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ROTORwrench…Tips, Tricks, and Info - November 2017

Posted 6 years 185 days ago ago by Scott Skola

Helicopter Maintenance Blog* 
November 2017

After writing about the “sunset” of several legacy helicopters this year, it was good to see the rebirth of one old workhorse: the K-Max. I never worked one, but been around a few over the years. Simple and rugged. Definitely a no-frills ride, especially since any pax have to ride outside, side-saddle.

As of 2015, Kaman cranked up the K-Max production line--which had ceased back in 2003--for a special 10 aircraft order. 

Now, recent reports from Kaman state they will extend production past the original 10 units due to “continued demand and interest.” Appears a few people miss the old girl.

Maybe for Christmas, I could wish for a brand spanking new… BO-105 CBS-4, or a 222UT, or even a new SA315B Lama?

“He’s making a list… and checking it twice… gonna find out who’s……………..”

And speaking of Lamas….

Airbus (Sud Aviation)
SA315B Lama

We’ve reached the Lama engine in our daily, the venerable Artouste IIIB1. We’ll look at the common start problems and how to get around some of them until you can make proper repairs.  In addition to these tips, a voltmeter or 24v test light is indispensable in troubleshooting where the current is and isn’t.  

The engine automatic start circuitry can be challenging, however, anything designed by one person can be understood and maintained by another. The key to the engine start system is the “light sequence.” There is a GREEN light for the starter, a YELLOW light for the Micro-Pump (start fuel pump), and a RED light for reset (stop/start). The various light sequences that occur are the key to understanding a problem.

During a normal start light sequence, when the control selector is switched to start, the GREEN light illuminates and starter engages. After a slight delay, the YELLOW light illuminates indicating that the start fuel Micro-Pump is operating and has tripped its pressure switch. This pressure switch sends current to open the main Electric Fuel Cock (EFC) and illuminates the YELLOW light. When the EFC opens it allows main fuel to enter the system causing the engine to light off and accelerate. The YELLOW light should go out after 10 seconds and the GREEN light should go out when the starter cutout switch trips (due to fuel pressure) and takes the starter offline around 14,000 RPM. The engine should stabilize at idle between 17,000 to 18,000 RPM.
One common “failed start” problem is when a normal start light sequence is followed by engine shutdown. This is due to engine vibration characteristics during the start which can interrupt the electrical contacts in the Start Command Box, causing the start sequence to abort. If this type of start failure persists, change the start scheduling at the start valve. In addition, the idle setting can affect the engine vibration characteristics during start.

If you switch to start and only get the RED light, check that the fuel lever is fully closed. There’s a micro-switch on the engine fuel pump that prevents starting with the throttle displaced. Or, if you try to start too soon after shutting down, the “start card” is not reset yet. Wait a few seconds and the RED light will go out.

The most common defect encountered in the Artouste IIIB automatic start system is switching to start and getting no GREEN light (starter) and no starter operation, but the YELLOW Micro-Pump light illuminates. This means the starter cutout switch is likely stuck in the open position. This cutout switch is held in the open position during engine runs due to fuel pressure and didn’t reset after the pressure drops back down during engine shutdown.

The temporary fix for a stuck starter cutout switch is to U-shape a piece of .040 safety wire and bridge pin receptacles B and C on its mobile plug. Go for the start again and when the engine reaches self-sustaining speed, around 14,000 RPM, remove the safety wire shunt and plug the connector back in. It will then close pins A and B to heat the T30 time switch.

The starter cutout switch can also stick in the closed position. This results in the starter staying online past 14,000 RPM and the pilot must pull the start circuit breaker to take the starter off line soon thereafter. A properly outfitted Lama will have a finger loop of safety wire on the 10A start circuit breaker to facilitate a quick pull when this anomaly presents itself.

Complementary to this defect, if you get a GREEN light and no starter rotation, it could be the starter relay. Or if you get the GREEN light and a solenoid “clunk”, the starter relay could be OK and the starter is bad. [Submitted by Lama-Nator]

Leonardo/AgustaWestland Newsletter Summer 2017:

: 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.