Helicopter Maintenance Blog*
Posted 4 years 208 days ago ago by Scott Skola
Good to see you survived another year.
As I mentioned last month, we will be using the Lama-Nator’s “daily inspection tip format” on other helicopter models for this year’s tips and tricks. And the first stop will be the ever present Bell 407.
We still have several Lama tips to finish up, so look for them highlighted in-between the 407 tips.
But first a couple notes on the 407 tip format. While the Lama-Nator used the standard “pre-flight” walk-around guide found in most flight manuals, I was originally taught a different approach to perform a daily inspection.
Back in the day of the red-colored 206 T/R blades, we checked the T/R assembly first during a daily. These particular blades had a few issues that would pop up just prior to a blade tip departing the aircraft at the most inopportune time.
By checking the blades first, we could get another T/R assembly on the parts truck ASAP if we noted any discrepancies. Since then, I have started all my daily inspections, regardless of aircraft type, first at the T/R then forward to the pitot tube. Hence, all my tips will follow that same format.
Also keep your eye open for a “colorful” addition to the blog in the coming months…
And so we begin…
TIPS and TRICKS:
While the Bell 407 probably should have been on a separate Type Certificate, it is technically a variant of the original Bell 206. And due to that family connection it also inherited several “genetic” issues like tailboom problems.
The first thing to note when you look at the aft end of a 407 is to ensure everything is still there. It seems the 407 is not too partial to anti-collision lights or tailskids (Fig 1). Some think it’s the 4-per of the M/R or simply the harmonic of the tailboom. But whatever it is those two items seem to depart on an irregular basis after a day of flight.
To help prevent these departures, there are a couple things to check. On the light assembly, ensure the proper lens gasket (Fig 2, #3) is installed and the retaining clamp (Fig 2, #2) is secure and oriented correctly. Also make sure the light deflector/mount base (Fig 2, #5) is secured. Sometimes the deflector tab itself will depart so check for it cracks.
Since we’re at the anti-collision light, a couple tips on troubleshooting light problems. First, check to see if the light assembly is physically there…;) If it is, but not flashing, stick your ear on the fuselage aft skin panel above the baggage door and listen for the light power supply building/discharging a charge. It will sound like a “whine” then a “ping.”
A quick reminder, it takes 10 minutes for the anti-collision light system capacitors to bleed down their charges. Nothing like providing a path to ground for those charges when you’re on top of a work stand or stuck above the baggage compartment to electrify your day. Follow all the maintenance manual warnings before disconnecting the powers supply and wires.
Now if the power supply is pinging, and a new flashtube (bulb) does not fix it, turn off power, and remove/disconnect the light flashtube/lens/clamp (Fig 2 #1-4) as an assembly (or use the convenient spare flash tube/lens/clamp in your tool box). Plug the flashtube directly into the OUT connector on the power supply and turn power on.
If the flashtube flashes, check the light wires up to the top of the vertical fin. The factory wire connector at the vertical fin/tailboom junction is a weak link due to internal corrosion and pin-crimp issues. A flat, 4-pin Whelen connector makes a great field replacement at that location. If the test flashtube doesn’t flash, or the power supply is not pinging, suspect the 24vdc supply voltage/ground or the power supply itself.
To get back on our “departure” topic, for the tailskid, give it a tactile check, i.e., a wobble check. If loose, schedule a time to rebond the skid into its vertical fin mount fitting (Fig 3, #2). Check for cracks on the skid bar and mount fitting when removed.
As a MM/IPC reference side note, you won’t find the tailskid in Chapter 53 with the vertical fin. It’s technically part of the landing gear and found in Chapter 32.
Be sure to use a new through-bolt (Fig 3, #1) for every tailskid install and coat bolt with a release agent or something to aid in the next removal. Also, to save the next guy some pain, cover the cotter-pin shop ends (Fig 3, #3) with the left-over tailskid sealant as that cotter-pin sits at the precise location you place your hand when ground handling the aircraft. [Submitted by Rw]
For those into K-Max porn:
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.