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Originally Posted by N121PP
Is the landing gear ever lowered before the flaps are extended? If so, any reason for doing so?
Most pilots are reluctant to add unnecessary drag and like to keep the airframe "clean." The normal routine during an approach is to lower some amount of flaps as the airplane slows (often in response to an ATC request while in the airport traffic area) and only lower the gear when established on final approach and starting down the glidepath. This is usually 5-8 miles out.
For example, flying into JFK in a 757 we might have a minimum clean speed of 215 kts. ("Clean" means having no flaps or gear hanging out; i.e. the airframe is "clean." The opposite of this is "dirty", which means to have flaps and/or gear extended. You'll sometimes hear the phrases "clean up the plane", i.e. raise gear and flaps, or "dirty up the plane", which means to extend flaps and/or gear.) Our clean speed varies according to the weight of the plane and our FMS gives us the clean speed for our current weight. During approach, we set a small plastic "bug" on our airspeed indicator to mark this speed.
This means that we need to select Flaps 1° (this includes leading edge spoilers) if we want to fly at, say 210 kts (below clean speed in this example). This requirement has to do with the maneuvering speed of the plane. The plane can actually fly slower than 210 kts in the clean configuration (i.e. it won't stall), but any abrupt maneuvering that increases g-load could put us closer to stall. To mitigate this, we put out flaps which provides a larger buffer between us and stall speed.
In this example, with a calculated clean speed of 215 kts, we would need to put out Flaps 1° before slowing to this speed. But we can't use this flap setting until we're below 240 kts due to limitations on the flaps (i.e. above this speed, having the flaps down could cause some structural damage).
So the procedure is to select "Flaps one" somewhere between 240 and 215 kts. The next flap setting in the B-757 is 5°. The maximum speed for flaps 5 is 220 kts and we need to use this setting prior to clean speed minus 20 kts (which would be 195 kts in this example). There are similar considerations for the rest of the flap settings (15°, 20°, 25° and 30°).
Normally, the landing gear is selected sometime after we already have the flaps out to 5°, and sometimes we might even have the flaps at 15 or 20° before putting the gear down. But we always have the gear out before going beyond flaps 20 and the plane will give us an aural alert if we select flaps 25 before the gear is down and locked.
Now, after this long-winded dissertation on use of flaps, I can get to your question, which was "Is the landing gear ever lowered before the flaps are extended?" The answer is yes, but not often. I've probably done this only two or three times in a year. The reason for doing this sometimes is that the landing gear is an extremely effective speed brake and it's helpful that the landing gear has a max speed that's higher than the flaps. I think the gear can be used below 280 kts (the limitation is printed right by the gear handle), though we normally don't use it until we're slower than 200 kts. So if we find ourselves in a situation where we're too fast, or we need to dramatically increase our descent rate, selecting "gear down" can be a big help.
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It's probably just my imagination, but whenever I'm on the B757, its seems the takeoff roll is always shorter than in an MD-80. For example, I was on a full B757 and watched the markers and it took us roughly 3000 ft to rotate. The same full MD-80 took over 6000 ft. I may be off on the numbers and the conditions I'm sure where different, but someone once told me the B757's engines were "over-engineered" and are much more powerful than needed for the air frame. Sounds strange to me. Thoughts?
I don't think the difference is quite as much you're saying here, but it's true that the 757 has a higher power-to-weight ratio than many planes. That's one of the things that pilots love about the plane. While many other planes really become a dog at some point during the climb, clawing for those last few thousand feet, the 757 gets right up to cruise altitude with good performance the entire way.
I flew the MD-88 for years off of short runways (LGA: 7000'; DCA: 6869' before they extended it to 7000' a few years ago) and I don't remember getting down to the last thousand feet before getting airborne...the pucker factor starts to go up when you see the end of the runway coming up.