United Airlines has had a turbulent time in recent years going into Chapter 11 bankruptcy protection, though things are now on the up. Pictured is a Boeing 777, one of 52 of the type it operates.

Seven regional carriers - Shuttle America, Gojet Airlines, Mesa Airlines, Sky West Airlines,Trans States Airlines, Colgan Air and Chautauqua Airlines - currently operate under the United Express brand. Pictured is an Embraer ERJ-145 of Chautauqua Airlines.

In its time United has been a launch customer for several significant types including the Boeing 767-200, the last of which was phased out in 2005. The airline still operates 35 -300ERs, which fly in three-class 193-seat configuration on trans-Atlantic, Latin American and some transcontinental routes. Some of these aircraft have a 244-seat two-class configuration and are used on domestic services and routes between the mainland and Hawaii.

United's low-cost subsidiary Ted was launched in 2004, while the airline was still in Chapter 11 bankruptcy protection. It operates a fleet of 58 Airbus A320-200s to destinations within the US and Mexico. Other major carriers have launched low-fare subsidiaries - notably Delta Air Lines with Song - however Ted remains the only 'airline-within-an-airline' currently operating in the US.

United currently operates 97 Boeing 757-200s and some of these aircraft are used for its ps (premium service) offering business and high-end leisure customers a higher level of service between New York JFK, and Los Angeles and San Francisco. These aircraft carry up to 110 passengers (12 first class, 26 business class and 72 economy class). Other aircraft are configured to carry up to 182 passengers in a two-class layout on other domestic routes and between the mainland and Hawaii.

Still a major Boeing 737 operator. United has over 64 -300s in service such as the one pictured. Together with 30 -500s, these aircraft are used extensively on United's domestic routes and on its services between the US and Canada.

One of only two US passenger airlines operating the Boeing 747-400 - the other is Northwest Airlines - United still has 30 in service and values them for their particular suitability for long transoceanic routes. The carrier believes they continue offer a high level of flexibility as well as capacity.