A pilot has revealed the one warning on planes you should never ignore, as it can cause “catastrophic consequences.”

Those of us who have travelled by air will be familiar with the warning sign in the on board bathroom advising not to flush anything other than toilet roll down the bowl.

American Airlines pilot Captain Steve regularly shares an insight into his life above the clouds on TikTok, also offering tips and tricks to passengers along the way. His latest piece of advice left travellers in fear as he revealed the terrifying science behind that warning.

“So you’re in the aeroplane bathroom and you’ve taken care of your business, and then you see that sign,” he began. Steve proceeded to include an image of the sign in his clip, which read: “Place trash in waste container near sink. Placing object in toilet may cause system failure.”

That may sound a little extreme, but Steve assured viewers it was true – and that even more serious consequences could arise.

He continued: “Is it because it’s going to back-up the system?” he asked. “Yeah, it might do that, but it might also be much more serious than that.”

Steve explained: “So there’s a flap on the outside of the aeroplane that’s held closed by pressure. But if something that’s not supposed to go down that toilet holds that little flap open, all of the blue juice that’s in the system comes out and it immediately freezes.

“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.” Steve closed by telling travellers to “always pay attention” to signs for fear of “bringing the whole aeroplane down”.

Responding to Captain Steve’s advice, scores of his 121,000 followers appeared to take it on board for fear of disaster. “All of my flight anxiety that you’ve cured has immediately returned,” one person penned.

A second added: “Captain Steve, with all due respect – I could’ve gone a lifetime without knowing this.” A third agreed, commenting: “Wish you hadn’t shared this. That info can get into wrong hands. I’m already a nervous flyer. Thanks.”

Meanwhile, a fourth TikTok user said: “Oh god! Now every time I see someone heading to the bathroom I’m gonna be terrified.”

According to Flight Radar 24, ice that formed from a leaking lavatory sink led to a partial loss of aileron control on board a Delta Air Lines flight DL211 in May 2023. The website adds, however: “Whilst this is rarely a concern for people on the ground, it can impact on board systems.

“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.”