Saturday, June 09, 2007

Avionics Upgrade - Part 9

36G's Extreme Avionics Makeover is nearly complete. The equipment has been installed and all appears to be working. The next step in the process is to do a complete checkout of the equipment with the engine and all electrical components operating. The key is to systematically test every function of every system in addition to following the test procedures in the install manuals. The manuals test the component, but do not necessarily test how they are integrated. You have to develop your own test plan to catch the interdependencies.

System Testing
The GNS-430 GPS has the most extensive checkout, so it makes sense to start with it. There are a number of tests that you are required to go through. One of the more confusing is the second radio transmission test. What Garmin requires is that you transmit on all COM radios installed in the aircraft (except the GPS itself) on several key frequencies while the GPS is locked onto the satellites and a direct-to is selected. The GNS430 is very sensitive and can lose the GPS signal if a transmission interferes with reception.

The transmit tests start with the second COM set to 121.150 and transmit for 20 seconds. Then switch to 121.200 and transmit for 20 seconds. You repeat the same process for frequencies 131.250, 131.275 and 131.300. These frequencies are the most likely to cause GPS interference. If you have interference while doing this test then you will need to install a 1.57542 GHz notch filter that is connected in the COM antenna line as close as possible to the COM causing the problem. A notch filter basically intercepts the erroneous signal and shunts it before sending it to the antenna. In most cases this will fix the issue. If not, it can be a bear to track down the problem. In most cases, however, the wires on the radio in question are probably not shielded/grounded properly. The COM antenna can also be faulty, the antenna may not be getting a good ground to the airframe or it is mounted too close to the GPS antenna. If you have any GPS glitches or any messages appear on the GPS during this test, it has failed and the aircraft cannot be returned to service.

The remaining tests are primarily functional. The Transponder has to send TIS data to the GPS, the XM weather has to send weather, the MFD has to receive flight plan changes from the GPS, etc. I also recommend doing these tests with high and low power settings and to taxi around the airport validating the signal is solid at all angles. If you have a VOT or VOR on the field these systems should be checked as well.

Don't forget that you are not only testing the radios, you are testing the controls, pitot/static system and all aircraft systems. NOTE: we disconnected the static lines during the install. When a line is disconnected for any reason a static test must be performed even if is not due by date. A new transponder and blind encoder was installed as well and must be certified before they can be used in flight. Avionic upgrades are a major alteration and anything can happen. Test, test and retest before releasing the airplane into service.

36G passed all of her tests with flying colors. There were no significant discrepancies. She's ready to fly!

Oh yes, I need checkout as well!
Speaking of flying, however, there is the little thing called currency. Yeah, that's right. I have to actually do that 3 takeoff and landing thing every 90 days! This project took more than 90 days complete and my free time has been spent putting her back together. Doing touch and go's right out of the gate probably isn't a good idea ;) It also isn't a good idea to go it alone for the very first flight. If something happens the more hands and brains the better, so I contacted a flight instructor and asked him to fly jump seat and assist with the checkout.

Flight Test
I must admit that it is a bit unnerving to takeoff in a plane knowing the extent of the work that was just performed; however, I can also say that it is a joyous feeling as well. Seeing the fruits of your labor come together in this moment is something that words cannot describe. It is very rewarding to know the project I just completed put new life into 36G. She will be a viable airplane for many, many years to come. 36G is now a Technically Advanced Airplane! That will, by the way, blow the doors off of nearly every other brand new $500,000+ single and/or multi-engine airplane you can buy!

The flight test went as planned. 36G quickly came up to power and launched off of the runway. It was very nice to be flying her again. The only issue we had was figuring out how all of the stuff worked! Testing on the ground is not the same as actually using the systems in flight. Technically Advanced Airplanes are not the same. Every one is different. You can have 10,000 hours flying behind a GNS430 and be lost in an airplane you are not familiar with. I felt the same way in 36G. Flying her was the same as usual, but navigating her...That was a different story. She's fast and wants to travel. It took awhile before we felt comfortable with how the systems functioned, which was a juggling act since we had to also make sure we didn't end up 200+ miles from home base.

Suffice it to say, we made it back on the ground safely. The systems worked perfectly! Not a single discrepancy. Every system was thoroughly tested and retested. We did some GPS approaches to full stop, ILS approaches to full stop, enroute navigation, holds, stalls, slow flight, etc. We put 36G and my flying skills through the ringer and we both came out with flying colors!

This concludes 36G's Extreme Avionics Makeover series. I hope you have enjoyed it. Feel free to email me with questions if you have any. I am more than happy to help a fellow pilot.

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