A Turkish Airlines plane was called back to Istanbul over a bomb threat.
Basel-bound flight TK1923 with 151 passengers returned to its airport of origin shortly after taking off.
The Boeing 738, due to arrive in the Swiss city around midday, has reportedly landed safely back at Ataturk airport.
BBC World Service reporter Seref Isler tweeted:
Bomb disposal experts were searching the plane for possible explosive devices, the local Dogan news agency reported, adding that a note reading "there is a bomb" had been found on board.
In a similar incident at the end of March, a Boeing 777-300ER flying from Istanbul to Sao Paulo was forced to land in Casablanca, Morocco over a bomb scare.
A note bearing the word "bomb" had been reportedly found in the plane's lavatory although later searches revealed no device.