On Thursday, American Airlines flight 835 from Tampa to Philadelphia went out without working water. According to a passenger on the flight, a gate agent announced that everyone should use the airport restrooms prior to boarding the scheduled 2 hour 41 minute trip (which doesn’t include 35 minutes spent boarding or time deplaning).

The customer found this – and the nonchalant way they reported the gate agent conveying the message – “ridiculous” and note that the aircraft “was sitting at [Tampa] all night” where the issue could have been addressed. It is possible that the issue developed overnight.

[T]he gate agent told everyone in the gate area that the bathrooms would not be available on the flight and acted like that was just normal and perfectly fine. And yes, it’s a 2.5 hour flight, but if you’ve flown so many miles, then you surely know that flights can end up sitting on the tarmac for quite long holds if there are weather delays, maintenance delays, no gates available, etc. I don’t understand how anyone who flies a lot could feel comfortable getting on a plane where they were told they couldn’t use a bathroom.

Once in the air, though, “It was not until we got on the plane that the flight attendants told us they “thought” we could use the bathrooms in flight but that we would have to use bottled water to flush them, and even then they admitted they didn’t know if it would work.”

What’s odd is that using bottled water to flush is not at all how airplane toilets work. There’s no tank on the lavatory toilet to dump the water into!

A recent video by an American Airlines mechanic explains how lavatories work. And a commenter offers this summary of the issue.

Under 16k feet there’s a vacuum pump that creates the suction to empty the toilet bowl. Above that differential pressure is used to create the vacuum. If the pump wasn’t working that would explain why the lavs wouldn’t work on the ground. Kinda surprised that they could dispatch the plane if the pump was inop.

Now, lavatory functionality is a little bit outside of my area of expertise. But my impression was that modern aircraft use vacuum flush systems that operate the same way regardless of altitude, with a vacuum pump (or ejector system) continuously maintaining the necessary negative pressure in the waste tank.

That vacuum isn’t “switched” off below 16,000 feet so that the pump does all the work on the ground and then differential pressure takes over above that altitude. Instead, the system is engineered to work both on the ground and in flight—the vacuum pump (or vacuum ejector) overcomes the higher ambient pressure on the ground and then works in concert with the pressure differential in flight.

Usually if the pump were inoperative, the system wouldn’t work properly at any altitude. However, if a component of the vacuum system—like the pump, valves, or seals—is marginal, cabin pressurization at altitude might assist a weak or partially failing vacuum pump, providing enough suction for the flush. On the ground, the same system might not generate a sufficient vacuum if its performance is degraded.

This would be caused by a weak or failing vacuum pump or valves that might not open or seal properly at sea-level pressure, but at altitude the pressure differential is enough to overcome those deficiencies.

The aircraft continued to operate on Thursday from Philadelphia to Chicago, back to Philadelphia, and down to Charlotte before heading to Wilmington, North Carolina to overnight.

The plane was N119US, a 25-year old Airbus A320 delivered to US Airways in 2000. Perhaps some aircraft mechanic readers can weigh in if older A320 lavatories did work the way originally described? I find this suddenly fascinating.

Of course, poor passenger experience across the board is the sine qua non of the basket of deplorables aging American Airlines A320 fleet. Older planes can be fantastic if they get the proper upkeep and investment which these haven’t (though are eventually slated to because they aren’t planned for retirement in the next few years).

American Airlines has flown New York to Chicago without a lavatory before but passengers knew in advance they’d have to hold it for the duration of the trip. (On a flight to Hawaii, American told passengers to go in a bottle when the lavatories became inoperable.)

There’s a certain length of flight where you might choose not to delay or cancel over a lavatory. At least passengers knew about the issue in advance and could make a quick calculation over whether they’re capable of flying under those conditions (some may even be wearing Depends!). However longer flights will certainly cancel.