题目内容：
根据以下内容回答题Getting Air Traffic under Control
A) The shortest distance between two points is a straight line---unless you happen．to be traveling in an airplane．Commercial airliners around the world follow circuitous flight paths, waste time in holding patterns before landing and burn precious fuel taxiing (滑行．．Part of the blame can be placed on crowded airports and airspace, especially in heavily trafficked (交通繁忙的) areas like New York City．But delays and inefficiencies in air travel are due in large part to an outdated traffic-control system that still relies on slow, ground-based radar stations and repetitive voice communication．
B) "At this' point, we're still operating with technology that dates back to World War II," says Marion Blakey, president of the Aerospace Industries Association and a former head of the Federal Aviation Administration (FAA) ．"We’re sticking with cassette tapes when we should be moving to DVDs．"
C) It's bad enough that this air-traffic-control system has led to pitiful performance: nearly 25% of U．S．flights were late in 2008．But inefficiencies in the air and on the ground caused by the system also mean fuel wasted and carbon dioxide (CO2) emitted at the very time when the air-travel industry is coming under scrutiny (审查) for its role in climate change．
D) Though airlines contribute only about 2% of global carbon emissions, that figure is set to rise as air travel expands, especially in the developing world And for frequent travelers, flights can enlarge their personal carbon footprint (碳足迹)一a round-trip journey between New York City and London emits 1．5 metric tons of CO2 per passenger．"We're 2%, but we are a very visible 2%," says Paul Steele, who directs environmental initiatives for the International Air Transport Association (IATA) ．
E) As the world prepares for the next U．N．Climate Change Conference, known as COP15, in Copenhagen in December, the air-travel industry will be under increasing pressure to cut its emissions---or pay a carbon tax．Though next-generation jet biofuels (生物燃料) made from algae (海藻) or coconuts tend to get all the green hype (大肆宣传) , the best immediate opportunity for the industry to control carbon emissions will be through improving fuel efficiency--and the best way to do that is to pull the airtraffic-control system into the digital 21 st century through what the FAA has named NextGen．"The overall goal of NextGen is to increase capacity to meet demand while at the same time not growing carbon emissions," says Vicki Cox, the FAA's senior vice president for NextGen．
F) NextGen is the FAA's long-term plan to replace the current radar-based air-traffic-control system with one that operates using satellites and a global positioning system．(Europe is working on a similar upgrade with its Single European Sky initiative．． Instead of a radar system that updates the positions of planes every 12 seconds or so, NextGen will use satellite data to locate planes in real time, thanks to the Automatic Dependent Surveillance-Broadcast (ADS-B 广播式自动相关监视) system．Instead of relying on time-consuming voice communication with a control tower, pilots will instantly know the location, speed and direction of the planes around them．It's not unlike the GPS system you might use in your car--if your GPS could tell you what every other vehicle on the road was doing all the time．
G) "The new system gives pilots a heightened awareness of the airspace around them and helps controllers efficiently direct the tens of thousands of flights that crisscross (往返奔波) the country daily," says Steve Loranger, chief executive of ITT Corporation, which is developing the ADS-B system for the FAA)
H) A satellite-based system like NextGen will allow for tighter, more direct flight paths--more A to B instead of A to C to B. Every minute cut from a flight plan means less fuel and less carbon emissions．And with jet fuel costing about $1．75 per gallon (46 cents per liter．, that could save the airlines millions．
I) Much of those savings will come during approach (进场) and landing．Because the current system is less precise, controllers need to give planes plenty of room as they lock onto the runway, descending in a slow, stepped approach．NextGen will allow planes to make what is called a continuous-descent approach (CDA) , essentially letting them turn off their engines, saving tons of fuel and reducing pollutants．
J) At the airport in Louisville, Kentucky, where UPS has been experimenting with a satellite-based control system, the shipper has been able to use CDA for landings and maximize the number of planes in the air at any given time．UPS estimates that the system has helped save 250 to 465 pounds (110 to 210 kg) of fuel per flight．"Making engines more efficient isn't easy or cheap," says Bob Smith, chief technology officer of Honeywell Aerospace, whose SmartPath precision-landing system will be part of NextGen．"But improving air-traffic management can be done just by optimizing the technology we already have．"
K) The FAA says that by 2018, as NextGen spreads around the U．S．, the new system will reduce flight delays 35% to 40% and save almost a billion gallons of fuel．There should be safety benefits as well: in an ADS-B trial in Alaska, the accident rate for planes fell 47%．But the shift won't be cheap: the FAA estimates that NextGen will cost from $15 billion to $22 billion, with a comparable cost for airlines as they furnish their planes with new equipment．
L) And not every airline expert is convinced that NextGen will live up to the FAA's promises, especially given the agency's management history．Even with a more efficient control system, the most heavily trafficked corridors may remain crowded because of sheer lack of runway space．"The satellite-based system is great, but it should have been put in place much earlier," says Mike Boyd, an airline-industry consultant based in Colorado．"I guarantee you, NextGen will not fix the delay problem．"
M) Even if NextGen delivers impressive efficiency gains, the airline industry faces a long-term climate challenge．With global airline-passenger numbers expected to continuously rise in the future, efficiency improvements may barely compensate for overall growth．If the airline industry is really going to reduce carbon emissions--in September the IATA promised to cut emissions 50% from 2005 levels by 2050--it will need to scale up low-carbon biofuels．But aviation (航空工业) is well behind the automotive sector when it comes to feasible alternative fuels, and some environmentalists argue that the only sustainable solution is simply to fly less．"Efficiency isn't enough," says Richard Dyer, aviation campaigner for Friends of the Earth．"To go on raising emissions isn't acceptable．"
N) Still, while high-speed trains can reduce the need for some short-distance flights, it's difficult to imagine the aviation sector shrinking．Expect airlines to be big purchasers of greenhouse-gas offsets if the upper limit to a global carbon is mandated in Copenhagen, while research continues on alternative fuels．
O) However, modernizing an out-of-date air-traffic-control system makes sense even if the globe never warms another degree．"Ultimately, this is about a better travel experience over the long term," says John Kefaliotis, ITT's program manager for ADS-B. "We've all got better things to do than waste time--and everything else--in the air．"
Express trains for short trips are unlikely to stop the air travel industry from developing in the future．
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