As of November 2015, blank parental consent forms for travel are on websites for U.S. Passport Service Guide, Spirit Airlines and Alaska Airlines. The Passport Service has a sample form on its site as well as a downloadable version. It is intended for custodial or non-custodial parents or legal guardians.
Spirit Airlines provides a consent form for children traveling alone or with designated chaperones. The form should be formalized by a notary. Alaska Airlines presents a consent letter for children traveling internationally. In some cases, even if the child is with one parent, the non-traveling parent must sign the form. Depending on the country of origin, the form must be notarized or have other legal certification.