Rain in the plane

Globe & Mail July 6, 1999
Krista Foss

This article was originally published in the Globe and Mail

Why won't they stop the rain in the plane?

Moisture is a growing problem that airlines are loath to admit. Passengers "have been literally drenched."

Health Reporter
Tuesday, July 6, 1999

Drip. Drip. Drip.

A vacationing flight attendant was flying home on a rival airline recently when she looked up and saw the rivulet running along the cabin ceiling.

She was mildly amused, but hardly surprised. Airline insiders have grown accustomed to experiencing "rain in the plane." While on the job, she frequently has to explain it to passengers, sometimes twice a flight.

Still, she used to consider it no big deal. She was told to blame the moisture on condensation from the plane's air-conditioning system, and that's what she did.

Now she's not so sure. Her employer has suddenly informed her that if she discusses the situation publicly and reveals either its identity or her own, she will face disciplinary action.

Why the corporate hackles? Because despite all their other problems -- sagging profits and now the threat of a strike by Air Canada flight attendants -- airlines realize that rain in the plane is a big deal.

The moisture has nothing to do with air conditioning. The cooling units actually pull in outside air that is as dry as cornstarch.

The real culprit is a rise in cabin humidity that has been caused in large part by the decision of some airlines to reduce the amount of fresh air circulated during a flight.

Over time the humidity condenses, and water collects in the blanket of insulation that envelops a plane. According to industry sources, the water can add 400 to 700 kilograms to the weight of a large aircraft during its first six to 12 months of operation.

Not only does this extra weight increase a big jet's annual fuel bill by as much as $500,000 (U.S.), it raises disturbing questions about aircraft safety and the health of the passengers and crew.

For example, what impact does such moisture have on the fuselage and electrical system?

And what about micro-organisms that thrive in wet places?

In recent years, most of the world's airlines have opted to save money by recycling some of the air in the passenger cabin, rather than exchanging it for completely fresh air, a practice that consumes more fuel.

Coincidentally, the ban on smoking in flight made this much easier. Now the air becomes stale less quickly, but the reduced exchange means that more of the approximately 100 grams of moisture exuded by each passenger every hour remains on board.

No longer vented out with the old air, the moisture accumulates and is driven outward by cabin pressure, escaping through the trim panels on the walls and collecting in the cool 10-centimetre space between a plane's inner skin and the fuselage. There it condenses in the blankets of insulation that swaddle the passenger cabin.

On some planes this buildup continues until the insulation is soaked to the saturation point. That's when it works its way back into the cabin, often as the plane angles upward or downward to change altitude.

"Rain in the plane can vary from a couple of drops to the other extreme; I am aware of people who have been literally totally drenched," said Michael Icke, an advanced-technology expert for a large aerospace consortium. The problem, he added, has become a pain for the industry.

In reality, airlines and manufacturers quietly acknowledged as early as 1993 that moisture had become a concern.

That year, a select group of technical experts, including representatives from Air Canada, Bombardier Inc., Boeing Commercial Airplane Group, Deutsche Aerospace, Canadair and McDonnell Douglas Company, gathered at an air show in Abbotsford, B.C., for a symposium sponsored by the Society of Automotive Engineers. The subject of the symposium was "moisture ingress in aircraft insulation."

According to the foreword to the summary of presentations made that day: "Today, more than ever, wet insulation continues to be a problem to the aircraft industry. This problem is compounded by the associated corrosion concerns and performance penalties incurred by the weight of wet insulation. . . . Operators and manufacturers are dealing with the problem, rather than solving it."

Six years later, questions remain -- especially regarding the long-term effect of the freezing and thawing that the water undergoes, given that most planes cruise above 30,000 feet, where the temperature is often -50 C or lower.

In addition, the wet insulation blankets and pools of water in aircraft bilges provide an excellent breeding ground for fungus, mould and innumerable microbes, said Mr. Icke, who trained as a microbiologist.

Those microbes, he said, may seep back into the air that passengers breathe, making the air quality even worse.

Poor air quality is already a contentious issue. Last month, unions representing flight attendants from all over the world met in Los Angeles to discuss the impact of air quality on their members.

According to France Pelletier, who attended the meeting, flight attendants increasingly suffer from respiratory ailments. She is director of occupational health and safety for the airline division of the Canadian Union of Public Employees, which is trying to link its members' ailments with the poor quality of cabin air.

The added moisture from the reduced ventilation simply compounds the problem, she said. At the very least, added Doug Walkinshaw, president of Ottawa-based Indoor Air Technologies Inc., the mould and mildew are responsible for the "dirty socks" odour that pervades some planes before the ventilation system is turned on.

"We are concerned about the water collecting and the microbial growths getting back into the cabin," Ms. Pelletier said. "The manufacturers have an anti-oxidant spray to stop the corrosion [inside the fuselage], and we are concerned about that getting back into the cabin air too."

If the flight attendants are vocal with their concerns, the manufacturers are more quiet about theirs. Last year, Seattle-based Boeing sent out a service letter to operators on installing felt blankets to prevent water from dripping into the passenger cabins of its 707, 727, 737, 747, 757, 767 and 777 aircraft.

According to the January, 1999 issue of AERO, a quarterly industry magazine distributed by Boeing, "Many operators have reported water dripping into the passenger cabin and problems with extremely wet insulation blankets. . . . Inspection also showed that water pooling on the upper surface of the ceiling panels and stowage bins migrated through joints into the passenger cabin. . . . Other service experience results showed that water dripping into electrical equipment has caused some failures."

In May, Boeing brought together 700 technical and maintenance experts in Costa Mesa, Calif., to discuss a range of problems with three-engined jets such as the DC-10 and the MD-11, the model involved in last September's Swissair crash. Rain in the plane was one of the top five issues the participants identified for quick action. Others, such as inspection of electrical installations and insulation blankets, were related.

Still, airlines seem hesitant to act.

The official response from Canadian airlines: "We recognize that some aircraft experience moderate buildup of moisture in the cabin, and are looking at ways to minimize "rain in the plane" in our efforts to improve general air quality inflight."

According to Ron Elvidge, Air Canada's director of fleet management and engineering, moisture is simply not a hot issue. "Yes, occasionally, it happens that we will find a wet insulation blanket," he said. "The ones that are very wet will be replaced or dried out."

He conceded, however, that a passenger jet flies between 15,000 and 30,000 hours before all the insulation is checked. This means that a plane can be in the air for four years or more without wet insulation being changed.

The fixes are costly, but so is the problem. Frank Sloan, president of Toronto-based Sloan Aerospace, which distributes a drying system, explained that sodden insulation not only inflates fuel bills, it also loses some of its ability to insulate. So heating the plane requires more energy -- "another cost of condensation," he said.

When all is said and done, the flight attendant asked not to discuss the situation sees a certain irony in it.

"It's funny that they can build a $250-million aircraft," she said, "but they can't figure out this problem."


Around the world, flight attendants are banning together to fight for better air quality for themselves and their passengers.

They are suing U.S. and Australian carriers over fumes from hydraulic fuel and lubricating oil, which they say have seeped into cabins and caused sickness, a problem that was supposed to be alleviated by a greater supply of fresh air.

How much fresh air is enough? The acknowledged authority in such matters is the American Society of Heating, Refrigerating and Air-Conditioning Engineers. ASHRAE recommendations are considered the gold standard for air quality in everything from office buildings to sports stadiums.

But putting together recommendations for passenger aircraft is proving controversial.

In public buildings, ASHRAE recommends fresh-air circulation of 15 cubic feet (.45 cubic metres) per person per minute. The U.S. Federal Aviation Authority recently recommended that the level for airplane cabins be no less than 10 cubic feet (.3 cubic metres) per person per minute.

Last month, a committee charged with setting standards for air quality in airplanes met during ASHRAE's annual gathering in Seattle, Wash. When the session ended, the committee, whose members largely represent manufacturers and airline operators, voted for a per-passenger minimum of five cubic feet (.15 cubic metres) per minute -- at the very bottom end of what airlines will admit to using now.

"We support the ASHRAE consensus," said Richard Johnson, lead engineer for Cabin Environments-Air Quality at Boeing Commercial Airplanes Group in Seattle and an observer on the ASHRAE committee.

Unions for flight attendants disagree strongly. Their representatives walked out of the meeting when the new standard went to a vote.

"We have grave concerns," said France Pelletier, director of occupational health and safety for the airline division of the Canadian Union of Public Employees.

"They are going to come out with standards that don't make sense."

And finally, here is a direct quote from a flight attendant.

"I have experienced many "water falls" in the aircraft cabin - Sometimes many diapers are taped to the ceilings and these become saturated - The worse part is that the liquid is not always clear but yellow/brown/green, sometimes even greasy feeling, which then stains customers/crew clothing - on one model the crew jumpseats are attached to the aft door,direct center of the aircraft - Upon takeoff the liquid will run along/behind ceiling panels to the lowest point - Guess where? This liquid rains down on the cabin crew strapped there - we have to sometimes cover our heads with a blanket - To leave our jumpseats at this critical phase of flight is not an option - With a liquid of mold/oils/fire retardent/etc. falling in the cabin - You could say cabin crews work environment is a ... flying toxic rainforest.... "

ECHO Air will solve the rain in the plane problem and allow aircraft humidification without aggravating this problem. Humidification on long flights when relative humidity values now fall as low as 6-10% will improve cabin air quality and associated passenger health and comfort.