If you look at their holiday brochure or look online it does say that there is a Prestwick flight. However, if you click on Prestwick as your departure airport it actually comes up as a Glasgow flight.

To reinforce what morh says, the Burgas Airport website certainly doesn't list Prestwick as a potential destination, whereas Glasgow [ Abbotsinch ] is shown, as are other UK regional airports.

Balkan Holidays 'Flight Information' page shows flights from Prestwick on Mondays, but test attempts to book various Monday dates between June 15th & August 3rd result in Glasgow or (in some cases) Edinburgh flights being offered instead.

If you go onto Prestwick airport site http://www.gpia.co.uk/ it only lists the following destinations:-

Flight Information
We are delighted to have a choice of 35 destinations. Choose your preferred destination from the list below and full details of the flight schedule, day of departure, flight times, airline, tour operator and how to book will be displayed.

Please check with your airline/tour operator for correct flight times as they maybe subject to change.
BARCELONA GIRONA
BELFAST CITY
BOURNEMOUTH
BRUSSELS CHARLEROI
BUDAPEST
DALAMAN,TURKEY
DERRY
DONEGAL
DUBLIN
DUSSELDORF WEEZE
FARO,PORTUGAL
FRANKFURT HAHN
GDANSK
GOTHENBURG
GRENOBLE
KATOWICE
KRAKOW
LONDON STANSTED
MALAGA,COSTA DEL SOL
MILAN BERGAMO
MURCIA
OSLO TORP
PARIS BEAUVAIS
PISA
POZNAN
RIGA
ROME
SHANNON
STOCKHOLM SKAVSTA
TENERIFE
TURIN
WARSAW
WROCLAW

Scottish flights seem to be a bit hit and miss this year. Thomas Cook and Thomson are still going from Glasgow, but starting later.

First Choice are advertising Glasgow -Bourgas, but when I tried to get details on their site, it came up as Edinburgh.

We really need a budget carrier out of Glasgow or Edinburgh to Bourgas to shake them up a bit.

Maybe if XL hadnt folded, their proposed Glasgow - Bourgas flights would have helped hold the prices down a bit.

Hi Joe, having been messed about so much in the past with flights from Prestwick-Varna(Manchester - Varna) , Glasgow - Varna (Glasgow - Bourgas) Glasgow - Varna (2days later) I'm reluctant to book Scottish flights to Bulgaria, ths why this year I have booked Newcastle - Varna fingers crossed

I always feel so disappointed at the lack of flights from Edinburgh/Glasgow going into Varna for the resort of Golden Sands.
I know many people that feel the same way too.

If there were Edinburgh flights to Varna I would most definately be on one of them as I love Golden Sands.