I cannot answer exactly. But a while ago, there was an article about the highest air time aircraft still flying with major airlines. The lead aircraft were a couple of 747s which had been crossing the Atlantic for years = w flights per day. But close behind them were some aircraft which had been doing "milk run" hops round the western states. And these had averaged nine flights per day over many years - i.e. including overhauls, holidays, repairs etc. So i would reckon that they did 11+ flights per day when working. Averaging these two, five to six flights per day seems reasonable.

This number is one that is really impossible to determine because there is so much of a difference between airlines and aircraft useage. Most major airlines have anywhere from four to six different types of aircraft in their fleet. Many smaller companies and codeshared regional partners may operate only one or two fleet types. Not to mention, we also have the cargo world to consider. With this much information, I don't see one particular equation that can accurately answer your question. I am going to spit out some of my estimations from my experience as an airline pilot. First, lets consider the the long-haul aircraft of the major US airlines. For kicks, lets make it an NWA 747-400. This plane operates international routes, usually from MSP and DTW to Japan. I think they also go to Amsterdam. This plane will perform only one flight per day, but it may be airborne for 18 or 20 hours a day. Then you have airlines that use their long haul planes for shorter high capacity routes. NWA does this with their A330s, as does Delta with the 767 and 777. So with these aircraft, the number could be only one or two flights a day, but is most likely higher and probably about three or four. Second, lets consider some middle sized fleet types, aircraft such as the 757, 737, MD-80's, A320. It's hard to group the 757 into either class because different airlines use it differently. These planes could perform eight or ten flights a day depending on range. A typical airline begins flying around 6 AM local time and will usually continue regular flights through 11 pm. After midnight, the only passenger departures tend to be trans-continental trans-timezone trans-dateline flights. So now lets focus on two planes from two airlines. First up is a Delta MD-88. After arriving in the hub late in the evening, it's first flight will be the early morning 6am departure. Its destination, anywhere from 2-5 hours away, will certainly be reached before noon. If you factor out the time, it could make nine two-hour flights, or four longer flights. Most of the time its in the middle. Our next plane is a Jetblue A-320. Jetblue flies its A320's on coast to coast flights, which really pushes the range if wind conditions aren't favorable. Jetbiue doesn't own any long haul aircraft so this flight is performed with their A320's, an atypical model for the route. So note a Jetblue A320 may have more time aloft but less flights per day than a United A320 or a Northwest A319. Then theres the load of small planes that congest airports, skies, and schedules. There are too many to list, but I'll give you the most common. If you've flown any fair amount of time, I'm sure you've rode in a Bombardier CRJ or a Saab 340. Other common models include Beechcraft 1900, DHC Dash-8, and the ATR-72 and ATR-42. Did I miss one? I'm sure I did. These planes run ridiculous numbers of short haul flights that usually alternate between hub and spoke. For instance, a Comair jet would probably keep flying from small airports to Cincinnati or Atlanta and then back again. These jets could easily perform fifteen or more flights in a working day. The higher number of flights are performed by the smaller planes since they typically travel the shortest distance at the highest frequency. Lastly, lets consider the cargo world briefly. Cargo companies operate freighter variants of just about every aircraft I've mentioned. Some cargo companies favor back-of-the-clock rotations, whereas others operate flights 24/7 throughout the world. A cargo 747 may be on the ground only to load and unload and could average more air time and more flights than a United 747. Also add to the equation, many airlines "convert" their passenger jets into cargo carriers for night time operation. So these jets may be working all day long as well. As you can see, we could average all these numbers together and come up with roughly six or seven flights. This doesn't accurately depict how our planes are working. I really see the only way to figure is to look at planes and airlines individually. I'll tell you this though, our planes get their fair share of usage and will be flying whenever its profitable to the company.