A flight attendant had to fill in for a sick co-pilot on a Chicago-bound American Airlines flight Monday. If she had been alone in the cockpit, could someone on the ground have coached her through the landing, as in the movies?

It’s possible, but it would be extremely challenging. Without expert guidance, a panicky, untrained person could easily doom an aircraft with one wrong move. The cockpit of a commercial jet is littered with buttons, switches, screens, and control levers, some of which can lead to a crash in fairly short order when engaged at the wrong moment—or not engaged at the right moment. (The American Airlines flight attendant had flown a single-engine recreational aircraft 20 years ago, but that experience would have been of no use in this situation.) Nevertheless, if a calm passenger stepped into the captain’s seat and quickly managed to establish radio contact, it’s possible that someone on the ground with experience flying that particular model of jet could coach her to a clumsy landing.

The chance of success would depend on the circumstances. If both the pilot and co-pilot collapsed during takeoff or landing, a crash would be inevitable. It’s unlikely that the autopilot would be engaged during these maneuvers, and a flight attendant wouldn’t have any time to figure out how to hand-fly the plane. If the pilots went down in mid-flight with the autopilot engaged, the flight attendant would have a chance to ponder her next move: operating the radio.

Sounds easy, right? It isn’t. Pilots usually activate the boom mic on their headset by pressing a button on the back of the yoke (i.e., the plane’s steering wheel). But that button happens to be right next to the one that disengages the autopilot. Unless she had some experience with the cockpit radio, the novice would be better off trying the CB-radio-style handset. She would have to make sure the radio was set to broadcast outside the plane, rather than to the cabin or flight crew. If this worked out, there’s still a good chance the radio would be set to the wrong frequency, since pilots have to change every few minutes as they fly between air-traffic control districts. If the flight attendant managed to get a response to her Mayday call, she would be switched to the emergency frequency and connected to someone familiar with the plane’s control panel.

This person would instruct the flight attendant how to operate the autopilot, which isn’t quite as “auto” as a panicked novice might hope. It can’t land the plane without significant human input on changes in altitude and airspeed, and when to deploy the landing gear. Autopilots also leave the control of the wing flaps to the real-life pilots. (These must be extended in stages during the plane’s descent, to control lift.) All this means that whoever’s flying will be pressing buttons and turning dials pretty regularly until the aircraft drops below 1,500 feet. For the coach on the ground, the biggest challenge would be to convey via radio exactly which buttons and dials the flight attendant should manipulate.

The autopilot can handle the final descent, but a human might have to take control when the wheels touch down, by using the rudder pedals to steady the plane’s lateral movement. (The plane’s rollout system, designed to center the plane on the runway, sometimes needs a little help.) * This takes some practice, and there’s a reasonable chance that a sloppily-landed plane will skid out of control. That wouldn’t mean certain death, but fatalities and injuries are common when a plane slides off the pavement.

Fortunately, the only time a passenger has ever had to land a commercial jetliner was on a Hollywood soundstage. (The scenario has played out several times in the real world with tiny private planes, which are far easier to fly.) Airline captains have to undergo physicals every six months to prove their airworthiness. Of course, that wouldn’t help them if they ate tainted fish for dinner.

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Explainer thanks Les Dorr of the FAA and Patrick Smith, author of AskThePilot.com.

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Correction, June 17, 2010: This article originally stated that the pilot always has to use the rudder pedals to keep the plane on the runway. In fact, commercial airliners are equipped with a system to handle that job, although it sometimes requires some human intervention. (Return to the corrected sentence.)