THY B773 near Toronto on Jan 16th 2014, unreliable air data

A THY Turkish Airlines Boeing 777-300, registration TC-JJI performing flight TK-18 from Toronto,ON (Canada) to Istanbul (Turkey) with 307 people on board, was climbing out of Toronto when numerous air data systems failed. The crew stopped the climb at about 15000 feet, declared emergency, dumped fuel and returned to Toronto for a safe landing on runway 15L about one hour after departure.

The Canadian TSB reported a fault was found with one of the air data reference units. The ADR was replaced.

Radar data indicate the altitude information of the aircraft dropped to zero while climbing through 14700 feet (on standard pressure reading).