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

Posted 5 years 78 days ago ago by Scott Skola

Helicopter Maintenance Blog* 
March 2019

Things don’t appear to be getting any better in the GOM. With the current oil price stagnant and helicopter demand at historical lows, those affected may be in for a longer ride than expected.

Most who read the blog know I’m a history buff and recently added the “history corner” below to highlight certain rotorcraft events. However, I’d like to take it a step further in this month’s blog.

Last month marked the anniversary of the birth of one of the most prolific aircraft designers in aviation history: Clarence Leonard “Kelly” Johnson. He didn’t dabble in helicopters, but was involved in the design and production of some of the most recognizable and important aircraft in aviation.

Starting with the Lockheed Electra, he worked on the P-38 Lightning, the Constellation, the P-80 Shooting Star, the F-105 Star Fighter, the C-130, the U-2, and the SR-71 Blackbird. Plus, he had his fingers in the initial prototypes of the F-117 stealth fighter which was completed by his protégé, Ben Rich. 

He also managed the Lockheed “Skunk Works” which handled all the black-bag research on the SR-71 and other aircraft. If you want a good read on this operation, I highly recommend the book “Skunk Works,” by Ben R. Rich.

One of my favorite Kelly Johnson quotes came from a 60 Minutes interview after the stealth fighter rumors were starting to circulate. Morley Safer, I believe, asked Johnson if the stealth fighter was real. With a grin, Kelly responded: “If I could talk about it, it would be obsolete.” Priceless.

Here’s some more on Kelly Johnson: https://www.thisdayinaviation.com/27-february-1910/

In the history corner: 




ATA 05 
Maintenance Checks

Keeping on target with the engine cowl, here are couple more tips.  The cowl door hinges (Fig. 1, blue) and door prop rods (Fig. 1, yellow) are another area to watch. The hinge pins that secure the door to the center cowl can migrate out over time--sometimes in flight. Here’s two options to prevent this. 

One way is to replace the original hinge pin with one a bit longer and slightly bend both ends outside the hinge loops. A second way is to drill the hinge pin ends with a small bit and install cotter pins or safety wire in the holes. Either way the hinge pin will remain in place.

While the 407 engine cowl door prop rod assemblies are an improvement over the 206 single prop rod, they consist of a number of parts that can wear out. A common situation to run into is after opening the engine cowl door you find some prop rod hardware laying in the engine pan.

Where possible replace the prop rod pivot pin retainer clips with cotter pins. However, it’s best to leave the clips installed at the rod/door attach point if you remove the cowling on a regular basis. Also, at every engine inspection take 5 minutes to check all the engine cowl prop rod assemblies for worn channels and hardware. Order as needed.

The same goes for the engine cowl door latches (Fig. 1, red). One common problem is the latch spring breaks which prevents the lower striker from popping out. While it may seem only an inconvenience item, it can be a safety issue as that latch may appear secured when it fact it is not. Keep in mind, when replacing these latches be sure to use the correct dash number as it corresponds to the thickness of the wear pad bonded to the lower striker.

If the new latch you install is difficult or impossible to secure it may be due to the wear pad being too thick. However, all is not lost as a portable die grinder or Dremel tool can be used to sand down the thickness of the wear pad. Sometimes it’s prudent to Cleco in the new latch and function check before the final installation.  

One more trick with the engine cowl.  Ever had to remove a 407 engine cowl in high winds--like on an offshore platform--to get to the N1 mag pickup? One unique quality with these engine door prop rods is you can lift and reposition the engine cowl assembly with the prop rods still connected.  

With all door latches and all center cowl Dzus studs unsecured, lift the cowl center section rear edge up and slide the whole cowling aft/up approximately 1 to 2 inches until its riding part way up on the exhaust stack. This motion will uncouple the engine diffuser vent fitting from the center engine cowl. Now, with the cowl assembly loose, lift while working the cowl from around the exhaust stack and reposition it left or right until the opposite prop rod reaches it limits. 

To reinstall the engine cowl, reverse the process, but ensure you stab the cowl onto the diffuser vent fitting. A little practice in no wind makes for a good day offshore. And don’t forget to hold your mouth right.

From an email: How long can I operate an aircraft with an inoperative piece of equipment? 

As usual, I get to use my favorite answer again--well, it depends.

The main issue is whether the aircraft has an approved Minimum Equipment List (MEL) or not. 
Under an MEL, there is a defined time limit listed. The time limit itself is dependent on how the item is classified in the MEL and whether there is any type of remedial action required. For example, if the aircraft was operated under Part 135, the maximum time limit most aircraft can be operated with a Category D item inoperative is 120 consecutive days or 2880 flight hours.

Now if the aircraft doesn’t have an approved MEL then the appropriate guidance is found in Part 91. While it can be a bit confusing, 91.213(d) and 91.405(c) allow an aircraft to operate with an inoperative piece of equipment for an indefinite time period provided–this is the important part--that the inoperative equipment is re-inspected/re-evaluated/re-documented/re-placarded at each required aircraft inspection. 


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.