Helicopter Maintenance Blog*
Posted 3 years 7 days ago ago by Scott Skola
Looks like things in the GOM are still not settling down. With several oil company mergers/buyouts on the horizon, as well as another major helicopter operator teetering on the brink, it should make this summer an interesting time. Especially, if there is an active hurricane season.
In other news, the Air Force has finally moved away from the UH-1N and replaced them with a variant of the AW-139, designated the MH-139. Appears the military is making good on their promise to use “off-the-shelf” products in non-combat operations. Too bad Bell didn’t keep up with that market.
And finally, an interesting article for those who like “black” helicopter stories.
https://www.airspacemag.com/military-aviation/air-americas-black-helicopter-24960500/the quiet one Hughes 500P
TIPS and TRICKS:
Continuing around the engine compartment, here’s a few tips on inspecting the engine fuel nozzle--which as a “feature” of Rolls Royce (RR) M250 series engines installed in Bell 206/407 products, can be a pain to get to. Not to mention a cut knuckle on the aft firewall from time to time. However, for a few extra dollars, you can procure one of several versions of the RR fuel nozzle wrench (P/N: 23007638), similar to the one shown in Figure 1.
When removing the fuel nozzle, be sure not to lose the nozzle spacer shims, or you’ll find yourself re-shimming that nozzle prior to installing it. And yes, these shims do matter in how the engine runs, but more specifically how the engine starts. So don’t misplace the spacers.
The RR fuel nozzle cleaning procedure is pretty straight forward as is the nozzle spray pattern check procedure. One trick is to combine the two. With the fuel nozzle removed and connected to the fuel supple line as described in the RR M&O, direct the business end of the fuel nozzle into a container. The plastic bags referenced in last month’s tip on engine oil filter changes work perfectly for this as you can monitor the nozzle spray pattern as well.
Procure an old toothbrush or the classic Allison brush. Following the RR nozzle spray check procedure, have someone motor the engine with the throttle open and gently scrub the fuel nozzle tip area with the brush as the fuel spray mists out into the bag or container. Monitor the nozzle spray pattern at the same time. If all goes well, the nozzle tip will be clean with a serviceable cone-shaped spray pattern.
How about a bleed air cabin heater tip? While there are several types of bleed-air heaters that can be installed on a 407, one of the most popular is the Air Comm model. It’s a simple system, but does have a few quirks at times--especially at the braided bleed-air line (Figure 2, blue) and the automatic drain valve fitting (Figure 2, yellow) installed in the engine compartment.
A leak at the braided line or the drain valve can lead to degraded heater ops or even low engine power check readings. If you suspect a problem, use a leak check product at the heater line and valve while the engine is at idle, or rig up an adapter and apply shop air to the line off the engine scroll adapter fitting. Be sure not to exceed the recommended heater bleed-air working PSI.
As an FYI: the operation of heater automatic drain valve is similar to the engine burner can drain valve in that they both have a ball and spring set up. When the engine runs, the engine compressor air pressure overrides the valve spring tension and pushes the ball down, sealing off the drain orifice. And just like the burner can valve, the heater drain valve requires regular disassembly and cleaning to ensure proper operation.
A couple FAA Special Airworthiness Information Bulletins (SAIB): one on Bell 206 T/R D/S damage and the other a revision to an earlier SAIB concerning UH-1 tailboom attachment failures.
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.