A number of questions came in this week relating to takeoffs and landings, and a few issues that passengers worry about. So, we’ll continue on last week’s Takeoff and Landing theme.
Eric asks this timely question:
I would like to know what purpose the wing flaps play in take off and in landing?
With the recent Spanair accident in Madrid, some reporters focused on whether or not the MD-80’s flaps and slats were extended for takeoff.
These devices, moveable panels on the back and front of the wings respectively, are used only for takeoff and landing.
A jet’s wing is designed to be at it’s most efficient while at altitude and at it’s design cruise speed. This same wing isn’t capable of flying slow enough to takeoff or land on a conventional runway.
So flaps were designed for most airplanes to increase the lift a wing can carry at these slower speeds. When the flaps are extended, the wing is essentially converted from a high-speed wing to a slow-speed wing, depending on the flap setting used.
Flaps are gradually extended based on the speed of the airplane, with the first set of flaps on an airliner usually extended when the airplane is slower than 250 knots.
For takeoff, the optimum flap setting is based mostly on the runway length. Using just the right flap setting improves efficiency and performance once the airplane is in the air. Airlines have a system for calculating that flap setting either manually in the cockpit, or through a computer print out sent via ACARS.
On the MD-80, the leading edge slats are extended and the trailing edge flaps are ‘dialed in’ to the required setting.
Taking off without any flaps extended isn’t possible for most airliners without an exceedingly long runway, maximum power set and some very careful handling by the pilot. This is why there are multiple checks prior to take off to ensure the flaps are properly set.
There’s also a loud warning horn that sounds if the throttles are advanced with the flaps not in the proper configuration for take off. Checklists, however, will likely prevent the need for the horn.
The last accident where flaps weren’t set for takeoff was a Northwest flight 255 departing from Detroit in 1987, and this might be why there has been some initial focus on the flaps as a possible cause behind last week’s Spanair crash.
It’ll be interesting to hear what happened to the Spanair flight, so we can learn from the accident. The media is rarely held accountable for the mistakes made when speculating as to a reason for an accident.
I wouldn’t hesitate to fly on an MD-80. In fact, it’s listed as the second safest airplane flying.
Dave brings up a takeoff related question:
I’m curious, if you have a severe engine problem after liftoff that you can’t recover from or go around, what is the procedure for finding a place to put down. I understand if there is a nice plowed field ahead that’s great, but what if you are in a congested area?
All airliners are required to demonstrate that they can safely operate after an engine failure at liftoff.
I suppose it’s conceivable that a dual-engine failure could happen (on a twin-engine aircraft), so in that case, the only possibility would be to land straight ahead, doing everything you can to avoid any congested areas.
Finally, Sandra asks a three-part question:
I am what I describe as a nervous flyer… I am curious to know why does the prep for landing alway feels so, well ominous?
Lights dimmed, and unless this is just my imagination…there is just something so dooming…
Some airlines require the lights to be dimmed to improve a flight attendant’s ability to see outside when on the ground. Part of their job is to assess the situation on the ground if an engine fire or other such problem were to occur and an evacuation became necessary.
Interestingly, not all airlines have that procedure.
Also, the last time I flew southwest, on final approach, the wings seemed to be dipping from left to right, right to left.
And then I flew the same airline again, and that landing was so smooth–I actually had to look out of the window to see that we were on the ground.
Ahh, yes. You’ve noticed the differences in pilot technique. Some pilots do get into what we call ‘pilot-induced oscillations,’ which are a bit annoying. You’ve had experiences with a bus driver or cab driver who wasn’t very smooth before, I’m sure. Well, you’ve just found the pilot equivalent of that driver.
What amount is attributable to the skill of the pilot, and how good a pilot is, with respect to landings??
Landings are a bit like golf. (Although I don’t play, I just had to take a swing at that analogy-no pun)
You can really feel like you have the landings perfected in a particular airplane, and then, sure enough, you can’t get a good one for weeks at a time. It’s kind of rare though to have an earth shatteringly hard landing after you’ve been flying a particular airplane for more than 6 months.
Do you have a question about something related to the pointy end of an airplane? Ask Kent and maybe he’ll use it for next Friday’s Plane Answers feature.