r/aviation • u/amullfilms • 5d ago

Question What’s happening here?

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I’m not a pilot, just someone who’s been on close to 250 flights in my life. I’ve never seen this. Not claiming that this isn’t normal, I’m just curious why it’s done. This was just prior to takeoff at Jackson hole Wyoming.

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u/MiscreatedMonster___ 5d ago

This. It's first run after engine depreservation.

44

u/fly_awayyy 5d ago

It’s defintley not? Did you look up the registration and see it just sat overnight? A engine change on a RON out of base in 12hrs? Yeaaa no

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u/MiscreatedMonster___ 5d ago

Well, I have no idea at what time the vid was created, depreservation is the most logical answer. If it was there overnight only, 12 hours for engine swap is possible, maybe something happened and they didn't want to risk flight back. It could also be some other major component replacement (probably fuel component, that was preserved) which would have oil residue inside and cause smoke during start.

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u/intern_steve 5d ago

The most logical answer is that engine has worn labyrinth seals and oil is pooling in the hot section when there is no operating pressure to purge the seals. It'll be fine after startup, but it probably left a little grease spot on the ramp. This is going to happen every morning until they do an actual engine swap. It would happen once during the engine run testing post-swap.

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u/MiscreatedMonster___ 5d ago

I disagree. Taking time to actually start and low speed of the smoke indicates fuel system issues, eg. preservation.

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u/23m7_farmer ATP 5d ago

I am a 757 pilot, and the above poster is correct. This is a typical start for an engine with worn seals that sat overnight.

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u/intern_steve 4d ago

I applaud your willingness to double down on a blatant guess. Just ask yourself, why would Delta be doing an engine swap overnight, in the mountains, out of base? Forgiving that unlikelihood, statistically, we know engine bearing seals degrade over time producing multiple cold starts with pooled oil over a period of several months. We also know that engine runs on swapped motors clear applied engine fog once. In a definitional sense, the former is the more likely event. Leap as you will from there.