I was recently on a flight - the aircraft was a 737-800 - where I had a good view of the front of the left engine. The situation in the title did not occur, but it seemed awfully close.

After pushback, while the plane was waiting to start taxiing under its own power, I looked at the tiny waterspouts sporadically forming in front of the engine (it'd been raining all morning). And then I noticed a piece of caulk (or tar or whatever it is) was being lifted from between two concrete slabs of pavement.

The strip of caulk looked like it might have been 30cm long and 2cm in "diameter" (it had a more rectangular cross-section, but you get the idea). It was still attached at one end, but it was directly in front of the engine, and its free end was being "tugged" up toward the intake in fits and starts, sometimes standing straight up.

Thankfully, it never went further than that. I considered alerting the cabin crew, but everyone was already buckled in, and I really didn't want to cry wolf on a airplane (so to speak). Still, I was very much considering it just as the plane started moving without any further drama.

As soon as we were in the air, I discreetly told a flight attendant, and she told the pilots. She came back a little later asking for a few specifics, so I imagine the pilots were radioing the airport we'd just left.

And I got a free cup of coffee (yay...)

My question is: What might have happened if that piece of debris had come loose and been ingested by the engine?

I wouldn't expect it to be catastrophic or anything (which is also why I hesitated in informing anyone while it was going on), but I would expect it to be expensive. I.e. it might ground the plane, at least for a short while. Probably some flames out the back. Maybe it'd even mess up the engine by gumming up the works.

I was never worried for my safety or anyone else's. I know engines are tough, and can eat all manner of crap. And even if they tear themselves apart in the process, they contain it. Not that I'd expect something like that happening at low power anyway.

But really: I don't know for sure what would happen. I'm not a pilot or mechanic, just a nerd with a nerd's interest in engines and airplanes.

Edit: Checking the airline's website, it seems the engine would be a CFM 56-7B26, if that's at all relevant.

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    $\begingroup$ FWIW, had I been the captain of the flight, and the flight attendant had relayed to me what you said, I would have made an maintenance log entry that a passenger reportedly witnessed some FOD (foreign object debris) enter the #1 engine. That would have caused maintenance to take a quick look at the fan for possible damage. Depending on where I was in the world, I might also have while still in flight asked ATC to relay to the airport the possibility of FOD on the taxiway/runway. $\endgroup$ – Terry Jan 28 '16 at 21:23
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    $\begingroup$ @Terry So, to make sure a good inspection is done, you'd make it sound like I exaggerated? :) Cool with me, actually. Out of curiosity, can you elaborate on the "depending on where I was in the world" part? Would there be a reason to not tell ATC that someone might've seen some FOD? Again, just curious. $\endgroup$ – Flambino Jan 28 '16 at 22:11
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    $\begingroup$ I would neither exaggerate or downplay. Actually in my ancient world (retired in 1999), it would be the flight engineer that made the log entry, which he would sign, and the captain would review and sign. Any FOD mention would cause a look at the fan blades. Also, looking at the leading edge of fan blades was part of the the f.e.'s regular pre-flight, and every once in a while they would remark that an engine's fan was showing wear. By that they meant there were places a fan blade leading edge had been smoothed by maintenance. $\endgroup$ – Terry Jan 29 '16 at 1:34
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    $\begingroup$ @Terry Gotcha. It'd make sense to me if there was a bit of exaggeration/rephrasing, though. I only saw something almost enter engine #1 - not something that did enter engine #1. But I'd understand why it'd be beneficial to treat it as the latter, just in case. $\endgroup$ – Flambino Jan 29 '16 at 13:01

Well, not an expert on caulking, but birds go through plane engines sometimes, and they seem to be roughly the same consistency overall (if you account for the dirt and pebbles that are sometimes stuck to caulking.) So it possible they would have the same effect.

If you're curious about what would happen if it's like a birdstrike you can take a look at the Miracle on the Hudson, or this 757 that had a birdstrike on takeoff. With the 757, they simply went around and landed the plane since they only lost one engine...

Anyway, you folks were still on the ground, so all that would have happened is that the engine would have flamed out while you were sitting there and the plane would need to be taken to service to check for damage. It would have been annoying to have to switch planes, but it wouldn't have been dangerous to any of the passengers or crew.

Nice of them to give you a free coffee though, considering you may have saved them a few hundred thousand in engine repairs if the next jet in that slot had managed to actually ingest the caulking ;).

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    $\begingroup$ Thanks for the answer. I do know what a birdstrike can do, but yes: We were on the ground, idling. And my bet would be that that strip of caulk would be less dangerous than a bird, even at take-off power. Nice to know I was right to not worry about catastrophic engine failure and such. By the way, the jet by the gate next to mine was a Dreamliner with engines that looked like they could suck a house of its foundation. I don't know if it would/did pass over the same spot of pavement after pushback, but... well. I'd like to think that airline owes me a coffee too :) $\endgroup$ – Flambino Jan 27 '16 at 20:29
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    $\begingroup$ @Flambino To be fair, the strip may have had stones or wood stuck to it, and small stones can cause all sorts of problems with engines too so... But yeah, I'd probably go collecting on a cup from the 787 as well, work it for as much free coffee as you can ;) $\endgroup$ – Jay Carr Jan 27 '16 at 21:06
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    $\begingroup$ Yeah, I did think that stones or sand in the caulk would be worse than the strip itself - but still pose no danger to anything except the engine. Really, a lot of thoughts went through my mind including everything I know about jet engines, compressor stages, and the effects of debris going into them. Again, layman's knowledge of the subject, but it all made me worry less, not more. The engineer in me trusts those machines. But yeah, if anyone knows someone working Qatar 787s, know that I like a bit of sugar with my coffee, but I'll settle for black ;) $\endgroup$ – Flambino Jan 27 '16 at 21:29
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    $\begingroup$ Also, for whatever it's worth, many bird ingestions don't actually destroy the engine, like the ones in the given examples did. Those were more exceptions than the rule (the double engine failure in the U.S. Airways flight was extremely rare... and is a good reason to remember not to fly through a flock of Canadian Geese.) Bird strikes on engines are actually pretty common. I've had a flight where we had to change planes right before boarding was about to start because the pilots found that one of the engines had taken a bird strike on the previous flight when they were doing the walk-around. $\endgroup$ – reirab Jan 28 '16 at 21:28
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    $\begingroup$ @reirab "Canada geese" is the term, I believe. They're not necessarily canucks ;) Canadian geese would be too polite to cause a double engine failure, I'm sure $\endgroup$ – Flambino Jan 28 '16 at 22:21

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