Helicopter Maintenance Blog*
Posted 3 years 235 days ago ago by Scott Skola
For those who are helicopter history buffs, I recently ran across an interesting website. It chronicles the 100 year anniversary of a familiar company from its roots in the fixed-wing industry through today.
And even though the company is no longer a stand-alone venture, it still holds one record of distinction in the annals of rotorcraft history: the world’s fastest helicopter.
While there have been several recent un-official speed records posted by the Airbus X-3 (293 MPH) and the Sikorsky X-2 (299 MPH); on August 11, 1986, a Westland Lynx zipped through the sky at the official record of 249 MPH.
For more on the Lynx flight and the history of Westland: http://www.westland100.org.uk/
And the Lama-Nator is back in the house with another tip.
TIPS and TRICKS:
ATA 72 Engine
Airbus (Sud Aviation)
SA316 Alouette III
Continuing with the Lama daily inspection of the Artouste IIIB1 engine: miscellaneous cases.
On the right hand side of the engine is a horizontal oil line that supplies the engine rear bearing. This bearing is a field-replaceable component consisting of a bearing “box” (a housing that bathes the bearing in oil) and three support arms. These arms are attached to the bearing box by bronze pins in bronze bushings and the outer ends bolted to the diffuser at the exterior of the engine.
As you inspect these areas daily, pay attention to the support arm bolts at the diffuser in addition to the attachment of the line to the oil tube next to the arm (banjo bolt fitting). They should be tight and secure. Just a quick hard wiggle will let you know. At the 400 hour inspection, you will be removing the bolt from each arm, one at a time, to feel the play in the disconnected arm which will tell you if the bronze pins and bushings for that arm are good at the bearing box.
A lot can happen with these pins and bushings in 400 hours. Sometimes your relief mechanic or someone previous didn’t monitor this situation attentively, or heaven forbid, pencil-whipped the bolt removal inspection at the last 400. Anyway, one day you notice the clamp that anchors the oil line to the diffuser at the rear bearing RH 4 o’clock position (as viewed from the rear) is broken. You replace the clamp, but 5 hours of flight later it is broken again.
You likely have an engine rear bearing box with worn pins and/or bushings, causing vibrations that crack and break the clamp. It’s possible to replace the bearing box, arms, and pins overnight with just enough time to have coffee before the pilot arrives at the pre-arranged time for run-ups and check flight before return to service.
However, there is one mistake that you can make that is critical: the gasket for the rear bearing box cover is not Murphy-proof. That is, you can install it one of three ways: correctly; incorrectly with the oil IN port blocked; or incorrectly with the RETURN port blocked.
Block the oil IN port and the bearing will last about 20 minutes; block the oil RETURN and it’ll last an hour or so, because, as the box floods, some oil is forced out the upper tube which is the vent, thus allowing some flow.
Incorrect installation of the rear bearing box gasket can be prevented by a) paying attention to the orientation of the gasket relative to the oil ports; and b) by conducting the procedure that is the last step as described in the maintenance manual for replacement of the rear bearing: Motor the engine and observe oil coming out of the return tube on the engine left side 8 o’clock position (as viewed from the rear).
It’s too bad that this mistake can be and has been made. A locating pin engineered into the cover and a corresponding hole in the gasket would have Murphy-proofed it.
The tail rotor blades can also be installed incorrectly, but that’s a story for another day.
An FAA SAFO and InFO:
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.