CSA AT42 at Prague on Nov 1st 2013, blocked static port

A CSA Czech Airlines Avions de Transport Regional ATR-52-400, registration OK-KFO performing flight OK-542 from Prague (Czech Republic) to Hamburg (Germany), was accelerating for takeoff when at about 70 to 80 knots the crew received a "DATA INVALID" indication at the digital air data computer. The takeoff was continued, during climb out the crew performed the relevant checklists and identified the air data reference unit #1 as defective, the relevant checklist items were carried out and the crew continued the flight. However, when the aircraft climbed through FL240 the crew observed the standby airspeed and altimeter disagreed with the values the left and right hand main indicators were showing. The crew consulted with maintenance and decided to return to Prague, where the aircraft landed safely about 25 minutes later.

Czech UZPL reported in their quarterly bulletin that a static port at the right hand side of the aircraft was found blocked due to human ground operations error. The incident is under investigation.