International Launch Services (ILS) has delayed the launch of a Proton rocket that will carry the AMC-23 satellite into orbit for SES Americom. Liftoff had been scheduled for Dec. 5.

The delay was announced after preflight testing found unusual behavior in the flight control unit on the rocket’s Breeze M upper stage. The vehicle will be returned to the processing facility for further investigation, ILS said. A new launch date has not been set.

AMC-23, built by Alcatel Alenia Space, will reside at 172 degrees East. The satellites 20 Ku-band transponders will provide service for the Connexion by Boeing satellite Internet offering to airline routes over the Pacific Ocean. The satellite also carries 18 C-band transponders, which will provide connectivity between North America and the Pacific Rim.