Oil Analysis Of A Jet Engine

[Cherrybomb]

I was just thinking of a time when I was looking out the window at the terminal at our jet they were checking out before we were to depart.Two techs drove up and took what I thought was an engine oil sample and drove off.They announced a slight delay.The techs came back and had an answer to the pilot.We left without delay or changing planes.My question does the Airline have an Oil Analysis Lab on site?We were in L.A.

 

[Astro14]

More of an aviation question. This may not have been an analysis.

Jet engines use oil constantly.

Might have been a simple top off and they had to run back to grab another couple quarts.

Moved to aviation.

 

[dnewton3]

Yes, UOAs are sometimes done on jet engines, but nowhere nearly that quick; they don't have ICP labs in airport facilities. This is not a typical commercial flight thing, though. I have a friend who retired from the F-35 engine program, and UOAs are used upon occasion. Certainly not on the tarmac as you experienced.

I would defer to Astro's answer. Much more likely that a low level warning went off, was a quick confirmation and top off.

 

[Cherrybomb]

Thanks,my wife asked me what was going on.I told her I thought they were double checking something,doesn't hurt to be careful no matter what equipment your using!

 

[jetman]

UOA was a part of all the mx programs for the jet equipment I flew. I don't recall how the sample was taken. I can count on 1 hand the number of times I had to have make-up oil added to a jet engine on an aircraft I was flying.

 

[tom slick]

Some reading:

https://www.stle.org/images/pdf/STLE_ORG/BOK/LS/Condition_Monitoring/Oil%20Analysis_Keeping%20Military%20Systems%20Running%20Smoothly_tlt%20article_July14.pdf

 

[ka9mnx]

Every time an F-16 landed an oil sample was taken. Before the engine was shut down. There was a sample port located behind a fuselage panel. We had an on-base sample lab. Never did get to see a sample result being a flight line knuckle dragger.

We never did flight line oil changes. They were done every 100 hours when the engine was pulled for inspection. Also, we rarely had to top off the oil. I only remember adding oil two times during my career. Ours were pushed by PW engines.

 

[Cujet]

Both our Gulfstream G600 and Pilatus PC12's Pratt & Whitney engines have annual Oil Analysis requirements. As does the transmission on our Eurocopter EC135. I have never seen the results. The tests are performed at the service center, and results are sent to Pratt for review.

Our Eurocopter transmission had a bad result one year, (too much moisture) and this drove the service center to remove the 2 drive gears (one each for the LH and RH engine) for corrosion inspection. As expected, there was one exceptionally minor (non critical) corrosion pit on each gear, visible only with a 10x loop, and just barely "feel-able" with a sharp needle. Replacement was not possible due to obsolete parts. Overhaul was required, $650K later, the transmission had all new gears. Utter nonsense.

 

[Astro14]

The question remains - what did the OP witness? A sample taken? A top off? A completely different maintenance action?

 

[john_pifer]

The CF34-8E and -10E (engines on the Embraers I maintain) frequently require top-off.

 

[oil pan 4]

Every time an F-16 landed an oil sample was taken. Before the engine was shut down. There was a sample port located behind a fuselage panel. We had an on-base sample lab. Never did get to see a sample result being a flight line knuckle dragger.

We never did flight line oil changes. They were done every 100 hours when the engine was pulled for inspection. Also, we rarely had to top off the oil. I only remember adding oil two times during my career. Ours were pushed by PW engines.

I did you weren't missing much. No addtives like in gasoline/diesel motor oil, so mostly zeros and single digits.

 

[edyvw]

This reminds me, maybe 2007-2009, flight ATL-LGW, 767-400. The engine pisses a good amount of oil suddenly from the left engine onto ground. Everyone on the left side saw it. Chatter: oh they will cancel flight; now we have to wait etc. 5-6 mechanics come, did something for like an hour, put everything together, start the engine, and off we go.
The atmosphere in the airplane? I think if one dropped a pin during the flight you could hear it

 

[Nuclear_42]

Most likely it was just an oil service. Oil samples are mostly performed on overnight during routine maintenance. Sometimes when there's engine issues you may need oil sample but that aircraft isn't flying anywhere anytime soon. Oil samples are way more common in the hydraulic systems on most commercial aircraft. Some aircraft engines are tight others are considered low margin engines. For real world usage a B737 or A320 family with CFM56 may hop around the USA all day and use 2-5 quarts an engine by the end of the night. Pratt's are mostly known for just barely sipping on oil. Most PW4000 on widebodies can fly several round trips across the pond and use 0 to 0.5 quarts an engine. It all depends on the engine. Most of the new PW 1500 family of engine can fly several weeks with zero usage. Back to the OP's original question they could of also been servicing one of the engines Integrated Drive Generator (IDG) most a/c require a fill to spill like a diff and hang a overfill bottle/ hose for a while to drain to proper full level. Servicing these units on a thru flight is way more common than sampling.

 

[FowVay]

Because jet engines in commercial use use the same lubricant to lubricate the mainline bearings (ball and roller) as they do to lubricate the gearboxes, the lubrication system is equipped with chip detectors which will alert in the cockpit of high ferrous loading in the fluid. Oil samples aren't very common on active aircraft.

Jet engines leak oil. They're constantly being topped off. They don't use seals and gaskets like you think of with a car engine. There are labyrinth seals around the bearings that essentially use pressurized air to blow the oil back into the lube circuit. They look like large threaded nuts with reverse threads that draw any errant oil backward and away from the outlet.

All of the output shafts on the accessory gearbox are sealed with carbon seals. These are just rings of highly polished, spring loaded carbon that rubs against a hardened flat surface and prevents fluid from passing. As the carbon seals wear, oil leakage increases.

It's hard to say what the observed maintenance event was. It could have been anything from a chip detector inspection, a fluid top-off, a top-off of the IDG (integrated drive generator - uses it's own lubrication source), or simply a stuck air valve that needed the assistance of a large mallet (common JT-8 persuasion method).

The big airlines employ metallurgists in their engineering departments that can take a miniscule sample from a chip detector and pinpoint the component that it came from. This isn't available at out-stations so unless you were flying out of the Lockheed skunk works they likely weren't taking an oil sample.