NTSB Factual Report

On June 20, 2011, at a time not given, a Cessna 680's flight control instruments gave erroneous indications during approaches to Austin (AUS) and San Antonio (SAT), Texas. The captain, first officer, and passenger on board the airplane were not injured. The airplane was not damaged. The airplane was registered to Chinn Aircraft Holdings LLC, and operated by Chinn Exploration Co., both of Longview, Texas, under the provisions of 14 Code of Federal Regulations (CFR) Part 91 as a business flight. Visual meteorological conditions (VMC) prevailed at the time of the incidents which operated under an instrument flight rules (IFR) flight plan. The cross-country flight originated and terminated in Longview (GGG), Texas.

During the ILS 17R approach to AUS, the crew noticed their glide slope indicators did not agree. The captain's glide slope indicator was lower than the first officer's.

While being vectored to the ILS 12R approach to SAT, final approach course interception was done in FMS mode. Upon interception, the pilot pushed the approach key and the course indicator change from pink to green. On passing the FAF (final approach fix), the inbound course changed from SAT ILS 12R to the inbound course of AUS ILS 17R. The flight director indicated a turn to the right and the autopilot system turned the aircraft to the right.