Generally speaking, no, you cannot take a knife in your hand luggage on a commercial aircraft, but there are very specific, limited exceptions depending on the jurisdiction. Under TSA guidelines in the United States, almost all knives—including pocket knives, Swiss Army knives, and kitchen cutlery—are strictly prohibited in the cabin and must be packed in checked baggage. The only exceptions are plastic or round-bladed butter knives. In some other regions, like the UK or parts of Europe, you may be permitted to carry a knife with a non-locking, folding blade that is less than 6cm (approx. 2.4 inches) in length, though this is entirely at the discretion of the security agent. Even if a knife is technically legal by the letter of the law, security personnel have the right to confiscate anything they deem a "potential weapon." To avoid the high risk of confiscation or legal trouble, it is always recommended to pack any bladed instruments in your checked suitcase, ensuring they are securely wrapped to prevent injury to baggage handlers.