Tiger Airways (J7X.SG) off 1.1% at 5-week low of $1.88, extending largely steady decline since reaching all-time high of $2.25 earlier this month, due to ongoing concerns over rising costs tied to aggressive expansion, recent sale of shares by several substantial shareholders, says Dow Jones.

Budget carrier’s decision to lease 2 planes to Southeast Asian Airlines of the Philippines, disclosed yesterday, possibly also deemed negative. Royal Bank of Scotland estimates move could lower expected increase in Tiger’s seat capacity to 26% from 37%, average seat kilometer to 27.5% from 33% for FY ending March 2011.

“We assume Tiger would have generated more profit running the aircraft themselves compared to just generating rental income from them,” says RBS which is reviewing its Hold call, $1.95 target.

Orderbook quotes suggest shares likely to hold above $1.85.