In short, it all boils down to economics.
The A320 and the 737 families are very similar aircraft for 95% + of missions, both in payload, range and fuel burn.
So, why one over the other?
If airline A has already a fleet of A330 and A340 for long range flights, it will benefit from commonality both in pilot training and in maintenance to have an all Airbus fleet.
In the mean time, airline B had been a Boeing customer ever since the 707 and 727, and now has an assortment of 747, 757, 767, 777 and 787s. As such, when it comes to putting an order for 50 737s with another 50 on option, Boeing will give them a deep discount.
Let’s say C is a startup company that needs 10 planes to get off the ground. They ask both Airbus and Boeing. Airbus can deliver the planes in 3 years with the first coming in 18 months, while Boeing can deliver the first in 12 months and all of them in 2 years, and, as a bonus, can get them 5 planes from a lessor until the deliveries begin.
In the end, let’s say D is an airline with an older fleet, a mix of 10 old A320s and 10 737 classics. Boeing offers a buyback offer for both the A320s and the 737s and a deep discount for 25 brand new 737 max-8 planes.
Of course, I’m over simplifying things, and I have no idea of what really goes on behind closed doors when airlines and manufacturers negotiate the purchase of planes (that’s a trade secret guarded with all care), but all of the above are plausible reasons why an airline would choose either Airbus or Boeing given their products are very similar.
Source : Quora
