very reliable unit and only came to the attention of Textron’s tech support department a few months . Tech support did some digging and emailed a detailed system diagram right away. Using that, we confirmed all the inputs and outputs seemed to be operating correctly. All the information pointed to a failure of the audio box.

A couple of days later the replacement box arrived and was installed, but we still had no “Fuel Valve” voice. We sent another email to tech support which sent them digging into the archives again. The information they found included installation data from PS Engineering. Unfortunately, nothing of usable value was turned up. More digging ensued.

In their relentless search effort, tech support went deep into the archives and found a pin to pin wiring diagram for the actual installation. This new information showed the audio box as installed on the Columbia was just a little different than the more generic drawings PS Engineering had originally supplied. The new diagram included an oil pressure sensing input that the earlier drawings didn’t.

Our original understanding was that the box sensed engine RPM to determine if the engine was running. As it turns out, the oil pressure switch has two outputs. One output turns on the low oil pressure warning light, and the other tells the audio box the engine is running. Just that one little bit of information allowed quick and successful troubleshooting. Within a few minutes we confirmed the oil pressure switch output to the audio box had failed. Replacement of the oil pressure switch is way less expensive and time consuming than the audio box.

Without tech support’s willingness to continue looking for documents related to an airplane long since out of production by a company no longer in business, we’d have been left to trace wires by hand. The man hours required to do that is more than I’d want to imagine or invoice to the customer.

There have been plenty of good and bad with the Cessna acquisition of the Columbia. I suppose every solution has its problems. The eventual loss of much of the old Columbia tech people combined with the recent merging of the Beechcraft support personnel has put Textron technical support department under a significant disadvantage. They are very well versed with the G1000 pre-Cessna airplanes as there isn’t huge difference with the current production TTX, other than the change from G1000 to G2000 avionics. Their familiarity with the Avidyne or steam gauge is less certain. What may be lacking in hands-on experience, they make up for in tenacity. We’ve found when troubleshooting issues arrive, tech support sticks with you and will dig deep into the Columbia tech information to find answers.