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Maintenance Minute - Blue Light Special

Posted 5 years 232 days ago ago by Admin

TIP #1 Power of the Pencil

You discover your Bell 206 Series battery relay does not come online after an engine start using an external power unit (EPU) due to a low aircraft battery. This relay requires a minimum residual voltage in the battery to actuate the solenoid and pull the contactor bar down.

While the aircraft is running and battery switch on, remove the round “label” from the top cover on most battery relays. Insert a wooden pencil in the cover hole and push down on the contactor bar. Reinstall the label or cover the hole with tape.  

TIP #2 Bump and Run

Ever push out a Bell 206L Series after an M/R blade or hub change and find the nodal beams are hitting the down stops during ground run track and balance with the collective full down? The primary culprit is usually that the M/R blade angle has been set back to its nominal setting.

The nominal settings are designed to provide sufficient M/R autorotation RPM in the event of an engine failure on the first flight. These settings induce a negative pitch into the M/R blades which in turn push the nodal beams down hitting the stops. Add a blade out of track and it can be a rather not-so-fun ground run.  

To get through the bounce, pull some pitch to get beams off stops until you finish the complete M/R track and balance, to include setting the autorotation RPM. Once the M/R is flown out and the autorotation RPM is properly set, the nodal bounce should go away.

If you run across an aircraft that’s flying smooth with a ground nodal bounce, first check all the nodal system elastomeric bearings. If the bearings look good, check that the autorotation setting is correct per the maintenance manual.

TIP #3 What a Gas

Do you find yourself needing compressed air to close an engine bleed valve for a compressor wash, spray paint a small area, or even run a drill motor, but the air compressor is a mile away, or worse, no power is available to run a portable compressor? No problem. Just wheel your nitrogen bottle/cylinder out to the aircraft.

Since most maintenance shops keep large 2,500 psi nitrogen bottles/cylinders around to service struts, tires, float bottles, etc., they can make a neat, portable “air compressor.” Ensure the nitrogen cylinder has a regulator to reduce the nitrogen gas pressure down to a user pressure of 100-125 psi. Then using proper air fittings and hoses, adapt the nitrogen cylinder regulator to a separate inline regulator and plug in your final air hose. Adjust the pressure of the second regulator to the required level. Most air tools run fine at 80-90 psi.

Remember: this is for nitrogen gas cylinders only. Never ever use an oxygen bottle/cylinder as it will be the last thing you remember in this lifetime. Have I emphasized nitrogen enough times?

Tip #4 Let it Out

Note: The  tip is only valid under several conditions: the aircraft has Apical floats; the float system has integral life rafts; and, the inspection/repacking of the floats is complied with by an external third- party vendor.

After complying with an actual inflation test on a line aircraft, it takes forever to deflate all the floats with the single test adapter found in the Inflate-Deflate Kit. Until now.

If you look on each inflated life raft, you will find a perfectly good test adapter stuck in a strap of material attached to the side of the raft. Now if by chance those extra adapters were “forgotten” in a toolbox after the float assemblies were routed to a vendor for inspection and repack, I would bet several inflation tests later, one would have enough adapters to dramatically speed up the deflation process.

Tip #5 Calm Needle Jitters

Ever struggle to match engines because the torque indicator needle(s) are oscillating back and forth? Before digital systems became the norm, some direct reading systems, like the BO105, were notorious for this.

A fluid (engine oil) does not physically compress like a gas (air). Anomalies (external or internal) can influence the pressure flow to the torque indicator and cause the needle to fluctuate. A quick way to cure this, or troubleshoot the indicator, is to install a “shock absorber” in the oil flow.

Disconnect one or both torque lines at the back of the indicator. Pull them away from the indicator and drain the oil from each line into a rag or container. Reconnect the lines.  

The small pocket of air captured between the oil filled indicator and the system oil flow will compress and absorb the intermittent pulses of pressure change while maintaining a constant pressure indication.  

If after several attempts the needle(s) still fluctuate, further troubleshooting may require installing a direct reading gauge at the engine side, or installing a replacement indicator. However, the culprit could also be an indicating system flex line that is collapsed internally or kinked, causing the oscillation.

Tip #6 Custom Cap It

Back when the only intake filter option for an AS350 Arriel engine was the bleed air type, it was a pain to leak-check the engine as the cowling had to remain installed with the filter bleed air line connected. There supposedly was a factory cap for the bleed fitting on the engine that enabled removal of the cowling/filter assembly, but we nor the tech reps could ever procure one.

Since it was metric, we did attempt to fabricate a cap similar to the pressure caps used on MBB products, which consisted of a proper sized “B” nut with a steel ball bearing nestled in it to seal at the fitting flare. Except these “B” nuts were special order and it was hard to justify destroying a $500 bleed air hose just for the fittings.

Then entered an enterprising machinist. It’s made from brass to allow ease of machining and provides a sacrificial mode in case someone tried to cross thread it.