The chief executive of Brazil's TAM Linhas Aereas resigned unexpectedly on Friday after less than two years on the job, prompting the airline to promote its chief financial officer on an interim basis.

TAM, Brazil's leading airline, said in a statement that David Barioni Neto stepped down of his own accord and that CFO Libano Miranda Barroso would replace him until the carrier's board names a new CEO.

TAM declined further comment on the management changes.

Barroso, who has spent most of his career in finance, has been a top executive at the Sao Paulo-based airline since 2004. He is 44 years old.

Barioni, a 50-year-old professional pilot who previously served as a top executive at TAM's rival Gol Linhas Aereas, took the top job at TAM in November 2007.

On his watch, the carrier has overhauled its branding and solidified its dominance of Brazil's domestic aviation market, fending off fierce competition from Gol and start-up Azul Linhas Aereas.

In the last year, TAM also has embarked on a strict cost-cutting program to weather Brazil's economic downturn, which turned out to be short-lived.

TAM's shares rose 3.45 percent on Friday to 24.00 reais before the announcement, outpacing a 0.49 percent gain by Sao Paulo's benchmark Bovespa index .BVSP.

(Reporting by Todd Benson and Cesar Bianconi; editing by Carol Bishopric)