Western727 From United States of America, joined Jan 2007, 784 posts, RR: 4 Posted (8 years 2 months 3 weeks 5 days 2 hours ago) and read 6895 times:
I came back home to MSP 2 nights ago on 31 Dec 06 and filmed the final approach/landing. Aircraft was a NW 753, N583NW, operating NW168 SEA-MSP. I am seated in 15A, the 2nd row aft of door 2, and am landing on 30L.
I was astonished at what appears to be the Nbr 1 engine ingesting FOD during this exciting night landing! Thank you to pal Jared for posting the video clip on Google video.
Shared my concerns with the FA who contacted the cockpit crew that later summoned me to show them the clip--talk about a great excuse to go to the office! The gentlemanly crew seemed appreciative and professional about it and I left.
A fellow in 16F then indicated that Nbr. 2 had an event as well, and the clip indeed shows the nacelle of Nbr. 1 being illuminated. This suggests that Nbr. 2 had a more significant ingestion event, whereas the sparks appeared to be contained within Nbr. 1.
Question: why did this happen?
Possible clue: snow had stopped falling about a couple of hours beforehand, and if you watch carefully you will notice deicing agent being kicked up by the reversers. So, what was the FOD? Fragments kicked up by the plows as they roared across the rwy surface? Any info would be greatly appreciated.
Dl757md From United States of America, joined May 2004, 1562 posts, RR: 16
Reply 4, posted (8 years 2 months 3 weeks 4 days 17 hours ago) and read 6749 times:
What you see in the video are sparks created by static electricity. This is totally normal and is not FOD. When the fan tips go supersonic you'll see this phenomena at night. It's also why it was seen in both engines.
Jerald01 From United States of America, joined Oct 2006, 161 posts, RR: 2
Reply 5, posted (8 years 2 months 3 weeks 4 days 11 hours ago) and read 6609 times:
I would agree that what is shown in the video is static electricity sparking. You will note that it is only visible after the aircraft has touched down, lost some forward speed, and the thrust reversers have been activated.
You would not expect to see it during normal flight, normal speed, normal thrust reverser positioning because the sparks would be so quickly sucked toward the back of the fan housing area that they would not be visible to anyone inside the aircraft. With the aircraft slowed down after touchdown, and with the thrust reversers deployed, the airflow through the engine is altered significantly and the sparks remain in the vicinity of the fan blades for a longer period of time, hence they are more visible.
Once the reversers are returned to their normal position the airflow resumes it's normal velocity and the sparks disappear once more (also, the throttle-down of the engines brings the blade tips back under supersonic tip speed and that helps decay the tendency for static electricity to form in the first place.)
"There may be old pilots, and there may be bold pilots, but there are darn few green cows"
Western727 From United States of America, joined Jan 2007, 784 posts, RR: 4
Reply 6, posted (8 years 2 months 3 weeks 4 days 10 hours ago) and read 6584 times:
Quoting Dl757md (Reply 4): What you see in the video are sparks created by static electricity.
Quoting Jerald01 (Reply 5): I would agree that what is shown in the video is static electricity sparking.
Fascinating. That does make sense, and what Jerald01 describes explains why I saw nothing in the PW2040 during takeoff from SEA and during climbout/cruise/final. Further, none of the passengers appeared to notice abnormal sounds during reverse thrust, which (I suppose) might have occurred had it been FOD ingestion. Thank you both.
May I also suggest that in Minnesota winters, conditions (cold, dry air) are prime for static electricy generation. A real pain in the butt while wearing trousers.
You're both right, just a matter of context. FOD causes FOD. If it's on the ground or in the air and could be a problem with an aircraft, it is Foreign Objects and Debris. Once it goes thru an engine or punctures a tire it becomes Foreign Object Damage.
A good friend will get you out of jail. A real friend will be there with you saying, "Damn that was fun!"
Quoting CCA (Reply 1):
It looks like the runway is wet and possibly dirt from the surrounding area has made onto the runway prior to a possible storm and downpour
Then blown forward by the reversers and sucked into the intake. I heard this happens when you apply reverse thrust below a certain speed. I.E that once the plane is going slow enough that the debris that are blown up by the thrust reversers catches up to and passes the front of the engine.
Avioniker From United States of America, joined Dec 2001, 1109 posts, RR: 11
Reply 11, posted (8 years 2 months 3 weeks 4 days 6 hours ago) and read 6438 times:
It is indeed static discharge. I've never seen it so dense on a wet runway but...
One explanation for it might be that the IGV's and stators behind the fan on those engines are situated in such a way that they cause an unusually high pressure/temp drop which makes it (or used to make it) necessary to advance the throttles during extended periods at idle in cold temps to blow the ice out of there so the engines wouldn't get FODded when spooled up for TO. Ah who knows?
In Phoenix on warm dusty nights running CFM's at power can cause discharges from the fan to the ground in front of the engine. That's really impressive. Techs doing leak checks stay the heck away from the front by a wider margin than normal. (not quite so impressive as the night the blue tarp went through the fan, but. . .)
One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533
Ex52tech From United States of America, joined Dec 2006, 559 posts, RR: 1
Reply 12, posted (8 years 2 months 3 weeks 4 days 3 hours ago) and read 6375 times:
You will see sparks forming like that during high power engine runs while the reverser is stowed. I have witnessed it many times while on a run-up pad, and you sometimes will see the sparks forming in the N1 compressor inlet (behind the fan), it looks pretty cool, but doesn't hurt anything.
"Saddest thing I ever witnessed....an airplane being scrapped"