The legislation aims to address a basic fact of flying: The air you breathe on planes comes directly from the jet engines. Under normal conditions the air is safe, but if there’s a mechanical issue, heated jet engine oil and other aviation fluids can leak into the air supply, potentially releasing toxic gases into the plane.

While homes and offices across the country are required to have carbon monoxide detectors, airplanes have no such requirement.

“We all are breathing contaminated air,” said Rep. John Garamendi (D-Walnut Grove), the bill’s sponsor in the House.

Like many Congress members, Garamendi is a frequent flier, and he has long worried about his own cumulative exposure to toxic gases, he said. Often, “there’s a strong odor that you’re breathing something you shouldn’t,” said Garamendi. “Anyone who’s been on an airplane when they start the engine knows exactly what I’m talking about it.”

The legislation would create new mandates for crew training and for reporting and investigating fume events. Planes would be required to be equipped with sensors to detect air contamination.

Lawmakers cited a Los Angeles Times investigation that found that dangerous vapors contaminate the air supply on planes with alarming frequency, sometimes sickening passengers and crew and incapacitating pilots during flights. Over a two-year period, nearly 400 pilots, flight attendants and passengers reported receiving medical attention after these “fume events,” and four dozen pilots were described as impaired to the point of being unable to perform their duties, The Times found.

“Our legislation takes action where the FAA and airline industry haven’t — requiring air detector and monitoring equipment, incident reporting, and investigations of these events to ensure a safer travel experience for all Americans,” Sen. Richard Blumenthal (D-Conn.), the bill’s sponsor in the Senate, said in a statement.

The bill is also co-sponsored by Sens. Edward J. Markey (D-Mass.) and Dianne Feinstein (D-Calif.) and Rep. Brian K. Fitzpatrick (R-Pa.).

Major unions across the industry representing pilots, flight attendants and mechanics are backing the legislation.

“It is unacceptable that airline passengers and crewmembers may be exposed to toxins while flying — toxins that may lead to respiratory and neurological conditions, including breathing difficulties, headaches, and fatigue,” Transportation Workers of America International President John Samuelsen said in a statement.

Scientists have long warned of potential dangers from breathing heated jet engine oil, which contains tricresyl phosphate, or TCP, a highly toxic chemical that can damage the nervous system. TCP can have immediate effects such as headaches and dizziness, as well as longer-term effects such as tremors and memory problems, experts say. Some pilots and flight attendants have experienced serious health problems, including brain damage, after fume events, The Times found.

The bill would require a major overhaul of current practices. No government agency tracks fume events or how often people become sick or impaired.

Without sensors to measure air quality, planes rely on a low-tech method: the smell test. Internal documents from airlines and aircraft manufacturers provide detailed instructions for identifying oil and hydraulic fluid contamination in the air supply by smells like “dirty socks,” “musty” and “acrid,” The Times found.

The legislation would require airplanes to have sensors that would “alert the pilot and flight attendants to poor air quality that is dangerous to human health,” and it would mandate that airlines and manufacturers develop procedures on how to respond to alarms.

The proposed Cabin Air Safety Act is not the first time lawmakers have tackled the issue. Congress has twice held hearings on airplane air quality — in 1994 and 2003. Similar pieces of legislation have repeatedly languished in committee.

Backers of the new bill hope that it can be included in the FAA Reauthorization Act — a potentially easier vehicle than passing a one-off piece of legislation.

It’s unclear what opposition, if any, the bill may face. Aircraft manufacturers Boeing and Airbus did not respond to questions about their positions on the legislation.

“Mandated regulations and monitoring requirements are premature in the absence of scientific studies that validate a health concern, reliable and accurate sensor technologies, and detection standards,” Marli Collier, a spokesperson for Airlines for America, the air carriers’ lobbying arm, wrote in a statement.

Studies on airplane air quality have looked only at normal flights in which no fume events were reported. No major research has ever measured the chemicals in fume events as they occur.

In 2003, Congress ordered the FAA to measure the toxic chemical levels in such events, but the airlines refused to let flight attendants carry air samplers aboard, according to an FAA-funded research report.

The FAA declined to comment on pending legislation. “Studies have shown cabin air is as good as or better than the air found in offices and homes,” the agency previously told The Times.

“The cabin air inside Boeing airplanes is safe,” a spokesperson for Boeing previously wrote in a statement to The Times. “Due to the high air exchange rate and HEPA recirculation filtration system, air quality on Boeing aircraft compares favorably to other indoor air environments like schools, office buildings, and homes, as numerous impartial, third-party studies have found.”

But HEPA filters can screen particles only above a certain size. They are not effective against gases.

Boeing previously told The Times that scientific studies have not proved a link between fume events and health problems. The company previously said it has not equipped its planes with air sensors because suppliers have not “demonstrated the existence” of devices that could “reliably detect contaminated bleed air.”

But the Times investigation found that Boeing managers had legal concerns that went beyond technological shortcomings. Senior Boeing engineers worried that data from sensors could prove damaging if used as evidence in lawsuits brought by sick passengers and crew members, according to internal emails and sworn depositions.

An internal Boeing memo described it as a “risk” to give air sensors to even one airline, according to a deposition of a Boeing executive.

“Flight attendant, pilot unions, and congressional supporters could use this effort as evidence that sensors are needed and … to drive their agenda forward to have bleed air sensors required on all aircraft,” said the 2015 memo, which Boeing turned over in litigation.

Garamendi, the bill’s sponsor in the House, noted that air monitoring equipment is “readily available.”

“For the airlines, ignorance is money. If the toxic exposure were known, then you’d be looking at long-term health effects that may lead to workers’ compensation” claims, lawsuits and requirements that manufacturers change “the design of the airplanes,” said Garamendi.

“So heads up, Boeing.”