On Expedia, a tiny set of arrows between the airline name and the flight number are supposed to symbolize that it is operated by somebody else. But only when somebody hovers their mouse over the arrows do they learn the actual operator. If they miss it there, two pages later -- once outbound and return flights are selected -- then Expedia displays the actual operator.
For instance a search for a non-stop trip from Charlotte, N.C. to Knoxville, Tenn. shows United flight 2717. Customers need to either mouse over those little arrows or click through to the third page to learn that it's not a United flight but actually one "Operated by: /PSA A/L DBA US AIRWAYS EXPRESS."
For those who can't read airline-speak, that United flight is actually a trip on regional airline PSA doing business as US Airways Express.
"We understand the concerns around this issue and are considering ways we can improve how we display this information," Expedia spokesman Adam Anderson told ABC News. "Of course we'll be working with the DOT to ensure that we are in full compliance with their requirements."
"A business traveler would learn that. But a casual consumer trying to make a ticket purchase is not going to know that," Maurer said.
An ABC News analysis of booking sites showed that of the big three sites, only Orbitz discloses regional carriers on the first search result page.
"They're doing an outstanding job of it," Maurer said.
A Department of Transportation spokesman said the agency "has taken enforcement action on many occasions" and "is currently conducting an investigation of major airline and large internet travel agency websites for compliance with our disclosure requirements."
The DOT on Monday levied a $600,000 fine against JetBlue, in part because the airline's phone agents allegedly failed to disclose that flights were being operated by regional airline Cape Air, a JetBlue code-share affiliate.
Most of the major airlines provide good transparency, Maurer said, except for US Airways.
US Airways assigns different logos next to each of its flight numbers to differentiate who is actually operating the plane. But travelers have to actually know that the different colored logos mean something. For instance, a black American flag symbolizes mainline US Airway flights, the type that Capt. Chesley "Sully" Sullenberger flew during the so-called "Miracle on the Hudson" landing. A light blue flag with a small "YV" or "PSA" next to it means a Mesa Airlines or PSA Airlines flight operated under the US Airways Express flag.
On that same search for Charlotte-Knoxville flights on the US Airways website, we had to mouse over the flight number in order to see: "Flight operated by PSA Airlines doing business as US Airways Express." There is also a legend at the bottom of the page explaining what each of the colored logos means.
Asked to comment on Maurer and other Buffalo crash families' concerns, airline spokesman Derek Hanna told ABC News: "US Airways is in full compliance with the federal disclosure requirements."
Tim Winship, publisher of FrequentFlier.com said there "is a woeful lack of transparency."
"There may be some token gestures made in the direction of letting people know but they are inadequate," Winship said. "The proof of that is the frequency of complaints from customers who say they thought they were booking a ticket on one airline and are actually flying another."
Winship noted that thanks to new global alliances, the number of codeshares has been steadily increasing. And, he said, "The airlines haven't kept up in making consumers aware of how these things work."