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ROTORwrench…Tips, Tricks, Info… and a Laugh - October 2019

Posted 4 years 216 days ago ago by Scott Skola

Helicopter Maintenance Blog*
October 2019

It looks like Airbus set another high altitude record. Last month, a H145 landed at 22,840 feet in the Andes Mountains. Having spent some time flying up in the mountains in various helicopters that is quite an achievement in a twin-engine, free-turbine aircraft. Congrats. 


Anticipation is building as the US Navy is poised to select its next training helicopter by years end. Regardless who wins, I think the industry as a whole has won a major advancement with the FAA certification of several single-engine IFR capable upgrades. If it hadn’t been for this competition, I seriously doubt this would have ever happened in the foreseeable future.

And finally for you Robbie fans, the R66 fleet just surpassed the 1,000,000 flight hour mark.


In the history corner:






Moving along…


ATA 05

Maintenance Checks



Perhaps now would be a good time to take a quick moment and review last month’s RADS intro and tips.

A few some tips and comments on the ground portion of RADS.

Remember RADS is merely a tool. It’s not magic. So you still need a basic understanding of the mechanics of track and balance work. If you ever worked with an old Chadwick 177 then you have those basics. RADS simply automates the same principals and tries to give one set of corrections for all track and balance move possibilities.

It’s this combined set of corrections that usually leads to other problems in the track and balance process. Fortunately, RADS does offer the ability to turn on/off possible corrective options: PC links, weight, tabs. And we will use this option when needed.

Several more quirks with RADS: it doesn’t technically “correct the clock” after the first run like you did with an old Chadwick; plus, all balance solutions try to achieve a perfect balance of 0 IPS;  and, RADS can be “insensitive” to weight amounts and their respective move lines.

If you’re having trouble “seeing the move lines” scroll through the CADU screens to find the IPS reading and clock angle. Or, make your own polar chart and physically plot the IPS, clock angles, and move lines on it. If the correction weights are shooting the move line through the chart center then reduce the weight as needed. But be sure to use this same weight reduction percentage for each future runs as well.

Another important option within RADS is the “view predictable.” This shows you where RADS thinks it will be after the next runs with its current selection of corrections. If the actual track/balance results are not following the predicted values in general, you will need to look into the reason.

Once you start your ground track/balance it’s important to follow the first 3 RADS solutions--exactly--to see how it is “reading” that aircraft on that specific day/time/weather. In general, RADS will compute solutions based on how the requested track/balance moves react on system. If you short a weight move or don't adjust a P/C link, and you don't subsequently modify RADS and re-compute, then you have just created a problem.

In some cases an unrecoverable problem, where after additional runs the solutions are out of sync and you have to start over. However, if RADS calls for a 1/8th flat or .0001g then common sense should prevail. If there is a larger vertical component to the vibration, turn off the RADS “balance weight” option and view track only corrections, but be sure to re-compute the corrective solution. Or, simply ground track first then turn on the balance weight option.

On in-service aircraft with time on the M/R system, sometimes you may encounter erratic ground readings which give varying solutions. Try applying a small amount of collective pitch into the system during the ground run. This will load up the M/R bearings and provide a more stable platform for taking the track/balance readings. Just be sure to use the same amount of pitch for every ground run.

A final tip. If you have reinstalled the M/R Hub assembly prior to ground track and balance be sure to torque check the M/R mast nut after the first ground run. If the nut moves, torque check it after the second ground run as well. Nothing ruins a day more than having a hub shift during track and balance.

If all goes well, you will achieve a ground track/balance level acceptable to RADS which will automatically take you to the next level, flight.

So tune in next month, same ROTORwrench channel, same ROTORwrench time.


Can I install non-PMA or non-TSO parts on my type-certificated aircraft?

That’s a great question that deserves a great answer. It depends. Ha, but first some background information.

Technically, there is no restriction in Part 43 on the type of parts that can be installed on a TC’d aircraft. However, there are certain Part 43 requirements in how that part is installed and documented. But in reality, it is entirely subjective to the installer on what parts they are willing to install and by extension what the next inspector is willing to accept during that aircraft’s subsequent required inspection.

Now if you want to produce (i.e., manufacture) a part for installation on a TC’d aircraft then yes, there are a number of requirements found in Part 21 which covers TSOs and PMAs. But as stated above, the installation of all parts is guided by Part 43.

So if a part was not produced under Part 21 then the only method available to install these non-PMA or non-TSO parts is through the Part 43 alteration process. So the answer to the original question is yes, you can install non-PMA/non-TSO parts on your type-certified aircraft.

For additional reading, here is a great article by VAL Avionics:





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.