Orion

Perhaps plane mile costs might be more meaningful than seat mile costs for comparing the fuel efficiency of aircraft types across different carriers.

businesstraveller2

You have a point there but only if it is free. I typically don't pay for DTV. If I stopped getting F upgrades altogether on UA I might just fly jetblue instead where the TV is free (and you get free bottles of water in the "even more legroom" seats.

prestonh

I think where there is comparable fuel characteristics is what is the operating CASM. There is over a 40,000 lb. difference in MTOW between the NG models which means there are trade-offs in range, payload, and operating costs. The 739ER burns more fuel per hour than the 738. If a carrier does not need the expanded cargo, range, and seats of the 739 it wouldn't make economic sense to put up a heavier airframe into the air for each flight. That is why you see derivatives selling because mission requirements vary by airline, routes, etc.

I suspect the reason UA is converting the older 752 is because the 739ER now nearly matches them for payload, range, and pax capacity. This was not true of the 738 before. I also understand that the PW engine UA uses is lower thrust than the PMCO 752, making it a poor candidate for TATL missions. The maintenance costs on the 752's are probably getting up there as well and who knows what the dispatch reliability is on the plane. Plus Boeing I'm sure cuts a good deal and if you can cash in on the residual value of the 752 versus parking them in the desert down the road, UA is probably money ahead.

JaysonW

I know the feeling. Now that UA has routed it's 744 fleet to SFO, I need to find a reason to tell my wife I need to fly out there and hop on one before they're gone, too.

fly18725

If that we're the basis of comparison, wouldn't the airlines be focusing on smaller props that would have lower trip costs? In reality, I think airlines look at cost per seat, since that allows them to make an appropriate comparison against revenue potential.

mduell

They're cheaper to buy, the engines last longer (same physical engine, derated, gives more EGT margin), and burn less gas.

They also weigh more empty.

jackal

My point exactly.

EsquireFlyer

My (limited) understanding is as follows. The 737NG The stretch versions do burn more fuel, but it's a very small (basically negligible) difference, compared to the number of additional seats they carry, so the fuel burn per pax is lower on the stretch versions.

Basically, the shrink versions have to carry almost the same infrastructure (e.g., engines and wings) that the stretch versions use, and they run on the same engines also.

What do you mean by "the laws of physics seem to agree with me"?

As for why carriers would keep accepting deliveries of the smaller versions, each 737NG variant was developed to replace one of the classic variants. The 736 for the 735; the 737 for the 733; and the 738 (and later 739) for the 734. And, as you predict, the 738 was by far the most popular of these. The various versions have different characteristics such as runway performance and range, and different option packages (such as extra fuel tanks for the 737ER). For example, the 737 has the longest range of the non-ER versions, surpassed only by the 739ER, which in turn is surpassed by the 737ER. But the longer range comes at the cost of lower pax capacity and higher fuel cost per pax. So the airline chooses the version based on its operational needs. For example, Hawaiian likes the 737s/737ERs because they can easily reach important cities on the mainland (beyond just the West Coast) from Hawaii.

Also, if an airline does not think it will be able to fill a stretch version, it might not want to pay the purchase price for the stretch version, if it can buy or lease a smaller version more cheaply. And there is usually a cost associated with "just converting all of those orders to 739s," although that is up for negotiation between Boeing and the airline. But the airline is not going to just automatically buy the most expensive version if they don't think they need it.

Buying a bigger version for more $ is not the best choice if an airline really does not think it can fill the seats, even though the shrink versions burn almost the same amount of fuel as the stretch versions do. (If it thinks it may be able to fill the seats in the future, then it's a long term vs. short term decision, but airlines sometimes do make short-sighted decisions.)

With regard to what you said about the 738 and non-ER 739 having less range compared to the 737, I believe you are talking about the nominal range with a full passenger/luggage/cargo payload. With capacity restrictions (flying less than full) they would have longer range, exceeding their nominal maximum range.

The 739 is also out of production now because it was unable to carry even its maximum theoretical payload, as a result of not having enough exit doors to comply with FAA regulations with maximum pax aboard. This problem was corrected by adding two exit doors to the 739ER, and as a result, the 739ER has replaced the baseline 739 on Boeing's menu.

In contrast, in the Airbus family, the A318 and A319 have more of a fuel savings vs. the A320 and A321, so the shrink version economics are not as bad (although the stretch versions are still more economical when full). I am not sure why Airbus is able to do this with the A320 shrinks and Boeing is unable to do it with the 737 family shrinks, but that is my understanding of the specs. (Either that, or Airbus is publishing inaccurate fuel burn info for its shrink versions.)