Focus on Maintenance: Reaching the finish line
By John Carinha
The flurry is almost over. The “full gas” days of fall and winter are done, and the operational season is upon us. For many of those tasked with maintaining utility aircraft, the marathon is almost over. For us, we’ve just come off multiple airframe rewire projects, plenty of avionics and radio upgrades, and a bit of everything else in between. Many of our clients operate fleets with multiple aircraft types. Their own staff are often tasked with a lot of the general maintenance, which at any time can leave an aircraft in a state of disassembly that goes beyond just removing seats.
We have been working with several fleet operators to get calendar items checked off and radios upgraded. Much of this work is mundane and straightforward. At times, consideration needs to be taken for how much of an aircraft is torn apart or needs to undergo active maintenance. At this time of year, it can be a mad dash to the finish line, as the rush to get aircraft out the door and generating revenue is imperative.
We were recently called out to add a third FM radio to a Bell medium helicopter. This particular aircraft had undergone some structural work and some of the overhead wiring was pulled back to facilitate this. When we arrived on site, the aircraft was buttoned up and sitting in the hangar waiting for us. Having reviewed the prior installations, we discerned that existing, unused USFS wiring would be repurposed and re-terminated to accommodate a new connector kit for our new radio, given it was already interfaced to the audio system. After a quick continuity test, power was applied and a successful functional test was performed.
I returned to the office and was preparing relative paperwork and certification when my phone rang. Our client described an issue (unrelated to the FM installation) whereby the pilot’s headset microphone was live to the PA speaker. Any voice transmissions made by the pilot on any selected audio source were heard through the speaker. This is not normal in any way, shape or form. Given the line of thought of “last place out, first place in,” there was a question as to whether something we had done was related to this new issue.
I sat in thought and started thinking about how it would even be possible to have something like this happen. The first – and easiest — troubleshooting step was to swap audio panels. The result was the same — no change. I then began thinking of anything aircraft type-specific, and it dawned on me that the Bell mediums run their pilot drop cord to an overhead terminal strip. The PA system has a radio option where you can parallel the pilot headphones and hear any selected receive audio through the PA speaker. The latter is for situations on the ground, where engines are off and radio chatter is required to be heard while in camp or at a landing zone.
Once it was confirmed that the particulars applied to this aircraft, a visual inspection was conducted. I instructed the crew to access the terminal strip. Microphone wires on the drop cord are red and green; phones wires are white and black. I asked them to see which two colors had additional wires tied to them at the terminal block. The response was red and green — which confirmed my suspicion. The PA audio input was mistakenly tied to the pilot microphone circuit — not the phones circuit. During re-assembly, the two wires were installed on the wrong terminal strip posts.
These sorts of issues can be an easy finger pointing exercise, but truth be told, as harmless as they are from a cause-and-effect perspective, there are a few lessons to be learned. Properly labelling wiring and or parts when they are removed is vital in ensuring their correct orientation during re-assembly. More importantly, however, is understanding HOW a system is wired. In other words, knowing now how a PA system might integrate with existing audio wiring, one should wonder or question why there are additional wires tied to a pilot drop cord audio terminal strip. The mere fact something “extra” is there should raise wonder — and provided that leads to greater understanding, the problem should never repeat itself.
