The death of a pilot on an American Airlines flight bound for Boston Monday was the eighth pilot death during a commercial flight since 1994, the Federal Aviation Administration said.
The number included both commercial passenger and cargo pilots and commercial charter pilots.
"The reason that it is only eight is that to fly commercial passenger service, pilots over the age of 40 are required to get medical checkups every six months," said Mary Schiavo, an aviation attorney and former inspector general at the US Department of Transportation. "Medicine's pretty good at identifying these problems."
Those under 40 years old are subject to annual medical exams, according to FAA regulations.
If a pilot feels sick leading up to a scheduled flight, they will likely opt against flying, said Greg Raiff, chief executive of Private Jet Services Group in Seabrook, N.H., which arranges flights for companies and government agencies. Commercial airlines have reserve pilots and crew members on call in case they are needed to fill in on short notice.
"Pilots want to get the job done, but they're not going to go do it, if they're feeling very ill," he said.
Aviation experts say incidents like Monday's emphasize the importance of the medical exams.
"We need to be sure these pilots are having state-of-the-art physicals on a very regular basis," said Gail Dunham, executive director of the National Air Disaster Foundation. "Their physical standards need to be higher than other professions."
"It's up to the FAA to be sure the pilots physicals are meeting the highest standards possible," she said.
When such an event happens aboard a commercial flight, federal rules dictate that the plane land as soon as possible.
"It becomes a race to the ground when you have only one pilot," said Raiff.
FAA regulations require that there be at least two pilots on US commercial flights, Raiff explained, so if one pilot dies, the flight is technically flying in violation of federal rules and therefore must make an emergency landing.
"The disability of the captain is certainly a situation where you'd need to have a backup pilot because planes don't land by themselves," said Paul Hudson, president of Flyersrights.org, an airline passenger group.
While "pilots are regularly trained for single-pilot events," and both sides of the cockpit have redundant controls to allow for one pilot to single-handedly control the aircraft, Raiff said, the pilot is responsible for "landing the aircraft — literally doing twice the work."
"It's a highly charged situation," said Raiff.
The pilot would radio the local FAA controller to declare the emergency and explain the nature of the situation.
"The FAA controller will typically clear the airspace and work with the pilot to get them to the ground as quickly as possible," he said.
Another FAA regulation, implemented after the Sept. 11 attacks, requires that there be at least two crew members in the cockpit at all times. So the pilot would also have to call one of the crew members into the cockpit.
Raiff said he was not aware of any federal rules about whether the pilot must inform passengers in such an event.
"It would be up to the discretion of the pilot and the specific rules of the airline," he said.
He said he imagined most pilots would tell passengers, without going into detail, that an emergency landing is being made because of a medical situation, and to remain calm.
Two passengers aboard Monday's flight said they were told the pilot was ill.
When the flight lands, "there's going to be first responders on site," and the death would be investigated by the local coroner. The FAA and National Transportation Safety Board may also investigate, Raiff said.
"Fortunately it doesn't happen all that often for pilots," said Raiff.
While medical emergencies and deaths among pilots are rare, planes more often make emergency landings for passenger medical emergencies, said Schiavo. She estimated that happens at least once a week in the United States. A 2013 study found that in-flight emergencies occur in one out every 604 flights.
The study, which looked at medical emergencies on five major airlines over a three-year period found that out of 12,000 infirm passengers, 31 died, a rate of 0.3 percent.