Noi Bai International Airport

All foreigners travelling on internal flights must have a valid passport that has been approved for entry and travel within Vietnam.
  Alternatively, United Nations laissez-passer; emergency travel documents issued by foreign representative offices in Vietnam; or foreign countries' documents issued to Vietnamese residing abroad (US green card, long-term residence card) are also accepted.
  For holders of temporary residence cards that include a photo and passport details, no further documentation is needed for domestic flights.

Holders of temporary residence cards or certificates of foreign passengers without a photo will require further documents to take domestic flights.
   If they do not have a photo, relevant authorities only accept temporary residence cards or certificates of foreign nationals for domestic flights in the following cases: temporary residence cards or certificates issued in a passport or in passport form; temporary residence cards, certificates or temporary residence extensions issued on the back of the separate visa with the photo and passport number of the passenger.
In case a foreign national has lost their passport and is issued an emergency travel document by a foreign representative office in Vietnam, the Immigration Department under the Ministry of Public Security will grant an extension of temporary residence to the document or attach a separate visa.
   The CAAV also noted that foreigners with border travel documents are only allowed to travel within the border area (for the Chinese border route); border province (for the border line of Laos and Cambodia); and border-gate economic zones (for border provinces).
If a foreign passenger is using a travel document with an entry stamp at the land border gate to take domestic flights, the ground service units will cooperate with the aviation security control force to notify and coordinate with the border gate police to check and determine the travel range of passengers.