Using restroom on airplane while fasten seatbelt light is on?

There are two levels of turbulence when it comes to the seat belt light. With minor turbulence the captain will turn on the seat belt sign and ask passengers to be seated. Cabin crew will be able to continue their duties (though they will sit down if it gets rougher).

With severe turbulence, the captain will turn on the seat belt light and tell everyone to be seated immeadiately (including cabin crew). In this case, the cabin crew will usually stow any carts and then buckle in.

Fortunately in most cases the pilots "see" the turbulence in advance so can warn passengers beforehand, but not always, hence always good to have your seat belt on.

In terms of having to go real bad ... with minor turbulence, the cabin attendants will usually allow you to take care of your needs, if you express the urgency to them. But with severe turbulence, the answer will be NO, sit down and hold it.

This apparently happens a lot (or at least between the countries I travel often) in AirAsia.

When the captain turns the seat belt sign on, that doesn't mean he or she is expecting turbulence by a 100% chance. It's just that his/her instincts and monitors show that there could be a turbulence. I have used the washroom many times when the seat belt sign is on, and I have even had the door from locked from inside when the sign turns on.

The flight attendants are used and trained for minor turbulence. The trollies (with wheels) have brakes on them. They are generally safe even during a minor turbulence.

If you are in the washroom when the sign is on, the attendants will knock the door and tell you to return to the seat. But I have never seen them insisting. They didn't even care sometimes.

If you have experienced a somewhat large turbulence, you have probably noticed the captain saying the attendants to return to the seat. If you hear that, buckle up and finish your glass of wine quickly.

If the sign is on, and you are in a hurry, the regulation is that you must stay in the seat. Hand gestures and a smile will do the trick. The call attendant button will piss them off. Just try to tell them you are in a hurry and you'll stay safe.

A few years ago I flew US coast-to-coast on a bad weather day (*). The flight was bumpy but the attendants were able to provide most of the expected services. I had this exchange with an attendant:

The 'fasten seat belts' sign has been on for three hours. Is it OK if I get up to use the restroom?

I won't say it's OK but I won't stop you.

I carefully picked my way down the aisle, always holding a seat back, used the restroom, and returned to my seat without incident.

Presumably the attendant's response was a compromise between recognizing biological urgency and limiting airline liability if I had been injured.

(*) Shortly after I landed, another flight to the same airport landed with turbulence-related injuries to some of the passengers. That bad.

I have heard that if you leave your seat with the belt light on and are injured you can't sue the airline. Don't know how that may fit into legalities of it all, nor why flight attendants may ignore violations. It is frustrating to see crew up and scurrying about while the light is on and I really have to go. I suppose they sign on to not sue the company due to injury. Still frustrating when the turbulence is minimal. I'm 65 but a scuba Divemaster with certainly as good balance as a 25 year old flight attendant. I rode Greyhound buses for decades and managed to get back to and use the bus washroom under far more difficult balancing situations than on most plane rides.