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Joined: Thu Feb 19, 2004 7:49 am

Corporate MX Techs-Your Favorite To Work On & Why?

Sun Mar 02, 2008 11:59 pm

I spent all weekend on call this weekend, mostly troubleshooting a Lear 60 with engine issues and a balky upper cabin door. As I was working, I spoke to many others who traverse thru our hangar and got to thinking about a topic of interest. For all you MX Techs out there, who have spent your days in the Corporate Realm, what biz jet do you prefer to work on over any other, and why? What made it better than another? I'll start by saying mine has to be the G-IV. It's a big aircraft with room to move in and out of, and everything was well thought out for the most part. I look forward to the replies..
"Failure to prepare is preparing to fail"--Benjamin Franklin
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RE: Corporate MX Techs-Your Favorite To Work On &

Mon Mar 03, 2008 9:38 am

I spend most of my time working on Lear 35s... but I can get my hands on many different models in the local corporate fleet. Over the past years, I've worked regularly on different Lears (mostly 35/45/60), Challengers (600/601/604 and now 300), Gulfstream (the good old G1 which is gone now and the GIV we currently have in the fleet), Global Express, Hawkers (700s & 800s), Cessna Citations (mostly II & III). As for the prop side goes, Jetstream 31s & King Air 350 & Piaggio Avanti experience.

So as you can see, I have compared products from Bombardier, Gulfstream, Raytheon (or whatever it's now called) and Cessna to give myself an idea of what I prefer and why.

I work avionics and my favorite would have to be the Challenger 604, although I almost just do inspections on 604s because they seldom fail. But sometimes, you're lucky enough to get a snag, so you get excited....  Smile Pretty much everything is easily done on a Challenger, except maybe replacing AOA vanes which often fail the resistance linearity check inspection. To do so, you have to remove interior components, which is touchy sometimes on 'nice' corporate planes. As for the 600/601, still good planes, but they are less "standard" than the 604, which sometimes complicates maintenance. What I mean is every 604 is pretty much the same, but on a 601, the same switch can be at 5 different places on 5 different airplanes. The new Challenger 300 is great too, almost never fails and is easy to work on, but I don't have enough experience on it to be my favorite just yet. Bombardier listened to maintenance people for their design this time, unlike what they did with the Global Express.

I don't like the Global Express, it's a big airplane, fast, a lot of range, great for the passengers, for the pilots, but for the avionics tech, it's awful for maintenance if you ask me. Just an example that I can't get over, it takes like 35 minutes to get to that CVR & FDR because they are near control cables in the aft equipment bay, and you have to remove the A/C tow bar and the ladder to get to them... really bad access. And one other thing is that avionics equipement bay access on the belly... there's like 50 fasteners to unlock before you can remove the access panel.... great idea. Take a CRJ for example, there's a simple handle mecanism so you don't lose any time gaining access to that compartment, much better for maintenance. Finally, I'm biased towards Collins avionics, so sure I prefer the 604 Pro Line IV over the Honeywell Primus in the Global (although that will change soon with the Collins Pro Line Fusion avionics onboard future Globals).

Hawkers seldom fail, but bad to work on sometimes, because you need special "english" tooling and parts, and some wiring blue prints take some time to get used to. Nonetheless, I like to troubleshoot the Hawker, because it is pretty much a straight forward plane when you get to know it. I'm always amazed by the offset tires on each main gear, you gotta love British engineering!  Smile (Have any of you hooked up a Pitot Static test set to a Hawker??? nice job isn't it, it will easily take an hour!)

I really don't like Cessna products, it's like they build a reasonable aircraft, but always put the lowest bidder parts in them. It just seems that when a Cessna comes back to base, you're bound to have a grocery list of problems that should not be routine. The wiring on the A/C is clean, but like I said everything looks cheap. I hate their maintenance documentation (mostly the wiring manual).... they draw them like Cessna 172 diagrams, but just add more wires... The Citation II isn't so unreliable, but sometimes simple jobs just get complicated on these planes. The Citation III is awful, always something broken, bad access, bad documentation, I've mostly worked on 2 separate Citation IIIs, and it's always the same story. I was on a test flight in one once, and on takeoff, it's similar to what you would feel in an Airbus A340, no real acceleration feeling, but hey to be fair to Cessna, this baby can cruise at a good speed (unlike the Slowtation II), and the landing was smooth. I have never worked on the Citation X, so I cannot comment, but I hear it's not that different.

As for Gulfstream, very straight forward planes, big (although cockpits are kind of small for the size of the plane). Documentation not bad at all, but I find Bombardier documentation to be easier to use. Rarely on a Gulfstream a maintenance task will have bad access or such. I liked my experience on the G1, and the GIV is almost never broken. The GIV we operate is like 20 years old and apart from minors issues, very very reliable airplane. I like to work on the plane, but ours was passed through different customers through time, so the customized wiring diagrams are sometimes inaccurate, but I can't blame the plane for that. I have to agree with G4Doc2004 that this is a great plane, and I enjoy working on it when I can.

Learjets, the core of my work, the one I know the best is the 35, but my favorite overall to work on is the 60, I'm excited because we're about to get a brand new 60XR, we haven't had a 60 in our ops for 2 years now, we just got exterior contracts. The 45 is bad to work on when you get into troubleshooting, especially if you have that APU in the back.... good luck getting to that DAU hidden behind... you have to unscrew the rack or else it won't come out. Talking about APUs, you don't want one in your Lear 60, because you have to remove it to get to your batteries, so don't drain them. Luckily, most operators don't take the APU option. Back to the Lear 45, nice for the pilots and passengers, and the technician doing very routine work, but often nasty access for maintenance workers the deeper you go... talk about the force sensors on the rudder pedals for the rudder boost... I believe they install them on the Lear assembly line before they put the skin on the fuselage. The 45 also has the Honeywell Primus, which sometimes has glitches, you turn the power off for 5 minutes, and then everything is ok. Ah well, the electronic era is here. With all that said, the 45 is fine once you fix all your problems and it flies. When that happens, you can be a long while before the pilots report something wrong with it. Finally, I really like the good old Lear 35, which I find much easier to work on than the 45 most of the time. The only thing I hate these days about the 35 is the FC-200 autopilot. It just seems that they are getting so old, the pitch & roll modules fail more often these days. Then you receive a serviceable part from let's say DUNCAN, and it fixes your problem but creates another one. For example, on an airplane with a long range nav issue, you replace the roll module which you've confirmed is bad, and the problem is fixed, but it ain't over yet, because while doing your tests, you notice the localizer does not capture. We've been has far as replacing the board 5 times before the problem was fixed. I suggest you get the parts from JET (now L-3), it's more expensive, but they test every single function before sending it, unlike DUNCAN or other cheaper suppliers.

I won't get into props, I got carried away big time.... good for you if you're still reading this.

Have a great week everyone,
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Joined: Mon May 19, 2003 2:16 am

RE: Corporate MX Techs-Your Favorite To Work On & Why?

Mon Mar 03, 2008 4:49 pm

I liked working on the Gulfstream 1 and 2, easy airplanes to work on and everything was easily accessible except the inverters on the G1, they were installed hanging below the avionics compartment and very difficult to remove. On the G2, they placed them in the aft compartment and you basically tripped over them, that’s how easy it was to get to them. I did my fair share of APU changes on the G2, an easy job as long as you had long arms to reach some of the ducts.

Of course my favorite airplane was the JetStar, it was easily a one man airplane to maintain, almost no need for any ladders or sky hooks to get to anything, but there were some stupid things that Lockheed did that I wish I could have wrung the neck of the engineers who designed that part. One was the placement of the upper rotating beacon, instead of putting it on top of the fuselage, they installed it on top tip of the vertical fin, it was impossible to reach to change a bulb even with a ladder on the horizontal stabilizer
Fortunately one Gulfstream operator in our hangar had an electric lift so I was able to borrow it.

The wiring diagrams were pure Lockheed, easy to read and other than the torque tip screws used through out the airplane no special tools was needed. Standard 10 hydraulic jacks were all that was needed for jacking up the airplane.

The other major problem was changing the main fuel pumps, on the Gulfstream it was a 45 minute job, they were in the wheel wells and were plug in type pumps, pull them out and the fuel lines had check valves that closed so no fuel poured out.

On the JetStar the pumps were internally submerged for cooling and required that tank to be drained, which presented a problem if the pump had failed. There was a way of getting that fuel out buy using the tank interconnect valves to slowly gravity feed the fuel to another tank and then hooking a long 2 ½” line from the defueling valve and then pumping that fuel into another tank. That was the easy part, the difficult part was getting access to the pumps, they were mounted inside a vertical panel that was part of the wing structure and held in by 50 or so bolts, after removing the bolts you had to lower the panel with the pump into the tank and then turn it sideways to get it out. And that was after removing the large belly panels and the wiggins fittings from the fuel lines.

It was basically a 2 day job if there was a lot of fuel in the tank and you hoped that when you reinstalled this panel with the large seal on it, it didn’t leak because it would take the better part of a day to remove and reseal it again.

About the only other pain in the ass problem on the JetStar was servicing the pitch trim mechanism, every 200 hours it needed draining and servicing, it was located in the aft compartment and access was through a small bulkhead opening, I would go in there and not come out until I was finished, an take my coffee in there because of the difficulty getting through the opening and getting past the control cables.

Other than that, the JetStar was a great airplane to maintain. Removing engines was a snap on the Pratt powered airplanes, 2 mechanics could have an engine out in less than 45 minutes, one mechanic or sometimes I even used one of our pilots on top of the nacelle used a manual cradle winch, which lowered the engine down. Sometimes it was easier to drop and engine out to change some components on the engine or the thrust reverser hydraulic actuator than to fight it with the engine in place.

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