"It requires an extensive crew, a dozen men, and they all have to be highly trained," said Steve Zaloga, a senior analyst at Teal Group in Fairfax, Virginia, and an expert in Russian military technology. "Some of the tasks are less complicated, like more administrative tasks, but difficult training is required either way."

According to Zaloga, it's not as if the pro-separatists just found the launcher and pointed it at the aircraft. First of all, operating the launcher typically requires two or three other other radar vehicles and a supporting command system.

"All of the vehicles have to interact together at the same time, which is why the U.S. government is suspicious about who was helping them use the equipment," Zaloga said.

he powerful Cold War-era Buk missile system was built to protect Soviet army units from attacking aircraft during wartime. Unlike fixed-weapons used for national air defense, a Buk system in the field being used by separatist rebels likely wouldn't have information from air-traffic control centers, said Steve Zaloga, a senior analyst for the Teal Group Corp. in Virginia.

"The Buk system is not designed for peacetime use where it interacts with air traffic control," Zaloga said. "They would have seen a radar blip at 33,000 feet, but that's all they would have seen."

Richard Aboulafia, vice president of analysis at the Teal Group, believes current narrowbody production rates are sustainable today, "but going up further can be a real problem. You can go up to 50 or 60 [aircraft per month], but if the slightest thing happens you are in real trouble." He cautions that "the idea to go up further is a great way to engineer overcapacity."

Both Airbus and Boeing have already decided to move production rates up for the narrowbody models—Airbus is boosting the A320 line to 46 aircraft per month from 42, and Boeing is moving 737 production to 47 per month from 38 and is pondering 52. Airbus is also looking at rates higher than 50 when the transition to the A320neo is completed.

Aboulafia also is concerned that some emerging players such as Lion Air or Norwegian may not fulfill their promises. Both airlines have large orders for new narrowbodies with Airbus and Boeing. From a macroeconomic point of view, this is worrisome, he says.

To an extent, the situation for manufacturers is as good as it is because of low interest rates (which encourage investment) and the high cost of fuel. These factors can change, and if Airbus and Boeing are unlucky, fuel will become cheaper and interest rates will rise in parallel. Therefore: "We are taking it too far," Aboulafia contends.

And as Emirates, the largest of the Gulf airlines, expands its flights to the United States, some aviation analysts say Delta's arguments are gaining traction. "This is a legitimate complaint," said Richard L. Aboulafia, an aviation consultant at the Teal Group in Fairfax, Va.

Mr. Aboulafia, the aviation analyst, said that Emirates and Etihad Airways, both based in the United Arab Emirates, had already expanded more significantly into Europe, causing problems for European airlines on routes to Asia. "I think that, in the minds of Delta executives, they've seen the future, and it looks like Europe," he said.

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Given the various costs in running an airline, he said, it can be hard to quantify that "a slightly lower capital cost on a plane played a key role in driving you out of a market." But, he said, European authorities had "added insult to injury" by focusing more on providing credit guarantees to help Airbus sell its largest plane, the A380, to the Middle Eastern carriers than on protecting their own airlines

And the RD-180 has its supporters. "There's nothing out there that's better in terms of weight-to-power ratio than the RD-180," said Marco Caceres, an analyst with the Virginia-based Teal Group. "I don't know if you can come up with an engine as powerful as the RD-180 in a short time from scratch. "It's really more about developing the least expensive engine that will make the Atlas V much cheaper commercially."