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Flying with a bad prop low oil light float switch...


ShadoFE
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Hey all,

I’m hoping some old Herk operators can help me locate some long lost information.

It happens from time to time that an aircraft is away from home station and qualified maintenance when the old prop low oil light comes on while on the ground.

This scenario usually has but just a few possible outcomes. The FE checks the servicing and…

1. The prop is a couple quarts low due to a slow permissible leak or lack of proper servicing. In the end, the FE services it up and off they go.

2. The prop is a couple quarts low and leaking beyond acceptable limits. They’re broke and require a prop/seal change by qualified maintenance.

3. Surprise! The prop is properly serviced. Possible bad float switch in the pressurized sump. At this point the FE has all they really need to know…the prop fluid is not low. However, maintenance will usually ask the FE to disconnect the cannon plug to see if the light in the flight deck goes out. If it goes out, this confirms a bad float switch, if not, further troubleshooting will be necessary to find the trouble. Likely a short to ground in the wiring.

It is scenario three I want to focus on. If the prop is not leaking, properly serviced and a bad float switch is confirmed, decision makers at the appropriate level must evaluate the risk of flying the aircraft home.

Recently this scenario played out and when discussing with the O-6 about whether or not to return the aircraft, I was told that years ago (10+ yrs) there was a written procedure in the flight manual for operating the aircraft with a known bad float switch. This was news to me.

I’ve been on Herks for about 10 years now and I’ve never seen anything in print about flying with a bad float switch. FE’s have always just applied systems knowledge and it has just been passed from one FE to another.

Anyone out there know about this long lost written procedure? If so, please let me know.

If not, what do you think it could possibly consist of?

Thanks!

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Can't speak for old tech data that doesn't exist anymore, but the 3-1-6 RESTRICTION AGAINST FLIGHT OF AIRCRAFT WITH KNOWN PROPELLER DIFFICULTIES contains the current direction for what propeller malfunctions are allowed to exist and still be allowed to fly. It supersedes a version from 1996. It makes no mention of a bad float switch, and it is pretty clear that there must be no known defects with the propeller and associated systems with only three exceptions: Synchrophaser failure, Automatic De-icer system failure (with manual working), and feather override button not popping out when the prop reaches full feather. Every one of these must be troubleshot to the specific part before release.

There is a note however, that an Exceptional release may be authorized by the MO or rated pilot serving as a crew member. Not sure if it's saying they must sign off if one of these three defects exist, or if either can sign off if another problem exists, but I assume the former.

Of course, I believe your local MEL/MESL can trump this tech data, and if it does, it will list flight restrictions associated with the defect, such as not flying during inclement weather if the brush block is defective or blade de-ice boot wires burnt. If that's the case, what you are looking for might be a local procedure, not an Air Force-wide procedure.

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That’s what we are having under section 5 page 1 of FM 382C-14E. (change 6 - April 1999)

NON STANDARD OPERATIONS

Quoting:

INTRODUCTION.

This section covers procedures that incur a greater than normal risk; therefore, they should not be routinely performed. These procedures may be safely performed by personnel who have been thoroughly trained in their use; however, due to the greater risk, they should be employed only when directed by appropriate authority.

PROPELLER LOW OIL WARNING LIGHT SYSTEM MALFUNCTION.

An airplane may be dispatched for flight with propeller low oil warning light system malfunction, provided the following is verified prior to the first flight of the day.

a. Propeller atmospheric sump oil level is normal.

b. There is no evidence of excessive propeller oil leakage.

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Thanks for the info. I think what tenten wrote sounds like what I had heard about. Not much to it really…just good common sense. I though it might give some guidance on some specific operating considerations beyond a daily fluid level and leak check. Like the following thought…

So, when operating in this condition, is the prop low oil warning circuit disabled or does the light remain on during the flight? If memory serves me correct, there is only one circuit breaker which provides power to all four warning light and master light circuits. So, I can’t just pull the breaker for that engine and extinguish my flight deck warning lights without rendering the other warning lights inoperative as well. I would think that disabling the individual circuit to enable the master light to function as intended would be optimal. What would be the best way to do that? Simply disconnecting and securing the cannon plug on the engine seems simple enough, but I can’t remember if anything else is on that cannon plug that I wouldn’t want disconnected. Can anyone verify?

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Removing the light bulb will not make the master go out.

Remove the light bulb and remove the diode (from the bad prop) that isolates/seperates the master from the other individual lights. This will extinguish the master so if you get a prop low oil condition the master will illuminate and the "other" individual light.

If you remove the cannon plug you will disable the 86 degree switch....

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Removing the light bulb will not make the master go out.

Remove the light bulb and remove the diode (from the bad prop) that isolates/seperates the master from the other individual lights. This will extinguish the master so if you get a prop low oil condition the master will illuminate and the "other" individual light.

If you remove the cannon plug you will disable the 86 degree switch....

Not sure which cannon plug is referred to, but if on the prop, you lose pressure cutout and pulse generator, too

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Remember flying out of the 16 TATS with 2 student pilots and an IP (I'm sure we all know the type) who thought he could just unscrew the light that came on in-flight and stated that we could continue with the training mission - we were flying PP at Barksdale. Guess he was trying to impress the 2 students. I got him off headset and told him that if he didn't shut-down the engine and head back to LRF that we'd be standing in front of the CC and the flight safety officer as soon as we got back to the squadron. Don't remember if it was a switch or low oil since they cancelled the flight and I never checked with maintenance afterwards. Point being - procedures.....

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