There is a program call SkyHour which offers this service, you pay a rate per hour of the flight, it works on over 350 airlines, you can give it as a gift, and multiple people can even contribute to one gift in order to help someone build up to a very big flight.
The downside is that it is not like a gift card where you can use it to pay for part of a flight. If the flight is quite long and you only gift them part of a flight they would need to buy the rest of the hours.
Disclaimer: I have never used this service. They seem to charge $60 per flight hour, which on some routes would be a good deal and on others may be quite a bit more expensive than average.
A quick search reveals Flight Gift Card to be quite suitable. From what the website says, it supports 300 airlines over 70 countries with a validity of 2 years for the gift card. They deliver the card via direct email, printable copy or an option to mail the physical card.
First, to be useful for purchasing flights, this card should work on plenty of merchants. This would include not only the airlines themselves, but also travel agencies. Those include both brick-and-mortar stores and online merchants like Priceline or Orbitz. They generally use the same merchant ID for all their bookings (flight, hotel, cruise, car rental etc), so filtering by merchant ID is not feasible.
Second, even airlines themselves sometimes use 3rd party processors; for example Blue Air uses “maxitours.be” for processing their credit card purchases.
Thus I doubt what you’d like to do is even theoretically possible using the suggested avenue (prepaid gift card).
The only method I can think of would be by invoking a third party. For example you can provide the money to a travel agency (or travel agent) you trust, and specify that those could only be used to purchase flights.
Indirectly. You can give them a voucher that tells them you will buy them a plane ticket of their choosing up to a given amount.
Far more personal too than simply handing some precharged card.
Credit:stackoverflow.com‘