Helicopter Maintenance Blog*
Posted 4 years 51 days ago ago by Scott Skola
As you read this, I should be tirelessly responding to all your emails sent during my absence. I greatly appreciate all of them.
Since I’m writing this three months in advance, it’s a bit hard to find a “current” topic to throw out there. However, one issue I noticed recently is the increase in incidents and accidents due to tool FOD.
I’ve been guilty of it myself. Nothing ruins a day more than someone else bringing your tools back to you, especially a pilot. Luckily for me, it never lead to any other “issues.” But as the industry tweaks its safety protocols to the nth degree, we as mechanics need to watch out for each other.
Whether you have a company tool control plan or not, get someone to double-check the aircraft for not only tools, but all FOD. It’s just the right thing to do.
TIPS and TRICKS
Airbus (Sud Aviation)
Another continuation of the Lama daily inspection and associated tips and tricks. Sump that fuel before disturbing the aircraft.
The Lama has leather boots on the upper and lower mast, as well as the tail rotor head and struts. A Lama field mechanic’s tool box should include a sewing kit to repair these, especially the upper mast boot which will admit moisture into the gearbox if it gets a hole. Sew it up and seal it with silicone. Replacement boots are available with a zipper so they can be installed without disassembling the mast.
Looking at the Mast Assembly, apply T/R D/S oil to the flowerpot/uni-ball lubricator (oil zerk like the T/R hanger bearings). Give this zerk 3 pumps only or the excess may wash the grease out of the swashplate bearings. If the Lama does not fly that day, do not re-oil the flower pot the next day. It just needs a little.
The Mast assembly has been known to lose its bearing preload around mid-life. This results in varying degrees of ground resonance and includes losing oil out of the lower mast boot due to the mast wobbling in the labyrinth seal at the top of the flared housing. Extreme cases of loss of mast bearing preload have resulted in severe ground resonance that persists even after the helicopter becomes airborne.
The Lama is generally susceptible to ground resonance due to its 3-bladed fully articulated main rotor. It is common to have to re-position it upon landing on uneven terrain. Many operators think the landing gear shock struts get air in them and cause ground resonance. This is partially true if you’re having ground resonance issues and after you bleed the struts the resonance is diminished for a while. But then the struts get air again and you have the proverbial vicious cycle.
The whole truth is that ground resonance starts “up top” at the Main Rotor Head. A properly tuned Lama should be able to land without the struts at all, because they are only there to cushion the airframe from the flex and shock of landing. They only dampen within a travel of a few millimeters and if the piston travels too far too fast, they grab air. Most landing gear dampers are defective anyway.
These struts are simple hydraulic piston and cylinder dampers. Moisture gets inside by condensation or leakage at the upper attach fitting joint and corrodes the steel piston. Keep your fluid pristine.
Remove the bleed screw and tap the sides of the cylinder to dislodge air bubbles clinging inside. After bleeding, seal the bleed screw with a swirl of silicone. Keep the fluid clean and topped to the bottom of the filler hole. You’ll know when you have air because it’ll make the fluid level rise and leak out the filler boot.
Let’s go “up top” to the Main Rotor Head. Check that the spacing cable attach bolts rotate freely and that their anchor post at each blade sleeve (grip) is perfectly aligned parallel to the sleeve. If not, use the tool to aim and align these anchor posts.
Tug on the blade spacing cables alternately leading and then lagging a sleeve while feeling and watching for play at the eccentric, the damper arm stack-up on the drag hinge, and at each damper attach point. First you should remove the sealant from the eccentric so you can see the splines. Let’s assume we have one or more that show slight play, not uncommon. We’ll adjust them next time.
[Submitted by Lama-Nator]
A couple more AgustaWestland newsletters from Autumn 2016 and Winter 2017:
SUBMITTING MAINTENANCE TIPS/TRICKS/QUESTIONS/INFO:
Have an old tip or trick you’d like to share with your fellow mechanics? Or maybe a question that you can’t seem to find an answer to? Or just some info to pass on? Send an email to: [email protected]
About the author:
After 32 years maintaining helicopters in various capacities, Scott concluded a full time career with a major operator in 2014. When not pursuing future writing projects, he can still be seen around the flight line tinkering on aircraft for beer money.
*To keep the hounds at bay, the information contained in this blog is for discussion purposes only.