Hello Avgeeks,

I just wanted to know what will happen if some one install the oil filler cap in a wrong manner or with a damaged O ring(that allows fluid leakage) or in the worst case, if the person forgets to install the cap and then the aircraft is released . For sure oil will leak out during the engine start and what I wanted to know is what will be the first WARNING/CAUTION triggered and when it will be triggered? I know that oil pressure indication in Engine System Display becomes amber below 80 PSI and turns red below 60 PSI. How much time will it take to drop the pressure below 60 PSI and will it occur during the engine starting, taxing, take-off run or in flight during the climb?

Regards,
Skywalker92

This should give you an idea. http://flytristar.tripod.com/article/art10.html

Most oil tanks have an anti siphon feature to hopefully lessen the chance of another total engine failure like the tristar incident. They still can lose oil so it is a big deal that the cap is properly installed. MD80 APU's oil caps have been improperly installed causing oil being sucked into the intake.

Every time I've seen this, and I've seen more times than I should of, it has resulted in an air turn back. Apparently, the oil does not begin to leak out the filler during ground operations.

Now, I will mention, that my experience on this has been CFM-56-2, JT9D & JT8 engines. I don't recall ever seeing it on the more modern engines.

mmo wrote:

This should give you an idea. http://flytristar.tripod.com/article/art10.html

It helped a lot mmo. Gave me an idea how worse it can be!

fr8mech wrote:

Every time I've seen this, and I've seen more times than I should of, it has resulted in an air turn back. Apparently, the oil does not begin to leak out the filler during ground operations.

Now, I will mention, that my experience on this has been CFM-56-2, JT9D & JT8 engines. I don't recall ever seeing it on the more modern engines.

Are you talking about a anti siphon valve or something like that??

Rolls Royce engines have a secondary flapper valve in the filler neck. I once received a B777 with Trent engine after an 11 hour flight from KUL to ARN., with the filler cap missing on arrival. We found it lying in the fan cowling and refitted it OK. NO oil uplift required. We rarely uplifted oil to the Trent on transit checks.
Also once a RB211-524 on a B767 arrived with the oil filler cap in the cowling, and again no oil uplift required. The V2500 has a similar flap in the filler neck.

skywalker92 wrote:

Are you talking about a anti siphon valve or something like that??

Not sure what you mean. I didn't specify any kind of component.

Are you asking why the oil doesn't leak out during ground operations? I've no idea, it may have to do with oil system compartment (tank, bearing) pressures. All I know, is that I've never heard of one do a block turn back for low oil qty/press resulting from a damaged o'ring or missing cap...always air turn back.

Picked up a 727-221ADV from Evergreen at Marana with the intention of ferrying it down to KMCO. About the time we leveled off the FE noticed that the oil quantity on #1 was going down slowly. Finally shut the engine down and diverted into KELP where some UPS mechanics helped us. Found the cap in the cowl as I recall? Back on the road fairly quick without any further issues.

Thank you all of experts for your valuable answers!

Can anybody explain about the anti-siphon mechanism fitted to the aircraft oil tanks. I went through many documents but unfortunately unable to find out anything related to aviation.

skywalker92 wrote:

Thank you all of experts for your valuable answers!

Can anybody explain about the anti-siphon mechanism fitted to the aircraft oil tanks. I went through many documents but unfortunately unable to find out anything related to aviation.

Siphoning by definition means xfer of fluid from a higher point (from the top level) to a lower point.

Oil tank installation on modern jet engines is generally done at a higher level relative to the consumers of oil. And ASV is present on the return line just upstream of the oil tank breaking the Siphoning effect. Even I'm curious to know exactly how it functions..

On the V2500 there is a simple metal flapper just inside the filler neck. Pouring oil in pushes the flapper up, and then it drops down and stops the oil returning.
On the RB211, there is a chamber in the oil filler neck that has a float in it.
In both engines, when the engine is running, breather pressure pushes the float/flap closed.
On the RB211-535 on the B757, the float regularly sticks in the closed position. But a very thin screwdriver pushed down the filler neck will dislodge it!, so you can service the oil.

StereoTechque wrote:

skywalker92 wrote:

Thank you all of experts for your valuable answers!

Can anybody explain about the anti-siphon mechanism fitted to the aircraft oil tanks. I went through many documents but unfortunately unable to find out anything related to aviation.

Siphoning by definition means xfer of fluid from a higher point (from the top level) to a lower point.

Oil tank installation on modern jet engines is generally done at a higher level relative to the consumers of oil. And ASV is present on the return line just upstream of the oil tank breaking the Siphoning effect. Even I'm curious to know exactly how it functions..

Tristarsteve wrote:

On the V2500 there is a simple metal flapper just inside the filler neck. Pouring oil in pushes the flapper up, and then it drops down and stops the oil returning.
On the RB211, there is a chamber in the oil filler neck that has a float in it.
In both engines, when the engine is running, breather pressure pushes the float/flap closed.
On the RB211-535 on the B757, the float regularly sticks in the closed position. But a very thin screwdriver pushed down the filler neck will dislodge it!, so you can service the oil.

What I thought was the anti-siphon mechanism and flapper mechanism is for the same purpose.
They are two different mechanisms that intended to serve different functions. ASV is to avoid flowing oil back to the users through the return line and flapper is to retain oil within in the tank without going out from the filler neck.

Dalmd88 wrote:

Most oil tanks have an anti siphon feature to hopefully lessen the chance of another total engine failure like the tristar incident. They still can lose oil so it is a big deal that the cap is properly installed. MD80 APU's oil caps have been improperly installed causing oil being sucked into the intake.

Engine oil entering the bleed system from any source is a major hazard we face. Pyrolyzed turbine oil fumes in the cabin is no bueno and causes health problems.

Off topic I know, but there are many articles out there on aerotoxic syndrome that are good reads.

A maintenance video about the GEnx oil servicing system, it shows how the flapper valve works.

https://www.youtube.com/watch?v=mlrVrwE8Ilc