Passengers and flight attendants have filed multiple lawsuits against Southwest Airlines, Boeing and Airbus in federal court, alleging that jetliners they were aboard leaked toxic air that sickened them.

The latest lawsuit seeking damages was filed in a federal district court in Birmingham, AL in late October by twin sisters who allege they were seriously injured during a suspected toxic air fume event on a Southwest Airlines flight from Los Angeles and now suffer from disabling neurological and respiratory symptoms.

Victoria Vaughn Holsted of Franklin, TN, and Valerie Vaughn of Birmingham, AL allege in their complaint that as a result of a toxic air exposure onboard a Boeing 737-300 jet aircraft operated by Southwest Airlines on January 27, 2009, they have suffered severe injuries, including motor skill deficiencies, loss of balance, vision impairment and uncontrollable tremors.

The sisters' complaint alleges that Southwest Airlines negligently operated and maintained the jet aircraft, causing their injuries. "I am worried that there may be other passengers from Flight 1705 who are also sick but don't know why. They deserve to be told. I think about this every day," stated Holsted.

"We are filing this lawsuit in part because we want to help our clients learn what chemicals they were exposed to on that flight so their doctors can provide them with proper medical treatment," stated Seattle WA-based Alisa Brodkowitz, one of the attorneys for Holsted and Vaughn.

Brodkowitz is also representing former flight attendants suing Boeing and Airbus for their roles in other contaminated cabin air incidents.

Two former flight attendants are suing Airbus, alleging that toxic "bleed air" from aircraft engines caused serious permanent injuries.

According to the lawsuit filed in U.S. District Court in Broward County, FL, Lucy Mayorga and Adriana Moravcik suffered inhalation injuries on Oct. 8, 2005 aboard a U.S. Airways Airbus A319-112 aircraft. Upon takeoff, they noticed a strange chemical smell, followed by their eyes watering, their throats tightening and debilitating symptoms, including headache, upper respiratory irritation and difficulty breathing.

They were later diagnosed with breathing injuries, and their symptoms continued to worsen until they had to give up their jobs. The lawsuit goes on to allege that defective design allows toxic chemicals from engine oil and hydraulic lubrication products to contaminate air drawn in to the cabin through the engines.

The problem of toxic 'bleed air' on airplanes has been known to the airline industry since the 1950s, says Brodkowitz. "The aircraft manufacturers have turned a blind eye to this problem and failed to equip their planes with sensors or filters to keep toxic chemicals out of the cabin. The only things filtering this stuff out of the cabin are the lungs of passengers and crew members."

Brodkowitz also represents former flight attendant Terry Williams who has sued Boeing, alleging that bleed air fumes sickened her aboard an American Airlines MD-82 in 2007, eventually causing symptoms so intense that she could no longer work.

Holsted is a real estate executive; Vaughn has a management position with the PGA and is director of golf at the Eagle Point Golf Club in Birmingham.

They claim that exposure to contaminated air while passengers onboard Southwest Flight 1705 has caused them to suffer serious and debilitating health problems.

About one-hour into the flight they, along with other passengers and cabin crew, began to experience hypoxia (oxygen deprivation), among other problems. Once alerted to the problem in the cabin by flight attendants, the flight deck crew increased engine power and conducted a steep ascent. "As this occurred, super heated air began to surge out of the ventilation system and onto the passengers. Also present was the appearance of a mist," the sisters recall. And at no time did the emergency oxygen masks deploy in the passenger cabin.

The captain announced to the passengers that there had been a "malfunction" after which Flight 1705 made an emergency landing in Albuquerque, NM. The twin sisters and the other passengers completed their trip aboard replacement aircraft.

Vaughn said she was "perfectly healthy when I boarded that plane and perfectly unhealthy since then." She said the symptoms started immediately and continue today, although they have tapered off somewhat.

They both said they suffer from tremors, lethargy, paralysis, severe headaches, numbness, rashes, memory loss and vision impairment. Stated Vaughn: "I feel 100 years old, but in a 45-year-old's body." And Holsted "is frightened she may wake up one morning blind."

Since the flight, the twin sisters, 45, have been forced to take extended leave from work due to their various symptoms.

Initially, airline passengers breathed in air supplied directly from the atmosphere using compressors. But this was an expensive proposition, so in the 1960s a system was developed to draw the "bleed" air from the engines.

Air is drawn out of the compression section of the engine and cooled. It then enters the cabin, where it mixes with re-circulated air that has passed through filters designed to remove bacteria and viruses. These air filters do not remove any fumes or vapors from the engine. So if engine oil or hydraulic fuel leaks, because of poorly designed or faulty seals, or even over-filled tanks, toxic chemicals can contaminate the air supply.

The bleed air can be laced with a chemical, tricresylphosphate (TCP), an organophosphate, or other toxic mixtures of chemicals that have been linked to serious respiratory problems, memory loss, neurological illnesses and even brain damage.

According to the Association of Flight Attendants (AFA): "the air you breathe in the aircraft cabin is supplied from the engines or auxiliary power unit (APU) and sometimes it gets contaminated with engine oils or hydraulic fluids that get heated to very high temperatures, often appearing as a smelly haze or smoke. That haze/smoke that enters the cabin air is a toxic soup and can contain carbon monoxide gas as well as chemicals that can damage your nervous system called tricresylphosphates. Exposure to TCPs can initially cause stomach ache and muscle weakness, followed by delayed memory loss, tremors, confusion, and many other symptoms," AFA added.

University of Washington Professor Clem Furlong is in the final stages of developing a blood test that will confirm whether 92 people who suspect they've been poisoned by toxic fumes in airplanes actually were. Brodkowitz said the Vaughn sisters were among the nearly 100 people who took Furlong's new blood test for TCP poisoning.