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2.
In Aviation, the operation of an aircraft with all or many of it's extendable surfaces in their extended state, such as Flaps extended, Landing Gear down, Slats out, Spoilers out etc. This increases drag on the aircraft and can be used to slow the aircraft. When used during a standard landing will reqire a higher thrust setting than Flying Clean to maintain the same descent and speed profile, increasing noise and fuel burn.
1:By the time we intercepted the glide slope the captain had all the hangy bits out, Flying Dirty to get the speed down for landing.

Flying a Clean approach is better than Flying Dirty for Noise Abatement reasons, for that reason it is best to delay extention of the landing gear and flaps till late on finals to reduce noise.
by Trent S Hopkinson April 30, 2006
 
1.
The act of sharting on a plane while in the middle seat and not acknowledging the smell.
I was on a flight down to Miami and I swear to god the fat fuck sitting next to me was flying dirty. I threw up my grilled cod fish salad all over the back of the head rest.
by Matty L December 30, 2005