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Plane Answers: Takeoff speeds, weights and lavatory drains
We're combining five questions that were recently submitted for Plane Answers. We'll look into who foots the hotel bill for a crew's layover, what is the typical speed and weight at takeoff, how pilots line up with a runway visually and where does that lavatory sink water go inflight?When pilots layover for a night before returning home, who picks up the bill?
The airline picks up the tab for each crewmember's hotel room. Meals are up to the employee, although often there's a small per diem of about $2 an hour that's paid by the company to cover these expenses.
I've always wondered what's the ideal speed for a plane like a 737 to takeoff.
The takeoff speed is based on the weight of the airplane which varies. But you can think of it as a speed between 135 and 155 knots or so. Add 15% to convert knots to m.p.h. and you'll have a liftoff speed of around 155 to 178 m.p.h.
What is the maximum weight that the average passenger plane (737,757 etc.) can carry and be able to takeoff and remain airborne? As a frequent flyer, I become concerned when I observe a number of 300 pound passengers boarding; and then there's the cargo below. On occasion, I have been on a plane where the weight load was so light, passengers were asked to shift around to balance the plane weight. Does the opposite ever occur?
All U.S. airlines use an average passenger weight of 190 to 195 pounds depending on the time of year. In the FAA's mind, people in the winter either put on weight after the holidays, or they just wear more clothing. The load planning computer is able to keep the weight distribution spread out evenly through the cabin for balance purposes. The cargo is weighed before it's loaded on to the aircraft so we know that number to the exact pound.
All of this data is totaled and sent back to the pilots who make sure that the actual weight is below the maximum allowed either structurally by the airplane's manufacturer, or below the maximum that the runway will allow based on the airplane's performance and the outside temperature. As an example, a 757's maximum takeoff weight, assuming it's not limited by a shorter runway, is 250,000 pounds. It's empty weight, without fuel or passengers, is around 130,000 pounds.
When flying the final approach visually, how do you line up the runway centerline visually?
It's not unlike lining up a car when turning onto a road. Controllers usually give us an intercept angle of no more than 45 degrees or so, and it's our job to join the imaginary extended centerline from the runway. Once on final, it's not hard to see if you're right or left of course. Small heading corrections using the ailerons to bank left or right and we're perfectly lined up. We also use any available navigation aids (GPS, ILS, or Localizer) to cross check our position.
This is kind of a goofy question but I always wonder about it when I use the restroom on a plane. Why is the drain stopper always closed? I notice that when I drain the water in the sink there's an "air" sound. Does it have to do with the air pressure in the plane?
The sink drain actually 'vents' out of a heated drain mast (to prevent it from freezing). If they left the plunger open, it would create a lot of noise, and use a tiny amount extra bleed air to pressurize the airplane, which I imagine would cause a small decrease in fuel economy.
I took this video that shows a 777 inflight when someone is draining the sink. Take a look--It's at the 1:14 point:
Have you ever been curious about what goes on at the pointy end of an airplane? Ask Kent and maybe he'll use your question for next Friday's Plane Answers feature.
All of this data is totaled and sent back to the pilots who make sure that the actual weight is below the maximum allowed either structurally by the airplane's manufacturer, or below the maximum that the runway will allow based on the airplane's performance and the outside temperature. As an example, a 757's maximum takeoff weight, assuming it's not limited by a shorter runway, is 250,000 pounds. It's empty weight, without fuel or passengers, is around 130,000 pounds.
When flying the final approach visually, how do you line up the runway centerline visually?
It's not unlike lining up a car when turning onto a road. Controllers usually give us an intercept angle of no more than 45 degrees or so, and it's our job to join the imaginary extended centerline from the runway. Once on final, it's not hard to see if you're right or left of course. Small heading corrections using the ailerons to bank left or right and we're perfectly lined up. We also use any available navigation aids (GPS, ILS, or Localizer) to cross check our position.
This is kind of a goofy question but I always wonder about it when I use the restroom on a plane. Why is the drain stopper always closed? I notice that when I drain the water in the sink there's an "air" sound. Does it have to do with the air pressure in the plane?
The sink drain actually 'vents' out of a heated drain mast (to prevent it from freezing). If they left the plunger open, it would create a lot of noise, and use a tiny amount extra bleed air to pressurize the airplane, which I imagine would cause a small decrease in fuel economy.
I took this video that shows a 777 inflight when someone is draining the sink. Take a look--It's at the 1:14 point:
Have you ever been curious about what goes on at the pointy end of an airplane? Ask Kent and maybe he'll use your question for next Friday's Plane Answers feature.
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Reader Comments (Page 1 of 1)
john May 16th 2008 10:59AM
As a heads up, it's 1:14 in when counting up, not down. There happens to be an aircraft on the video at 1:14 counting down and I replayed it again and again looking for something noticeable.
(It's at about :41 counting down)
eqd May 16th 2008 1:35PM
thanks so much for such a soothing video; the views mixed with the data displays covers most of my curiosities.
Cristella May 19th 2008 12:55AM
That classical music sounds like what UAL uses onboard.
I laughed about RAMP throwing you your H2O bottle.
(When I worked RAMP at IAD, I would've been sure to have tossed it to ya the first time.)
Anyway. Reading your posts and watching yer vids make me nostalgic for the airport.
SIGH. At least I got to walk on some airplane wings today. That made my day.
G'day
Greg Marino May 21st 2008 2:09AM
Sorry fellers...Not a lavatory/galley drain in action but indeed a fuel purge or surge valve doing it's natural act from an APU.
Hope i didn't ruin anyones day...
Greg
Kent Wien May 21st 2008 8:16AM
No sweat, Greg. If I'm wrong, I want to know about it.
But have you noticed the heated water drain masts that occasionally have water pouring from them on the ground (especially fun when you're doing the walk-around). Are you suggesting that this sink drain water is diverted and held inside while in flight?
Since the APU isn't running usually halfway across the pond, and the main tanks vent out close to the wingtips, I'm not sure I'm sold on the fuel purge.
If you feel ambitious, let me know what you find.
Thanks!
Kent
scott s. May 21st 2008 6:32PM
Unfortunately I got to pick up the hotel tab for some ATA crew -- $800 worth :(