A pilot has issued a stark warning about a sign on planes that holidaymakers should never ignore, as it could lead to “catastrophic consequences”. Frequent flyers are well-acquainted with the notice in aircraft lavatories cautioning against flushing anything other than toilet paper.

Captain Steve, an American Airlines pilot who often shares insights and tips from his aviation experiences on TikTok, has recently sparked concern among his followers with his explanation of the science behind the warning sign.

He said: “So you’re in the aeroplane bathroom and you’ve taken care of your business, and then you see that sign,” he said, referencing an image he included in his video which states: “Place trash in waste container near sink. Placing object in toilet may cause system failure.”

While this might seem overly cautious, Captain Steve confirmed its validity, suggesting the repercussions could be extremely grave. He posed the question: “Is it because it’s going to back-up the system?” before answering his own question, “Yeah, it might do that, but it might also be much more serious than that.”

He went on to explain that there is a flap on the outside of the plane which is kept shut by pressure, reports the Express.

If an inappropriate item flushed down the toilet prevents this flap from closing, all the blue sanitising liquid in the system would be expelled and instantly freeze due to the sub-zero temperatures at altitude.

Captain Steve has given a chilling warning to airline passengers about a potentially serious safety hazard due to an ice-related phenomenon. He explained: “That gigantic ice cube [that forms] could then fly off the aeroplane and through one of the engines – it’s happened in the past and it had catastrophic consequences.”

He urged flyers to “always pay attention” to avoid inadvertently “bringing the whole aeroplane down.”

Flight Radar 24 reported an incident in May 2023 where ice from a leaking lavatory sink contributed to a partial loss of aileron control on Delta Air Lines flight DL211. The website suggests these instances are not typical and don’t normally pose a threat to those on the ground, but they can affect systems on board.

It assured readers: “In reality, such occurrences are exceptionally rare. Airlines and aviation authorities take such incidents very seriously and investigate them thoroughly to prevent them from happening in the future.”

Many of Captain Steve’s 121,000 followers quite rightly took his caution seriously, with reactions ranging from renewed flight anxiety to wishing ignorance of such risks. One follower commented: “All of my flight anxiety that you’ve cured has immediately returned,” while another expressed: “Captain Steve, with all due respect – I could’ve gone a lifetime without knowing this.”

Additionally, someone else shared: “Oh god! Now every time I see someone heading to the bathroom I’m gonna be terrified.”

One voiced their concern, writing: “Wish you hadn’t shared this. That info can get into wrong hands. I’m already a nervous flyer. Thanks.”