Darkly handsome, powerfully built, with combed-back hair in the style of the Fonz, the 40-year-old Zaccheo is also known as One-a-Day Zack for his frequent showdowns with other controllers. One colleague remembers the first time he saw One-a-Day: Zack was standing at his scope and yelling at a controller through his headset, "I'm gonna come over there, and then I'm gonna rip your lungs out!" But Zack, who did four years in the Navy before joining the F.A.A. in 1982, has accepted the challenge of self-improvement. "They made a rule you can't threaten another controller on the job," he says, bringing his fingers to his enormous chest. "Somebody like me, I had to change my operating way."

So far, the day has been sunny and mild around the New York region, but if anything the good weather has increased the traffic as the skies, already filled with back-to-back holiday flights, have become further clogged with "pleasure" pilots hoping to catch what may be the last good flying day of the year. Just after 3 P.M., Zack straps on his headset (or helmet, as the ex-military jocks call them), leans over the controller he will replace and listens as his colleague swiftly briefs him on the status of each plane on his scope. Because traffic is already heavy, the transfer occurs like a baton pass during a relay race, with Zack fairly jogging in place and then, still settling himself into his chair, emitting a tongue-twisting barrage of instructions to catch up for lost time: "Continental 301, eight miles from the outer marker, turn right heading 190, maintain 2,500 feet until established on the localizer, cleared I.L.S. runway 22 left approach."

Between issuing commands, Zack listens for each pilot to read back his instructions; asks a nearby controller if he can "borrow" some airspace for one of his planes; coordinates, over an outside telephone line, a tricky landing with the Newark tower, and writes down on individual "flight strips" every altitude and speed he gives to pilots. If Zack's radar goes down -- or he goes down the pipes -- those flight strips are the only way a supervisor, running to bail him out, can figure out which way his planes are headed.

Some controllers, ever fearful of going down the pipes, work only the minimum number of planes before asking their supervisor to hold new traffic. But Zack won't surrender. "I can take it! I can take it!" he yells as the planes stream onto his scope until the supervisor himself decides he's had enough. "Around here, I'm the Man," Zack says, punching his chest. "That's 'cause I'm not afraid of the airplanes. I always tell my supervisor, 'Put me where the action is.' 'Cause I want it. I want the traffic." Zack emits a percussive, high-pitched laugh. "We call the weak controllers the Papier-Maches. You know -- it used to be, guys were made of steel, but now they're made of papier-mache. Ha, ha!"

Zack turns back to his scope, and once again it's filling with jets: five from the south, two from the west, three from the north -- all heading toward Newark International. Of the sector's six radar scopes -- one for Newark arrivals, one for departures, two for the satellite airports and two that feed planes to the other scopes -- the Newark final scope is the hardest, for the goal is to take those 10 jets, arriving from wildly divergent angles, and actually point them at each other so they will converge in a tight line leading to the runway. According to F.A.A. rules, the Tracon's controllers must keep jets separated by at least three miles laterally or 1,000 feet vertically. But because the skies are always filled to capacity, the F.A.A. allows controllers to reduce the space between two planes if one pilot confirms he has the other plane in sight.

That's what distinguishes the Men of Steel from the Papier-Maches. A weak controller, spotting two jets six miles apart, won't agonize over the unused airspace. But Zack sees that gap as a chance to push more traffic, looks for a third jet to slide between the two and then -- by using visual separation -- packs the jets even closer in the sky. On the final descent toward Newark, planes travel one mile every 11 seconds; Zack can't hesitate or miss a turn, or the entire chain of jets will collapse. But he doesn't. Like a shrewd billiards player, Zack calculates the angles that will transform his 10 random jets into a 30-mile chain, then commands the pilots with unassailable authority. "Pilots are like dogs," he says under his breath. "They can smell fear in your voice. But if you sound confident, they'll do whatever you tell them to do." He pauses to appreciate his handiwork -- 10 blips, each three miles apart, heading like geese toward the Newark runway. "Now that's crisp vectoring! Make a plan, make it work, but don't think about the plan. Real educated people, somebody with real smarts, can't do this because they're always pondering. I don't have time for that." A criminal smile lights up his face. "With this job, you will get yourself cornered. The question is: How good are you at getting yourself out?

"The key is picturing the scope in three dimensions," he goes on. "Can you picture these blips as airplanes, all making the turn in the sky? If you can't picture it, you can't do the job." Zack points to one blip. "Look -- that's a 737. It's got two engines, two pilots, four attendants and probably 150 passengers reading the paper and drinking their Bloody Marys. You can actually feel the power of one of those airplanes, and you know what it'll look like if it crashes." Zack appraises the scope, filling once again with blips. "Jeez, airplanes everywhere -- two here, four there -- you gotta love it!"