American Airlines passengers have seen many delays in recent weeks, including a four-hour delay when two flight attendants reportedly argued about a cell phone.
One flight attendant went so far as to announce on the public address system that all passengers had to turn off their cell phones, "including the other flight attendant," according to a local television report in Washington.
The dispute, according to a local television report, forced the captain to turn back from a runway at John F. Kennedy International Airport in New York and find a new crew before resuming the flight.
Delays today at New York airports, however, were all labor-related.
American, whose parent company has filed for bankruptcy protection, was forced to delay nearly 40 percent of its flights, with most forced to be late or even cancelled by an "unprecedented and very significant" increase in maintenance issues.
ABC News correspondent Martha Raddatz experienced the problem firsthand today.
"We go out to the runway to take off and the pilot comes on and says 'Sorry, we have a mechanical problem,'" she said. "The motor that starts the engine is not working [and] we have to go back."
ABC News has learned the FAA is concerned enough to have stepped up scrutiny of American during its bankruptcy. So far, there is no indication safety has been compromised, but federal monitors are making more ramp checks and fly-alongs with pilots to make sure.
Today's flights were punctual only 64 percent of the time, compared to the normal 82 percent for September.
In a statement to ABC News, American apologized to customers but blamed pilots for the delays.
"The recent disruptions are primarily due to the significant increase in maintenance write-ups by our pilots, many right at the time of departure," the statement read.
These "disruptions" led to 547 delays today. On a normal day, the airline sees about 100 delays.
The airline added that pilots are calling in sick 20 percent more than normal, which "impacts the availability of reserve pilots, which can ultimately lead to cancellations."
The pilots union said there is no sanctioned work action underway and disagreed with American's accounting of sick leave and crew cancellations.
"We have verified that pilot sick rates have not deviated from normal historical rates," said the Allied Pilots Association, which represents American Airline's 10,000 pilots. "We have likewise verified that crew cancellations remain at normal rates."
Instead, the union blamed the unreliability on mechanical problems within the airline, saying it "isn't surprising," given the large number of furloughed mechanics and closing of "one of its largest maintenance facilities."
The Wall Street Journal's travel editor, Scott McCartney, took the rare step of warning would-be passengers to fly another carrier.
"My advice is until things get straightened out with the operations, if you have a choice you ought to book another airline," McCartney said. "It's just not worth it."
The airline pre-cancelled 300 flights this week, hoping to re-accommodate passengers in advance. It also has reduced its schedule by 1 to 2 percent through October.