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Propeller Low Oil warning light


mechanic80
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A FALSE low propeller oil warning light has caused many shutdowns in air. the culprit was oil level float indicator...Hydraulic used is 5606..and oil level float indicator part no is 519661...

do u guys get the same problem with the floats or there is another oil level float being used..please tell any other reliable float(s) that don't make a false warning.

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Those float switches are a craps shoot. Seen some last 20 years, seen others last a month. I've never seen a correlation between part numbers and failures. I just think it is a poor design, and nobody's cried loudly enough to the right people to get a redesign. Might be something to bring up at the next T56 user's conference. I would personally like a quantity indicator to replace a dummy light. That way the engineers can write up the props when they are a quart low every time they land so we don't have to check servicing all the time.

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  • 2 weeks later...
  • 2 weeks later...

man those pressure switches are always going bad, but just like a macaws panel. Its good until it breaks enough and you need to do a tcto that changes some system warning back into the way older-style aircraft have it...

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Any reason why lockheed havn't come up with a fix for this known problem? We have also being asking for years for a permanent fix for the doppler panel. Changing the paneloc fasteners when enough have gone bad takes a long time and keeps the aircraft out of service for a few days. A real pain when the doppler has been removed.

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  • 3 weeks later...

This issue is an active item and was briefed at the 2010 T56/Propeller Users Conference.

Inflight engine shutdowns due to propeller low oil level indications have been an issue for many years. The main causes are normally either incorrect propeller servicing or the propeller oil level indicator / float switch float sticking or shorting out.

I truly believe that if you check your oil levels while the hydraulic fluid is hot (within 30 minutes after shutdown) it will minimize the error of improper propeller servicing. If you wait hydraulic fluid bleeds back from the pressurized sump to the atmospheric sump which is why you have to run the auxilary feather motor to scavenge the oil back into the sump to check the oil.

For the sticky floats keeping the hydraulic fluid as clean as possible helps. The use of MIL-H-87257 in lieu of MIL-H-83282 is supposed to help. These two fluids are compatible and can be mixed together if necessary. MIL H-5606 has not been used in USAF C130 aircraft since the early 1980's.

For the shorting issue the USAF tech order is going to be changed to go back to putting sealing compound in the float switch cavity or using small rubber wire boots to prevent wires from shorting out against each other. In addition, there has been consideration of redesigning the pump housing assembly.

The other issue is that an inflight shutdown is not necessary if an aircrew encounters a low propeller oil indication unless there is a visible oil leak or a RPM fluctuation indication. But, we all know how that goes.

Hopefully, we will be able to get a handle on this through diligent maintenance, education and of course engineering efforts and redesign. I will not hold my breath on the latter.

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