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ROTORwrench…Tips, Tricks, and Info - October 2018

Posted 5 years 247 days ago ago by Scott Skola

Helicopter Maintenance Blog* 
October 2018

To all those flying and wrenching in the Carolinas and beyond, I wish you good luck and support.

I think everyone has an FAA story. For most of us, we usually remember only the bad ones. You know: “Hi, I’m with the FAA and I’m here to help you.”

While I’ve been fortunate to have some great “blue badges” working around me, especially in the GADO days, I too have had a few conflicts.

Regardless of your personal belief, I believe the FAA has improved their support to mechanics. One such avenue is the ever increasing maintenance support documents on their website. Another area is safety based (https://www.faasafety.gov/default.aspx) and includes material directly related to mechanics under the submenu of “Maintenance Hangar.” 

Check it out one day.

And now… back to the 407.

ATA 05 
Maintenance Checks

Before we move forward into the engine compartment, a few tips on T/R driveshafts. These shafts consist of the forward short shaft, oil cooler blower shaft, aft short shaft, and five segmented shafts that run atop the tailboom. 

These shafts are similar to the 206 series, but are more robust. However, they also suffer from some of the same 206 issues. 

The forward adapter fitting mount nut (green circle, Figure 2) on the segmented shafts can loosen over time and under the right conditions cause the associated splines (red circles, Figure 2) to strip out. Any time the T/R D/S fairing is off, give them a quick check by twisting the shafts opposite each other and look for movement at the adapter.

They also tend to crack the flexible disc packs. Main reasons are the beveled washers are installed incorrectly or the mount bolts have lost torque. If the aircraft is on a Bell inspection program there is a scheduled torque check of the disc pack bolts.

A long time ago there were some issues with the T/R hanger bearings failing but those issues have since been corrected. However, it’s still important to ensure they are greased regularly, with the correct grease and amount. More grease is not better in this instance.

And even though the shafts and hanger bearings are heavier and stronger, they must be installed with the correct tools. While the 206 type T/R shafts and bearings only required loosening the bearing hanger nuts and performing a short ground run to align them, the 407 is more exact.

Aligning the segmented shafts requires the use of a hanger bearing alignment/adjustment tool to ensure the shafts are properly installed. However, it’s the installation, alignment, and condition of the oil cooler blower shaft that is most critical.  

Most operators perform regular dynamic balancing of the blower shaft as its balance affects the entire drive chain. This balancing act—which can be a bear sometimes—will be the topic of December’s tip. Till then…

Received a question on what FAR directs aircraft empty weight and balance computations. Good question I might add.

When it comes to an aircraft’s empty weight and balance (EWB), and associated empty weight center of gravity (ECG), you’ll find minimal FAA guidance. As for what FAR directs EWB/ECG calculations, there it isn’t one, at least in Part 43 or Part 91. The reason is the EWB/ECG is part of an aircraft’s type design/type certificate and that requirement is found in Part 23, 25, 27, or 29.

In other words, when an aircraft is manufactured and is presented for its original Airworthiness Certificate, the EWB/ECG is considered part of that aircraft. This is further shown in aircraft Type Certificate Data Sheets (TCDS).

Most TCDSs contain a note which directs the requirement of a certified empty weight and balance:

NOTE 1. Current weight and balance report including list of required equipment and list of equipment included in certificated empty weight, and loading instructions when necessary must be provided for each helicopter at the time of original certification. The certificate empty weight and corresponding C.G. locations must include undrainable oil and unusable fuel for the appropriate model.

Since the EWB/ECG is technically part of an aircraft, the only time it needs recomputing is after a repair or alteration that exceeds the minimum weight change requirements: >1 lb. for aircraft less than 5000lbs. MGW; >2lbs. for aircraft 5,000-50,000lbs. MGW and so on.

In addition, being that an alteration/repair is the defining source of a potential change in EWB/ECG, only an A&P can compute and certify a new EWB/ECG. So as you can see, there is no single regulation that directs when to calculate new a EWB/ECG.

A complete explanation on aircraft weight and balance can be found here: http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/faa-h-8083-1.pdf

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.