I have a few questions about ER aircraft.
1) I belive to make a plane ER, the manufacurer just makes the planes have a higher maximum take off weight so that they can carry more fuel. Am i right or is there more to it?
2) Why do airlines operate ER and non-ER version of the same aircraft? (example: UA 777-200s) Wouldn't it be easier to have all the planes the same? In the case of UA, if all the 777s were 772ERs they could use any plane on any route and not worry during planning about if the plane will have the range. If you don't need the range is it more economical to use the non-ER version?
Can anyone offer a little help here?