The company, which operates 31 routes across the Scottish Highlands & Islands and the rest of the UK, increased profits to £7.2m from £5.8m the previous year.
The annual results revealed that turnover in the year to 31 March increased from £87.3m to £93.6m, thanks in part to a 13% rise in passenger numbers on scheduled services to 656,036.
Loganair chairman David Harrison said: “2015 was a challenging year but we have a very robust and comprehensive plan to further improve our fleet and enhance the comfort of our passengers.
“It is our number one priority and from April 2015 to April 2016 and we have committed more spend than we have ever done to achieve those ambitions.”
The £15m investment programme will include the purchase of new aircraft, upgrades and a new spares hub at Glasgow Airport.
Harrison added: “We started the new financial year in a position of strength, and look forward to pursuing our strategy of controlled expansion in both our scheduled service network and our dedicated long-term charter contracts.
“As well as the acquisition of another Saab 2000 and the new expanded spares hub, having two dedicated spare aircraft based at Glasgow and Aberdeen enables us to improve back-up capability across the network.
“These investments are all designed to significantly improve operational performance and we are confident they will each have a positive effect on service levels.”
During the year three new routes were added outwith Loganair’s traditional Highlands and Islands heartland - Norwich to Edinburgh, Dundee to London Stansted and Glasgow to Manchester.
Subsequently, two months ago, two more routes linking Inverness to Manchester and Dublin were launched.