Whether it is necessary to specify halal requirements in advance for airplane meals depends on the regulations of airlines and restaurants. Some airlines allow passengers to explain their requirements for Muslim food to restaurant staff on the plane or before eating in the restaurant. In this case, the restaurant will provide corresponding halal meals according to airline regulations and passengers' requirements. However, some airlines do not require passengers to explain Muslim food requirements before eating on the plane or in restaurants. In this case, passengers need to respect airline regulations and restaurant arrangements to ensure that their dietary needs are met.

If you have Muslim food needs, it is recommended to contact airlines or restaurants in advance before the flight to consult their regulations and requirements. If you don't know the regulations of airlines and restaurants, I suggest you explain the requirements of Muslim food in advance to avoid unnecessary trouble.