I'm not an expert by any means, but this is almost the opposite of what I've heard, and the fact that most airlines are either Boeing or Airbus exclusively supports that idea.
In particular, I've heard that maintenance and pilot training are big issues. If you've got half your pilots on the 737 and half on the A320, you're much less resilient to scheduling issues than having all of them on one or the other. Similarly, I believe maintenance facilities tend to be one or the other, so if you've got half your facilities for each, at the margins you're going to have more scheduling issues for maintenance.
There are economies of scale with anything to do with scheduling flexibility, and dividing like this essentially halves those economies of scale.
The only airlines that are Boeing or Airbus exclusive are low costs (like Ryanair or Spirit Airlines) and tiny airlines operating a handful of planes. Otherwise it's all mixed fleet (Delta, Air France, JAL, ANA, Lufthansa, UA, etc.). If you separate wide-body and narrow-body then your statement is more correct: as going narrow-body Airbus and wide-body Boeing (or the other way around) is not rare.
The threshold I've read on airliners.net is at about 30 frames. Below that costs of a sub-fleet are too high and you should aim for commonality. Above 30 frames you should pick the best plane for your routes, regardless of commonality.
So for example running two fleets of 30 A350-900/1000, and 30 787-9/10 would be perfectly rational. But having 50 A350-900/1000 and introducing a sub-fleet of 10 787-10 is unlikely to be a wise choice, even for routes where the 787-10 would beat the A350-900.
> The only airlines that are Boeing or Airbus exclusive are low costs (like Ryanair or Spirit Airlines) and tiny airlines operating a handful of planes.
This isn’t true for the reasons you are implying. Most of these smaller carriers fly to regional airports with smaller runways and smaller demand which the 737 specifically is ideal for (since that’s what it was designed). It’s also one of the most common planes out there, so when smaller carriers are looking to buy, that’s what’s available. It’s not that they are looking to be a single vendor airline. It’s just that the one vendor made the plane they need.
On the lower end the 737 has competition from Embraer, Bombardier (and now Airbus through the CSeries/A220), ATR, etc. Turboprops in general (and thus ATR) are not popular in the US, but they are quite popular elsewhere.
But the specific example I had in mind is Air Tahiti Nui, and its grand total of four 787-9. It’s simply an airline specialized in bringing tourists to Tahiti from far, far away. Hence high density 787-9.
But even a very small airline like Air Senegal has a pretty diversified fleet, of 9 aircrafts…
Type ratings are not prohibitive to achieve once a pilot has achieved an ATPL. It’s about 5-6 weeks per pilot. Yeah, it’s a pain but it’s also not a devastating road block.
Ironically if you hear some airlines talk about the whole point of MCAS and no extra type rating requirement didn’t actually factor in as much as Boeing thought.
Training and aircraft expense is actual minor compared to fuel efficiency and availability of aircraft. If you’re running 20 year old 737NGs the new engines on the MAX are going to save a tonne of money, even after potential reputations damage. It’s all risk management.
Edit: in regards to maintenance a lot of airlines are outsourcing maintenance to bigger providers so that’s less of a deal than you’d think as well. Fuel really is one of the largest factors in this and an extra 5 years of expensive gas while waiting for a new plane may be too much for budgets to bear.
Thanks, that's interesting to know about the outsourced maintenance, that does make sense and would certainly increase that flexibility.
Re: pilot training. I could imagine that going from a 737 to a 787 would be substantially easier than from 737 to A320, due to standardisation in interfaces, processes, documentation, etc, within one manufacturer. Is that the case? 5-6 weeks does still seem like a lot of downtime for a commercial pilot, and rolling everyone through that sounds like it would be prohibitively difficult for many airlines. Plus my understanding is that it's sort of a one way street, pilots don't typically (or can't feasibly?) stay rated for two aircraft types for long periods, so it would still reduce flexibility if an airline split its fleet right?
The 757 and 767 are quite different airplanes, but they were designed to minimize the differences as the pilot sees them. This increases safety by pilots not getting confused about which airplane they are driving in a crisis.
In particular, I've heard that maintenance and pilot training are big issues. If you've got half your pilots on the 737 and half on the A320, you're much less resilient to scheduling issues than having all of them on one or the other. Similarly, I believe maintenance facilities tend to be one or the other, so if you've got half your facilities for each, at the margins you're going to have more scheduling issues for maintenance.
There are economies of scale with anything to do with scheduling flexibility, and dividing like this essentially halves those economies of scale.